Flying Plank for Thermal

[ericfly]

I searched the Thermal Forum for planks and couldn't find anything.
I fly both slope and thermal gliders. On the slope I started to make some planks like the JW and Moth, but lighter. I noticed they can fly on light lift, when just my fast thermal ships would fly, so I thought: Why not making a thermal plank? The advantage of a plank would be less drag and less weight (no tail, less servos etc.), and the disavantage would be the need of a near-to-zero pitching moment airfoil, with a little reflex, to keep the thing stable.

Do anyone know a thermal plank? I know there are some F3J Flying wings, like the Paoli, but I haven't seen any plank for thermals.
Since I don't want a slow plane, I was wondering about a 2meter (78") plank, with S5010 or MH45 airfoil, 10" root 7 1/2" tip chords.
What would be the behavior of a poly wing? I am concerned about braking the wing, for precision landings: Flaps are just impossible, since it is a flying wing. Has anyone an idea of the likely behavior on crow or a spoiler on the middle of the wing?
Any Suggestion?
Regards,

Eric

[johnsocj]

It's been done yo- and big too!

Check out the B2 Streamlines website, the source for "RC Soaring Digest"

RCSD has been publishing flying wing analysis for years, and has done multiple versions of the late Dave Jone's Blackbird, Raven, R2 built-up "planks" if you will- from the two meter versions to expanded standard class and giant three meter versions, with many modifications. Rudder, Elevator, Aileron, Elevon, and Spoilers. Beautiful aircraft that apparently fly quite well. I for one really want to build one.

The material that this organization has produced and published is incredible and informative- we should all carefully read the common-sense notes on flight trimming by Gordy Stahl.

[tsunami]

have you got a link to it

[CactusJackSlade]

Here is my experiment...

Although not a plank wing I did use crow mixing for some stopping power with OK results.

If I used only moderate crow it worked good, but under full crow it becomes a little pitch unstable.... and I imagine that would be magnified in a plank.

This wing is very stable compared to a plank... or even a conventional flying wing for that matter...

Photo 1... the bird shaped flyer.
Photo 2... full crow mixing

Hope this helps!

CJS

[windsox]

I suspect the stock build instructions include excessive sparring for thermal only use imho. If you lightened up oin the fuse covering and spar I bet It would thermal even better.

my Boomer DLG is a delta flying wing and thermals quite nicely from a handlaunch in hands more experienced then mine.

[ericfly]

Tks a lot for your replies! I'll make a 2m plank, maybe powered by a gws 350D motor, and post the result.

CJS, could you give me the specs of your bird? Span, chords, sweepback and airfoil?

Best Regards,

Eric

[the_canuck]

I personally have seen a moth 48 thermal to the clouds off a bungee launch flatland flying. We were in the Pawnee National Grasslands Park in North Eastern Colorado.

Andrew

BTW altitude is 4500 - 5000 feet there so air would be a lot thinner than sea level.

[Bernd Brunner]

Hi eric,

look at http://www.das-nurfluegelteam.de/co5_2m.html

that´s easy to build with excellent performance.

Bernd

[Daemon]

I've specked out my 48" Moth many times, and often use it as a scout
for the local paraglider pilots. I do cheat though as I often still
launch from a slope even though the flying is often mostly thermals.
I've bungeed it up a few times and believe that if I were consistent
about it, I could thermal it just fine launched from a flat field with
about a 150 foot launch. You're right about the challenges though.
Low camber and zero pitching moment doesn't make for a high lift,
slow flying airfoil. The advantage to a plank over a swept wing
however is that you don't have to worry about tip stall and washout,
so you gain back some efficiency you'd have lost dealing with those,
and you can pretty much pull back on the elevator as much as you
want when you're in big lift and it'll just go up and up, or put the nose
down and get out of sink fast. Not to mention that coming down from
speck altitude is a lot of fun too.

ian

[MikeC]

Bernd,

Have you built the 2 Meter CO5?

I am interested in hearing from someone who has built one about its thermalling abilities.

thanks,

Mike

[11b2c]

You may want to check out a design called "EL Condor" published in RCM in may of '94. As I recall the plane is an electric based on the Windfreak design. The plans are still available. It is plan pl-1168: go to rcmmagazine.com and follow the links to the sailplane plans.
Here are the specs:

80-3/8" span, 985 sq. in., 05 electric motor, 3 ch., built-up balsa, plywood, and spruce.

I never saw one fly but it looked like an interesting project and the basic dimensions may help you out for your project.

[Ollie]

http://www.aerodesidn.de/english/profile/profile_s.htm

Cm > 0.007 for plank. Not for S5010 or MH45 Cm < 0.005.

[ericfly]

Tks a lot for the replies. I'll use these models to inspire my design.
Ollie, the S5010 is the Moth airfoil (I guess), and the MH 45 is the Gulp DS (?) and many other planks. I tested it on two of my designs, a planks and a swept back wing and it performs very well, since you find the correct CG.

Best Regards,

Eric

[Ollie]

No plank for Cm < 0.005. No S5010 or for MH 45!!!!!

Go for plank airfoil for Cm > 0.007 !!!!!

[windsox]

I suspect elevon trim is used to to get the moment up on mh45 based planks. also , if you look at the 1/4 chord line sweep of a number of popular delta'ish planes (boomer, red herring etc) you notice that from an planform perspective the planes have a small amount of effective sweep despite the straight TE, hence the lower moment requirement makeing mh45 work well. It has also been observed that the mh45 likes to be flown at reynolds numbers near 100,000, which means larger spans and or higher speeds required for optimal cl/cd. I am not trying to make out that I am some kind of authority on this by any means ,I am mostly just regurgitating oppinions expressed by others as I walk up the aeordynamics learning curve. I believe the re stuff was stated/confirmed in a post by mtngoat who thought that his 78 inch delta(purple thermal easter) flew the best after trying a number of different span lengths. I love the way my boomer flies, you just have to be carefull not to nose it up to much, at certain angles of attack a delta becomes a parachute/airbrake. check out that nurfleugal.de sp? link for some good plank foil suggestions.


No plank for Cm < 0.005. No S5010 or for MH 45!!!!!

Go for plank airfoil for Cm > 0.007 !!!!!

[ericfly]

Today I made some experiments on Profili, trying to find the best foil for my model. It will be a plank with no sweepback, 78" span, 12" root 10" tip. I did some calculations based on Simmons's book and found my model will fly between 100k and 200k (Reynolds number), and the weight will be about 18oz without motor, but just 4-5 oz more with motor. So, the Coefficient of Lift will be around 0,15-0,25, up to 0,4 ballasted. In this situation I compared some foils (polars) and found the following:
The MH45 is better than the s5010.
The MH45 has very good L/D even on high Cl (1,2...), it means it will do sharp turns without loosing energy (good for DS and slope racing) but it costs some extra drag on lower Cls, and since this model is not for race, but for thermals, I do not need that low drag at high Cls. I just thinned the profile by 30% and WHAT A DIFFERENCE!!! Up to a Cl of 0,8 it has much less drag than the stock MH45.

But maybe there are 2 problems: 1)The Profili uses the Xfoil to draw polars, and it may be not accurate. 2) Thinning the foil would change its pitching moment? Would it get unstable?

[Ollie]

HS 130
Slope Soaring, DS

JWL-065
Allround, Slope Soaring

EMX-07
Plank. F3B

Phönix
Plank, F3B

HS 2.0/8.0
Plank, Slope

HS 130
This airfoil is very popular in Germany for very fast planks, e.g. dynamic soaring and everything else you need for slope soaring. Less drag and very fast. Thickness can be reduced to 7,5% without modification of camber. In german "Aufwind" magazine you can find a detailed analysis of this airfoil. Elevons: 25% chord. This airfoil is optimized for use of elevons. HS2,0/8,0 is outdated, you should use HS130 if you want to use an airfoil of my series for slope soaring. Minimum chord 150mm due to Rn. Please note that "classic" plank airfoils need 250mm and more! Aspect ratio 8-13, not more; e-powered planks up to 16.



