Modernizing the Aquila Grande airfoil?

[Keith Watson]

I've wondered if it is possible to take an existing Aquila Grande rib set and modify them to be close to a modern flatbottom airfoil like the AG-3X series. Has anyone thought about this? Tried it?

When I print the Aquila airfoil (not Grande) and the AG-35 on paper and hold them up to a light bulb the differences are that the leading edge needs lifting and the mid chord needs to be a little thinner. With the only tools I have on hand it looks like the next step is to scale the printout to a rib in my kit and eyeball that.

Does anyone have the Aquila Grande coordinates?

I'll also look at the HT21 airfoil for the tail. When I get around to building the kit I might as well try some improvements. :p I've already gathered some tips from other threads.

[Keith Watson]

OK, here is the old fashioned way of comparing airfoils. :rolleyes:

This is the AG-34 and the Aquila Grande root rib. The lower lead in is identical! The leading edge is too pointy. There is about 1mm missing from the first 5% on top. Then the top from 20% on back needs thinning.

Does anyone have the Aquila Grande ribs in file format they would be willing to share? I could throw in the airfoils I want and send it to a laser cutting shop.

[Ollie]

Use PC:
http://my.athenet.net/~atkron95/pcsoar.htm
and
http://www.profili2.com/eng/default.htm

[Keith Watson]

Thanks, Ollie. Profili I know about and is nice. I didn't know about PCSoar and it looks quite interesting. I'll have to give it a try soon.

[ferincr]

Thanks, Ollie. Profili I know about and is nice. I didn't know about PCSoar and it looks quite interesting. I'll have to give it a try soon.
Hi Keith,
Please keep me posted about this project, having an AG and an AXL (which I'd love to experiment a little with more modern airfoils for it) I'm interested in seeing what you come up with.
Fernando

[Keith Watson]

Hi Fernando,

I started looking into this project 3 years ago. But it was your recent Aquila threads which rekindled my interest. :) My time this week is diverted to finishing the build of my own design DLG. Then I will start on the analysis of the AG wing.

Coordinates and polars (computed and wind tunnel) are available for the Aquila airfoil. It is my understanding that the A and AXL use the same airfoil. I have been unable to find coordinates or polars for the AG. I'll get coordinates off my rib set and plug those into Profili (XFoil) to get some polars. Then there is some measuring to do on the plans to get enough data to feed to PCSoar.

I'll post progress and results as I go along. :)

Regards,
Keith

[Ollie]

http://www.charlesriverrc.org/articles/drela-airfoilshop/markdrela-ag-ht-airfoils.htm
Both coordinates and polars.

[Keith Watson]

I just KNEW someone was going to interpret it that way. :D I was using Fernando's nomenclature of Aquila (A), Aquila Grande (AG), and Aquila XL (AXL).

Great link though. I have used it before for a DLG I'm about to finish. Once my Profili license arrives I will be importing the AG-3X series coordinates from there. And since neither Profili nor UIUC Airfoil Data Site (http://www.aae.uiuc.edu/m-selig/) have the Aquila Grande airfoil I'll measure those coordinates myself.

This is going to be fun! :p

[Keith Watson]

Lots of measuring, lots and lots of transferring numbers by hand (aren't computers great), and I have some info.

Polars were generated with Profili/XFoil. PC-Soar was used to generate the airframe comparisons. The Aquila Grande airframe was used in each case, the only difference was using the airfoils from the Aquila (A), Aquila Grande (AG), and AG-34 (AG34).

L/D numbers were the same up to 22mph flight speed.

At 24mph the L/D improves 10% changing from A to AG, and 2% more changing to AG34.

At 28mph the L/D improves 18% changing from A to AG, and 7% more changing to AG34.

At 34mph the L/D improves 23% changing from A to AG, and 22% more changing to AG34.

So the Aquila Grande airfoil is pretty good. But when it comes to penetration the AG-34 is even better.

[ferincr]

great info Keith!!!
This is quite motivating to start another set of wings for my AG and AXL!!!

[Keith Watson]

Fernando, here are some graphs from Profili. They give more info than PC-Soar. I still need to learn the details of reading polars. :)

PC-Soar reports that for this airframe a Reynolds number of 100,000 is 15mph and 200,000 is 30mph.

[ferincr]

Polars are way up too far for me to even know what they are... :(
I've been fiddling around with pc soar, profili and compufoil to decide which one I want to pay for, but still waiting to learn more about planes before I make my conmitment, so far everything is like advanced chinese to me. :eek:
Some day..... May be....
Fernando

[Ollie]

ferincr,
Begin with the concept of polars. Study them if want to use the ideas. If you have questions, we will help you over the hard parts.
http://home.att.net/~jdburch/polar.htm

[Keith Watson]

Fernando, here is what I have found so far from using PC-Soar and Profili. PC-Soar appears to calculate Reynolds numbers based on the size of the airplane and uses polars for comparison, that's it. Ollie's link is describes this output. Profili of course generates polars. I have not yet used the rib templates or wing layout features in Profili. When I looked at the Compufoil website there is a long list of paid options to pick and choose what features you want.

