Suggestions, Comments and Criticism Welcome..

[coldwaterak]

I posted this in the Builders Workshop as well, but thought I might be able to find some useful criticism here too. This is the first rough CAD modeling of a glider/flying camera project I am starting into. The wing is lofted from a Gillroy airfoil, that is found in the collection accompanied by Profili. I plan on scaling this build around a 74mm ducted electric motor. Any suggestions, comments, or ideas for the build are greatly appreciated.

The plan is to build molds for a fiberglass makeup.....

Any suggestions for software to test this models flight char.?

I can provide the CAD file to anyone interested...

[ATA Flyer]

Other then the cool factor, what is the reason for the inverted V tail?
Is it for the cleaner air above the wing?

Have you flown anything with a tail configuration like this before? Just wandering what the effect of a tail configuration like this would be.

Also, I really like the camera pod idea with the ducted fan. No prop blades to causing unwanted video interference and a full 360* view.

[JetPlaneFlyer]

Why the ducted fan rather than a conventional prop? Is it just for field of view as suggested above?
Ducted fans of relatively small diameter (compared to a prop) are generally much less efficient than a regular prop and produce poor thrust at low speed (hence require long take off run or bungee assistance). Fine for a scale jet where you don’t want a prop spoiling the looks but for a camera plane it looks like an odd choice to me? If field of view is the issue just raise the thrust line a bit so the prop arc is out of the camera’s view. This would also improve the handling characteristics because as you have it the thrust line is very low so the model will pitch up strongly when power is applied.

And what about landing gear?... if you want a clear 360 Deg view then this would have to be retractable and EDF leaves no space in the fuselage to store the gear. If you are hand launching then the camera is going to get knocked around on landing.

Steve

[BMatthews]

I'll echo the note about the fan vs prop. Fans are incredably inefficient at converting power to thrust in our sizes.

Also while the very small diameter tubes look high tech you're going to find that tubes to scale with your drawing are far too flexible to support that size of tail properly even if they are in carbon.

I thought that a carbon tube I had was super rigid as well and it almost cost me a new electric glider when at high speed the drag from the T tail was enough to bend the boom down and all the up I had wasn't enough. I was extremely lucky in that I'd gotten a thermal early in the flight and was stupidly high when I decided to see how fast she'd go and suddenly found it bunting to a vertical dive despite full up elevator. I was lucky and had enough time to go ahead and push full down and 1/4 loop to inverted and then 1/2 roll. It was an extremely slow remainder of that flight, let me tell you.

Either go for a larger tapered form or at least use two tubes separated by a wedge of wood as a "webbing" so there's more vertical stiffness. The yaw direction flex isn't anywhere near as critical but ANY flex in the pitch direction will be too much.

[Erich Preitler]

Hi,

any landing gear planned? Landing on the camera may cause problems ;)

The tubes for the tail look really very thin, make sure they are stiff enough, could lead to bad, no, or even inverted reactions at higher speeds. The inverted V imho is ok, no objection to that.

And what's the reason for the ducted fan? Got one lieing around? You'll need heavier/stronger batteries and motor to get the same performance as with a big prop.

Erich

[GeeW]

Wings mounted on pylons are known weak points and are aerodynamically inefficient (Martin Simons). With the EDF shown then there is no reason to pylon mount the wing, as the efflux will be clear of the tail.
I agree wiith Erich that EDF gives poor power for weight, I would recommend an outrunner with a folding prop which will be every bit as clean and give loads more thrust on the same battery.
Inverted V (or A tail as it is sometimes refered to) work very well as well as looking pretty.

Regards

Gordon

[coldwaterak]

Thanks everyone, this is exactly what I was looking for. I'm going to start a revamp today and I'll try and get some picture up later.

I plan on removing the pylon and bringing the fuselage up under the wings. This will bring the thrust line up to a more central point. Now that I look at it, your comment about it inverting seems plain as day. I also have remodeled the wings with about 5 degrees dihedral and another 5 on the tips to add stability and to work with the inverted tail.

I am honestly dragging my feet regarding the EDF... I went into this knowing full well the inefficiency associated with them. But I liked the lines and cleanliness of the model with the ducted motor:
(http://www.ductedfans.com/impellers_moki_90.html) .
Regardless I might put the motor up on top of the wing with a folding prop design in mind. I'll play with it and post what I come up with.

Also does anyone have more experience with carbon fiber tubes? I have looked into the tapered tubes available, but wonder how stout I will need them to be.

[eflightray]

................
I am honestly dragging my feet regarding the EDF... I went into this knowing full well the inefficiency associated with them. But I liked the lines and cleanliness of the model with the ducted motor:
(http://www.ductedfans.com/impellers_moki_90.html) .
Regardless I might put the motor up on top of the wing with a folding prop design in mind..............

.

Why a motor on top of the wing?, on a pylon?

A pusher at the back of the fuselage with a folding prop, would blend in much better. Folders can fold backwards.

Otherwise, nice looking model.

[GeeW]

Coldwaterak
What span are you thinking of? I used 7mm dia carbon tube (not tapered) for a twin boom project which was adequate, although the model was not a particularly fast model. If you do a search on QTB here it should come up.
I am likely to build another and would use the same again though with a strip of 5mm sq spruce laminated under to stiffen it up a little.

