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Old Jan 08, 2008, 06:42 AM
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A further note: "Equivalent Dihedral Angle" ("EDA") is the single dihedral angle that has the same effect as some combination of polyhedral angles along the wing. There's a detailed explanation if it, as well as instructions on how to calculate it, here:
http://www.rc-soar.com/tech/spiral_eda.htm
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Old Jan 08, 2008, 07:21 AM
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Sorry for the slow response, But it was a hectic evening
I tried to load a picture of the unlimited bird, but I keep losing it.
I verified with tape measure and computer, the same numbers, which are:
Vertical tail area--171.5 sq"
moment of vertical --31 "
span of 'old bird' 144= (72)
Area of wing total--1280 sq"
Thanks Don for your method, I think it's a litlle more user friendly, but I admit i get lost as to the definitions of equations. If ANSI standards were in place, at least we would talk the same language!
If I tracked with your numbers correctly, I got a vert. Coefficient of .028.
Doing it Ron Van Putte's way, I got .260, which according to him was large.
OK, now for the details,
The 12 footer (on my avatar) is the mentioned tail area. this bird was lost to a dfust devil/ wind storm, and just before all rudder control was lost, she was blowing totally broadside in about a 30 mph wind. The first flights in less than 10 mph winds gave excellent results in the turning radius, and responses.
Now chuck, I've gotta tell ya that a sailplane isn't gonna be making snap rolls and other fancy highly aggresive manuevers. I call an inverted flat spin a "soft" manuever. but nonthe less, there is plenty of authority with the used dihedral.
YES, the dihedral of the (red) big bird is more flat than previously done, and according to Don's info, I would agree that it is too flat-- which is why I will be 'adjusting ' it for this springs' run.
I will get to the data for the Blue/yellow bird, which is a Butterfly 2's wing.
If you have seen the video at Canardly Soar, you can see there is plenty of authority. that filming was in 12-15 mph breeze, and a pleasurable day of 6-10 minutes wave lift, compared to the 'standard' 4 minutes @ that highstart length.
I'll get some pictures posted so we can "tear it apart" later.
Johnny
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Old Jan 08, 2008, 08:49 AM
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Quote:
Originally Posted by Captain Canardly
... I verified with tape measure and computer, the same numbers, which are:
Vertical tail area--171.5 sq"
moment of vertical --31 "
span of 'old bird' 144= (72)
Area of wing total--1280 sq"
...
If I tracked with your numbers correctly, I got a vert. Coefficient of .028.
Not sure where you got the .028.

Semispan = 144/2 = 72

Vvt = (171.5/1280)*(31/72) = .0577

Thats the vertical tail volume coefficient, and it's based on the half-span, not the full span. .0577 is about half of what it should be, so the plane is going to be "soft" in yaw stability and rudder authority. It may be adequate, depending on your expectations and flying style, and how much turbulence you have to deal with.

Vvtd = (171.5/1280)*(31/72)^2 = .0248

That's the dynamic volume coefficient for the vertical tail, based again on the half span. Again, that number is low, about a third of what I typically use on conventional tail arrangements. Then again, I like lots of dynamic stability, it makes for delightful handling. However, on a canard layout, it's tough to do much better, it just isn't practical to get a decent vertical tail moment arm. Compounding the problem is the fact that the canard fuselage tends to have a lot more side area and mass at the extremities compared to a pod-and-boom conventional-layout sailplane, which further degrades the yaw stability.

Quote:
.... this bird was lost to a dust devil/ wind storm, and just before all rudder control was lost, she was blowing totally broadside in about a 30 mph wind. The first flights in less than 10 mph winds gave excellent results in the turning radius, and responses.
Uh-oh, I hope this doesn't get into the downind turn myth again.

If you're talking about straight-line winds of 30 mph, outside of the dust devil, that should not be a factor other than the turbulence asociated with ground obstructions, and the optical illusions caused by drift over the ground as perceived by a ground-based pilot.

However, the turbulence associated with a dust devil can be horrendous, and even a plane with strong control response could be a handful. Of course, having one with softer control response will be that much worse.
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Old Jan 08, 2008, 01:08 PM
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Many Thanks !!

You guys are just SUPER! I hope others are watching and also appreciate your efforts. John, your hunch was right that I did not consider the ailerons on that fleet of simple dihedral sailplanes. My polyhedral angle measures 8 degrees and It will be raised to 9. Considering the Captain's 12 foot span and only 31" of distance from the rudder to the CG, it seems that a 90 sq. inch vertical tail at a 26" distance will be adequate for me. My four wing sections each measure 18 inches. The chuck glider is heavy with it's solid body and 1/8" wings. I added a degree positive to the main wing and it glides better balanced right on CG. It has a built in left turn which I found to be caused by the tiniest amount of error in glueing the tail on. I will make the rudder moveable with metal hinges to see how sensitive it is.I feel better about the design now and will be cutting ribs just as soon as my body gets over this winter bug. BTW, My Graupner 2M sailplane has a similar wing with 15" final sections at 7 degrees with a 24" distance from the CG. It has great rudder authority.. Charles
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Old Jan 08, 2008, 06:22 PM
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Quote:
Originally Posted by Don Stackhouse
In the case of tail sizing, we call those numbers the horizontal and vertical "tail volume coefficients".

