BWooster

I would welcome any advice on choosing an airfoil for an 'approximate' scale Mosquito I'm just starting to draw.

The span is 54", 13.5 " root chord, 5.5 " tip chord. (I have reduced the taper from the original.)
The wing area is approximately 500 sq in. I'm thinking twin .15's.

I am not a speed demon. Predictable and gentle stall charactistics figure high in my books. I want to keep it simple, so no flaps. I'm looking at the original RAF 34, and it looks not too bad. But I do these things by eye, not science.

Any thoughts?

N1EDM

My Feedback: (2)

I modified a Sig 4*40 to take a Selig 8036 (it might be listed as a S8036 or a SD8036). The airfoil is semi-symmetrical and was pretty quick (though I know that you aren't looking for speed). If you're not familiar with them, look up Dr. Michael Selig (University of Illinois, I think - but not sure). He developed these airfoils strictly for small aircraft use. I don't know if they were developed strictly for R/Cers or not (could have been developed for AUV's but I'm not sure). But they're optomized for the Reynolds numbers that we fly at.

Also, the 8036 is used by Top Flite for a couple of it's scale Gold Edition planes.

I intend to use it in a 1/4 scale Thompson racer with a 66" wing span that I'm drawing up, little by little.

Just a suggestion.

Bob

BMatthews

More importantly the 8036 was meant to work well at slower speeds with higher wing loadings typical of many scale models. I suspect you could do a lot worse than that airfoil for your Mossie.

In the end the only real path to slower landing and stall speeds in any given size model is with light weight. The rest is just bandaids. Often neccessary bandaids I grant you but bandaids none the less. So keep the scale close by when choosing wood and use air to replace other materials where practical.

ArthurD

Bob,

The Eppler 195 was developed specifically for the los Rns of model flight and it has very low profile drag. It may be an ideal choice for your project.

You can find this and many others in "R/C Model Aircraft Design", page 64, published by the publishers fo "Model Airplane News".

See Air Age, Inc[/u]. ISBN; 0-911295-40-2. Reprented 1999.

Arthur

N1EDM

My Feedback: (2)

Arthur and Doc,
Thanks for the reply. Actually, it was Snitch who asked the original question, but I liked the feedback too.

I have some experience with the 8036 (versus the stock airfoil in the 4*40, my 'experimental model') which is how I was able to base my answer. I don't have any experience with the Eppler 195 though I did read about it in RC Model Aircraft Design.

Snitch, what are your thoughts on these airfoils suggestions so far?

Bob

newtech

The Selig S8036 is a nice well mannered airfoil. I used it on my carbon fiber, Speed 400 Vans Aircraft RV-7. The airfoil has excellent qualities and the model is a blast to fly. Slows down very nicely.

BWooster

Thanks guys.

I don't know anything about the selig S8086 -- which just goes to show you how useful this forum is! I'm going to check into it.

The Eppler makes me nervous. I built a lovely airplane (the 'Golden Snitch') with an Eppler airfoil (168?), and it had a vicious tendency to tip stall - but was it ever fast! So, for no reason other than primal fear, I'll try the Selig first.

I completely agree that building it light avoids a host of problems. In fact, I'm thinking that with the Mossie, the vast majority of the shock loads are going to be through the nacelles. So I'm thinking of an integrated plywood box, (suitably lightened with holes), on which to mount the engines and gear. If I can lock that into the spars, then the rest does not have to be bulky at all. The fuselage really just sits on the wing, and is barely subject to any load.

BWooster

Had a look at the Selig. 16% thickness is a bit of a surprise. If I have any linkage problems, I can send my 6 year old to crawl through the wing and fix it!

Thanks again.

N1EDM

My Feedback: (2)

Glad that you like the airfoil, but don't blame the tip stall on the Eppler... lots of things could cause that (including airfoil, admittedly).

I kitbashed a 4*40 to take the Selig, so that I could see how it performed. My intention was to compare it against a stock 4*0 that I also had.

It might have just been me, but I 'seemed' to notice an increase in speed from the stock airfoil (not sure if that was real or imagined), but it satisfied me enough to want to use it for my scratch-built scale plane.

For the record, I don't think that Dr. Selig gets any royalties for this. I think that he puts his airfoils out in the Public Domain for everyone to use just because he likes to do things that way. From what I can see, he's developed a lot of airfoils, especially for gliders.

