Aquila Washout

[Gliderguy]

Just picked up a nice looking Aquila. I flew it a couple times and it was acting a little unstable. Then I noticed a little wing warp which looks like it should come out Ok.

1. Does anyone know how much washout I should be putting into the wing?

2. Should it be at the tip or midpanel?

I also would like to install a little larger wing joiner and maybe sheet the bottom to the first poly break.

[LVsoaring]

About 1/8" washout should be sufficient. I've just recently learned that putting the washout at the outer end of the inner panels usually works better than putting it at the tips.

[Thermaler]

From the Aquila instruction book:

" Introduction:
... Polydihedral is used because of the superior turn characteristics over Vee dihedral. The change in leading edge radius on the tip panels eliminates tip stalling and avoids the loss of lift caused when washout is used for this purpose."

"Wing:
... (24) ....IMPORTANT NOTE: The tip panel leading edge must be shaped so that it becomes progressively blunter toward the tip. ..."

If I read them right Lee did not intend for the Aquila to need or use wahout.

Joe

[kzimmerm]

About 1/8" washout should be sufficient. I've just recently learned that putting the washout at the outer end of the inner panels usually works better than putting it at the tips.


I was going to say 1/4".... FYI, as a routine, I check my wings at the start of every flying season. I have found that over time twists will develop and have to be corrected. For the start of this flying season I placed the wings on a glass top table and had to flatten them out as well as add washout.




Kurt

[markdrela]

I was going to say 1/4".... The best place to add washout to a poly wing is on the inner panels (or on the mid panels for a 5-panel wing). Even 1/16" will make a noticable difference, and 1/4" is serious overkill.

The reason for twisting the inner panels is that tip stall typically occurs just outside of the outer poly break, and not at the extreme tip. So you want to rotate the inner part of the tip panel, not so much the outer part. Twisting the inner panel simply rotates the whole tip panel by the same amount, which is a good compromise.

[kzimmerm]

Thanks Mark. Going to redo my wings before the next time I fly..

Kurt

[LVsoaring]

The best place to add washout to a poly wing is on the inner panels (or on the mid panels for a 5-panel wing). Even 1/16" will make a noticable difference, and 1/4" is serious overkill.

The reason for twisting the inner panels is that tip stall typically occurs just outside of the outer poly break, and not at the extreme tip. So you want to rotate the inner part of the tip panel, not so much the outer part. Twisting the inner panel simply rotates the whole tip panel by the same amount, which is a good compromise.

Thanks Dr. D! I think it was one of your articles where I read about putting the washout at the inner panel. Thanks for the memory refresher!

[Gliderguy]

Thanks all!

It has some serious inboard wash-in at present with a bunch of wash out at the tip on one wing. I should have noticed it before flying but was real anxious to fly and had a small window of opertunity to do so. Anyway I'll be fixing her and dialing it in. :D

[Thermaler]

Mark,
What is your observation of Lee Renaud's idea of tip stalling and a blunt LE at the tip? Should we add washout to the outboard part of the inner panels of our Aquila's? Or would it detract from the performance?

Joe

[woro]

Joe, I'm not Dr. Drela and I'm sure he knows million times more about aerodynamics than I do but I'll try to answer. The blunt LE is IMO better because it works much cleaner. The change of LE shape will change stall characteristics without adding a lot of drag. The shape of fwd part of anything is not as important as the aft part. Just have a look at some small FF HLG's. If the 10 years old builder forgets to round the LE, nothing happens. But watch the difference between sharp and blunt or square TE!
The washout steals a lot of lift and adds more drag than the blunt LE. OTOH, the washout works better. It's a tradeoff between stall characteristics and glide.
I would choose the blunt LE, because I think that if the stall characterics are sufficient, there is no reason to spoil the glide by trying to improve the stall characteristics-it probably worked well so why do you want to add drag?
I've made this mistake a few times-I had so much washout that the tips kept the plane flying and the center worked as a brake-the plane was able to fly at almost 15deg aoa! Of course, the LE's were soooo blunt too...
And another reason to use the LE shape change-it is what you can see on some 1:1 real planes-but they have sharp edge on mid part of LE. I think this thing with LE is quite cool idea

[markdrela]

The blunt LE is IMO better because it works much cleaner. The change of LE shape will change stall characteristics without adding a lot of drag. The shape of fwd part of anything is not as important as the aft part. Just have a look at some small FF HLG's. If the 10 years old builder forgets to round the LE, nothing happens. But watch the difference between sharp and blunt or square TE! Those are some mighty broad brush strokes. First of all, "blunting the LE" is an awfully arbitrary recipe, and at our Reynolds numbers increasing the LE radius doesn't necessarily increase maximum lift. Sometimes it can do just the opposite, depending on the starting airfoil.

The washout steals a lot of lift and adds more drag than the blunt LE. Not necessarily. On the Aquila, with its untapered inner panels, adding some washout will definitely improve span efficiency and reduce the induced drag. And adding only 1 degree washout (that's usually all it takes), will not push the tips outside their drag bucket at high speed if the "Miller mod" is used. So the slight washout will probably reduce drag at all speeds, and give better thermal handling to boot.

[markdrela]

Should we add washout to the outboard part of the inner panels of our Aquila's? Or would it detract from the performance? On a 4-panel wing, the best place to add the washout twist is on the outer half of the inner panel. This is better than twisting the entire inner panel. On a 5-panel wing, like on the Ava or Majestic, it's best to twist the entire mid-panel linearly.

I'm also curious here:
Does the Aquila really have a tip stall problem? I've never flown one, so I don't know. Looking at its planform and dihedral layout, it doesn't look like it would be prone to tip stalling. But that's just a guess, since I haven't run the numbers on it.

[Phoebusflyer]

The Aquila I built many years ago had no problem with tip stall and I built her just as the plans told me too. Lee Renaud did a masterful design with the Aquila. If flew great, thermaled great and was a real joy to fly. Wish I still had mine, as well as the Grande I built.

[cosmicpossum]

Just my .02, the Aquila I just refurbed and now fly has 0 degrees washout and flies perfectly. It is a bit "washy" as I call it near stall speeds, but that's why I fixed the spoilers, so I don't have to slow down that much until landing.

[2motheus]

Just my .02, the Aquila I just refurbed and now fly has 0 degrees washout and flies perfectly. It is a bit "washy" as I call it near stall speeds, but that's why I fixed the spoilers, so I don't have to slow down that much until landing.

Fixed the spoilers?

[Thermaler]

I have not had any tip stall problems with my Aquila.
I have had a problen with the canopy cracking in the middle which I believe is due to the tight fit and the forces of opening it up. I have added extra reinforcement to the canopy deck but...
It also might be that since the first one was broken in a bump with terra firm it was replaced with a thinner, cheap, crappy version from a place I will not mention or buy them from anymore.

Joe

[cosmicpossum]

Fixed the spoilers?

Yes, when I received the plane, the spoilers were taped down and the spoiler servo mount removed.

[Ich Bin]

Great Aquila thread on washout and mods. Thanks for sharing everyone. I am resurrecting an Aquila with a fiberglass fuse that I was given from a club member. It looks cool.

E

[dave440c]

Flew one for years in the mid 70's. Set it up per the plans and Lee's instructions. Never had a tip stall problem that I can recall only bent wingrods due to learning to winch instead of high-start. :D Have a NOS Kit that my son found for me and it will be my winter build this year! I will however give some consideration to Dr. D's washout comments. Maybe even do a build thread if the interest is there. :eek: