I am struggling to set up a plane I just finished. It was originally designed and built as a C/L plane, profile fuse, covered wing, solid tail and stabs. Wing profile is symmetrical airfoil. Has ailerons and elevator but a fixed rudder. It looks like it was built for speed. I put an OS PET on it and that seems to be about the right amount of power for a spirited flight. However, under power the plane wants to climb to such an extent that I have to feed in down beyond my ability to trim down. It's extremely nervous both up/down and left/right, hard to achieve any kind of stable flight. Lots of up/down oscillation. I have adjusted the c of g forward quite a lot and it's still nervous, but not hair-raising as it was to start (the first flight gave me gray hair and ended in a nose dive into terra firma that broke the tail off.) After moving the C of G forward as much as I dare, it's all I can do to get the plane to fly roughly where I want it to go. The other day, while I was battling with this devil plane, the engine suddenly died (I later discovered my fuel tank stopper came out in flight). The plane immediately went into an uncontrollable spin/dive. Fortunately, the hay is coming along so it wasn't destroyed. (On a previous occasion, the electrics mysteriously died and the plane flew itself on a wild ride for about two minutes circling and porpoising before diving into the ground at 45 degrees on full power but that's another story.)

After pondering the possibilities, I came up with two. First, the prop had a touch of down thrust relative to the fuse midline, but a LOT of downthrust relative to the wing airfoil midline, as the wings have a rather high angle of attack on this plane (it was built that way by someone who is probably no longer with us). The second is that there is about 5 degrees of decollage, for the same reason.

I also noted that the plane was built with the nose pointing left, presumably to encourage it to fly in counterclockwise circles. I have already offset this by mounting the engine so it points about 2.5 degrees to the right, relative to the wing centerline. It misbehaves as outlined above, despite what I think is now correct left/right engine alignment.

My question is: which misalignment is most likely to cause the flat spin behavior when the engine dies? I want to adjust one of these angles at a time, not both together. It will be easier to remount the engine to pull straighter relative to the wing airfoil in the vertical plane. Adjusting the decollage will involve taking a slice out of the profile fuse under the stab and regluing it to increase the angle of attack of the horiz stab, or cutting off the horiz stab, filing the fuse, and regluing. I prefer the former as there is some reinforcing cloth glued to the fuse to keep the stab attached.

This is another of those thourghly impossible questions to even approach an answer without some good photos.

Not much is making sense for even a workable controlline plane much less an RC airplane. First and formost controlline planes are not built with the "nose pointing left" and would be a problem also in an RC airplane. The next problem controlline airplanes are almost always built with zero degrees decollege not five degrees. Although Vintage type RC airplanes sometimes use that much but the set has to be right and those generally use high lift airfoils as well as underchambered to acheve the desired pitching moments.

The OS Pet which is an .099 is not all that powerful and I operate one on a vintage RC type plane.

Is there anyway you can post a photo to see what you are dealing with?

John

Agree about the photos. Also, need wing area and weight. You said built for speed, so thin airfoil? High wing loading and thin wing can spell a lot of trouble.

The person who built this really could not have known what he was doing. As above, a CL plane should have right thrust and be set up 0-0-0. The fixed rudder is usually canted right for CL. I'm not sure how much effort I'd put into a poorly built, poorly set up plane, but that's your call.

But part of this is easy...the incidence difference between the wing and the stab is what causes the need for so much down trim. There should be no difference or very little difference. Also, it is likely you need more vertical fin/rudder area.

Most CL types modified to RC have the fuselage lengthened, but then consider the Sig Wonder or many of the RC combat planes...very much like CL types. People fly stop signs, witches on broomsticks, and lawn mowers, so almost anything is possible. But figuring it out from a description is probably not going to happen.

On the plus side, it can be a learning experience to mess with a problem airplane, and fun if you like that sort of thing.

Jim

Here's a pic of the Devil Plane. The nose pointing left may be due to the nose plant after the electrics died on an early flight (I think the battery ran down but the switch may have gotten oil in it as well). The fin originally pointed out but I fixed that before I flew it for the first time.