Bob

ArthurD

Bob,
Mr. Eppler made many airfoils, not just one. Anything you see with an E in front is one of these. Examples are E197, E168, E226, E211, E230, E214. Each does a specific task better then the others. It's a lot of fun to pick the one you think works best for the application you have.

Did you buy a Delta Fighter 90? If you have only half as much fun as I have it will be money well spent.

BWooster

I just checked my plans. It was an Eppler 197. I don't think the airfoil was the cause of the tip stalling. the biggest cause was the person typing this message, who was at the controls. The second biggest cause was the person who built the airplane 1/2 lb heavy (same guy).

But, I have never had an airplane that stalled so catastrophically. If you did not have a couple of hundred feet, it was hopeless. So I'm nervous about the 197.

I have checked out the UIUC website. It is an amazing resource, and should be bookmarked by all.

The E197 is a 13.49% airfoil. A 16% airfoil should be gentler, and the entry looks a bit more gentle too. That's why I want to try it. No disrespect intended to Dr. Eppler.

Let me ask a follow up question: do you think I need washout, and if so how much?

ArthurD

Snitch,
You need someone a lot smarter than I to design a proper wing. Plenty of aerodynamic sorts at RCU to pick from. I wish you well.

N1EDM

My Feedback: (2)

Hello ArthurD
Nope, never bought the Delta Fighter 90. As it turns out, I was at my club Auction and I got a tremendous deal on a BTE Vortex, already built.

I need to get a few flights under my belt before I try this. Everyone talks about how great that it handles, I can't wait to find out for myself.

I've had to put a my radio into it (not that hard, once I figured out the programming for the rudders) and now I only have to mount the rx and the battery, break in the new Magnum 91 2S, and I'm ready to fly.

I would have built a Vortex from scratch myself but there was no way that I had room enough to build one in my teeny shop.

Didn't you already have a Delta Fighter? I don't want to take this thread away from Snitch... want to be careful that we don't sidetrack the conversation here.

Bob

ArthurD

Hello Bob,
Yes, I have the Delta Fighter 90, and love it. If you got a BTE cheap and it's in good shape, I know you'll have a good time flying yours too. You may find it interesting to go back and take a look at a previous message from me to you about the setup I'm using, just as a starting point. My engine is a Thunder Tiger while your's is a Magnum. I have no idea how the two compare. You'll want to prop it for speed; a small diameter prop with a large pitch. Assuming you like speed, that is.

One thing to look for is the fuel line being cut by the metal nose wheel collar that keeps the strut from slipping out of it's bracket. You'll find it just below the fuel tank lines coming through the 1" round hole in the firewall. My tank had to be held up 1/4 inch with more foam to keep the fuel line from being cut on that collar. The plane is upside down when you view this area and it wasn't obvious (at least not to me) that the fuel line would be cut by the wheel collar on the gear strut when the plane was in an upright position and the tank shifted downward in the fuse.

You may also want to use more slim wheels to reduce drag. The BTE I saw had big and fat wheels and an old .90 which didn't go very good.

Let me know how it works out. I'm interested in hearing about your first flights.

N1EDM

My Feedback: (2)

Hi Arthur,
Thanks for the info. I'll look up that note on the Delta Fighter thread (I presume that it's there). Thanks for the heads-up about the fuel line... I'll check it and make sure that I don't have any problems.

Sorry for diverting this thread, folks. Hope that you didn't mind.

Snitch, what type of flying are you going to do with the plane? If it's for general sport flying, then washout would be a good idea... If you're building an 'approximate scale' Mosquito, perhaps 1/4" to 3/8" would be nice. Also, that's a pretty severe taper, so could you widen the tip ribs to make them wider than 5" and still keep with the 'looks' of the mosquito? Your wing is going to do a lot of flying in the center, but not have a whole lot of lift at the tips. I'd vote for the washout.

Bob

BWooster

Bob,

As for the type of flying, I'm really doing this to satisfy my curiousity for a) de Havilland airplanes, and b) a first twin. I'm hoping for a mid-performance airplane, that has reasonable landing speeds. As for the rest, that's part of the fun: let's see how this works!

I'm buying sport engines (Norvel Big Migs).

The taper looked too severe for me, so I did change it, and it still looks okay. It tapers from 13.5" at the root to 5.5" at the tip. The total wingspan is 54. I get just over 500 sq ins. I think I can get it under 72 ozs, so around 20ozs/ft2. I'm drilling holes everywhere.

