Slow delta wings?

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

BDD

Well-Known Member
Joined
Apr 2, 2005
Messages
388
Location
WI
GTEX-09

What was the cause of the instability which caused the crash? C.G. location, airfoil selection, some wing or elevon configuration issue, etc?
 

gtex09

Active Member
Joined
Apr 13, 2010
Messages
38
Location
France (Lille)
Hi BDD,
Well, I guess that was because I made too much changes in the plan shape between the 05 and 06 version....
Actually, if you look in detail to v06, you will see that the wing size is really much more smaller than the v05, for te same length of airplane.
It was much more sensible to the CG location than the previous version.
That's the reason why I came back to the same plan form for the v07 version.....
GTx
 

deskpilot

Well-Known Member
Joined
Jun 30, 2009
Messages
1,125
Location
Morphett Vale, South Australia. Just south of Adel
Hi guys, been a while since I last posted. Here are a few images of my Eagle-Ray. Still a long, long way to go. The green represents F/glass although the turtle-deck side walls and all under side surfaces might be fabric as there are no con-cave curves included. The frame is riveted alloy, either square or rectangular.
 

Attachments

ThadBeier

Well-Known Member
Joined
Dec 28, 2010
Messages
79
Location
Los Angeles, California
deskflyer, this is a remarkable progression of design. I am a huge fan of low-aspect ratio airplanes -- I think they have a lot to recommend them. They can be light, very strong, simple to built, have a lot of interior volume, and aren't too fast. The Arup planes were an early example, and yours might be the most recent one. Another example of a low-aspect ratio plane, not completely unlike yours, is the Pelican -- see pelican

I agree with your analysis that your wing area will have to be rather large to get the stall speeds that you want. The Vermeer wing mentioned upthread stalls at way too high a speed, but it's tiny -- 10 ft long and about 15 ft span. (3.3m by 4.5m) Making it a bit bigger is a good idea. His design was a true delta (except that it isn't swept enough, I suppose) and he needed the dihedral to eliminate dutch roll. Your wing has much less sweep, and probably won't have the odd rudder response that the Vermeer wing has.

Good luck!
 

ThadBeier

Well-Known Member
Joined
Dec 28, 2010
Messages
79
Location
Los Angeles, California
I've been thinking about your design for a while, and have come up with something similar for similar reasons. I am struck by how similar this is to the RANS S-11 Pursuit -- check it out!
 

deskpilot

Well-Known Member
Joined
Jun 30, 2009
Messages
1,125
Location
Morphett Vale, South Australia. Just south of Adel
I've been thinking about your design for a while, and have come up with something similar for similar reasons. I am struck by how similar this is to the RANS S-11 Pursuit -- check it out!
A few years back, I saw a picture of the S-11 but it was parked behind another aircraft, and wasn't referred to in the write up. Since then I've tried to find out what it was and yesterday, I finally found it. A very nice looking plane and it's a great pity it didn't make it into production. I'm sure it would have been a winner in only they could have solved the problem that caused the second aircraft to crash (seniors moment)
 

orion

Well-Known Member
Joined
Mar 2, 2003
Messages
5,800
Location
Western Washington
The aircraft was plagued by control and stability problems due to the wide fuselage. This is what I try to warn folks about when they endeavor to design aircraft with strakes and wider bodies. The geometry can set up various forms of vortex flow, which tends to be unpredictable and very destabilizing due to non-linear behavior. Secondary issues also include pressure shifts not coordinated with wing characteristics and blanketing effects.
 

Topaz

Super Moderator
Staff member
Log Member
Joined
Jul 29, 2005
Messages
14,110
Location
Orange County, California
Everyone was excited about the S-11 when the proto started making the airshow and magazine circuit rounds. The big question was, "When are you going to release kits!??!?" The company played it cagey, saying "this is only a concept demonstrator" - for a transport airplane, of all things. Later it was revealed that the airplane was a real handful to fly, for the reasons Orion states above.
 

Lucrum

Well-Known Member
Log Member
Joined
Jun 10, 2008
Messages
956
Location
Canton, GA
I don't even pretend to be an Aerodynamicist but just eye balling it I don't care for how the forward fuselage is blended on the S-11.
 