[CoastalFlyer]

Great work so far. I'll be watching this thread closely.

[Keith Watson]

I tried doing some research on understanding polars and my statement above is not correct. "Polars" including many different pieces of information and what PC-Soar generates are also considered to be polars. The PC-Soar output is just the easiest for a pilot to directly apply to flying an aircraft.

OK, now that I've proved to myself an updated airfoil is a good direction to go I'm switching my priorites back to my own design DLG for a while. I will continue to post updates to this thread as they become available.

[Keith Watson]

Here is the difference between the Aquila Grande airfoil and the AG-34 airfoil. The AG-34 airfoil is from the coordinates. The Aquila Grande was traced by pen directly over the plans. The lower surface matches close enough to be considered exact.

The numbers 1-9 along the bottom of the airfoil coorespond to 10-90 percent of the chord.

[Keith Watson]

I have yet to find airfoil manipulation software that is accurate for taking pieces of one airfoil and using them in another airfoil. So I'm doing it by hand. :rolleyes:

I rotated the Aquila coordinates (by hand) so the flat bottom has Y coordinates of zero just like the AG-34 does. This makes hand manipulation inside the files much easier. The attached picture is now an accurate comparison of the Aquila (not Aquila Grande) vs AG-34. Remember, the Aquila Grande bottom leading edge has the same curve as the AG-34 and the same upper surface as the Aquila.

So one more step is completed.

Maybe this thread should be in the Modeling Science section. :D

[ferincr]

I'm starting to get excited about this project. :D
I posted a couple of questions on the Sailplane talk forum.
I already started experimenting with the new fuse, according to the plans calls for 1/8 ply sides, I'm making balsa ply with 3 sheets of 1/24 glued with epoxy to see differences in weight and resistence. :confused:
I'm also considering to carve a pod in balsa to make a mold for FG fuses, the only thing putting me off this is how many would I make??? Is it really woth it?
The other idea I got was to try to make the mold in a way that the wing root area is neutral so then you can put any airfoil you want in different fuses.
Ok,ok, ok,.... enough dreaming, I'll give you your thread back now.
Fernando

[Keith Watson]

Hi Fernando. When I get a chance I'll go see what you are doing in the other forum. :)

There was a very recent thread about someone in the UK looking for a glass Aquila fuse. Sounded like he was going to use the existing cracked one as a plug for a mould.

About the wing root, you can see from the airfoil overlay I did today that at least the flat bottom will match up. I expect the places which don't match (upper leading edge) can be puttied up to have a nice fairing.

[ferincr]

Hi Fernando. When I get a chance I'll go see what you are doing in the other forum. :)

There was a very recent thread about someone in the UK looking for a glass Aquila fuse. Sounded like he was going to use the existing cracked one as a plug for a mould.

About the wing root, you can see from the airfoil overlay I did today that at least the flat bottom will match up. I expect the places which don't match (upper leading edge) can be puttied up to have a nice fairing.
Actually the only thing I'm doing in the other forum is driving people crazy with all my questions.
Yes I saw the post by the Britt, but I'm afraid of ruining my original and stil working fuse in the process, that is why I rather make a plug.
I have no experience at all with FG (appart from all the patching up) and I think it would be better to have two halves, anyway, all this still in the wishing stage yet.
I was considering buying Profili today (which is quite a process living so far). I tried to play a bit but it's hard having all the locked features.
Well, I don't distract you any more.
Thanks for keeping us posted,
Fernando

[Keith Watson]

I'm glad you saw the update. I was going to send you an email but had to rush off after posting.

I mentioned the guy in the UK because if he is going to make one, have him make you one. :) Otherwise I don't know anything about making moulds except I can't draw or sand a pretty curve! :D

After I payed for Profili with PayPal Stefano sent me a downloadable version and a registration key and I started using it that day. The CD came less than a week later in the mail all the way from Italy. Stefano is good about responding quickly.

I don't know if using thinner plywood glued together would way less than thicker plywood.

[ferincr]

Since I crashed the AXL yesterday :( (only minor repair needed :) ) and more convinced than ever that I need a second pair of wings so I can keep flying if I break one I'm decided to start building them. I TLARed the AG-34 to the cord of the AXL 12.2" from your previous post).
Now, before I make the template to start cutting ribs, I was thinking in sheeting the whole wing with balsa instead of having the open bays, I have the choice of 1/16" or 1/24" and what I would like to know is:
Is it better to go with the 1/24 or 1/16?
I mean, I guess a fully sheeted wing would be stronger than open bays (isn't it?)
Or the weight I might save with the thinner balsa is insignificant compared to the strenght I lose? :confused: :confused:
Any inputs?
Thanks,
Fernando.

