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Jan 16, 2009, 04:11 AM
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cgraf's Avatar

Airfoil for high aspect ratio wing, HP-18 glider

Good morning

I am looking for an airfoil idea or an evolution of airfoils for a high aspect wing.
The plane I will build is a 1:4 scale version of the american kit glider called "HP-18" . Wing Span will be 3.75m.
The wings will be bagged, fiber over foam.

As I already have enough planes for the slope, I would like to set this one up as a thermal ship (I think the shape of the fuselage and the V-Tail will help).

The wing is has a simple trapezoidal shape, which makes things not easy I suppose (harder to get the "elliptical" curves ???)
Aspect ratio will be around 18-19 (cannot measure as the fuselages are not produced yet)

I would be very glad to get some ideas of what kind of airfoils to use...
Using profili2 I can compare airfoils, but I do not have the knowledge to calculate the whole wing...

Best regards

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Jan 16, 2009, 06:44 AM
Registered User
It was a similar tread a couple of days ago. You should check what was said recently there.
For a single trapeze of this aspect ratio the HQ-W series would be a very good choice. If thermaling is the main design driver a 3.5 camber with a 13% (up to 15%) thickness should be in the right ball park. At the tip, check the Re number and make sure you have at least 1.5 degree washout. Personally I would go as well to a thinner but more cambered section.
Jan 16, 2009, 07:18 AM
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cgraf's Avatar
Thanks for your advice!
HQW would be one of the choices, but I am looking for an alternative...
What do you think about S3021, for example ? Anyway, the differences are not huge and I do not build out of cnc-milled moulds :-)


Jan 16, 2009, 08:36 AM
Registered User
This is a tough one to answer... Because it implies personal preferences... I am a BIG fan of professor Quabeck work, not as much of Selig. I believe that the HQ-W is a better overall wing section giving for your application a broader flight envelop.
Jan 16, 2009, 09:07 AM
David Layne
I have to agree with fnev. Having used Selig's and Quabeck's airfoils extensively, for your application you will find the Quabeck airfoils superior to the 3021 in particular. If you really feel strongly about using a Selig airfoil, investigate them a little further, there are better onse than the 3021.

Good luck,

Jan 16, 2009, 09:08 AM
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cgraf's Avatar
Just to be clear: I have NO problems at all with HQ (the contrary is the case)... At the moment I have a project ongoing with HQW for an oldtimer glider (the one in my Avatar)...

I already was thinking about HQW3/13 to HQW3.5/12 with 1 washout... well we will see...

fnev: What kind of planes do you design ? real ones or models ?


Jan 16, 2009, 11:25 PM
Registered User
Another problem with the 3021, is it is way too thin, the HP has a very skinny wing, you will need something with at least 13% thickness or more, the HQW at 14% with 3 or 3.5 camber is the ticket.
Jan 17, 2009, 03:01 AM
Registered User
When choosing a wing section don't get overwhelm by the theoretical polar as they only apply to a wing of infinite span... The results are not necessary consistent when in a 3D air flow. Furthermore, the profile drag is NOT as critical as the induced drag. In short, when choosing a wing section, the profile polar is a good start to help "prune" the different initial options according the initial requirement (performances). The next exercise is to design the wing (geometry) (single/ multi trapeze(s), single/multi sweep(s) (forward and rearward), single/multi dihedral(s), washout, etc). The whole "trick" is to make the best combination to get the best compromise OR the best performance for one specific task. A good example would be the current F3B designs where the duration task has (relatively) NO influence as any glider launched at the achievable altitudes today will in dead air fly the required time. These gliders are designed for speed AND the handling of the turns both mechanically (stress) and aerodynamically (drag/lift).
I hope it helps and again good luck.
I design airplanes for UAS (Unmanned Air vehicle Systems). They range from 8' to 40' in span with masses from a few pounds to over 1000 lbs. Most of them are for observation related tasks, some of them with very stringent endurance characteristics. For these the design constraints are very similar to the ones of gliders...
For fun I design my own gliders (13' to 17') and build them when I have time!!! I just restarted after a 10 years break from the hobby. Sometimes it is difficult to have the envy of playing with models when you are in this type of environment all day.
Jan 20, 2009, 12:04 AM
It is also very important to remember that if you choose to build a scale sailplane, the design of the wing is already done. You have no real ability, assuming you want it to look scale, to change the shape of the wing - it's designed already.

It is likely we choose to fly scale because we like the looks of a particular design. It takes our "fancy"!!

So, the best we can do on a scale model is to review the taper ratio on the wing planform and make educated guesses or use generally available software to analyze the airfoils we choose.

You can, of course, take the next step and design custom airfoils to best utilize the wing planform, taper ratio, aspect ratio and any other characteristics of the scale subject you have chosen and design airfoils for your flight preferences. If you're not up to this then it's probably useful to use what has worked in the past.

The HP 18 is not really that high in aspect ratio (21.4), its lower than the ASW20 (>25). It's taper ratio is also relatively low. As I usually say (!!) HQ or HQW 3013 at the wing root to the aileron root. From the aileron root transition to the HQ or HQW3512 at the tip with a degree of washout.

Alternatively, if you want a little faster aircraft, lower the cambers - say 2.5 and 3.0. If you're on the slope and want it to cook, choose the 2.0 and 2.5 with same washout requirements.
Jan 20, 2009, 03:39 AM
Registered User
cgraf's Avatar
Thanks a lot for your answers

@SoarScale2 (Tony?)
I read your article which is really interesting. I am really tented to try out your idea (either with HQ/W-3,0-14 to 3,5-13 or 13 to 12... as stated in your paper... with 1 of washout. I will implement flaps anyway, so the bird will fly, I suppose...

Best regards

Jan 20, 2009, 12:16 PM
dare to thermal



please look at
Scroll to the bottom of the page. There you will find a set of airfoils based on the A-7026, which was discussed at the german rc-network. May be you can understand a bit german...

Im building a AK-8 (based on a DG-600 fuselage) with these airfoils.

Jan 20, 2009, 06:26 PM
Registered User
AMBeck's Avatar
Cgraf, I have to ask, is that Al Uster's Mosway in your avatar?
Jan 30, 2009, 07:16 AM
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cgraf's Avatar
Sorry for the late answer...
The Moswey (not Mosway) in my Avatar is based in the western part of Switzerland, was completely restored and belongs to a Swiss guy.

Best regards

Jan 30, 2009, 08:36 AM
70 is the new 50
bobthenuke's Avatar

However you decide to go with this project I hope you keep posting here regarding your progress. As a past owner of a full size HP-18 I naturally have great interest in a model of it. Good luck with the project and please consider selling wing and fuse parts if this is something that interests you.

I'm not even close to being fluent in airfoil design and discussion but since the HP-18 uses the same polar as the Pik 20 perhaps a model of the Pik with a similar size wing (I think there are some out there) will work for you. I may still have the construction manual and some plans for it if this will aid you.

Thanks so much,

Feb 02, 2009, 02:26 AM
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cgraf's Avatar
Hi Bob

The project will be delayed (unfortunately) due to health issues of the fuselage manufacturer...
But anyway, by the end of summer he should have around three fuselages ready.
I got a nice airfoil calculation for the wing and the stab from Mr. Quabeck, so the plane(s) just have to be built...

I keep you updated when the fuselages are ready...

Best regards


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