Hey guys, I'm thinking about scratch building another plane, but I need to find the right airfoil. Here's what I'm picturing:

-A big plane. Maybe 100+ inches in span, with an aspect ratio of around 5 or 6.

-A light plane. Foam ribs sheeted with balsa, stick built fuselage and empenage.

-Minimal wing loading. I mean minimal. I want this to be a floater, probably the biggest slowest thing at the field, maybe even three channels; just a relaxing sunday flyer.

-Something that resembles a Kadet sr. but with less fuselage, or a throwback to the old timers.

-Definately a tail dragger, and definately a high wing.

There you have it. I just need to find an airfoil to get going. Thanks in advance.

I've designed and built three of my own models. Latest is an Ultimate bipe. Two of the three designs were 120-140 size. Might be able to help, but need more information. What is your estimate of the final weight. Which engine (electric or glow), What kind of manuverability would you like.

I'm thinking I would like it to come out around eight-ten pounds ready to fly. I will power it according to the final build weight. Likely a .91 four stroke, but I've also been toying with the idea of doing around a 130" span and powering it with a spare O.S. 1.60 FX. My goal is to have enough power to get off the ground in only a few feet and have an excelent climb rate, but I really do not care about speed or aerobatics in the least (at least not this plane). I just want to have a relaxing sunday flyer that's big enough to be interesting. A flat bottomed airfoil would be perfect, and if I can get a good suggestion, I could probably print it out and blow it up to the size I need. It will be throttle, rudder, elevator only.

Steve, if you're not afraid of a few balsa sticks I really suggest you get plans for one of the big cabin Old Timer designs. Lots of character and all the float you could ask for. But if you do select one then cut WAY back on your weight and power allowance. No need for that big mill. The model built to Old Timer design specs will come out easily light enough that you can power it with a 60 four stroke and it'll do what you want at 100 inches.

As a yardstick to compare to I built a Roger Hammer Flamingo a bunch of years ago. It's got an 86 inch span with a huge chord so lots of wing area... closer to aspect ratio of 4 or 4.5. Despite the size it came out to 5.5 lbs ready to fly with an OS Max 35 in it. And here's the kicker.... The Flamingo had a LONG nose for it's time and a full 1/2 lb of that all up ready to fly weight is lead that I had to add to the TAIL to make it balance even half way decently. And the model used spruce for the wing spars and the 3 main fuselage longerons. I didn't spare the wood, within reason, and it still came out that light. With that lowly 35 in it the model lifts off in about 15 feet in a dead calm and rolls about 20 on landing. On a few days with even light winds I've seen it lift off in as little as 3 feet. Climbouts are at a 30 degree angle with a stable but slow climb. I've soared it at idle and deadstick in thermals for some longer flights on many an occasion.

It's not the power that will lift you off the ground quick. It's the light wing loading and light weight. A light model will accelerate faster and lift sooner. If you want to do what you're intending then think light. Overpower by all means but start light. But be warned... I've seen a 6 foot span Goldberg Piper Cub that came out very light (a miracle kit I guess ) and the guy had powered it with an OS 60. I flew the first flights for him and even with a tickover idle it would not land. Every time I tried to flare it would just start "gliding uphill" even at tickover. Every landing with that power loading had to be a deadstick to place it down. So it IS possible to build too light and overpower it easily to that point.

Most of the old timers for the 60's of the day had around a 72 to 84 inch span with only rare exceptions outside of that region. So if you chose to pick one of those then you'll need to blow it up. If you got the 91 then I would recomend that you go straight for the 120 inch size and expect perhaps a 10 lb or less weight at that size with even moderate care. You'll need a good strong wing spar design to substitute for the typcial weak designs of the time. In otherwords it need not be a hangar queen but it won't like winds much above 5 to 7 mph. But then nothing of that size and slow speed capability will like much wind.

Oops, almost forgot.

For a slower flying model put in the extra effort to cover and build with an undercambered airfoil. The one on my Flamingo has a Gottingen 501 and it works great. Super slow when wanted but a surprising turn of speed with the nose trimmed down a touch to punch out against the wind. It's no racer of course but it does surprisingly well for what it is. The higher mean line camber of the "undercambered" shapes will provide a lower stall speed than the other options. It's like having lifting flaps deployed all the time.

If you insist on flat bottomed then there's really only one sensible option. The basic good ol' Clark Y. There's more modern flat bottomed sections used by some of the sailplanes but they are lower camber than the Clark Y and set up more for speed than slow flying as you've described.

Thanks guys. Where can I find plans for the big cabin old timers, or where can I find a profile for a good undercambered airfoil, or even the Cark Y? Is there anywhere on the web I can view and print out airfoils?

www.profili2.com for a program that'll set you up with more airfoils than you ever knew existed. As for old timer designs start with google and the keywords old timer model airplanes and get a feel for what you want. Also don't be afraid to seach the Vintage and Old Timer forum here at RCU for some back threads about old time free flight models converted to RC and ask for suggestions and, most importantly, pictures. There's literally hundreds of really cool looking old cabin designs.

With the passing of the old Model Builder Magazine and the seemingly loss of John Pond's plan service we lost a great source of updated plans for old timers. It's harder to find this stuff out now and that's a true shame as there were some great classic designs.

In particular a really nice one is the Dennyplane. A quick google turned up this site for a teaser....

http://www.ctie.monash.edu.au/hargrave/dennyplane.html

There's also a scale plans guy out in Cali that makes laser cut short kits for a lot of old timers. His name escapes me for the moment....

Thanks again. I really appreciate the help. You're right about it being a shame, losing the availability of the designs of yesteryear. Their are a few at my local club who fly Old Timers like the playboy, and they are spectacular.

I have attached a file of the Clark Y.

Mike Selig has an airfoil page too, with tons of them. I have lost the url for the moment.

If you are really interested, the NACA did windtunnel tests of the Clark Y and other airfoils of the day in the late 20's/early 30's. I found the papers online at NASA. You can get the polar curves there.

Good luck!

The guy that does the plans and laser cut short kits is Bob Hollman. For a slight extra charge I think he'll also do an enlarged special order. And he also sells JUST the plans. They are all redrawn CAD plans for doing the laser cutting from so it's relatively easy for him to do a special.

http://www.bhplans.com/oldtime.htm

Check the Gassies for inspiration.

PS: on page 2 there's a Lanzo Airborne enlarged to 108 inches plan. Might be just the thing for that .91 you got. Definetly over powered but should do just exactly what you described. But don't come crying to me if you find that you need to kill the engine to let it land....