I think a 1/4" washout is the way I'll go. Another possibility would be to use the Selig 8037 at the tip, but because I use a rudimentary drawing program, I'm not confident I can taper to that smoothly.

I'm already cutting balsa, so if you're interested, I'll keep you posted.

L

N1EDM

My Feedback: (2)

Hi Snitch,
Yeah, I'd be interested. I'm in the middle of a scratch design myself (not to the balsa chip stage though). My wing is similar, but not as severe. It'll have a 14" root and about a 7" - 8" tip. It's a Marcoux-Bromberg racer from the 30's.

If I remember correctly, the 8037 is a slightly fatter version of the 8036, so if you do put that out in the tip, it could be a big help, especially with the washout. I notice that many of those Top-Flite Gold Edition kits do that - 8036 at the root, tapering to a 8037 at the tip. If I was more versed in it, I'd probably make a foam wing cuz it'd be easy to have someone cut the cores like that. But, I've never built with foam (yet) so I'd rather experiment on something not as 'exotic' as my first Scale job.

Keep me/us posted. I think we'd all like to see how your project is coming along. When I start mine, I'll reciprocate if anyone is interested...

Bob

BMatthews

Close N1 but it's not thicker. Profili shows them both at 16% but the 8037 has 2.7% camber vs the 8036's 1.85%. But the effect is still what you want... a delayed stall at the tip. A form of aerodynamic washout.

N1EDM

My Feedback: (2)

Thanks for the clarification... I'm thinking more and more about foam to get the transition from the 8036 to the 8037 right. I need to get the specifics right for the LG etc.

Please keep me posted on how your project is coming...

Bob

BWooster

N1EDM,

I dropped the Mossie project over the summer, but I'm back at it. Here are some progress photos. I rushed it in some places, so it is not a fine example of craftmanship.

I built another little craft to 'test' the Selig 8036. It is exactly what I was looking for. Thank you.

I weighed almost everything together today. With radio, motors, batteries, fuel tanks, wheels I am at 3lbs so far. So I should be comfortably under my target weight of 4.5 lbs. This will give wing loading in the 19-20 oz range.

BMatthews

Lovely job you're doing there. I think you'll find that if you can stick to the 4.5 lbs it'll be a nice flyer with a pretty decent landing speed.

Dragondawn

Hi guys,
I too am looking for suitable airfoils for a scratch-design and I see the Selig sections mentioned often. But I have a question about the amount of washout used.... so with a root chord of 15" (& an S8036 'foil) and a 7" tip chord (& an S8037 'foil) - this seems very similar to N1EDMs - does anyone have any idea how much washout I should add?

(Design is based on a lates '30s racer, 71" span and hopefully around 12lb, but I'm not interested in the speed, just a stable, predictable flyer).

Any help &/or advice would be much appreciated!

N1EDM

My Feedback: (2)

Snitch, nice job! Is that a DeHaviland Comet (Grovesnor House?) I'd had my eye on that design for some time myself, if it is.

I don't know why, but I haven't been getting updates to this thread, until today. I have some catching up to do.

Dragondawn, I don't have anything but a seat-of-the-pants guestimate for the washout. When I get my wing under construction, I'm going to put about 3/8" under the wingtips. That's nothing but a S.W.A.G.

I hope this gives us some fodder for discussion...

Bob

Dragondawn

Hi Bob,
Using your approximate dimensions above for the tip chord, say 7.5", with 3/8" under the trailing edge you'll have about 2.9degrees of washout.

I've seen 2-3 degrees (washout) often mentioned in my web searches but I was hoping someone out there would have more experience &/or knowledge with respect to the Selig 'foils mentioned.

Looks like empiricism is the way forward...

Steve

P.S. S.W.A.G. ??? [sm=confused.gif]

BWooster

Hi guys,

Steve: here is a picture of my Selig 8036 test bird, which I built to look like a 30's racer. I think I put about 3/8" washout on a 8.5" chord, so that's a lot. It has never tip stalled, though I have pushed it to try. Also, slows right down and lands like a trainer. I would not hesitate to go with that.

Bob: good to hear from you! De Havilland Mosquito, not Comet. I reduced the taper, and lengthened the tail moment for more volume -- makes it look a little different. I have finished the nacelles, and last night I molded the canopy and cowls (See Tips and Techniques thread - 'Vacuum Forming ideas') How's your racer coming along?

Lou