JWL-065
This airfoil is the opposite of HS130 in many cases: center elevator is the right choice to reach optimal performance. Do not slow down using Elevator, the cm is somewhat higher than HS130. Elevator is just used to rise speed and nothing else. The basic trim is low speed (thermal) and pitch down is just for gliding/speed. Elevator: 20% chord. Minimum chord 150mm due to Rn, aspect ratio 8-13, not more.

EMX-07
Modern airfoil designed by Martin Lichte. Seems to work very well as on Stefan Siemens flying plank "Niveau". I flew against him and I can say that this section is not a bad choice!!! Ok, I killed him in gliding performance using my "Aeolus" but in thermal soaring he was always a challange!




Phönix
Well known since it emerged at the Plank of Perlick/Kowalski. Seems to be dreadfully good. The somewhat smaller cm0 is something more for fast/heavier planks. No, I do not have a reliable value in addition. I estimate it according to experience on approximately +0.0 max +0.01. Due to this the Phönix is not the right choice for lightweight designs, some (mass-) inertia behind it is recommended to get rid of the low-cm problems.
Lightweight constructions can be detected by a classic rodeo flight style (instability pitch axis). Gyroscopes can conditionally help, surely not the hit. A heavier model absorbs alone due to its mass inertia this possible fast pitch nick frequency ("wippen" like SB-13).
Conclusion: On of the best sections for vacuum bagged planks I have ever seen!




HS 2.0/8.0
This section has been developed for fast plank concepts (slope soaring) and is based on "Phönix" not the worst reference I think. It was a rainy day when I got the idea that I would like to have a section between speed and sections like Phönix or EMX-07. Models like "Sturmtänzer" and E-powered flying planks are the destination of this section. Why? The low cm design needs some mass intertia behind so it is not a good idea to build a lightweight plank with this kind of section.


Where I got this experience? HS06 and HS22 used just the same wing. HS06 is an E-powered flying plank and it was quite well. I destructed this plank by passing a thermal with a lot of speed. Not a good idea having an open bay construction without D-Box and doing this! Some years later I remembered the good performance of this plank and I build HS22, a thermal plank, using the parts of the old HS06 wing. The handling was terrible! It is like a rodeo ride around pitch axis! HS3,0/9,0 has been used. Ok, now you see that things can work just because of mass inertia and in other case, same section, same wing, absolutely not!!! And believe me:



NEVER USE CM0=0 SECTIONS FOR FLYING PLANKS!!!
This might work as before mentioned but normally does not!


The Phönix's trailing edge is somewhat fat due to building technologie. But on a speed plank concept like "Sturmtänzer" nothing except vacuum bagging makes sense. This building technology do not need any compromise in airfoil design so we get some more performance...
This difference is quite substantially, especially at low cls we have longer laminar run on the lower side. At low Rn the airfoil is something better too so there is no disadvantage in doing this.



*


*

[windsox]

QUOTE=Ollie]HS 130
Slope Soaring, DS

JWL-065
Allround, Slope Soaring

EMX-07
Plank. F3B

Phönix
Plank, F3B

HS 2.0/8.0
Plank, Slope

HS 130
This airfoil is very popular in Germany for very fast planks, e.g. dynamic soaring and everything else you need for slope soaring. Less drag and very fast. Thickness can be reduced to 7,5% without modification of camber. In german "Aufwind" magazine you can find a detailed analysis of this airfoil. Elevons: 25% chord. This airfoil is optimized for use of elevons. HS2,0/8,0 is outdated, you should use HS130 if you want to use an airfoil of my series for slope soaring. Minimum chord 150mm due to Rn. Please note that "classic" plank airfoils need 250mm and more! Aspect ratio 8-13, not more; e-powered planks up to 16.



JWL-065
This airfoil is the opposite of HS130 in many cases: center elevator is the right choice to reach optimal performance. Do not slow down using Elevator, the cm is somewhat higher than HS130. Elevator is just used to rise speed and nothing else. The basic trim is low speed (thermal) and pitch down is just for gliding/speed. Elevator: 20% chord. Minimum chord 150mm due to Rn, aspect ratio 8-13, not more.

EMX-07
Modern airfoil designed by Martin Lichte. Seems to work very well as on Stefan Siemens flying plank "Niveau". I flew against him and I can say that this section is not a bad choice!!! Ok, I killed him in gliding performance using my "Aeolus" but in thermal soaring he was always a challange!




Phönix
Well known since it emerged at the Plank of Perlick/Kowalski. Seems to be dreadfully good. The somewhat smaller cm0 is something more for fast/heavier planks. No, I do not have a reliable value in addition. I estimate it according to experience on approximately +0.0 max +0.01. Due to this the Phönix is not the right choice for lightweight designs, some (mass-) inertia behind it is recommended to get rid of the low-cm problems.
Lightweight constructions can be detected by a classic rodeo flight style (instability pitch axis). Gyroscopes can conditionally help, surely not the hit. A heavier model absorbs alone due to its mass inertia this possible fast pitch nick frequency ("wippen" like SB-13).
Conclusion: On of the best sections for vacuum bagged planks I have ever seen!




HS 2.0/8.0
This section has been developed for fast plank concepts (slope soaring) and is based on "Phönix" not the worst reference I think. It was a rainy day when I got the idea that I would like to have a section between speed and sections like Phönix or EMX-07. Models like "Sturmtänzer" and E-powered flying planks are the destination of this section. Why? The low cm design needs some mass intertia behind so it is not a good idea to build a lightweight plank with this kind of section.


Where I got this experience? HS06 and HS22 used just the same wing. HS06 is an E-powered flying plank and it was quite well. I destructed this plank by passing a thermal with a lot of speed. Not a good idea having an open bay construction without D-Box and doing this! Some years later I remembered the good performance of this plank and I build HS22, a thermal plank, using the parts of the old HS06 wing. The handling was terrible! It is like a rodeo ride around pitch axis! HS3,0/9,0 has been used. Ok, now you see that things can work just because of mass inertia and in other case, same section, same wing, absolutely not!!! And believe me:



NEVER USE CM0=0 SECTIONS FOR FLYING PLANKS!!!
This might work as before mentioned but normally does not!


The Phönix's trailing edge is somewhat fat due to building technologie. But on a speed plank concept like "Sturmtänzer" nothing except vacuum bagging makes sense. This building technology do not need any compromise in airfoil design so we get some more performance...
This difference is quite substantially, especially at low cls we have longer laminar run on the lower side. At low Rn the airfoil is something better too so there is no disadvantage in doing this.



*


*[/QUOTE]

[ericfly]

Ollie, tks for the tips. Most of the foils you listed are not on Profili2's database. Where can I find it? Could you email-me the dat/cor files? ericfly@uol.com.br .

Best Regards,

Eric

[Ollie]

#12
http://www.aerodesidn.de/english/profile/profile_s.htm
http://www.aerodesidn.de/english/profile/profile_s.htm
http://www.aerodesidn.de/english/profile/profile_s.htm
http://www.aerodesidn.de/english/profile/profile_s.htm

[Ollie]

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[Bernd Brunner]

Hi Eric,

another link http://leinauer.de/aero/schiski/?jwl=zeichnung
it´s a plank with jwl065. Should thermal very well. It will also be build in epp
http://www.epp-fun.de/frame.htm?/schiski.htm
I will look for reports about thermaling with the co5 2m.

[ericfly]

Tks a lot Ollie and Bernd, the information will be very useful!

Best Regards,

Eric

[Charlie C]

Many years ago when Dave Jones and I were designing planks I built a Raven and used a split rudder for an air brake. The rudder servo was set up like an aileron servo with a pushrod to each side of the split rudder. Another servo was used to slide the rudder servo forward to open the rudder. Much easier to do now with computer radios. It was very effective for hitting a spot. On the Raven it caused some pitch up when deployed which was counteracted by mixing in some down elevator.

Flaps work well on planks, but are vulerable to damage on gliders. I have a 100 inch span plank powered by a Saito 91. Since it has a landing gear flaps are ok. They are large and mounted under the main spar on the inner wing panels. This plank has polyhedral wings, but no ailerons. It can be wicked to take off in a cross wind, but once in the air it's a joy to fly.

