mayday

Forgive me if this has already be posted. I did my best to research before posting, but I can find nothing on this plane.

I have a 24" Herr Engineering Pitts Special rubber power kit. I want to convert it to R/C. I have the building skill, as I've built several glow and rubber power kits. What I don't completely understand is the loading limits. For a 24" biplane, how do I calculate the maximum flyable weight?

Has anyone converted one of these, or a similar size plane? I'm making the wild assumption that a 24" biplane has the lift of a 48" regular plane. Is that a bad assumption?

Any advice on setup/equipment would be appreciated. I tried to convert an 18" guillows piper cub to RC and failed miserably after putting way too many hours in. Rolled over, sunk like a brick and did the old rapid disassembly trick.

Thanks,

Mayday

Lynn S

those wings look really small. Did it cost $69??

mayday

I got it from a private seller. I've looked them up though, and I believe that's the one.

Bottom wing is 4.25" x 24"
Top wing is also 4.25" x 24", but it is the V shape per the Pitts design.

Simple the top wing is simple to calculate, 24 x 4.25 = 102 sq in
The bottom wing, as part of it is hidden in the fuse, and thus doesn't produce lift, is 21.50 x 4.25 = 91 sq in.
Total sq. in. of lifting area is 193 sq. in. (unless I have to subtract the wingtips. The last 1.5" are rounded.

What's a good weight per sq. in for an r/c plane?

dgliderguy

Mayday,

Sure, you can convert the RP Herr Pitts to R/C, nowadays. Five years ago this would have been almost out of the question, but miniature equipment is available now like never before.

I fly a 30" Top Flite Cessna 172 on a Pee Wee .020, and would expect the little Herr Pitts to fly at about the same weight and wing loading. Your assumption of doubling the span for an equivalent monoplane is WAY off, but if you do a simple cubic loading calculation you will find that an equivalent monoplane would be about 30" or so.

I would suggest that you add some 1/16 sheet balsa between the stringers in the nose, back to about the leading edge of the lower wing, to take up the torque and vibration of a PeeWee .020. Also, you could make the cockpit into a removable hatch, from the headrest to the rear cabanes, for radio access, and use the little Cirrus 5.4gm servos and a pico-receiver with Lipo or 50mah Nicad battery. My Cessna flies fine with 9gm servos and a 110mah nicad pack, and a HAS3MB receiver, about 9.2oz AUW.

Go for it! Send us pictures!

Don Bailey

P.S. The 18" Guillow's Super Cub you chose was too small. Shoulda converted the 24" rubber Guillow's Super Cub. That coulda been a good one.

phuffstatler

My Feedback: (20)

193 sq in is fine for an .020 flyer. Being a biplane, the 'effective' wing area could be a bit less. Keep in mind, weight is the enemy! Anything you can do to lighten it up without making it too weak is a good thing.

You might try one of those new FMA low voltage receivers that works on a single Li-po. That will help a bit. smallest servos you can put in there, keep the linkages small and light. I can't remember mine right now, but I think you may want to beef up the wing spar arrangement a bit, as it was meant for FF.

Also, try that new light iron on covering, instead of money-kote, to save more weight. I can't remember the name right this second, darn it!

anyway, hope this helps a bit.

phil in austin

Bipe Flyer

I remember reading in a magazine that someone had converted one to R/C - electric I think.

My 1/2A Ultimate has a span of 25" and 250 sq in of area and if flies great on an .061; I also have a little .010 powered bipe with a span of 15", so 24" shouldn't be a problem.

I'd shoot for 10 to 12 oz. Use a 120 mAH NiMH RX pack, HS55 servos and a GWS RX or a Hitec HS-05MS RX, if you can find one, and you should be easily able to come in under 12 oz.

I think covering that Phil is thinking of is Solite.

Dan Vincent

Mayday,

Unless my memory is failing the old rule on effective wing area of a biplane was 80% of the total wing area unless the distance between the wings exceeded the Chord of the top wing.