As for flight characteristics if you work out tail volumes for both vertical and horizontal areas and follow say Andy Lennons guidelines you'll do fine. I would be generous on tail volume as you want a nice stable platform to take pictures from :) As for airfoil I take it you have seen how the projected airfoil works at the reynolds numbers you'll be flying and landing at? Profili's good at that... :)

Gordon

[coldwaterak]

Here is a modeling of where I am with the Gilroy Wing... I added 5 degrees dihedral and an additional 5 on the tips. With the inverted tail I assume it will help with stability. If anyone is interested in playing with it I can post the 3d model file.

I have started working with the Reynolds number for this wing, but it is simply speculation for flight speed right now. Although it will be a powered glider and of course slower. The math involved is a bit beyond me, and my motivation is a bit lacking until I get a more concrete model together with wing area.

Thanks for the input on the spars, I think I will go with straight tubes and stay with a large tail area.

Any and all instruction to get an idea of the flight char. is welcome. I work with robotics in the water, so flight is a whole new realm for me.

[GeeW]

Have you seen this?

http://www.gliders.dk/aerodynamic.htm

[coldwaterak]

Here is a new revision with the suggesitons I've gotten. I spent some time looking through motors and went with a AXI 4120 to model the plane around. I think the pictures will explain more than I can. I assume flight speed somewhere in the neighborhood of 15-20mph. I'll figure out the wings surface area and chord lengths tommorow when I get some more time. Also I modeled the AXI-4120 and its up for grabs is anyone would like a scale 3d model of an electric motor to work with.

Thanks again for the feedback...

GeeW, looks like I be gettin the pen and paper out tomorrow...

[JetPlaneFlyer]

It's coming together nicely.
The tail area looks very large considering the long moment arm. I think you will be able to reduce both area and boom length and still have a good tail volume number. I've not done numbers but I'm sure you could half the tail area and still have plenty. Reduction in tail span would also allow the booms to be pulled inboard which helps structurally. Also no point in having the booms longer than needed if stiffness is a concern.

I assume it's going to have ailerons? If so then you may want to re-think the polyhedral as this will make aileron implementation very tricky. You could either go for straight dihedral or move the dihedral break inboard (to approx. 50% of semi-span) so that the ailerons only had to be located in the outer panel.
If it's rudder/elevator only then more dihedral would be wise to ensure good rudder turn response. For a rudder model I'd suggest about 8 Deg on the inner panels and at least another 12 Deg on the outers.

What about landing gear?

Steve

[GeeW]

For tail boom spacing I would go with the largest prop you could conceivably put on that motor and add 3". I use 3" because it gives a clearance from the prop when you have your little fingers holding the tail booms and accidently nudge the throttle........dont ask!!!!! :D

Regards

Gordon

[coldwaterak]

I've been playing with the idea of landing gear today. Now considering having a folding prop I don't need to worry about prop clearance upon landing as long as I keep off the throttle. My only worry is to keep the camera gimbal clear of the ground. My favorite idea so far is one retractable wheel in the fuselage and two permanently fixed wheels on the end of the tail Booms. What'ya think?

About the ailerons: I had originally wanted to stay with a simple rudder/elevator for use with an auto setup. My goal was to be cruising around in large circles while using the camera. But the more I consider the long term work involved in modeling this plane, I think that might be boring. Might as well have a plane I can fly. I think I'll keep the polyhedral design, but will bring the break much closer in to provide a decent amount of surface area for ailerons. Also with some mixing, I think I'll get much flatter turns this way.

Anyhow, I'll be playing with the tail size tonight. I put the long tail booms in simply because the .5 inch carbon fiber tubes come in 35 inch lengths. But the more I can bring them into the wings the stronger. I'll look at some folding props as well and that will give me some reference for spacing. Also after a remodel of the polyhedral wing sweep, I'll have a better idea of where to put them. Anyone have any suggestions for good folding props?

[coldwaterak]

Here are some measurements for the wings... anyone who can lend some advice for design please feel free.

[coldwaterak]

Have you seen this?

http://www.gliders.dk/aerodynamic.htm

This mentions the known critical Reynolds number for an airfoil... any idea of how to get this? Or is this the same number I come up with doing the math for airspeed vs. altitude just at the point where the wing quits giving lift?

[JetPlaneFlyer]

This mentions the known critical Reynolds number for an airfoil... any idea of how to get this? Or is this the same number I come up with doing the math for airspeed vs. altitude just at the point where the wing quits giving lift?

Re number can be worked out reasonably accuratly by the following formula:

Imperial units:
Re = speed in miles per hour * chord in inches * 770

Metric:
Re = speed in meters per second * chord in centimeters * 680

Of course to calculate minimum flying speed you will need to work out weight and wing area.

[eflightray]

Coldwaterak

I added this post to your similar thread in the Builders Workshop (not sure which is your main thread) -

It's a great looking plane, if I could add one 'but'.....but it looks like you can't disassemble it for transport.

A hobby A.P. plane I would have thought needs to pack down to a handy carrying size for those days out, holidays, camping, hiking, where you would love to film the surrounding area.