I'm getting back into soaring and thinking of upgrading some of my old plank designs with a modern airfoil.

Check out B2Streamlines!

Chuck Clemans

[ericfly]

Charlie, your plank is very interesting, as your reply. Could you post some pictures of that model? It would be even better if you post pictures of your flap system too.

Regards,

Eric

[Charlie C]

Eric,

I hope the pictures are ok. Each of the four wing panels is approximately 24" in span with a 17" chord. Total span is 100". Each flap is 3" x 16". I published the Gross Vogel II design in Model Builder Magazine in the Feb. 79 issue. The flaps were added much later to help in landings. It would float forever! If you have questions or if the pictures don't come through, email me at EagletHanger@aol.com

Charlie Clemans

[ericfly]

Charlie,

Very nice design! How did you determine the correct position of the flap in the chord, to avoid and pitching problem? Would you reccomend full-span flaps?

Regards,

Eric

[colin wavell]

This is a 60" design from a plan byDave Jones and Nigel Brewer. QFI plan 1995 MW 2496 available from Traplet publications. I first built this as an electric plane but now have an unpowered slope version. There is a 100" thermal versioncalled Max100 MW2604 where the center section has been enlarged. These are all built up and very light! the big one should thermal well.

[Charlie C]

Eric,
I think I read in B2 Streamlines that the flaps on a plank should be at 40% chord, I don't remember for sure. Since they were an add on and not part of the original design, I put them as far forward as I could immediately behind the second spar. This plank weighs 13 lbs and the flaps are very effective. I would not reccomend full span flaps.

The original Gross Vogel was the same size and planform, but much lighter. I think it weighed only about 3.5 lbs. It was powered by a Cox .09 glow engine mounted in the aft end of the fuselage and was hand launched. It was seriously underpowered. It then became a tail dragger with various engines in the nose because of cg considerations. It was powered by a Cox .15, .35, Enya 45, Super Tiger .56, and eventually an Enya .60.

GV 2 has been powered by an Enya .60, Super Tiger .90, and Saito .91. Once in the air most flying is done at half throttle or less. Low and slow figure eights over the runway are most impressive!

The inspiration for the Gross Vogel was a towline model designed by the late Dave Jones when he was living in Torrance, California. If I build another model of this type I'll probably call it the Albatross since it is so ungainly on the ground and so at home in the air. Gross Vogel is not good for much except that it's very unusual and great fun to fly.

I've been playing around with a reflexed version of the Eppler 205 which I'd like to try on my next plank.

Happy Landings,

Chuck Clemans

[sloper steve]

Plank for super light EPP sloper?
Going to try some epplers or the HS

[WimH]

Hi Eric,

another link http://leinauer.de/aero/schiski/?jwl=zeichnung
it´s a plank with jwl065

Johannes Leinauer (JWL) died, much to young, of cancer last week. He will be missed by those who knew him, especially his wife and children...

[steelhead]

Thanks for posting those coords- I've been working with a few different airfoils for my projects... nice to add a few more :)

Dean

[kak8]

I have several homebuild slope planks, and I`m working on a thermal plank too. I`ve made a mould for the fuselage and vacuum bagged the wings- I mean I covered the wings with glass/balsa in vacuum. My plank is about 3m. I just don`t know how to make some kind of air brake.
I have 3 sugestion. A,B,C

If I find it out, I will cut my long aileron in 2 pieces and build the rest, so I can tell you how the MH45 plank flies, so let me hear some sugestions :)

[glydr]

http://www.aerodesign.de/english/

Great site for 3-views. But you probably knew that already.

Enjoy

[kak8]

Yes, I know that. The only place I know where to get some usefull informations about planks and wings is a pdf book somewhere on the internet called " on the wing" - part 1 and 2. Really good one if not the only one for home builders of thermal wings/planks.
But theory is not enough for me, so I have to use one of my slope planks to do some experimens. I`ve allredy try to high launch one of them without problems. So the next is to cut my elevon in 2 pieces ( elevator and aileron) and se how it works. Later I will try to use the elevator as a flaps/air breaks.

[histarter]

Fellas, I wanted to build Low Aspect Ratio planks for getting the most out of a wingspan restriction of 60 inches, but ran into one primary problem for thermalling the machine. Conventional designs, CL can exceed 1.0 for airspeed to accomodate the thermal model; whereas with planks operating at CL 0.5 or less means that the plank's loading for equal airspeed is cut more than 1/2! I can build conventional down to 4.5 oz/ft - but am uncomfy with the thought of 2.0 oz/ft sailplanes. :eek:

To beat that limitation I selected a compromize of using a stabulator in conjuction with elevons to reduce the reflex needed for slow flight, so as to raise CL to 0.8. This brought me right back to using conventional - but using short moment arms with profiles that will yield CL 1.2 approx. - that does the job simpler/better. :D

I am curious how you handle the extremely light loading needed for thermalling? :confused:

[BMatthews]

For my own plank or swept flying wing rule of thumb I always based my wing loadings on 2/3 of the true wing area. That is based on the idea that 2/3 of the wing area is for flying and the other 1/3 is just along for the ride and to provide pitch stability. I know this is just something that I pulled out of the air but I suspect it should be fairly close to real life from the flying wing models that I've seen fly.

As to how to deal with the lower max Cl's just let the model fly a little faster so you don't need to push up to that high a Cl. But you're right in that the total wing loading needs to be lower.

[histarter]

As to how to deal with the lower max Cl's just let the model fly a little faster so you don't need to push up to that high a Cl. But you're right in that the total wing loading needs to be lower.
Taking a GL config, I find my prefered loading for that profile for conditions below a 12 mph breeze is 6.75 oz/ft^2.
CL for that profile is about 1.3, so changing profile to Dr. Drela's series for the nominal airspeed to be the same 6 mtrs/sec that I am content with, the loading would have to change to 4.15 oz/ft^2. :rolleyes:
Then to build a plank for the same span, but with more area (lower AR) we are talking about 2.5 oz/ft^2; :( and that is what makes the wing concept so tough to out thermal the stock GL, let alone my stubby version. The problem is the spoiling action of the reflexing elevator, and this is what led me to my compromise design of using a programed reflex to control a large wing area, and a tiny stabulator to drive the flying surface above and below nominal alpha - to add more speed range onto the config. :D

Flying faster makes the wing physically work - however to enjoy all the nuances of thermal flight (bank angle, airspeed to run between lift, spiral stability, control damping) one will find himself cheated by this solution. :eek:

[steelhead]

HighStarter- what ever became of your small moment wing?

KAK8- How's your 3M project? Also, nice plank over in foam cores, no vac thread. Looks like a 48 incher I was working on last spring. Had to put her down for a little while over summer. Thermal season is almost back though.....Was experimenting with swept forward wings. At about 1 inch total sweep I got best results, even tried tip launching it, but needed a larger fin. Did you glass that one too? Looked like a no flex bungee launch.

Nice Pacific Storm threatening to kill the power, so I'll log off tonight and dream of low reflex high speed wing airfoils.

Dean

[Ollie]

I am starting a thermal design plank.

Airfoil EMX-07
Span 78"
Wing area 1248 square inches
Root chord 20"
Tip chord 12"
Aspect ratio 4.9
Washout 3 degrees
Design lift coefficient 0.4
Design weight 35 oz.
Design L/D 16
Design sinking speed 1.4 FPS

Structure
Skin: 2mm Depron, .75 oz. fiberglass, epoxy (~$15)
Ribs and shear web: 2 thickness 2mm Depron, .75 oz. fiberglass, epoxy (~$5)
Spar cap: carbon 2 x 0.04 x 0.166" = 0.08 x 0.166" (~26)

Based on shape of Blackbird.

