Dihedral in a Delta?

by Arend | August 16, 2013 | (7) Posted in Projects

Over and over again my planes use the "nose dive" or "cartwheel" maneuver to tell me that I am not a very good pilot. In particular yank and bank airplanes somehow elude me. I had a tad bit of success with a delta, and I look forward to build my FT Versa Wing. However I also decided to make it easier for me. One of my main issues with "yank and bank" and particular flying wings is the fact that they don't automatically stabilize. Once I have them flying in an angle I have trouble getting them upright. My Old Fogey does that so nicely by herself... I know that dihedral can help, so I decided to build a delta wing with dihedral. Reading about this tells me that dihedrals on a delta is apparently a not so bright idea. All the more a reason to try it! I looked into several plans and came up with this design:

As you can see I added something similar to winglets. They are in fact 25 degree dihedral tips. They are about 4 inch long, and continue the airfoil the wing has.

The plane has a 24g motor with a 18amp ESC, and the prop is 8/6. The flat part of the wing itself is 32 inches wide, and about 40 inches in total, but I used only 2.5 sheets of foam board.

I was a little concerned about the climb rate, but as you can see in the video, the plane shoots up like a rocket. Most of the time I fly it between 1/8 and 1/4 stick. The airfoil allows a super smooth glide. I also added a 3-axis gyro stabilizer but I turn it off once I am high enough and turn it back on to land. I also "landed" the plane roughly a couple of times and it took the beating. The wing is made stiffer with a small glass fiber rod. You can see a small fixed patch on the back left side, which comes from an NTM 28/22 I tried earlier - way too much power for me. Check out the video, it also features (a little blurry) my first intentional roll that did not end in a crash. Ignore the voices, me and my wife "argue" in German about the best angle and that I of cause fly way too high:

All in all I love this plane. It is stable, glides nice, forgives mistakes, I would call it a beginner wing. Let me know if you want to see plans or an article about the build. In the meantime I practice some more to finally fly my Versa Wing with confidence!

Cheers Arend

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COMMENTS

the nerdling on August 18, 2013
PLANS PLEASE :)
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Arend on August 20, 2013
I would love to see someone else build it, and comment on the flying abilities, I am working on the plans and a making off. Cheers Arend
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alibopo on August 26, 2013
Hi Arend, anything that adds stability is good in my book! I was looking at dihedral (to do with the dutch-roll issue I'd been experiencing with my Old Fogey) and I came across this interesting fact. A swept back wing has the equivalent effect to adding dihedral. Which means your plane already has a dihedral or balancing effect built-in. In fact on some jet planes, to counteract the dihedral effect created by the sweep-back, the designers have pointed the wings down to reduce the stabilising effect! This seems to indicate that introducing more 'sweep-back' will give you a more stable platform without the addition of the winglets - a much easier build. I imagine the core 'user group' for flying wings want something that is more manoeuvrable, so most designs reflect that - possibly there's other more stable designs already out there? I'd be interested to know if you can go 'hands free' with your wing - does it self stabilise? I've heard discussions about this, with reference to FPV flying, as wings need constant flying attention unless they have onboard auto stabilisation - plenty of wing and tail planes self stabilise when you let go the controls making them a lot less work for the FPV operator.
If you are going to stick with winglets I wonder if a flat sheet winglet would have the same effect? A lot easier to join to the wing - a single angled cut on the wing rather than mating a whole wing cross-section. Another possibility might be to leave off the bottom of the wingtip as is being done on recent Flite Test designs - spitfire & cruiser etc. That of course creates a definite topside. Fascinating stuff! I love that by using the foam board it's possible to experiment like this. Cheers, Alibopo.
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RandallJ on August 19, 2013
I had much the same problems with wings at first.. The "yank and bank" is not really so much as a lot of trying to keep the wing a bit flatter in turns.. I would get too far on edge and lose control.. By keeping the wings a bit more level or rolling out of the turn when in trouble was a key to more success.. The dihedral is doing just that for you but I think if you concentrate on just leveling the wing when in doubt, you will have a bit more success....
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Arend on August 20, 2013
Thanks for the tip RandallJ!
I found out that indeed the leveling is an issue for me. Using a classic straight wing with stabilizers on the tips is trickier to level for me, which is not necessarily the same problem for everyone. This dihedral delta indeed levels much easier, and flying it way more often now also shows that getting it into a smooth curve is very easy but making an aggressive roll is hard.
I lowered the throttle and pulled up to see it stall, other than most planes that tip forward after a stall, this one flips backwards if the incline is too high. I guess due to the weight of the winglets. That looks shocking but it catches itself very quickly and doesn't need to dive as much as a conventional stall would. Which makes this one have a strange flipping stall characteristic, but catches itself faster and more level after a stall. I tried tip stalling the plane and I couldn't, guess that is a good sign, or me not being able to provoke that on demand. I also found that landing is a bit trickier, since the glide rate is great. I turn off the motor and have to glide in from much further away until I reach the ground. This speaks for the plane, but makes it harder for me to estimate where I end. Cheers Arend
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dlggliders on April 27, 2018
some notes ive been taking for many years on delta style flying wings, yes in fact winglets will in deed stabilize your plane if angled as you have in your build,,a few notes, if you look in nature, an eagle or a hawk or any good size glider raptor always folds its wings to gain speed on a dive, and opens its wings to glide or thermal,,having said that, the more sweep you have on your flying wing, the more it has the tendency to drop and not be as stable as say a more forward swept wing,, in fact these raptors when soaring in a thermal glide, you will notice their wings are far stretched in a forward sweep and they also raise wings in an angle or dihedral,,my point is, if you want a more stable flying wing, go with a more forward sweep and either add a few degrees of a washout on the tip chord or add a few degrees of dihedral,,swept back wings are more for speed and agile flying and adding dihedral is a no no :)
you can see some great examples of forward sweep flying delta style wings here https://www.microbirds.com
cheers :)
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Dihedral in a Delta?