Hm appears to possibly be a Jr flitestreak or similar. For this to work your engine needs to point straight forward, and the wing as well as the stabilizer incidence needs to be zero. 0-0-0 means the wing, stab and engine are all pointing in the same direction.

Also measure carefully to make sure the left wing is not longer than the right wing (this is common with some controlline airplanes but it won,t work in RC)

Ballance the airplane no further aft than in this case about 20% MAC. Thats one fifth of the wings average width from the leading edge. Yes that is further forward than much of RC practice but will be neccessary for this airplane to acheve pitch stability. It also is further back than what would be normal for this airplane as a controlline ship.

The ailerons are to small in cord near the tips to be very effective at any but the highest speeds so they will be ineffective at low speeds adding to the flight difficulties. A control set up like this with no rudder and just elevator, ailerons and throttle can work well but for the already mentioned smallish ailerons.

Part of the control senario i.e. Elevator, Aileron and Throttle is also limited by the engine. The OS Pet .099 with the early Bottle insert carburator, this from about 1959 or 60 is essentially a two speed carburator. The barrel in the bottle has two holes (high speed and idle) and there is no mid range bleed or needle making anything other than full throttle or idle a non issue.

What prop are you using?

John

I am using plastic 7x5 props. Whoever built this plane built it for C/L (the bellcrank was in and there was a lead weight on the far wingtip) but put ailerons on it. Couldn't figure that out. I was going to fly it C/L but then decided it would be a fun belly-lander for my hay field out back of the house.

I think you are right, it's a Jr. FlightStreak. These are currently being made by Brodak. They say "George Aldrich notes, "All of the Streaks can be balanced to give characteristics that suit the flyer. The farther forward the balance point is, the less sensitive the airplane will be. If you balance the airplane as shown on the plans, the design is very maneuverable and will perform nearly anything the flyer wants to do".

Because the Flite Streaks are much more sensitive than most models, George suggests moving the balance point up to the front of the leading edge and adjusting for minimum control movement as you get used to the Flite Streak's maneuverability"

Does anyone know where the plan says the balance point should be? Balance at the LE seems outrageous.

I measured the wings, one is 15", the other 15 1/4" long. Is that just builder error is that we can balance out, or is that the end of the road for the Devil Plane?

Mr. Aldrich is absolutely correct And that is exactly as I would have advised however it is no longer a controlline airplane. RC airplanes and controlline airplane have completely different requirements. Agine if it were mine I would balance at 20% MAC aft of the leading edge.

I could not say for certain whether or not this airplane was designed with the unequal span or not, However that makes the problem even more difficult with your limited ailerons. If the airplane came with the ailerons then they were never intended as ailerons but flaps that were mechanically mixed with the elevator and the purpose was to operate opposed to the elevator and tighten up inside as well as outside loops.

Are you an experianced RC pilot? You see while RC to controlline conversions are relatively simple, controlline to RC are not and loaded with many problems. So if you where hoping to use this as some sort of RC trainer then that was a bad choice.


John

I own and fly a bunch of RC planes but most of my experience has been powered gliders (eclipse, calypso, aspire, cularis) and electric flying wings (Combat Wings). I own and fly a few nitro planes but they are all high wing "trainers' except for a SkyLark Jr. that is underpowered and needs something more than an stock 049 Cox. I have destroyed a couple as well that I am not counting. This Devil Plane is the touchiest darn thing I have tried to fly and I have to say it's humbling, downright scary at times. Regarding the motor, I have found that if I set it rich it will respond to partial throttle (sometimes it works better on partial than full) and as the tank empties it leans out. I had a heck of a time getting the motor to start until I got rid of the integral tank which would siphon into the engine laying on its side, and installed a larger tank positioned a tad below the spray bar orifice.

Yep, it's a Jr. Flitestreak...I had one with a Cox .15 TD...HOT plane! But it had a thick airfoil, and I don't see how anyone could get the wrong wing incidence...it slid into a slot in the fuse. It actually looks fine to me. But then it shouldn't require down trim to fly, so something is wrong. It should require very slight up trim, if it is 0-0-0.