[Kai@UCSB]

Ollie,

Please keep us updated and pictures will be great :)

-Kai

[kak8]

Steelhead - thanks, there is glass fabric under the balsa and a spar with some carbon under and on top of it.
I`m still trying to figure out how to cut the ailerons. I think I will make a small flaps/air brakes close to the fuselage, and ailerons on the rest of the wing - maybe in 2 pcs so there is to servos runing parallel. That way I will still have a chance to try to mix them.
I don`t expect thermal records :) but I´m affraid it will end as a sloper and that wasn`t the point.

[Ollie]

Kai,

A week ago I order the Depron 2mm sheets but I have not got the sheets.

I have not started the building yet. I'm improving the design on paper.

One of the reason that good planks are thermal types because wood is too heavy and too weak for the job. You will note that the wing loading is very low.

I changed the airfoil too.

Airfoil JWL-065 *
Wing span 78"
Wing area 1248 square inches
Root chord 20"
Tip chord 12"
Aspect ratio 4.9
Washout 3 degrees
Design lift coefficient 0.4
Design weight 26 oz. *
Design L/D 16
Design sinking speed 1.1 FPS *
Sweep angle (of 25% chord line) 8.8 degees

Structure
Skin: 2mm Depron, .75 oz. fiberglass, epoxy (~$15)
Ribs and shear web: one thickness 2mm Depron, .75 oz. fiberglass, epoxy (~$5) *
Spar cap: carbon round rod 0.08 "Dia. (~$12) *

*Changed

The airfoil thickness at the root is only 1.5". Design of the spar was over kill. Redesign of the spar caps cuts the carbon cost and weight. Using the skins with one side covered with fiberglass saves weight. The new weight of the structure is about 26 oz. and wing loading down to 3 oz. per square foot.

Next time I will calculate sinking speed, air speed, Reynolds numbers and, L/D for Cl=0.1, --0.2, --0.3, --0.4, --0.5, --0.6, --0.7, --0.8. The low Cl comes from high speed, for medium Cl comes for maximum L/D and for high Cl for minimum air speed and winch or hi-start launch.

Compared to a floater with a tail, this floater plank uses ~1/2 the Cl, ~1/2 the wing loading, ~1/2 the aspect ratio, ~2 times the Re and less than ~1/2 the parasitic coefficient of drag.

[histarter]

Steelhead, the wing wore me out. I got too old to DSL, (even my collection of boomarangs became sticks!). The proto was too heavy to fly at the airspeed needed - meaning I was forced to go to open bay structure to make it light enough - that I wasn't too keen about doing.
Michael Richter has executed my concept (without the stabilator) with his Alula - just a lot smaller than what I was looking for, but a far better scheme. If I could still fly (just got too old too fast), I would go after my design variant with gusto - even though there would be no popularity because everyone wants to work the upper air. :rolleyes:

Ollie, your plank specs are looking good -- and the Blackbird is a great design target for working the upper air. 4 oz/ft sounds right for the typical (20 mph) airspeed needed to work the upper air mentioned. The Blackbirds downward spoiler system should work quite well - acting both as a flap and divebrake. Wish you success on your undertaking. :D

[BMatthews]

Hey Ollie, you have a link to that JWL-065 airfoil?

I'm not sure I like all that foam and 'glass what with me being a dyed in the wool Balsaholic but I'm going to be very interested in seeing your wing come together and hear about the flying.

Never mind. Google is my friend. I just didn't think it would pop up that easily.

Slippery looking as a eel that airfoil is. I'm even more interested now.

[Kai@UCSB]

Ollie,

Thank you for the information.
Do you consider about 2 or 3 piece wing as well ? One another advantage for plank might be the easier transportation.

-Kai

[kak8]

I`ve build this DLG wing with JWL-065 airfoil last year. It flies good when its light. After a few throws I had to add a carbon tube as a "spar". I could throw higher but the gliding performance wasn`t that good anymore.

[Ollie]

Bruce,
http://www.aerodesign.de/english/profile/profile_s.htm
http://www.aerodesign.de/profilelight/pl09_bild_01.gif
http://www.aerodesign.de/profilelight/JWL065.dat

The 2mm Depron has a density of about 3 pounds per cubic foot compared to balsa density. When you put one side with 3/4 oz fiberglass and epoxy you double the weight. When you put two sides with 3/4 oz fiberglass you tripple the weight. It's stiffness is depending how you want it in the application. I like the 2mm Depron because it has a plastic skin and it so dent free.

Kai,
I will use a two part wing panels, with two jointers in the wing center. The jointers are blade type. The blade (~ 1.25" x ~ 3/32" x ~8") about has 2mm Depron, 0.08 dia. carbon rods along the edges and wrapped with four layers of 3/4 oz. of fiber glass in epoxy. The flat tubes for the jointers are made with Aramid Braided Sleeves in epoxy.

kak8,
The reason I picked the structure with skin and ribs was to remove some foam core weight.

This afternoon I will post the calculations.

[Ollie]

I begin the wing design by using the spanwise lift distribution Wing Analysis Program:
http://aero.stanford.edu/WingCalc.html
I use the range angle of attack (AOA) from stall to very small lift cofficient.
AR 4.9, Sweep 8.8 degrees, Taper 0.6, Twist 3 degrees
AOA 14.5, 13, 11.5, 10, 8.5, 7, 5.5, 4, 3 degrees,
coresponding to Cl’s 0.886, 0.816, 0.712, 0.607, 0.503, 0.398, 0.294, 0.189, 0.119

Air speed = ( air density x wing loading / Cl)

Air speed 13.3, 13.9, 14.9, 16.1, 17.8, 19.8, 23.3, 28.9, 36.25 feet per second

Reynolds no. = avg. chord (ft.) x air speed (FPS) x 6080
Re=101k, 106k, 113k, 122k, 135k, 151k, 177k, 219k, 275k

Using the airfoil polar Cl vs. CDo graphs for Re 100k and 400k I estimate the interpoltion for this aircraft.

CDo = 0.03, 0.022, 0.017, 0.016, 0.014, 0.013, 0.011, 0.009, 0.001

Used CDi from the Wing Analysis Program:

CDi = 0.051, 0.043, 0.033, 0.024, 0.016, 0.01, 0.006, 0.002, 0.001

L/D = Cl / (CDo + CDi)

10.9, 12.6, 14.2, 15.3, 16.1, 17.4, 17, 16, 12

Air speed / L/D = Sinking speed

1.22, 1.11, 1.05, 1.05, 1.1, 1.14, 1.7, 3 FPS

My next job is to cut the 11 rib formers from Formica.

By the way, the Depron sheets were delivered last evening.

[Cebola]

Ollie

Can you sugest me a good design for a Flying Plank ?

It's for thermal, but light enought to be used in light conditions, and , made in balsa.


regards


Cebola
Brazil

[Ollie]

Cebola,

See:
http://www.b2streamlines.com/
http://www.b2streamlines.com/OTW.html
Backbird 2M
http://www.rcsoaringdigest.com/
Download RCSD 2004, 2005 and 2006 PDF's month by month.

[Whorges]

Ollie,
Thanks for posting the math. I find it very interesting as it relates to design and as it relates to flying.

Something that I find suprising: Lowest sink rate doesn't occur at just above stall speed.

14.9 to 19.8 fps is your still air speed range in thermal vs. neutral air. But you still have a good glide all the way up to about 29 fps, sounds like a nice bucket.

Please keep us posted for the build and fly, and let me know when the kit comes out :O)
-Whorges

[Ollie]

Last night, I desided to stop building with 11 rib fromers and cutting ribs with an razor blade and not build the wing with a foam hot-wire jig to hold the wash out. I am building a plywood jig that holds the rib blanks and sub-ribs in position and in spacing. With two hot-wire cuts with 11 rib and 11 sub-rib blanks. After the ribs and sub-ribs are removed, the rest of the blanks (top and bottom) will hold the washout for the assembly for the wing panel.

[B2Streamlines]

Because of the publishing demands of RC Soaring Digest, we just are not able to follow all of the threads on RC Groups. Our thanks to those who pointed out this thread to us, and to Ollie for recommending our "On the 'Wing..." series. All three completed volumes are available through the B2Streamlines web site, and the fourth volume, still expanding, is available as well.