Sorry :o

[GeeW]

I am very curious as to why you chose the Gilroy airfoil?
This airfoil is incredibly peaky in its performance, making any model using it a monospeed device.
At the tip chord shown you have a Re of 50000 (approx) when at a landing type speed, at the root it is a little better at about 80000. At this Re this (and almost all others ) perform very badly. For comparison the MPX Easy Star has a tip chord of nearly 6" which yeilds a Re of circa 90000. At the root the ES has a chord of 8" giving a Re of about 135000.
Most airfoils stop working efficiently at Re numbers much less than 70000/80000 and you get into a different game aerodynamically where turbulators get suddenly interesting. Working at numbers below the critical value for an airfoil will give you poor and unpredictable performance....and when applied to a tip section a nasty tip stall!
My thoughts for your wing would be a root chord of 8", a tip chord of 6" on a similar span.
[Now fitting flame suit and tin helmet before I put my neck out!] :eek:
Either a S7055 airfoil for a reasonable trainer like handling model. For a bit better performance over a wider speed range then the S3021 is an old favourite.
If you're still talking to me then, I will happily add some more later? :)

Regards

Gordon

[coldwaterak]

Well it was a long day at work and I didn't much time to tinker with the design. But I did have some time to check the forum and give it some thought. First off let me tell ya how much I appreciate the feedback. Its great to learn all of this, and even better to bring it to reality.

Anyhow, about transportation, I had thought of installing permanant tubes in the wings and tail for the booms to slide into. With a snug fit, a pin arrangement could secure the booms for flight and then allow them to be removed for easy storage or travel. To be more specific, a small molded plate with two pins could be fashioned so that when inserted into the holding tubes and boom it would fit against the airframe, blending in. This might be confusing, but I'll try and model it for a visual. I'm still a bit tied up about what I'll do with the wings... either having them detachable, or having the fuselage/wings one solid piece.

Regarding the wing, I'm not going to try and pretend that I even made an educated guess. I picked the Gilroy wing because it looked like it was designed for a specific speed.... perhaps creating lots of turbulance if too much speed was forced. Maybe suitable for a glider. Regardless I am all ears when it comes to suggestions. Also I am going to remodel the wing again to allow space for ailerons, so I might as well do it right.

I've been playing with Profili and Designfoil, and trying to read up on as much of it as possible. Again this is all new to me, so trying to learn up as quick as I can. One question I do have is, on the graph you sent me, what does Cl and Cd reference? Pressure and Speed? Thanks for the airfoil suggestions it will give me something to work from.

Another thing I wanted to add, is that I plan to add a decent amount of electronics to this model, so there will be some weight. Nothing ridiculous though... but still more surface area is a needed upgrade as well.

Again, thanks for the input... anything is welcome, flame suit included.

[GeeW]

A couple of thoughts on what to make detachable. My QTB has a removable wing and the tail booms are also removable.
When the tailbooms are removed the whole tail unit is very vulnerable to damage so I dont do it very often except for maintenance. The wing and tail unit combined is a bit big and a little awkward to fit in a small car.
On my QTB#2 I will be going with detachable tips, outboard of the t/boom wing join. I will also still have the tailboms removable as per QTB#1. This will make it fit in cars a lot easier. There are a couple of good images on how this works on the Twin Boom Pusher (QTB) build thread by Qrome by the way.
More later as chores are incoming :(

Gordon

[lincoln]

Someone said that wings on pylons were draggy. I guess on the human powered airplane that flew from Crete to Greece, it was too easy and they wanted to make it more sporting? Same with the Supra? Supergee?

Maybe Martin Simmons was thinking of the British gliders with wings on pylons and the pilots head strategically placed to mess up the flow.

If I'm not mistaken, the optimum pylon is pretty short, but it's there. You want some of the leading edge free, and you need 10% or 20% (I forget exactly) of chord away from the fuselage. But that's all. However, this is based on a dim memory of a discussion years ago. Makes sense, though. I was also present for a lecture by Michael Selig where he suggested this as a future direction for sailplane design. I dislike arguing from authority like this, but it's not something easy to calculate and I'll admit that I haven't done a massive literature search to see what kind of wind tunnel stuff there is out there.

A pylon does raise some structural issues.

[lincoln]

...

[lincoln]

If you want your glider to act as a glider, i.e. catch thermals, escape sink with speed, etc., then you need speed range in your airfoil. If you're just going to cruise around and take pictures on days when it's not too windy, then a one speed airfoil is probably good. But the one you show may be a bit thin and tricky to build. If the last few percent of efficiency don't matter, then the 7055 is not a bad suggestion, or the Clark Y, or perhaps the Momfoil, though I don't remember where the coordinates for the Momfoil are.

[GeeW]

Lincoln. I believe the issue with pylon monted wings are the wing root vorticies. Having an root endplate (fuselage) imiproves the local airflow. I know Schleicher built a (full sized) ASW15 with pylon wing and the performance was well down on the standard one.
I agree on the Clark Y (better still thinned to 10%) but am not familiar with the other one you mentioned.