Rather than going through the whole calculation process here, there's already an article in the "Ask Joe and Don" section of our website that does that:
http://www.djaerotech.com/dj_askjd/d...tail_coef.html
Don, Thanks for the all the info you have provided about vertical tail size and dihedral. I am applying them to my HLG model. The EDA calculation gave me a higher EDA figure than I was expecting.

Inner panel = 360mm
half span = 570mm
Inner dihedral = 3.2 degrees
Outer dihedral = 3.2 + 13.7 = 16.9 degrees
3.2 * (1 - 0.47) = 1.696 degrees for innner panel
16.9 * (0.47 - 0) = 7.943 degrees for outer panel
EDA = 1.696 + 7.943 = 9.64 degrees.

This seems like a lot of dihedral since I have made a serveral shoulder wing powered models before, and I found that around 7 degrees per side seemed to be optimum for rudder-elevator control.

For the tail volume co-efficient, Is it correct to use the "Lv" coefficient for tail moment as the distance from the COG location to the 1/4 chord point on the vertical tail area?
Another issue that made me a bit confused was your write up on tail volume co-efficient says it uses normally uses the full wingspan for the calculation, not the half span as your calculation for the Captian's model above. In my HLG design I am looking at the following numbers:

Lv = 13.3", half-span = 22", W = 267 sq", Av = 29 sq"
Vvt = (Avt/W)*(Lv/half-span) = 0.0657
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Old Jan 08, 2008, 07:34 PM
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Quote:
Originally Posted by John235
...I am applying them to my HLG model. The EDA calculation gave me a higher EDA figure than I was expecting.

Inner panel = 360mm
half span = 570mm
Inner dihedral = 3.2 degrees
Outer dihedral = 3.2 + 13.7 = 16.9 degrees
3.2 * (1 - 0.47) = 1.696 degrees for innner panel
16.9 * (0.47 - 0) = 7.943 degrees for outer panel
EDA = 1.696 + 7.943 = 9.64 degrees.

This seems like a lot of dihedral since I have made a serveral shoulder wing powered models before, and I found that around 7 degrees per side seemed to be optimum for rudder-elevator control.
However, typical shoulder winged sport models have less inertia about the yaw and roll axes than a sailplane. Also, tastes vary on how crisply folks want their planes to respond. In addition, more dihedral means less yaw required to get a given rate of roll, so less fuselage drag.

Quote:
For the tail volume co-efficient, Is it correct to use the "Lv" coefficient for tail moment as the distance from the COG location to the 1/4 chord point on the vertical tail area?
That's usually close, but technically the moment arms are measured between the aerodynamic centers. C/G is a variable location in a design, while the AC's are fixed by the plane's geometry. In addition, when we're talking about tail surfaces, what they're mostly trying to deal with is the aerodynamic loads on the wing, so the distance to the wing's AC matters more than the distance to the C/G.

Quote:
Another issue that made me a bit confused was your write up on tail volume co-efficient says it uses normally uses the full wingspan for the calculation, not the half span as your calculation for the Captian's model above.
Both are correct, but full span seems to be more common from what I've seen. What matters most is that you know which method was used for the numbers you're looking at. The Captain used the half-span in his calculations, so I used that method in my comparisons just to be consistent. However, in my own calculations I normally use the full span.

Quote:
In my HLG design I am looking at the following numbers:

Lv = 13.3", half-span = 22", W = 267 sq", Av = 29 sq"
Vvt = (Avt/W)*(Lv/half-span) = 0.0657
Or, based on the full span, that's .0328. That's on the low side of normal, which is typically more like about .045 to .055 based on the full span. If you're planning to discus-launch, you'll need even more yaw stability.

The other factor to consider is the dynamic coefficient. In your case that's (13.3/44)^2*(29/267) = .00992 (again based on the full span). Again, in my experience that's low.
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Old Jan 08, 2008, 09:35 PM
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Quote:
Originally Posted by Don Stackhouse
... based on the full span, that's .0328. That's on the low side of normal, which is typically more like about .045 to .055 based on the full span. If you're planning to discus-launch, you'll need even more yaw stability.