[Keith Watson]

I do not know for sure but from all sorts of planes I've seen it seems that a D-box is all the strength that is needed, so fully sheeted would just add weight. Or if you want to fully sheet part of the wing, do it where strength is needed in the center section.

Don't use the AG-34 for the entire wing. Use a higher number as you proceed outward. The Bubble Dancer for example starts with AG-35 at the root and proceeds to AG-38 at the tip. Attached is a comparison from Profili.

[ferincr]

Yes, I considered that issue with the airfoil change at the tips.
I read somewhere that you have to put wash out so the tip is not the first part of the wing to stall.
So to avoid that the LE should be lower in respect to the TE towards the wing tip.
I noticed that the Aquila Grande manages that simply by reducing the phillips entry towards the wing tip and ends up with the last rib being flat bottomed.
So, I kind of TLARed that too, basically I modified the ribs towards the tip from AG-34 to "almost" an Aquila airfoil lowering the LE.
So far all I did is paper templates but it took the whole day.

About the full wing sheeting is because I read that open bays deforms the shape of the wing and if you sheet with balsa keeps the airfoil better. I don't know how much benefit I can get in this kind of airfoil (not being top of the line).

Another question, the plan is to put flaps and ailerons on these wings, should I also consider putting spoilers? Or would it be an overkill?
I mean, is it enough with crow mix with flaps and ailerons?
Fernando

[markdrela]

I read somewhere that you have to put wash out so the tip is not the first part of the wing to stall. On a poly wing, tip stall typically occurs just outboard of the outermost poly break. For this reason, any washout twist should go on the inner panels, where it is vastly more effective --- less than 1 degree washout at the outer poly break will usually suffice. The tip panels are flat, but rotated overall by the inner washout.

Trying to get the same tip stall delay by twisting only the tip panels will require a massive amount of washout -- as much as 5 degrees or more. This is probably the main reason why washout has gotten a bad rap. It's actually extremely effective, but only if it's put in the right place.

I noticed that the Aquila Grande manages that simply by reducing the phillips entry towards the wing tip and ends up with the last rib being flat bottomed. Removing the Phillips entry may or may not improve the stall properties. I couldn't predict the effect reliably without doing actual calculations. You're also changing the airfoil the most at the extreme tip, where it won't help much to alleviate tip stall anyway. But it will definitely cause lots of drag at higher speeds. I would use the AG34,36,38 across the span, and wash out the inner panels about 1.0 degree or less.

[markdrela]

I have the choice of 1/16" or 1/24" and what I would like to know is:
Is it better to go with the 1/24 or 1/16? Keep in mind that the LE sheeting requirements vary drastically across the span. On the Bubble Dancer, medium-hard 3/32" balsa on the center panel is barely adequate, and super light 1/16" balsa on the tip panels is overkill.

I would not sheet the whole chord, because this will make the wing more prone to flutter. For flutter resistance, it's essential that the CG of the wing cross section be as far forward as possible. Putting weight behind the spar is bad, even if it makes the wing a bit stiffer in torsion.

[ferincr]

Removing the Phillips entry may or may not improve the stall properties. I couldn't predict the effect reliably without doing actual calculations. You're also changing the airfoil the most at the extreme tip, where it won't help much to alleviate tip stall anyway. But it will definitely cause lots of drag at higher speeds. I would use the AG34,36,38 across the span, and wash out the inner panels about 1.0 degree or less.
Thanks a lot for that, since I have no idea about aerodynamics design I was just copying what I saw in the Aquila Grande. But considering who is advicing now I think there is not doubt about what Keith already suggested.
Back to the drawing board :o
Thnaks,
Fernando

[ferincr]

Should I change the airfoil along the main pannels too, let's say start with AG-34 and finish with AG-36 and move on to the tip to AG-38???
Or could I keep AG-34 all along the main pannel and add wash out at the end of it, and just change the airfoil on the wing tip??
Thanks again,
Fernando

[Keith Watson]

Looking at the spanwise airfoil change Mark does the difference is the thickness of the airfoil. I noticed on my rib set what you mentioned about the tips having no Philips entry. I wonder why they did that. The Aquila airfoil at a positive angle of attack has more lift but at a negative angle of attack higher drag.
About the full wing sheeting is because I read that open bays deforms the shape of the wing and if you sheet with balsa keeps the airfoil better.Where you having problems on the original AXL with covering sagging? I know somewhere on the Charlers River website Mark has some airfoils where the upper aft section of the ribs are straight(er) instead of curved just for the purpose of having less sag between ribs.