Dan

airborneSGT

My Feedback: (15)

Anyone build this thing yet? This is my first kit build since I was 11. I have been putting together ARF's for a while and this is a way to refresh my building skils. I plan on using a 370 Brushless and some LiPos. Any suggestions would be apreciated. I am also modifying it to look like a Christen Eagle just to be different.


abnSarge

ajcoholic

My Feedback: (10)

I have one allmost finished (just need to finish the tissue covering job) I started it about 1997/98!! Never got around to finishing it..

I have a Gmot 120 cubic mm CO2 motor in mine, and was thinking to try RC but dont know if it will be worth the trouble (was going to leave it free flight). I think it would handle a peewee 020 just fine.

AJC

BMatthews

The 80% rule is a pretty good way to compensate for the effectiveness of the wing area. I also agree with BF about the 10 to 12 oz limit. But I think it can be built within that limit with a Norvel 061 RC and full house controls if the gear is selected from the parkflyer variety. I would also work at beefing up the wing spars but I would do it with the idea of functional rigging so the upper and lower spars help support each other through the rigging like a biplane is intended to do. This will greatly limit the weight increase from adding proper gas model spars.

If you can keep the weight closer to 10 or even less ounces I think you'll have a bigger grin on your face when it flies though. Hint, use lightweight parkflyer covering or tissue and dope. Monokote and other heavy plastic films would kill the weight on this model. Every gram in every part is going to count. Wheels, landing gear wire cabane struts, pushrods and even hinges will need to be chosen or built to be the lightest possible that will do the job.

airborneSGT

My Feedback: (15)

I apreciate the help. I plan on using the lightest materials possible. This is a slow project for me and the journey is worth more than the finished project. I used some different silk covering thats a little more tough than what came with it, but still able to put on using dope and still just as light.

BMatthews

I'd look forward to seeing the build pics for either the glow or electric version here. The Herr Pitts is definetley one of the better options for a crossover type model that fits with either power option.

combatpigg

My Feedback: (3)

On a plane with only 4.25" chord wings, I think the 80% rule needs to be bumped back a little for figuring effective area, but at any rate I think it will fly superbly at 12 ozs. This bipe probably doesn't have a section of unsupported span longer than 6 inches, so the conventional thinking for what is needed for strength here is probably way too much. I have never seen a model bipe of any kind fold its' wings. I think 1/8"x1/8" hard balsa spars would work, with 1/8" bamboo skewer struts. The only area that I would beef up if any is the engine mount area, just strong enough to keep the engine from tearing loose during a hard cranking episode. A 1/16" ply firewall backed up with a balsa block works here with #2 sheetmetal screws. The screws act as a weak link in a delicate model, and will rip loose from the firewall before something else does. Thin CA and balsa dust packed into the screw holes puts everything back in order. For a project like this it is good to gather all the neccessary equipment, and kit wood, then weigh it. You already have a target weight. The balance, [if there is one] will be made up with the weight of the covering, glues, fuel proofing, etc. After doing all this homework, if you have the luxury of adding any wood here and there for strength, the interplane strut hard points are highly stressed, and a couple of spar doublers out to the strut ribs might be a good investment. 1/2A planes tend to build tail heavy, so extra wood up front is better than adding lead after the model is done. Shimming the engine forward is a nice option too, that is why I like to use 1/4"x3/8" maple rails that have extra length.

buzzard bait

One of the magazines had a color photo of one of these and it was beautiful--much better looking and much more scale than the larger Herr Pitts that was designed for RC. With light silk yours will be gorgeous. Consider silk thread or light fishing line, like Fireline, for scale wing bracing. That should reduce or eliminate the need to beef up wing spars. Make sure you use a low shrink dope on those wings and tail surfaces. Jim

ghendrix01

My Feedback: (1)

Here is a pic of the one I converted to RC about 3 yrs ago. It has an OS10fp in it. I covered the fuse with 1/64 balsa and the wing leading edge to spar with 1/32 balsa (both wings). It uses 4 ch of control although I haven't the courage to try to fly it. It weighs about 30 oz empty.

George