The other factor to consider is the dynamic coefficient. In your case that's (13.3/44)^2*(29/267) = .00992 (again based on the full span). Again, in my experience that's low.
Don, Thanks for your comments. I appreciate your time taken to go through these canard design issues. As you have mentioned, the fuselage area at the front of the model will be a further detriment to yaw stability. On the other hand there may be a redeeming aspect of the canard layout to improve yaw stability. I think that the lateral area of the wing due to dihedral/polyhedral will benefit yaw stability much more than with a conventional layout, since the main wing is entirely behind the aerodynamic centre in a canard model such as the gliders in question.
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Old Jan 08, 2008, 09:45 PM
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Request permission for 2 stupid questions!


What does OTOH mean, and does a spreadsheet mean the computer does the work?
OK now, let's cut and paste the data obtained, as I got done collecting it, but not computing it, but first, Don, I don't know which way I inverted the numbers to get the wrong answer, and now I must delve into this quandry of lost memories for the right stuff!
----------
OK a Butterfly 2's wing is:
10.5" chord, 20.5" to poly break (1/2 span) 420sq" total,
6" tip@ 29" outerpanel= 478.5 sq."--(16.5X29)
I broke the wing 2 times thusly;
20,5" poly has 1.5 degrees Dihedral,
7.25 degrees @next 20.5" break (41" half span total) and the last 8 inches @13.00 degrees
The canard is as this:
7" root,
4 inch tip, 34.5 " total span, and 32" falspar span (16" panels) @ 12 degree dihedral ( included angle)
189.5 (190) sq." canard
898.5 (900) sq. inch main wing
---
vertical/ rudder as 64 sq. inches
moment of center@ 25" rudder
moment @canard -c Chord(1/4 chord) 23 "
moment -c main (1/4 Chord) @ 5.875=
28.875" L total of 1/4 chord's ( main to canard)
now other than being a 4 year old box fuselage that I used to get in the air "quick and dirty" a couple summers ago, the dynamics of flight are very satisfactory, and i did have the pleasure a few times to watch it "get on step" with somewhat noticable results. not as vivid as a Bird of Time, but pretty close. If you were able to see the AVI (Mac) driven video, you can see that just before the landing, she looses energy a bit more dramatically than say the Sagittas or OLY 2's or 650's , but generally is in a bit faster envelope more of a Bird of Time type than a Gentle Lady.
I consider a tight turn in the 75 foot radius, and have not been smaller than that as best as I can tell. I usually fly about 300 feet in front of the ship, as I need to be that far ahead if I would be in competition for a spot landing. generally a 'bad' landing is a wing tip catch'er and a 100 foot walk


Now I'm going to Don's site, see ya later!
Johnny
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Old Jan 08, 2008, 10:53 PM
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And the facts
After all, it was my first film to digital piece of history! nah, can't get 3 frames a second with a 'single action' shooter
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Old Jan 09, 2008, 08:49 AM
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Hi, these are my sketches for my canard glider...

Can someone comment on em'? Looks like it'll work, I just need to find out the size of the vertical stabs and rudders.

AUW should be about 400 - 500 gms. Hope it'll work!
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Old Jan 09, 2008, 08:57 AM
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OTOH = On The Other Hand
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Old Jan 09, 2008, 09:14 AM
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I love those shots Captain! Did you tow it up? Sunfire, Thanks for showing. How will you power it or is it tow? I would extend the rear and add a rudder as discussed here. It looks like ailerons and elevator? The rudders and winglets work better the further they are from the CG. Glad you are with us. Charles
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Old Jan 09, 2008, 09:36 AM
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Quote:
Originally Posted by canard addict
I love those shots Captain! Did you tow it up? Sunfire, Thanks for showing. How will you power it or is it tow? I would extend the rear and add a rudder as discussed here. It looks like ailerons and elevator? The rudders and winglets work better the further they are from the CG. Glad you are with us. Charles
Hi, I intend to power it, it'll be great if it can thermal. Extend the rear and add a rudder? I intend to make it pusher (just a preference). Rudders and winglets work better the further from the CG? Ok.

Thanks! I like canards, esp the gunderson S1 glider.
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Old Jan 09, 2008, 04:36 PM
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Thanks Speedy- I never even considered getting close to that one!
yes Chuck, she is a towhook type
Now I'm gonna go to"Don's House", figure what I have, and then fly some video game, and set some ribs
Check canardly soar in thermal for more pictures- lots of the blu/yellow bird!
Johnny
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Old Jan 09, 2008, 04:41 PM
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Johnny, Thanks for posting the details of the Butterfly2. It seems to be 98" span. I appreciate you posting these figures as it seems like a good reference. It is interesting that your canard area is 21% of the main, which is a bit smaller than what I was planning. I feel that larger canard area should be a more conservative design. Do you know if there is any reason not to use larger canards?
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