Coldwaterak. Are you still thinking of using the AXI 4120? Do you already have a battery pack in mind? I also would like an estimate of what your camera gear is likely to weigh. I have gone back to first base and would like to put some numbers in. :)
The Cl/Cd graph is an amalgam of two other graphs which are referenced to angle of attack. There is also the Cm plot (pitching moments vs angle of attack) to take into account
The reason you do want a reasonable speed range is that some of your photo targets will be downwind and punching back into a 10mph head wind will require you to fly at say twice your normal cruising speed. If you want more drag to make steep approaches then flaps or t/e airbrakes are easy and only use one servo even on a RET model...if you have ailerons then making them work as spoilerons works really well but requires two servos.
To put a few typical figs, for some of the airfoils that have been recommended, on the Cl/Cd plot.(flame suit back on here) :D
Stall Cl=just over 1.0
Minimum sink/ scratching Cl= say 0.8 to 0.9
Flying at twice scratching speed Cl= 0.2 to 0.4
Obviously these figs are just ball park and differ will every design of model. Just put them in so you can start to see the bit of the polar we are interested in.
EDIT With a 1.5lb max payload I believe that a 300 to 350 watt motor will see it and keep a compact model. With a 1lb payload this can be reduced to about 250 to 275 watts. Payload is for camera gear/turret and excludes main battery weight.
The two books I would recommend are
1. Andy Lennon- RC Model Aircraft Design. Chapters 2 and 3 are worth the cost of the book alone. He simplifies where he can using constants which helps a bit.
http://www.amazon.com/Basics-Model-Aircraft-Design-Techniques/dp/0911295402

2. Martin Simons- Model Aircraft Aerodynamics (4th ed). Quite a serious book but excellent. Quite a few formulaes here, but good explanations.
http://www.amazon.com/Model-Aircraft-Aerodynamics-Martin-Simons/dp/1854861905

If you only want one book go with Andy Lennon.



Regards

Gordon

[coldwaterak]

What a fantastic project this is turning out to be... I am really eager to start making the plugs, but also want to make sure the details are sorted out.

I played with the 7055 airfoil and it is actually alot easier to work with when modeling. I need a few opinions on deciding between a dihedral or polyhedral wing. The idea is to have a Picopilot on board, so smaller ailerons for mixing with the rudder is kinda what I'm aiming for. Trying to get nice flat turns.

As for weight, I added up everything except the battery(s) and it looks like about 3.5 lbs. This includes:

-Rangeview OSD
-Pico-NAT
-4 solar panels (2 micron thick, with adhesive backing for trickle charge .8 oz. total weight)
-7 servos
-Camera
-AXI 4120

A update to the model is that I need to increase the scale. This is due to the camera I've chosen... might as well go with a higher res. Anyhow I am planning on having the gimbals diam. about 4 inch. This will bring the fuselage width to about 4 inches. This will also bring alot more room between the tail booms for a nice large prop. The 4120 shows that it can push about a 10lb glider, so I should have around 6 lbs to work with for the plane itself.

I ordered Andy Lennons book today and am really looking forward to getting it here in a few days. Anything to shed more light on this project.

Regardless... with the 7055 and the estimated weights, any suggestions on chord lenghts and wing area? Also what would you recommend for batterys and servos? I figure I would use all micro servos except for the landing gear. Well I can't wait to hear your thought... thanks again.

[GeeW]

Typical wing loadings for gliders range from 8oz (calm weather floaters) to about 15oz per square foot (F3x slope racers). If we are not too worried over soaring then we can let it come up a bit. Much more than that and the approaches will be very much on the hot side. This can be sorted a bit by use of flaps.
Power loadings. At 100Watts per pound you will have near vertical performance. At 50Watts per Lb you'll have gentle parkflyer performance.
Most sport e-gliders have 65 to 75 Watts per lb which gives a respectable climb without going stupid about it.
So dividing down. Your upto 10 lb model is about right. If we use (say) 12oz per square foot as an anticipated wingloading, you'll need 13.3 square foot of wing to support it.........
We now want to think of Aspect Ratio (span of wing relative to chord) . Some small models make do with an AR of 4 or 5. Most power (.40sized) end up with an AR in the region of 6. Gliders AR (F3x) about 12.
Lets not be greedy I'll take AR=9 And assuming a parallel chord wing (yuk) to keep life simple at the moment......

Can you see where this is going? This is going to be a bit on the big side you might say!!! :D :D

Just for fun- taking your wing data from post#16, gives us 1.6 sq feet of wing x 12ozs wing loading = 19oz AUW ready to fly :eek:
[By the way I am well jealous of your CAD modelling skills :o ]

OK Lets go right back to the beginning and harden up on some of the design requirements. Going round in what feels ever decreasing circles seems to be intrinsic with any aircraft design :D
How big a car has this got to fit in?
What are your landing areas and approaches going to be like? If confined we dont really want a high wing loading or a huge span.
Payload? (Yes I know I mentioned it before..) I'm still guessing 1.5lb would see it?
I know you want to do AP or AV from it so I would suggest advanced trainer levels of stability so you can concentrate on the imaging rather than having to fly the model the whole time, even with some sort of autopilot.

Another good thing to do is look at what other people do..many have an armoury of different models to cover every eventuality. But what they will do is get you general dimensions in the ballpark for what you wish to do.

