AirFoil Selection for WWI Fighter - RC Groups
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Aug 04, 2017, 05:26 PM
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John Boren's Avatar
Discussion

AirFoil Selection for WWI Fighter


I am in the process of designing a Bristol Scout. Below is an image of the airfoil section used on the full size airplane. Apart from being much more difficult to build then your standard flat bottomed airfoil is there any other reason not to use such an airfoil. From what I can tell it seams most WWI RC models use an airfoil more like a Clark-Y. I seldom even see a simple under cambered foil that are used on Old Timers most of the time. Does anyone have flying experience with WWI aircraft using airfoils that more closely resemble the ones used on the full size machines.


John Boren
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Aug 04, 2017, 08:04 PM
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John Cole's Avatar
Hi John;
I've used scale foils on some of my models. I'm surprised that more folks don't use them. They do fly differently than more commonly used model airfoils, but not worse. Just different.
Also, they are not really difficult at all to build. Again, just different. Proctor Enterprises uses under cambered foils in their kits, but they are probably not true scale sections, but rather a close approximation to full scale.

I would encourage you to try using a scale airfoil on your project. It will give you a better idea of what the full size AC was like.

John
Aug 05, 2017, 06:12 AM
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That Bristol section was reportedly used on a 1/4 scale Scout, some years back, in the pages of WWI Aero (magazine dedicated to reliable data for full size and model reproductions, even some original restorations etc.) The builder flyer reported that his model flew poorly and attributed it to the airfoil. He later padded the upper surfaces to give a rounder LE. This reportedly fixed the "hunting" erratic problem. That said, I know of a 1/6 scale Bristol Fighter, which also use the exact same (scale ) airfoil, and had no problems with it. I suspect the larger Scout model had other issues, possibly with loose fittings or even flutter. I tend to favor scale airfoils on scale models.
Aug 05, 2017, 06:41 AM
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Just remembered that late, great, modeler and draftsman Stan Teachman's OUTSTANDING Scout plans appear here:
https://www.rcgroups.com/forums/show...-Bristol-Scout

You may also want to read his comments about the issues he felt he had with scale airfoil at 1/4 scale, from older AMA mag article, which also appear in the linked thread.
Aug 05, 2017, 08:10 AM
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KMK001's Avatar
Something like a Clark Y on something like a Fokker DR-1 simply LOOKS wrong! That said, I am currently collecting the parts for a SE-5 build based on Dave Platts plans from the 60's. Dave shocked the RC world with this model by not only winning the NATS in scale with it, but by using the original RAF-15 under camber airfoil. Some went so far as to claim it wouldn't fly. But it did and it flew well! Dave also did a P-51 with the scale laminar flow airfoil. It too flew well.

Proctor Enterprises http://www.proctor-enterprises.com/, long known for their Antic series, Nieuport 11 and Curtiss JN-4 Jenny among others. All of which use under camber airfoils and the most beautiful machined 1/32 plywood wing ribs.

Do they fly different? I've never thought about it or noticed it. They are a slower airfoil so don't expect to set any speed records with them. I guess they're a little like flying with 10 degrees or so of flaps out all the time. But at the same time you can back them down to a walk and enjoy the multiplicities of flight. They'll turn on a dime and do it slowly so you can watch. And the barrel rolls look as the barrel roll should look.

I have a Proctor Min-Antic, 54 inch wing mono-plane, that is some 37 years old. It has a nice under camber on it. I run an old OS 35 RC on it. I can fly it out of a football field in 30 mph winds and drop it to a walk to land with a 3 foot roll out. It will loop, roll and do all the basic maneuvers you'd want.

The only added difficulty to building such a wing is covering the bottom. Start by applying something like Sig Stix-It brush on adhesive. And use a fabric covering, not the plastic junk. Nothing looks worse than a shiny plastic covering on a Sopwith Camel or similar. My preferred covering for these is silk and dope. But that's a whole nuther story! It's all in the knowing of what you have and what to expect from it.
Aug 05, 2017, 08:15 AM
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KMK001's Avatar
Oh, and for the Scout. Find a laser cutter to cut the ribs from 1/32 ply. Then cap strip them with 1/16 or 3/32 balsa. Hardwood LE and TE. You'll be surprised how strong and light the wing turns out.
Aug 05, 2017, 11:50 AM
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radfordc's Avatar
A rough approximation of the early thin airfoils is a flat plate. And surprisingly enough a flat plate wing can fly very well.