One of the big fallacies of planks is that some amount of washout is needed. Planks do not need washout, and in fact washout can be detrimental to stability. Build your plank wing with no twist! (That includes planks with small amounts of quarter chord sweep back, like the Blackbird.)

Once you get into planforms with true sweep back, you can start thinking about adding washout. We highly recommend the Panknin formula for determining how much twist you really want/need.

So far as plank airfoils, we're very pleased with an airfoil designed by Barnaby Wainfan, the BW 05 02 09. Coordinates are on our B2Streamlines web site. This airfoil may take well to thinning. We have an aircraft drawn up which will use a 6% thick version of this section, and it should be flying this summer in the Seattle Area Soaring Society Multi-Task Event.

Anyone having specific questions about tailless aircraft can contact us through the B2Streamlines web site <http://www.b2streamlines.com>.

Thanks!

[Ollie]

Bill (B2Streamlines),

Thanks for your correction! Just now, I used Dr. Pankin's formula with JWL - 065 and Cm of 0.0298 and too much 8.8 degrees washout! If I use an airfoil HS130 with Cm of 0.015 I get about 3 washout. What is the Cm for the BW 05 02 09? Please, check me out, Bill.

Cebola,

I was thinking about your question and about building with balsa and not foam and carbon. You can reduce the structure loads by using two launch hooks and reduce spar weight and other structure weight. With low weight srevos, receiver and battery you can use mass span loading distribution along with lift distribution. I'll show how to use the details later.

Whorges,
We could use the nice bucket near the stall airspeed and low L/D by K.I.S.S. the design. Maybe we could forget spoilers and with mushing for spot landing. The induced AOA with low aspect ratio and the high pitch attitude shows the pilot a visual clue to airspeed.

I'm not finished the design. While I am building the jig, I will design the spar and the hook positions tomorrow. After tomorrow I will design the vert. tail and the calculation for parasitic drag coefficient for the poorer L/D and sinking speed.

[B2Streamlines]

Ollie,

You give the dimensions of your plank wing, but neglect to let us know the sweep angle of the quarter chord.

We're going to assume that since you've based it on the Blackbird, that the trailing edge is a straight line. If the Panknin formula is telling you to use washout, the airfoil you're using is not producing a large enough positive pitching moment for the other parameters you put into the formula.

It sounds like you're expecting too high a CL for this design, especially since the aspect ratio is so low. Remember, you want the twist based on the design CL, which should be cruising speed, not thermalling speed. For thermalling, you'll be pulling some up elevator which will make the pitching moment more positive.

The smoothed BW 05 02 09 has a zero lift angle of -0.33 degrees and a pitching moment of 0.014 at Re = 300K (XFoil numbers). You can always download the relevant BW 05 02 09 documents from the B2Streamlines hame page links.

Let us know if we can be of further assistance!

[Ollie]

I have changed the airfoil to HS-130. Denoted by * for new numbers.
I begin wing design by using the spanwise lift distribution Wing Analysis Program:
http://aero.stanford.edu/WingCalc.html
I use the range angle of attack (AOA) from stall to very small lift cofficient.
AR 4.9, Sweep 8.8 degrees, Taper 0.6, Twist 3 degrees
AOA 15.5*, 14.5, 13, 11.5, 10, 8.5, 7, 5.5, 4, 3 degrees
Coresponding Cl’s 0.991*, 0.886, 0.816, 0.712, 0.607, 0.503, 0.398, 0.294, 0.189, 0.119

Air speed = ( air density x wing loading / Cl)

Air speed 12.6*, 13.3, 13.9, 14.9, 16.1, 17.8, 19.8, 23.3, 28.9, 36.25 feet per second

Reynolds no. = avg. chord (ft.) x air speed (FPS) x 6080
Re = 96k*, 101k, 106k, 113k, 122k, 135k, 151k, 177k, 219k, 275k

Using the airfoil polar Cl vs. CDo graphs for Re 100k and 400k I estimate the interpoltion for this aircraft.

CDo = 0.03*, 0.022*, 0.018*, 0.017, 0.016, 0.016*, 0.013, 0.017*, 0.011*, 0.01*

Used CDi from the Wing Analysis Program:

CDi = 0.064*, 0.051, 0.043, 0.033, 0.024, 0.016, 0.01, 0.006, 0.002, 0.001

CDp = 0.012*

L/D = Cl / [CDo + CDi + CDp x (tail area / wing area)] *

10.4*, 11.9*, 13.2*, 13.9*, 14.9*, 15.6*, 16.6*, 12.1*, 12.6*, 10*

Air speed / L/D = Sinking speed

1.21*, 1.12*, 1.05*, 1.07*, 1.06*, 1.14*, 1.19*, 1.93*, 2.3*, 3.6* FPS

*Changes.

From Dr. Mark Drela:
"Cv = (A_vert/A_wing) * (tail_arm/avg_wing_span )
A well-sized tail will be in the range...
Cv = 0.02 - 0.035
If the Ch and/or Cv are below the minimum values, the handling will suffer."
I use Cv=0.02 and 20'' tail arm. The result is a tail area of 97 square inches (~1/12 of the wing area).

Later I will position the hooks and design the spar.

The HS-130 airfoil is even slower and better with thermals but it penetrates poorly compared to the JW-065 airfoil.

My Mac computer doesn't run Window's programs. I don't have Profili 2 and XFoil. XFoil is the best tool for the design job. If I had XFoil, I would use the airfoils with control surface deflections for the airfoil's polar graphs Cl, CDo, Cm, Reynold number, etc.

Almost two years ago, I had a stroke. I am recovering with aphasia. I fly, I build in my workshop and I design. For my age I don't have many problems with my body. I think best with concepts but I have problems with words, including spelling and grammer. I use this forum with my aphasia exercises daily. I love this forum and I love this hobby/sport.

[Ollie]

Bill,
I found the BW 05 02 09 (smooth) with Xfoil, Re=300k, alpha=-.327degrees, Cl=0, Cm=.0143 and alpha=2.5, Cl=.3075, Cm=0.0161.

With my design with a wing loading of 3oz. per square foot, the reynolds range is about 100k to 275k.

I put the design: 78" span, 20" root chord, 12" tip chord, 8.8 degrees sweep back, static margin 0.05, 26 oz. weight, Cm= 0.0161 (BW 05 02 09 airfoil) in the Panknin Twist spreadsheet. The results were twist alpha Geo. = -3.1 degrees and Cl=0.4

Not to worry about the twist.

Best regards, Ollie

[BMatthews]

Ollie and Bill. If I remember right the Panknin spreadsheet works great for finding the CG of a plank. To do this you need to "cheat" a little by putting in either a minimal sweep angle like a tapered wing would have or in the case of a constant chord plank you input a small angle of sweep like 1 or 2 degrees. Then you input the airfoil Cm and alter the CG location until the twist you're told to use is basically zero. That is then the best CG for that particular airfoil that will not require any elevator trim which would ruin the Cl range or result in too much down trim and an unstable airfoil.


Given what I read about the SWL 065 airfoil it sure looks like a movable CG would be the best way to trim the glide. They mention that the CG should be set for the minimum speed and then only slight down trim used for speeding up. No up trim to slow down should be used. That just screams "MOVABLE CG" to me...

Edit: don't know where the SBW came from but I'm reffering to the SWL 065. Corrected above.

[kak8]

I have build a 48" slope wing with HS-130 airfoil and its not slow, comparing to the other wings. Out of 30 slopers I`ve been flying the finals and somebody turned the radio on the same channel :-(
I have build a 48" plank for my friend with the same airfoil and this is his favorit slope wing. That tells something about flying in lift - like thermal. I don`t know how good/bad it is without thermals.