Examples on RCG
Kd7ost....he's got quite a few designs, ranging from very big downwards.
John O Sullivan....Eyespy with different wings for different days
Icebear...Lots of kit shoehorned into off the shelf models...sorry Bjorn :)
Gray .... several versions of Easy Star to carry some quite big payloads
MarkJayne..... Serious abuse of several EasyStars to carry payload.

More later......if you are still up for it :)

[coldwaterak]

Thanks again... this is really helping me refine this design. I was assuming about a 7-8ft wingspan depending on the AR; I'll play around in the neighborhood of a 9-10 AR. Not to be loose with the design, but I'll model the wing and decide on chord lengths then. Any input on the benefits of a forward swept design vs. an aft swept wing design? How much do you think I could count on the effect of flaps for landing with smaller ailerons?

The 10lb max weight is definitely a rough estimate. I would like to think 7-8 lbs is more realistic, but having some room to fudge seems comforting. Also from my previous wing data, it looks like I was a bit generous. So with my increased scaling of the fuselage from 3.5 to 5 to accomodate the 4 inch gimbal I could aim for around a 6-7 foot wingspan. Please correct me if I'm off here.

As for size restrictions, I'm not too concerned... i'm still cookin up the dis- assembly idea, but I have plenty of room in the back of my truck. Also we live on the coast, so I aim to take off and land on beach... lots of room. Anyhow I'll add some more later.....

[Brandano]

Moderate FSW has better stall behavior, but is mechanically more complex and might turn out heavier. Better stick to a straight wing for a glider. On full size gliders a moderate FSW is usually there just to get the main spar behind the cockpit, to allow the pilot a better view and to keep both the pilot and the ballast (usually stored in the wing) near to the ideal CG. I haven't really seen any full size glider with a normal swept wing, unless you consider the semi-elliptical planforms as having a sweep. I think there was a design for a flying wing glider with a relatively large sweep, but I don't know if it was ever built. The design was interesting, with the wing roots ahead of th cockpit and the tips carrying the vertical surfaces well behind it. I imagine it would limit the pilot view somewhat. Horten gliders were obviously swept wings, but in a smaller AR range.

[GeeW]

Coldwaterak
OK so we try at 8lb(=128oz). So about 10 sq' of wingarea. 8'6" span on a 14" chord giving us an AR of 8 and a bit.
Power train and gear weight

Motor+ESC+Prop =16oz
Servos say 4off at 2oz ea +Rx and S-Bec=12oz
Payload =56oz
Battery 5s 5000(?) =18oz
Total =102oz

Target weight minus gear weight = 26oz = empty airframe weight= :eek:
Looking at http://www.rcgroups.com/forums/showpost.php?p=10638575&postcount=1
Model rtf weight is given at about 115oz and I am sure it would be easy to get 8oz out of that.(Just look at the undercarriage)
So lets make the wing another foot longer and 2" wider,and call it a 9lb model.
Now we have the wingloading and powerloading in the right area.

Target weight is now 144oz minus 102 oz = 42oz for the model...much better.
Also perhaps look at the Thunder Tiger 60 Trainer as these are used to haul a RC Skydiver aloft ...my RC Skydiver weighs in at just over 3lb (fatty). Wonder what the shipping weight is on a TT60...which would give us a clue as to how much the airframe weighs.......back soon.
:)

[coldwaterak]

Sorry for the late reply... been jumping through airports for the last few days. Anyhow I modeled up the s7055 and played with a few configurations. I'll have some more time now to devote to gettin all the details worked out, but I wanted to drop a post on here with some pictures. Once I started modeling this wing and playing with it in the neighborhood of 10-12 sq/ft. I realized how darn big it was going to be. The picture with the top view, is only about an 8 sq/ft wingspan, and still seems large. Anyhow, maybe I need to rethink the electronics that I am hoping to add and try to get a more feasible wingspan. I'll add more later but wanted to hear everyone's .02 cents.

[GeeW]

Looking good there. The drooped camera-ball on the nose does still look pretty vulnerable? Have you looked at the idea of a retractable/lowerable cam-ball assembly.
Also to keep it quiet try not to have the prop spinning close to the t/e. Suggest 3" clearance at least.


Regards

Gordon

[coldwaterak]

I've been shopping around for different retractable landing gear setups so I can have some dimensions to work with. I plan on having the gear extend out of the fues. right behind the gimbal. I'll drop a picture on here when I get it together. What are you refering to: t/e in regards to the prop noise?

[GeeW]

Brad
re the right hand image in post #32. The back end of the fuselage looks to be at the trailing edge of the wing. Given the prop will be on the back of the fuselage it will be close to the trailing edge whist under power. The closer the prop gets to an object in front of the blades the noisier it will be. Keep the plane of the spinning prop well clear of the trailing edge, and this will keep the noise down.
This is why electric pusher flying wings are so noisy.

Gordon

[coldwaterak]

Just a quick question to throw out there regarding folding props. I have been looking around at what is available for large folding props, but it seems they are all designed for pulling function on the front of the aircraft. I ran across a few left handed props, for pushing application, but nothing large enough for this project. My question is: if it is possible to simply swap the blades around so that they fold forward of the spinner, then reverse the direction of the motor? Again I am new at this and plead ignorance...

I'll start digging through the forums to see if there are any post associated with this situation.