Aerobatics (1 min 25 sec)
Aug 05, 2017, 11:58 AM
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portablevcb's Avatar
Under camber and flat bottom airfoils are just a little more difficult to deal with than others.

They tend to be 'one speed' wings, ie, if you add throttle and speed up the plane will climb. Decrease throttle and it will descend. It is very obvious if you are used to warbirds where you can slam the throttle forward and it just goes faster. That kind of action on an under camber or flat bottom will get you a steep climb (and sometimes a loop).

charlie
Aug 05, 2017, 12:57 PM
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What's worse than a Clark-Y on a Triplane? A fully symmetrical section on a Dr1!
Aug 05, 2017, 02:39 PM
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fairweatherflyer's Avatar
a slightly undercambered and thinner section worked great on the morane N - flew with mega-age-warps as well - model is approx 30 years young and lots of airtime under its wing. In fact one trip out to a scale meet we actually did reasonably well and didn't finish in our honary position at the bottom of the board.
The coanda section should be good to model. If you don't follow them there is a flying replica based in UK who rebuilt the plane from their grandad's rudder bar, magneto (if you got to a certain rank (think it was navy) you could retain your own magneto switch, and joystick. What size are you building, I started on renovating and getting ready for flying one dad partially made many years ago and never finished. The very idea of it was to build it with a scale section to see how it went. However, the project is shelved as I decided to go for something with a larger span that can fly in a little extra wind. would agree strongly with charlie that the sections don't like flying outside their comfort zone and things can get twitchy or you get that climb and attempted loop over. somewhere there are acres of the original drafting sketches - will see if I can find them again on the net for you.
https://bristolscout.wordpress.com/page/40/

https://bristolscout.wordpress.com/
Last edited by fairweatherflyer; Aug 05, 2017 at 02:59 PM. Reason: pictures and links added
Aug 05, 2017, 03:45 PM
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portablevcb's Avatar
FWIW there are a few WWI models out there with near scale airfoils.

AerodromeRC models (Manzano Laser sells them) has several. For smaller ones look at Andrew Hewitt's models at Brodak/Dare (his are Free Flight, but, can be converted). Proctor also uses scale airfoils.

If you want to see some full size look at the Memorial Flight site from France. They have a ton of photos from rebuilding their planes, including a SPAD, SE5a and Dr 1.

charlie
Aug 07, 2017, 04:02 PM
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Nergall's Avatar
My BUSA Sopwith comes with an undercamber, so it would seem plenty common enough since most of the large scale WWI models I see are BUSA?

The only issue I've seen with it, is that it's a bit trickier to get the covering to stick on the bottom.
Aug 07, 2017, 07:24 PM
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KMK001's Avatar
Quote:
Originally Posted by Nergall
My BUSA Sopwith comes with an undercamber, so it would seem plenty common enough since most of the large scale WWI models I see are BUSA?

The only issue I've seen with it, is that it's a bit trickier to get the covering to stick on the bottom.
Next time pick up a product from Sig called Stix It. Basically it's a heat activated glue you paint on the frame before covering. Works great! There's a couple of others similar products out there if you can't find the Sig.
Aug 07, 2017, 07:34 PM
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Nergall's Avatar
Quote:
Originally Posted by KMK001
Next time pick up a product from Sig called Stix It. Basically it's a heat activated glue you paint on the frame before covering. Works great! There's a couple of others similar products out there if you can't find the Sig.
That's exactly what I used.
Aug 30, 2017, 02:12 PM
Bernoulli was only guessing.
Tspin's Avatar
I would consider going with the same airfoil the Proctor kits use; it has a proven track record. If you want I can scan and send you the airfoil.

You should also look at the WACO UPF7 (Clark-Y), Piper Cub (USA 35b) or Aeronca Champ (NACA 4412) airfoils, all proven to work well on models and have excellent flying, landing and most important stall characteristic.

The goal is to have fun and prevent returning home with your plane in a paper bag










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