[Ollie]

Kak8,

A little of airfoil, a little of size, a little of loading, a little of of this and that makes a good design. Don't say a airfoil is good except in its special application. The quote from Don Stackhouse:

"Similar threads have argued over the shape of the "ideal" planform, the "best" airfoil, the "optimum" aspect ratio, and the validity of modified airfoils or of blending from one root airfoil into a different tip airfoil. All this controversy reminds me of one of my favorite stories:

The Four Blind Men and the Elephant (an old Hindu parable)

One day four blind men encountered an elephant for the first time. They approached it cautiously, but with great curiosity. The first one grabbed hold of the trunk and declared "Aha! An elephant is just like a snake!" The second found an ear and replied "No, an elephant is exactly like a tent." The third bumped into a leg and decided the elephant was just like a tree, and the fourth caught the tail and maintained that the elephant was just like a rope. They all went home arguing, each steadfastly insisting that he was right and the other three were wrong."

[histarter]

Kak8,

A little of airfoil, a little of size, a little of loading, a little of of this and that makes a good design. Don't say a airfoil is good except in its special application. The quote from Don Stackhouse:

"Similar threads have argued over the shape of the "ideal" planform, the "best" airfoil, the "optimum" aspect ratio, and the validity of modified airfoils or of blending from one root airfoil into a different tip airfoil. All this controversy reminds me of one of my favorite stories:

The Four Blind Men and the Elephant (an old Hindu parable)

One day four blind men encountered an elephant for the first time. They approached it cautiously, but with great curiosity. The first one grabbed hold of the trunk and declared "Aha! An elephant is just like a snake!" The second found an ear and replied "No, an elephant is exactly like a tent." The third bumped into a leg and decided the elephant was just like a tree, and the fourth caught the tail and maintained that the elephant was just like a rope. They all went home arguing, each steadfastly insisting that he was right and the other three were wrong."

In the world of the individual, there is no right or wrong. i.e. If one wishes to live on a slope, and he designs and flys his sailplanes accordingly, sucessfully, he is content; however, his total soaring outlook will be biased by his endevor. Profile selection included. :rolleyes:

I found my slice of soaring centered upon the short histart, and my outlook is the excitement of the climbout - with a large sailplane, with the impetus of learning to be consistant with a reasonable task time. This attitude was developed from my exposure to Nordic TLG competition. Conceptionally: I can launch to my old bunting altitude, work lift with radio assistance, and return safely. A tremendous improvement over a free flight! However, my design and profile selection becomes totally specialized, and doesn't favor those that want to dominate full size soaring territory (majority?). :rolleyes:

There is enough gradiant in individual capabilities that (regardless of preference) some techniques will work better than others, and this is what the commraderie of entusiasts try to share...And it should be "without prejudice". :)

[Ollie]

Bruce,

You have good advise. I reread the application of JWL-065 from
http://www.aerodesign.de/english/profile/profile_s.htm
"JWL-065
This airfoil is the opposite of HS130 in many cases: center elevator is the right choice to reach optimal performance. Do not slow down using Elevator, the cm is somewhat higher than HS130. Elevator is just used to rise speed and nothing else. The basic trim is low speed (thermal) and pitch down is just for gliding/speed. Elevator: 20% chord. Minimum chord 150mm due to Rn, aspect ratio 8-13, not more."

I could "modify" the JWL-065 airfoil with a span wise elevator (22% width) with about 2 to 3 degrees down for the neutral position. That would bring the Cm from 0.0822 to ~ 0.015 for a design Cl=0.4 for elevator rigging.

I'm slower, Bruce but, I now get it. Thanks.

Design is back to the JWL-065 airfoil.

I expect the wing building jig finished in 3 or 4 days.

[Roy Walton]

This is my redesign of WindFreak using a modern airfoil and materials. About the only thing that did not change is the outline. A tremendous flier!

Roy

[Ollie]

Cebola,
The plans of the WindFreak are from R/C Modeler magazine:
http://www.rcmmagazine.com/e/env/0001WuO6bACO5TwRNw5I1O3/store/store-plans-list-5.html?link=/store/store-plans-catalog-tem.html&item=plans:pl-743
I built one about 1980. I built the fuselage with fiberglass (bad decision). I built with hard balsa. I used a heavy radio. I balanced it with 5 OZ of lead in the nose. I should have kept the plane much, much lighter.

Roy,
Which modern airfoil did you use? What is your WindFreak weight? Do you fly it much in thermals? Do you like the pivoting hook?

[Roy Walton]

Cebola

Here is the rib. It was arrived at by experimentation so has no name. The smaller ribs at the tip are the same thickness as the other ribs (mainly just scaled horiz and the nose blunted a bit.) This helps prevent tip stall without washout.

RTF is 41oz. I also had to add a huge slug of lead in the nose.

It outperforms the Nostalgia (all that is flying at our field) and my Chrysalis. All we fly is thermals.

The swiveling tow hook works fine. I launch really close to vertical if there is even a slight breeze.

No spoilers means that it goes faster when coming down. To counter this, it can fly in a nose high mush and still maintain good control.

It is truly a different plane. Very gentle, yet capable of moving at zorching speeds (is a handful then). Can be flown at walking speed.

Roy

[Tuomo]

I wish someone would start to sell ARF Windfreak :)

[BMatthews]

Ollie, I'm guessing that even if you use a sliding weight to alter the CG for speed trim you'll still need the elevator for holding up the nose in the turns. What I'm not sure about is what this would do the wing section's lift as far as the amount of drag the extra reflex causes. It would certainly alter the max lift coefficinet available to the reflexed area before significant drag is produced.

I totally agree with your use of full span elevons instead of a center surface. At least that way the whole wing alters it's camber and lift coefficient in a turn vs only the center and thus resulting in a twisted wing as long as the elevator is away from center.

[Ollie]

Bruce,
With elevon area of 20% of the wing area, the elevator deflection is very small and about plus and minus about 3 degrees full throw. With aileron deflection, the full throw is much larger with 20% if the uniform chord along the span. The elevon design should small chord at the wing centerline and larger at the tips. In effect, with elevons deflecting, twist gives the wing under control.

This a case of design comprises between airfoil Cm, CG position , elevator deflection, aileron deflection, low drag, stability.

A master designer, like Dr. Drela, has very best decisions balances of the comprises for the type of aircraft. I'm just a want-a-been designer.

The next subject is spar for this floater. It depends on lift distribution, hook position, mass distribution and neutral point.

Why do we want the spar? You say because of the lift load. That's part of the answer. But if the mass span distribution matches the lift distribution then the bending load is zero and the spar weight, strength and cost is zero or just for the ride. Yes, a span loader has the mass floating with lift an no spar.

That's brings up the question of mass (or weight) budget. The battery 2 oz., receiver 0.5 oz, two servos totaling 1 oz., nose weight ~ 2.5 oz. and lead in nose and 2 oz. for the fuselage and tail. That leaves 18 oz. for the wing structure. Most of the wing structure distribution matches the lift disriburion. After the launch most of the spar is along for the ride. The problem is the lift focus in the hook and line tension high loads not the lower inertial mass loads. The lift increments sums distribution from tip to center line for the maximum shear. The shear sums distribution from to tip to center line for the maximum bending moment load. That's the assumed the one-hook center position.

However, the designer could assume two hook positions half way between tip and center line with a yoke to line. The tension load is in half. The moment arm is half so the maximum bending moment 1/4 load is compared to one center line hook. I think that is a very neat design decision! It reduces the carbon spar caps by 1/4 the cost, weight, flex and strength. It reduces the shear web is 1/2 the cost, weight and strength.

Tomorrow I will discuss the rest of the hook position problem.

[histarter]

Cebola

Here is the rib. It was arrived at by experimentation so has no name. The smaller ribs at the tip are the same thickness as the other ribs (mainly just scaled horiz and the nose blunted a bit.) This helps prevent tip stall without washout.

RTF is 41oz. I also had to add a huge slug of lead in the nose.

It outperforms the Nostalgia (all that is flying at our field) and my Chrysalis. All we fly is thermals.

The swiveling tow hook works fine. I launch really close to vertical if there is even a slight breeze.

No spoilers means that it goes faster when coming down. To counter this, it can fly in a nose high mush and still maintain good control.

It is truly a different plane. Very gentle, yet capable of moving at zorching speeds (is a handful then). Can be flown at walking speed.

Roy
Thank you Roy.