[GeeW]

Folders. First fit the blades facing the wrong way on the yoke.
The only modification you need to do on a folding prop is to limit how far they can fold. Most folders are designed to have a fuselage to limit max folding angle. You somehow need to create a limit so that the tips of the blades do not go past the extended centreline of the motor shaft.
When spinning the folder props do not come past the 90degree position so a forward limit should be un-necessary.
Photos to follow later

[eflightray]

On my big flying wing with a folding pusher, I cut a piece of plastic from an ice cream tube lid, (my favorite material, ....no....not the plastic...the ice cream).

It needs a bit of trimming and playing with, but one I cut lasted two years.

Hope the picture explains it.

[coldwaterak]

Sorry for another late reply... The holidays have been a whirlwind, and I've only had limited time to devote to the project. But I did want to post the progress I have had. I am in the neighborhood of about 9.5 square feet of wing area. I can already tell that the tailwing is too large and needs to be scaled down a bit. Maybe even extending the tail booms a few inches wouldn't hurt either.

I have played with the landing gear plenty, and can't decide between the two wing retracts show in the pictures, or a single retract coming out of the fues. The tradeoffs go both ways... wing retracts=more space in the fues. and a stable landing platform, while fues. retract=less weight.

Anyhow I have just recieved the Model Aircraft Aerodynamics book and will be pouring through that after the holidays blow by. It seems I might need to try for a larger AR, and perhaps some sort of dihedral too. I'll post more later, and can't wait to hear your thoughts.

I hope the holidays have treated you all wonderfully.... enjoy the New Years!

[GeeW]

Brad
Just use Andy Lennons little formula for working out tail volume/area. I would run with his suggested 20% or maybe a little less but not below 15%.
Hope you have a good new year.

Gordon

[BMatthews]

It's been a while since this started but I see that things are changing as you learn more about the realities of your design.

In your latest version the stabilizer area is far bigger than it needs to be. Something about 2/3 that size would be just fine.

You also still need to ditch the soda straw booms in favour of some with a more realistic and stiffer cross section. You just will NOT get sufficient rigidity with those small tube sections regardless of the material chosen. Especially with the new weight realities tossed into the mix.

[Montag DP]

It's been a while since this started but I see that things are changing as you learn more about the realities of your design.

In your latest version the stabilizer area is far bigger than it needs to be. Something about 2/3 that size would be just fine.

You also still need to ditch the soda straw booms in favour of some with a more realistic and stiffer cross section. You just will NOT get sufficient rigidity with those small tube sections regardless of the material chosen. Especially with the new weight realities tossed into the mix.Frankly I'd be more concerned about the attachment in the wing. Will it be wood or foam construction?

Personally, I think the tail booms will be fine if they're made out of carbon fiber. They're not very long, and this will be a slow-flying plane anyway.

If it were my design I'd probably do built-up balsa booms that are taller than they are wide. But I don't think he will have problems with flexing with his system.

[BMatthews]

Slow flying yes. Light? Not so much from the recent posts. Still, you raise a very valid point about the mounting points.

Having had a model that diverged into an unrecoverable dive due to a "stiff" carbon boom that flexed due to airspeed I'm still going to suggest bigger diameter booms.

In my case I managed to save it only through luck. The drag from the T tail caused the problem in the first place and I was lucky enough to be high enough to think it through and push full down to bunt it inverted and then use the rudder to roll it out and back to upright. And even then it came >< that close to tucking again and I would not have had enough room to pull out a second time.

Small diameter carbon tubing isn't as rigid as it seems and "that feels pretty stiff" isn't good enough. Trust me on this. Only when you try to bend it and you can't see any at all is it "good enough".

But aside from the boom diameter I have to agree. How it is mounted is at least as important as how stiff it will be. And that brings up the need to match the stiffness and strength of these two items with the proper strength and stiffness of the wing's center area at least out to the boom mounting points. The elevator in particular is going to be providing a fair amount of leverage pressure on the wing. Most of the time we can use just one spar and some D tube enclosure on the leading edge. For a regular wing that results in a nice torsionally stiff structure. However for wing mounted booms I'd suggest that it would not be enough. I would plan on a rearward stub spar to assist with supporting the tail booms. The rear spar should be located fairly far back but far enough forward that the depth is still more than 1/2 the depth of the main spar. Even then I'd cap the top and bottom with carbon to both strengthen and stiffen it.

[coldwaterak]

This is great to hear... I am weighing my decisions between carbon fiber tubes or fiber glass tubes for the tail booms mostly based on cost. Right now the model has 1" od tubes and I am assuming that at minimum 2" od will be needed if I go with standard fiber glass.

From experience can anyone lend what size of booms I should aim for? I'd rather overshoot the size and strength when I order, instead of a hand flex test after its already bought. I'll shop around and maybe find a slightly larger carbon tube....

My present plan for a wing is for a foam core, and a glass skin. To maintain strength through the wing and boom interface I plan on bringing the booms clear through the wing to the leading edge. On the leading edge of the wing, the boom will be faired and glassed, as well as on the trailing edge.

Let me know if you think this idea is practical?

I have the tail remodeled and will repost hopefully tomorrow will the larger 2" booms.