Planes with crow mixing are quite effective at going slow on landing. I have seen one 4m plane which also had bladed spoilers. My guess is those would be effective at higher speed and put a lot less stress on things than if flaps or crow were used in the same situation.

The question about where to change airfoils goes beyond my understanding.

Mark, thanks for the information on tip stall and washout.

[ferincr]

Ok, everything goes to the freezer again for some time.
I got my books today (Old buzzard's and model aircraft aerodynamics) so it's time to read and trying to learn some stuff.
Fernando

[markdrela]

I know somewhere on the Charlers River website Mark has some airfoils where the upper aft section of the ribs are straight(er) instead of curved just for the purpose of having less sag between ribs.
You're talking about the AG3x series which I recommended. To make best use of these, it's necessary to duplicate the skin-support structure of the Bubble Dancer or Allegro-Lite. By this I mean you want the top sheeting to extend back to 45% or at least 40% chord, and you must have the top support strip at 65% chord. All the open bay areas will then be perfectly flat, giving zero covering sag. You don't need the piecewise edge-on top support strip shown on the BD and AL drawings. Just use a continuous strip set into rib notches. Something like 1/8" x 3/16" laid flat should work OK.

BTW, I think the Aquila Grande has diagonal strips behind the spar, correct? If so, I would just leave them out, since they are pretty useless. If you want to add torsional stiffness using diagonal members, they must be nearly the full depth of the airfoil (i.e. they must be ribs). Small-section diagonal strips add mainly weight, with very little added stiffness. It's much better to add that weight in the form of denser or thicker LE sheeting.

[markdrela]

Should I change the airfoil along the main pannels too, let's say start with AG-34 and finish with AG-36 and move on to the tip to AG-38???
Yes, that's what I meant. AG34 at the center, AG36 at the poly break, and AG38 at the extreme tip. All the intermediate airfoils will be linearly interpolated.

For the inner panels, you should be able to make the ribs by stack sanding between the AG34 and AG36 templates. For the tips, individual cutting may be needed because of the sharper taper. Dunno.

[ferincr]

For the inner panels, you should be able to make the ribs by stack sanding between the AG34 and AG36 templates.
Good that was the main reason of my asking (phew!!!!)
I got a bit discouraged if I had to cut every single rib (it's enough with the tip pannel ones).
The Aquila Grande has a second "semi" spar (3/8 x 1/8) on the top going parallel to the main one from the root rib to the end of the spoiler blade (or so).
My project is for the Aquila XL which it has only the main spar (built first with solid 1/2" end grain balsa shear webs between the sparcaps).
I think my next wings for the Grande I'll build them that same way.
I cart weelied on landing the other day (150" span and over 100 oz.) and I only broke apiece of the seehting on the tip D tube.
Thaks for all the input again, it's great having allthis support.
Fernando

[markdrela]

The Aquila Grande has a second "semi" spar (3/8 x 1/8) on the top going parallel to the main one from the root rib to the end of the spoiler blade (or so).
OK, but definitely put it at 65% chord. The airfoils are specifically designed for it. Looky here to see the wing structure which intended for these airfoils, specifically where the film is to be supported:
http://www.charlesriverrc.org/articles/bubbledancer/markdrela-bubbledancer-3m.htm
http://www.charlesriverrc.org/articles/bubbledancer/PDFs/wing_plan_V2b.pdf

[ferincr]

Thanks for those links.
I need to read more to be able to understand what to look for, otherwise you can look at things without really seeing anything.
The more I learn the more things start to make sense.
So I'll look at them again once I get the knowledge to be able to understand how everything works together.
Actually my last crash was an eye opening to me. The way the wing tip flexed I thought the LE and spar where broken and to my surprise once I cut through the only problems were one shear web unglued and part of the sheeting cracked and I became a believer that everything works as a team there. How much rigidity the wings lose when things are not working as supposed.
(sorry a bit out of subject, but is another step in my learning curve)
I appreciate your patience,
Fernando

[Keith Watson]

I just checked my plans (really for the first time) and the stock wing has that second top spar centered at 47%. So it looks like the top sheeting needs to be changed to extend back that far and all the way to the tip, plus the support strip at 65%.

Thanks for pointing this out Mark. I couldn't remember exactly where at Charles River I had read that.

Also, the Aquila Grande does not have diagonal structures in it. In the last week or two I did see a picture of something which did.

Great info!

[ferincr]

the Aquila Grande does not have diagonal structures in it. In the last week or two I did see a picture of something which did.
I think I saw it too, and if I'm not wrong was at the Challenger build thread.
Fernando

[markdrela]

I think I saw it too, and if I'm not wrong was at the Challenger build thread.

The Challenger does not have diagonal sticks in the wing.