Since 1995 I was looking for a wing design that would thermal, because I realized my low launch system was best served by a short coupled sailplane with a large surface area (low AR), and the flying wing would be a natural if:
1. I could build it light enough, or
2. find a profile that would have enough CL.

I had heard of the Windfreak, but could not get any reliable user information on it at the time; especially one with bottom spoilers (since I had landing point interest at that time).

Towing the machine up was another problem - that seems to be solved with a "swiveling towhook"; and this perked my curiosity. I guess I should get the Windfreak plans - especially if the tow hook detail is included, or any other source of info on this type of hook would be appreciated.

I still envision a 60" plank light enough for the low speed needed (which is not a flying wing's typical forte'), and the 4 lb typical 50 mtr HL histart.
Following the Windfreak program may be the answer I am looking for, i.e. to be able to launch and soar - though crippled and vision impaired. [Obviously not for competition, but for just sport flying] :)

[steelhead]

Roy- Absolutley stunning :) Do I see different wing dihedral breaks?

Dean

[Roy Walton]

HiStarter,

The RCM plans come with a long article on flying WindFreak (that alone is worth the price of the plans). I could not find the parts for the hook in the article so I used a drilled block of wood at the swivil point. The hook wire was bent double and bent at the holes in the bloc so as to fasten there. The bottom part of th hook has the wire bent together and then bent again for the actual hook. I can do you a sketch if you need it.

I used the existing plan shape although I did widen the fuse a touch. The 2 center spans are glued to the fuse and the outer spans are removable. This allows good strength at the center where needed without a joiner weight penalty. I used .007 CF for the spar caps. To make installation easier, the CF is lammed to 1/16 bass (spruce just not available). Full width shear webs (a sandwich of two 1/4 balsa webs) and less wide at the tips.

Your observation of low aspect ratio being a good thing is echoed by Captain America 2 in the picture.

Steelhead - The wing has a break at the center section and again about half way out. And thank you for the ego inflating comment!

Roy

[BMatthews]

Histarter. There's no big secret to the pivoting tow hook. A plank wing does not have very much pitch control authourity due to the short leverage baseline. But putting a towhook below the wing creates a leverage that wants to pitch the model up strongly. A pivoting towhook helps prevent that by sort of extending the pull up to the wing joiner rod or special pivot point that is higher in the fuselage so the pitching forces induced by the line pull are easier to deal with by the lower elevator forces of a typical plank. But altering the towhook position becomes much more complex as it needs to have a special structure inside the fuselage to allow placement. Fortunetly a plank's acceptable CG range is very narrow as it is set largely by the airfoil's Cm and the location can be determined using the Panknin spreadsheet before any wood or other material is ever cut. So the towhook pivot can be placed 2 to 3% of the chord in front of that point and a suitable movement slot in the fuselage set at the planning stage.

[histarter]

Roy, you are an artist with Capt. America 2. I am flying something simple, that is quite sneaky. An updated version of Cecil's Shuttle. Raising the rudder area was a bit counter productive, however it flys great!
It has a thin profile, plump fuse to hold 24 oz ballast, plate wing structure (rigid and strong), and with tripping is very quick and smooth, yet flys slow enough for weak lift on very calm days. Tailboom is tilted 2.5 degrees to yield basic decalage program while bypassing wing downwash vector. Simplicity at 6 oz/ft wing area. To date, it is the only sailplane that maxed out the HAM postal (after 2000 or so attempts with it, and 57 other pilots and sailplanes that failed).

As soon as I can figure out the RCM site, I will order the Windfreak plans. Right now I am attempting to build a new wing for a Slow Stick that uses my profile. This is not a big project, but will still tie me up for a month. Hope it will (re)gather building skills to make a mini Windfreak as pretty as yours.

My attempts at making a flying wing profile with a CL closer to 1.0 failed. Airspeed, forward highpoint, and bubble recovery theology needed a more advanced designer than myself. Cheating with a stabulator kinda looses the main thrust.

The swiveling hook is another answer, and saves me from putting a hole in the underside to latch a controline connector (doubling as a tow ring) onto a hook that was close to the CG location. (4 lb tension is easy to handle, but tricky making parts small and light enough). In fact, it may be wise to make the ballast holding assembly part of the hook’s anchor point (another bonus of casset ballasting cartriges i.e. now with a tunable hook location for each cartridge). [ Note: I do like flying in a breeze of 15 mph because thermal skill, planning (i.e. piloting), and performance become important - as a balance, so I am always stuck with the ballast necessity. Having a light sailplane that will still fly empty (by my definition) is just a bonus for successful evening (supposedly) “dead air” thermalling!]

Thanks for the education. :)

[Roy Walton]

HiStarter,

Thank you for the compliment. Although my new hat will not fit now.

Sounds like you have it under control!

I am not sure that the hook really needs to pivot. Like B. Matthews observes, hooking on to the spar in the wing should work just as well and a lot easier to do. In fact the flex of a long wire hook exiting thru a slot should work as a pivoting one.

I set a stop on the fuse bottom at the rear point where I want my hook to "work". Makes it a little adjustable.

I flexing wire hook would allow a divided ballast to be added.

Roy

[Ollie]

Today I finished the wing building Jig. I started the airfoil formers to cut the ribs from foam. Tomorrow I will try to post some pictures.

I caluclated the mean aerodynamic chord. It is 16.3" long and 17.9" from the wing's center line. With static margin of 0.05 of the mean aerodynamic chord, the CG position is 7" (along the wing center line) is from leading edge. The positions of the two hooks are along the left and right mean aerodynamic chords, 3.8" from the leading edge along the mean aerodynamic chords.

[Cebola]

Cebola

Here is the rib. ..........

Roy,Ollie & All

In the past I build a wing name Raven, to big and whit a big sink ratio.

At this momment I am thinking on a wing like the drawing below, can you give your opinion?

And...Roy, is that airfoil good for this conception?

Regards


Cebola
Brazil

[Ollie]

Cebola,
Try SD7003 airfoil.

I'm having a problem with my camera. I took a picture but it is blank.

[Roy Walton]

Cebola,

First and foremost the plane you show is closer to a high aspect ratio than a low aspect ratio. The wing you show is built with a very complex twist (see Horton designs) using an ever changing rib shape to set this geometry. That sort of wing is really a "fast" wing and not a soaring wing. I have never attempted such a wing and understand that it can be pretty complex. I will do some checking and see if I can find my info on a site to send you to with info on that type wing. An interesting thing about these wings is that no vertical stab is needed!

The Raven really has to be light. I have heard of one flying with a new thinner airfoil and is said to fly well. Raven is a good looking plane and (one day) I may look into redesign there.

If you take the WindFreak (or Zon Zoeker as my redesign is named) wing and put in a sweep back, starting at the polyhedral breaks, it should work. There will be some CG research to find where it really should be. You could also taper the wing toward the tips. All this will only be eye candy though and will reduce performance.

WindFreak is basically a rectangular plank. Some curving has been done to the trailing edge (the ribs there are just like all the other ribs) that may be just eye candy. It does help the "bird of prey" look in flight.

Wings are easy to design and fly if you don't mind a lot of sink. A thermal wing is much harder to do. Mainly, it must be light and have little drag. The rear 1/4 of the wing (plank) is non productive liftwise and can create drag. This is the trade for the drag a horizontal stab would have on a conventional plane. A well designed wing will minimize this drag. Sharp, sharp TE's are a huge help.

Maybe build some small hand launch free flight planes to test your ideas.

Roy

[Roy Walton]

Cebola

Here is the site.

Good info.

http://www.mh-aerotools.de/airfoils/flywing1.htm

Roy

[BMatthews]

Cebola, by adding the sweep in the tips you remove your design from the plank style of wing. And becuase of that you need to then use a slightly different airfoil combined with some washout twist in the tips to achieve stability and performance.

You see a plank style wing gets no stability from washout since all the ribs are located along the same line along the wingspan. Instead it relies on the reflex and overall shape of the airfoil to provide a positive pitch response.