[coldwaterak]

In addition glassing the boom into one or possibly two spars as well as the wings glass skin on the leading and trailing edges will be needed. Perhaps two sub spars as suggested could be included and glassed that terminate past the boom...


Would you suggest a balsa frame wing? I have gathered that a foam wing would be more practical for this size....

[BMatthews]

Balsa builtup would be fine but so would foam. Both are valid formats and it just depends on which you're most comfortable working with.

In your newest spar viewI'd say the middle one between the black main spar line and the rear stub isn't going to do much. You've located it at the virtual pivot point between the main and rearmost spar where it'll do very little to aid with supporting the boom. If you're wanting to use a third stub spar it would be better to locate it ahead of the main wing spar so that the main spar sees less load from the boom. In effect move the main wing spar towards the lower stressed "pivotal" center point. Now this won't happen given the spacing but it'll reduce the boom's levering loads if you do it that way. You'll just need a couple of plywood or otherwise strong ribs to tie the rear and forward stub spars together and then mount the boom to this tie in grouping.

The selection of booms is tricky. You need to realise that there's two factors. Strength is one and stiffness to resist flexure is the other. These two factors have little in common. A smaller carbon boom can be very strong but not stiff enough.

Chances are that a decently thick walled one inch diameter carbon boom will be adequitely stiff. It's certainly MUCH larger than the 3/8 inch boom I used on my 2 meter electric glider so that'll help heaps. Especially when you understand how stiffness and diameter of the tube are related. Stiffness goes up at a far bigger factor than the linear diameter change. Only buying a length of each and testing will tell the truth. Or you can go with the carbon tube and if in doubt add a spine top and bottom of some carbon rod or strip stock to further stiffen the far more critical vertical plane stiffness if it even seems like it may be required.

Now this is only a guess but if you can hang a 10 lb weight from one end of this carbon tube and see a deflection of less than 1/8 to 3/16 then I would say that it is stiff enough as it comes. If it flexes much more than that I think given my previous "near death experience" I'd be adding some vertical plane stiffening spines top and bottom. But that's just me and YMMV. The problem is that we don't have the sort of resources to analyse this type of stuff other than building and flying and HOPEFULLY not losing a model due to a bad decision. So we tend to overcompensate much as I'm suggesting.... ESPECIALLY after having a near disaster on the first day out with a previous model.

[coldwaterak]

Adding reinforcement to the vertical strain of the boom is a great idea! Even a strip of balsa glassed to the top and bottom of the boom would provide a huge amount of rigidity vertically.

Any suggestion for Spar material? Fiber glass tubes?

Also in compufoil it suggests 1.6 degrees as the best angle of attack.... I assume that when the wing is attached to the fues, in reference to the horizontial center of the aircraft, this is the 1.6 degrees of tilt I need to figure in?

[CompuFoil]

Adding reinforcement to the vertical strain of the boom is a great idea! Even a strip of balsa glassed to the top and bottom of the boom would provide a huge amount of rigidity vertically.

Any suggestion for Spar material? Fiber glass tubes?

Also in compufoil it suggests 1.6 degrees as the best angle of attack.... I assume that when the wing is attached to the fues, in reference to the horizontial center of the aircraft, this is the 1.6 degrees of tilt I need to figure in?

Don't mean to but in, but happened to notice your post. The 1.6 degrees is actually the theoretical angle that provides the least drag. Typically, you will need more than that depending on the weight you are trying to keep aloft and the total lift of the wing that needs to balance it out.
By the way, this is one cool project!

Regards,
Eric Sanders
http://www.compufoil.com

[coldwaterak]

Don't mean to but in, but happened to notice your post. The 1.6 degrees is actually the theoretical angle that provides the least drag. Typically, you will need more than that depending on the weight you are trying to keep aloft and the total lift of the wing that needs to balance it out.
By the way, this is one cool project!

Regards,
Eric Sanders
http://www.compufoil.com

Would I be right to guess that even more of an angle would be needed for the slower flight of a glider type such as what I'm trying for? Perhaps in the ballpark of around 2? Any arithmetic to help me get to a more concrete value?

[coldwaterak]

I have never built a wing before, and am open to any and all suggestions...

I have although decided to go with a foam wing and glass over it. I have lots of experience with surfboards.... go figure, and I think foam and glass will leave a lot less guesswork out of it.

I have found someone would would be willing to hotwire the wing for me, but there are quite a few details that I need to work out first. Following is a drawing of some proposed spar placement. This wing will be cut in several sections and I have staggered the spars to accommodate this.

I think fiberglass tubes will work best for spar material, but this is also speculation...

What do you all think?

[JetPlaneFlyer]

Conventional construction would be to put one spar at the wing's thickest point. The panel and centre join can be done with carbon rod and carbon tube, plus a small locator peg/socket near the TE. The rod and tube joiner need to be solidly keyed into the spar, not just located into foam. The spar itself can be carbon strips or rod, one strip/rod let into the upper surface and one into the lower.

[BMatthews]

Coldwater' keep in mind that any spar system needs to form an I or a [] box section. The most extreme upper and lower portions carry the tensile (stretch) and compressive loads while the vertical portions form the web that joins and locks the upper and lower straps together. The webs also withstand the compressive forces that the spars see that are trying to kink the upper spar and jam it into the lower spar.