ThadBeier

Well-Known Member
Joined
Dec 28, 2010
Messages
79
Location
Los Angeles, California
Everyone was excited about the S-11 when the proto started making the airshow and magazine circuit rounds. The big question was, "When are you going to release kits!??!?" The company played it cagey, saying "this is only a concept demonstrator" - for a transport airplane, of all things. Later it was revealed that the airplane was a real handful to fly, for the reasons Orion states above.
Back in the day, there were not the computer power or the publicly-available software to do simulations of these vortex flows. Would it not be possible today to design a plane that could reliably take advantage of them, rather than have them make the plane difficult or dangerous to fly? And I know, I've seen the abomination of the vortex-breaker on the F/A-18, that was made necessary by exactly these same kinds of missed-predictions (even with the resources of Northrup to do the simulation and testing.)
 

orion

Well-Known Member
Joined
Mar 2, 2003
Messages
5,800
Location
Western Washington
Possible? Maybe. Affordable? Not to the small airplane company. But the biggest problem here is the lack of applicable design experience more so than simulation software or other technologies. The S-11 was a radical departure from their regular product line and done by a seemingly unqualified designer to take on something that unique.
 

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
13,053
Location
Memphis, TN
If I remember the first S11 crashed after takeoff of an engine seizure almost killing the the head honcho, and the second plane crashed after 250 hours when a regular employee decided to test the slow flight and spun it in. I know a third was built but with such bad karma it was probably time to quit.
 

delta

Well-Known Member
Joined
May 26, 2011
Messages
2,168
Location
Brookside Utah
Hi Doug

I'm going to second the motion that your CG will be to far forward in your current configuration. I believe it's marked close to right in your drawing, but in full scale I don't think the aft portion of your airplane will offset the weight of the engine and pilot. Build some rubber band thrown flying models with paper, balsa, and then a powered RC to fine tune your CG. You might consider a mid engine, a push pull twin, or a really light pusher to keep your cranked arrow configuration. I think you will find that it will fly nice, land on a dime, but be anything but slow.
If the tractor configuration is more important to you than the cranked arrow, then you can have an unstraked leading edge. You will probably wind up with more than a 60* sweep. I've gone from 45* to more than 90* with RC and the more sweep the further aft the CG has to be.
I wish Jubaru or Rotec would build a nice long stroke, big bore, opposed twin for under $500, but I'm not going to hold my breath.
Good luck with your project and wish me luck with mine. I'm going for a super light, roadable amphibian. I'm in the early stages and still looking at power options before going to much further. I've even considered a 2a016 genset running a bunch of giant outrunners.

Rick
 

deskpilot

Well-Known Member
Joined
Jun 30, 2009
Messages
1,125
Location
Morphett Vale, South Australia. Just south of Adel
Hi Rick, thanks for your input. I haven't done a lot lately except rethink my wing profile. I think I've stretched it too much and now it's too shallow, something like 9.5% at the root. Should be in the region of 15% I believe.
I'm in the process of making a chuck glider but I don't think it will provide and useful info with regard to lift or AoA. Still, must keep dreaming

Good luck with your design, don't understand your final sentence though.
 

delta

Well-Known Member
Joined
May 26, 2011
Messages
2,168
Location
Brookside Utah
pa3.jpgpa2.jpgpa4.JPGpa1.jpgpa5.jpg

Hi Doug

Everything's going to change a lot when you start working on the full scale anyway. The models are a good way to explore stability and CG. When you build a bunch of them you get a feel for what works better and why.
The 2a016 genset is a small US military generator. The giant outrunners are brushless electric model airplane motors that the outside housing rotates. I'll probably use a belt reduced two stroke swinging the largest prop I can.

Later...

Rick
 

Attachments

delta

Well-Known Member
Joined
May 26, 2011
Messages
2,168
Location
Brookside Utah
Choices, choices, and yet another ^&*@#$$* choice... Here's my current one and I'm sticking to it, maybe...

Later...

Rick
 

Attachments

Top