However a swept wing can use washout in the swept back tips to provide the "reflex" that is needed for pitch stability. So you can then use airfoils that are close to a Cm=0 pitching moment or even slightly negative. The Martin Hepperle website has such airfoils that are intended for this application. Such airfoils are able to operate at higher lift coefficients.

The design in your picture can be set up to thermal well but it will require the right airfoils, the right twist and the right CG position. It's more these factors that determine how the model will perform than the overall top view.... as long as it isn't too extreme that is. But the sketch you show doesn't look overly extreme to me.

[Cebola]

Bruce, Roy, Ollie & All

I build a small model a HLG of this wing, and I use the same airfoil concept, but thinner on tips, whit 3° of washout.

The model has a good performance, whit a amazing glide ratio.

But, dont ask me where did I found the CG location, was only on feeling's, or putting ballast and make experiment's.

In fact I never design a model that did not fly, but I build many models that flyes on a different brieffing that they where criated, and the most conservatives are the worst :) :)

Believe me


Cebola
Brazil

[Roy Walton]

Cebola,

Sounds promising! Keep us posted if you do an RC build.

Roy

[Cebola]

Another view, of my wing.

Elevator on central panel & aileron on tips


Cebola
Brazil

[BMatthews]

Cebola, put the elvator at the tips as elevons instead of at the center. That way your pitch control is further from the CG so it has more leverage.

Also I suspect your tip fins are a little small. The fuselage and prop will act as de-stabilizing forces and you need larger tip fins that are behind the CG to counter the nose area. And upward pointed fins will be less prone to landing damage and also provide a positive dihedral effect while downward pointed fins cause an anhedral effect.

[Cebola]

Cebola, put the elvator at the tips as elevons instead of at the center. That way your pitch control is further from the CG so it has more leverage.

Also I suspect your tip fins are a little small. The fuselage and prop will act as de-stabilizing forces and you need larger tip fins that are behind the CG to counter the nose area. And upward pointed fins will be less prone to landing damage and also provide a positive dihedral effect while downward pointed fins cause an anhedral effect.


Bruce

I agree, that the elevator is on a wrong position, on this layout it will gonna work like a cannard wing, the wright thing to do is use the ailerons like elevons.

The wing chord is 12" at the center panel, 10 on mid panel, 7" 1/2 on wing tips, for 100" of wingspan.

Cebola

[BMatthews]

Cebola, OK, I see where you tried to go with the center elevator then. And if the flying wing had a far more extreme sweep angle then it would work that way. But the wing design you showed is not anywhere extreme enough for the center elevator to work that way.

[Cebola]

Cebola, OK, I see where you tried to go with the center elevator then. And if the flying wing had a far more extreme sweep angle then it would work that way. But the wing design you showed is not anywhere extreme enough for the center elevator to work that way.

Bruce

On the small model, I use the elevator has elevon and works fine.

Cebola
Brazil

[BMatthews]

Yes it would. When you use tip elevons you are placing your elevator as far behind the center of gravity and the neutral point of the wing as possible.

But if you move the control surfaces closer to the CG they loose effectiveness.

[histarter]

Yes it would. When you use tip elevons you are placing your elevator as far behind the center of gravity and the neutral point of the wing as possible.

But if you move the control surfaces closer to the CG they loose effectiveness.
Cebola, the most prolific and successful wing designer I know in England, follows the basic configuration of the earlier subject i.e. Windfreak - regardless of the sophistication of controls, tripping, etc. ;)
Its just the basic (crude) 'get the most area into the plank for wingspan' without abusing the concept of too low an AR. The freak solves the problem of operating a light loading at low CD; and the extremely short coupled moment arm (without getting into the sophistication of variable profile shape, sweep, and twist. :confused:
I do believe you would be better off using your talent to recreate the Freak (making it your way for lightness), see how it fits your limited soaring world (that I suspect it will fly competitively to your current conventional designs) and then move forward with more sophistication. It is far easier to finesse and trim a working design then to create a new invention! :)

[Cebola]

Cebola, the most prolific and successful wing designer I know in England, follows the basic configuration of the earlier subject i.e. Windfreak - regardless of the sophistication of controls, tripping, etc. ;)
Its just the basic (crude) 'get the most area into the plank for wingspan' without abusing the concept of too low an AR. The freak solves the problem of operating a light loading at low CD; and the extremely short coupled moment arm (without getting into the sophistication of variable profile shape, sweep, and twist. :confused:
I do believe you would be better off using your talent to recreate the Freak (making it your way for lightness), see how it fits your limited soaring world (that I suspect it will fly competitively to your current conventional designs) and then move forward with more sophistication. It is far easier to finesse and trim a working design then to create a new invention! :)

histarter


Do you have some indicatios or photos of Windfreak?

Maybe a 3 view plan, will help.

Cebola
Brazil

[Roy Walton]

Cebola,

Earlier posts in this thread have a picture and another a link to RCM for the plans of WindFreak.

Here is a copy from the RCM plans catalog. I think it is small enough and old enough that RCM will not object.

Roy

[Cebola]

Cebola,

Earlier posts in this thread have a picture and another a link to RCM for the plans of WindFreak.

Here is a copy from the RCM plans catalog. I think it is small enough and old enough that RCM will not object.

Roy

Roy

TKS a lot, for many years I was lookink for that plan :p

Cebola
Brazil

[Roy Walton]

Glad to help.

Here are a couple of pix.

Roy

[histarter]

histarter


Do you have some indicatios or photos of Windfreak?

Maybe a 3 view plan, will help.

Cebola
Brazil
Roy is really the expert on the Windfreak. And thanks Roy, for the PDF to jog memory!
http://www.dream-flight.com/ has the Alula by Micheal Richter. Although small, the design looks promising for your intent. I believe RCM has a detailed article on this machine. If you can DSL, it may be just what you are looking for; and I am sure you would be able to develope and enlarge the little guy for high starting. ;)
The Rudder on the Freak looks like it should handle the large area behind the CG (divergent force). Bear that in mind if you think poly and Alula. :eek:

[analucius]

have you got a link to it

http://www.rcsoaringdigest.com/pdfs/

Read on. Theres is a plethora of info for your kind of wings. I'm also starting to build an R-2 with the modifications Bill & Bunny Kühlmann made.

Beautiful ship.

Regards

Morten Hansen
Denmark
+45 4098 0898

[bluefork]

Here is a plank 2m balsa glider I'm working on. It is a blast to fly. I'm currently starting to build a improved verson.
http://boiserc.com/Forum/viewtopic.php?t=1939

[atjurhs]

No spoilers means that it goes faster when coming down. To counter this, it can fly in a nose high mush and still maintain good control.

It is truly a different plane. Very gentle, yet capable of moving at zorching speeds (is a handful then). Can be flown at walking speed.

Roy

If spoilers were mounted outboard of the elevators and kept fairly small (two or three bays wide) would the elevator be able to compensate for it, and thereby slow it down?

If this seems like a reasonable approach, then I'll try it when I build mine.

Today I ordered the plans from RCM :)

[Roy Walton]

The designer of WindFreak says (I think, has been awhile since I read the build it article) that the elevator does not have sufficient authority to counteract top wing spoilers. That said - there is a chance that locating them FORWARD of the spar might work. OR maybe even aft of the spar!

Try this - Build a little simple 12" balsa hand glider, trying to sand the airfoil into it and trim it to glide. Now, fasten (removable) spoilers to the wing, say, right at the spar. Glide and record what it does. Now move the spoilers forward a bit and try again. Record results. Based on this data, you will know whether to keep moving them forward or if they need to move rearward.

Keep in mind that the ENTIRE TE is upswept and is stabilizing the plane! Thus, the position (spanwise)of the spoilers could cause lost of the downforce on the TE which keeps the plane balanced. I doubt that this will occur until the spoilers are pretty far aft (say 50%).

We all await the results of your tests!

Roy

[kiwi_pete]

Just a curious note here, I built a 2M (80") wing with double dihedral about a year ago and never got around to doing a fuse for it. Now having seen this WindFreak, I was wondering about converting my wing into something similar.
The question is, where approx is the c of g on the WindFreak please?