As such round tubes are by far one of the worst possible spar arrangements. The small upper and lower sizes of the portions that'll hold the loads are poorly joined by the semi circular side portions that are free to flex and shatter under the loads that a tubular spar would encounter.

If you're reading this to mean that I'm saying "don't use glass tubes for the wing spars then you're right. Tubes do not make good spars. I know a lot of folks use them and get away with them but it's not the wisest choice for a spar or a joiner or almost anything else that is seriously forced by bending loads.

[kcaldwel]

Would I be right to guess that even more of an angle would be needed for the slower flight of a glider type such as what I'm trying for? Perhaps in the ballpark of around 2? Any arithmetic to help me get to a more concrete value?

You would need to calculate the wing Cl (lift coefficient) required at your expected "cruise" speed:

L = Cl * 1/2 * ro * v^2 * S

L = Lift = Weight in level, non-accelerated flight
Cl = lift coefficient
ro = air density at the altitude you are flying at
v = velocity
S = wing area

You must use consistent units.

Once you find the required Cl for your airplane, you can find the angle of attack required for your airfoil from the airfoil's polar graph at the appropriate Reynolds number for your wing. You will have to apply a correction for the wing aspect ratio, since all airfoil data is for 2D flow, or infinite aspect ratios.

Or you can run a XFLR5 analysis (fairly big learning curve), or a Lift Roll analysis using the Java script here:

http://www.amadistrictii.org/cjrcc/wing2/wing.html

or spreadsheet available here:

http://www.geocities.com/jebbushell/COOKBOOK.htm

Hope that halps.

Kevin

[Wendi Smol]

You would need to calculate the wing Cl (lift coefficient) required at your expected "cruise" speed:
L = Cl * 1/2 * ro * v^2 * S
L = Lift = Weight in level, non-accelerated flight
Cl = lift coefficient
ro = air density at the altitude you are flying at
v = velocity
S = wing area You must use consistent units.
http://www.amadistrictii.org/cjrcc/wing2/wing.html

Hope that helps.

Kevin

Hi,

isn't that far too complicated and early for a novice? :o Not that there is anything wrong with that way, but did he not only want an estimate for the rigging angle of the wing to the fuselage? :)

For a profile with a flat underside it is very common to use this as a datum line parallel to the fuselage centre line. That way the plane will fly with the fuselage horizontally when the wing has an AOA of around 3 deg to the profile chord line. :cool: I dont think one should frighten "coldwaterak" with too much theory too early. He first needs to get accustomed to the more practical thumb-rule approach, which works equally well for a start. :D

More importent is in my view to simplify the design process: it would be easier when the centre part of the wing (between the two booms) would be a straight rectangle without dihedral. Centre wing, booms and empanage could be built as a unit to be bolted to the fuselage top and then the outer wing panels added with the appropriate dihedral and taper. It's not only easier to build but also flies better. ;) :p

In respect of the spars I agree with BMatthews though when it comes to joiners you will find that most are actually some form of tubular arrangement.
I think we should help coldwaterak with some sketches - would that be ok with you? Not that you think I intend to interfere with your design. :(

Has the profile selection been finalised? My suggestion would be NACA 3412 for the root (the rectangular centre section) and NACA4208 for the wing tip. The whole wing panels could be built flat on the table. :cool:

Regards

Wendi UK

[coldwaterak]

So i've got a ton of stuff on my plate right now, but don't assume I have forgotten about this project... I am absolutely enthralled with this design. Also the prospect of getting all the details worked out in CAD before starting the physical project is awesome...

So back to the project: I would love some sketches.... and like I have said before I am open to all input, and am very eager to have this project taken in several directions.

The airfoil that I have currently chosen is the s7055 both for the root and tip... I really do like the idea of removing the taper from the wing between the fues. and booms... Perhaps with being one piece and the outer parts of the wings detachable, it will be a good option for transporting it.

Now what do you all think of adding about 3 degrees of dihedral outside the booms?

I looked around and found some square 1" carbom tubing that will work great for spar material. Thank you for the suggestion... square stock makes so much more sense now that it has been mentioned; much more vert. strength Much like an "I" beam....

Do you think that one spar down the center of the wing would suffice? Or perhaps one down the middle and another along the leading edge of the wing?

[coldwaterak]

This project has not fallen to the wayside... I managed to dive into the project of building a CNC machine in my garage as a direct result of modeling this plane. The world of hobby CNC is a fantastic place to invest plenty of time and study if anyone has considered it.

Regardless I am now in a place to start pursuing the creation of this powered glider again.

Over the next few weeks I am going to start creating the fuselage and camera gimbal. Any and all help that I can get coming to a more finalized destination with the wing and also tail area would be greatly appreciated.

[stiwari98]

hey coldwaterak ..jus went through al da stuff quickly ...ur design seems pretty interesting ....ma suggestions are dat fr the tail boom u shd use more reinforcements as in more carbon fibre rods..actuali i had made a VATOL on similar lines and the major problem i faced was the weak boom section ..also each time the plane lands it comes out worse at the tail section ...and going by your design i believe that the landing gear is not enough fr ur plane 2 land smoothly..id rather suggest a tricycle landing gear .... try doing this by reducing the length of the boom and extending the gear from the fuselage ...