I agree those ailerons are not ideal because they are so narrow at the tips and wide near the fuse. They were usually fixed, but could be set up as flaps to operate opposite the elevator, to give tight corners on square maneuvers. I'd be tempted to cut them in half and fix the inner half and use only the outer half for ailerons. As it is, aileron deflection is probably causing more drag than turn.

Still curious about the weight, and also the CG. You might have to come forward a little more because it's got a big wing, a little stab, and a short tail moment. That's a recipe for pitch instability.

With the CG far forward, you'd better be ready with the down elevator if the engine quits. The plane will tend to quit flying too, so get the nose down and keep up the air speed.

Keep us posted.

Jim

Well I think that explains the spin: the engine pointing too far to the left was offset by aileron trim. And the excess decollage/nose down attitude of the motor offset by a lot of down elevator trim. When the engine quit, the plane was left with ailerons offset to turn right and elevator down = spiral nose dive.

I'll try it again with the motor pointing 2 deg right and 2 deg down, and see how that goes. Then if I still need a lot of down trim on the elevator, I will adjust the angle of incidence of the elevators by taking a narrow wedge out the the tail section of the fuse.

Worst that can happen is that I retrieve my hardware from a pile of matchsticks and move on. Anyone suggest a good sport bellylander (our hay field is too bumpy for wheels) that will take an OS Pet motor? The higher the motor sits the better, as that makes prop breakage on landing less likely. Or perhaps I will re-fuse the whole thing just re-use the wing. I don't really care for the profile look anyhow as there is no place to put the battery, servos etc.

OK thanks vh2 just needed to get that out of the way as to how much flying you have done.

If I were you and you wanted to make this a successful airplane here is what I would do. First make sure there was no up down or side thrust either way with the engine Then I would make sure the incidence of the wing (a line straight through the farthest point forward of the leading edge and through the furthest point aft of the trailing edge) is paralell with the thrust line, this is the chord line. Then I would make sure the stabilizer (the fixed portion of the horizontal tail is also paralell with the thrustline and wing chord line.

Now we have to move onto the CG, This airplane will not work with the CG at the leading edge it is no longer a controlline airplane. Balance this airplane at 20% No further back (this is important).

Now its also likely that you have far to much elevator throw if you have followed controlline practices. Set the throws at no more than 1/4 inch up or down at the trailing edge, no discussion. If you have a modern radio perhaps 25% expo plus or minus depending on radio make required to acheve soft center.

On the ailerons I would add surface area especially near the wing tips perhaps squaring them off a bit.

Throttling an OS pet with that carb is at best difficult, its a two speed carb and was never intended for anything except full speed or a high idle. Throttle response is, well it is an after thought.


Just an opinion

John

Hm there is no such thing as a "Devil Airplane" only a confused an bedeviled pilot

To give a straight answer to your question about going to another plane and using this engine, it's not practical to do so. If you want to stay with small planes, .15-.25 size glow engines designed for RC are plentiful and cheap, and electric components that make similar power are getting that way. You'll spend more in balsa and covering doing repairs in the long run than you would in getting an appropriate power plant. As for plane recommendations, I have a Parkzone Stryker that is my go to windy day belly lander. It practically flies itself and is fast enough to be fun.

Jester's absolutely right. I've picked up .09s, .10s, .15s etc at swap meets and fleabay for very little and those old Enyas and OSs are pretty bullet proof. Mine are all great runners even if not great lookers, and the carbs are way better than the one on your Pet .099. Step up to 1968 and enjoy the technology! It'll probably cost you 25 bucks, or splurge and get a nice one for $30. One tip...the airbleed carbs often work best with a good hot plug, like Enya #3 or McCoy 59. Just switching to a good plug usually gets rid of any hesitation when advancing the throttle.

Jim

I have 2 electric flying wings already, so Stryker doesn't really appeal. I like fiddling with real motors, even if they are finicky, so I am looking for a nitro belly lander. I have lots of motors that are not in service, including an 020, many 049s, couple of 051s, two OS .15s and then the bigger stuff but I want to keep this project small scale, ie .015 or smaller. I also have a 09 TD and a Norvel 061 but those are in use on a 100" vintage glider and a small hi wing Cessna trainer (with wheels) respectively. I do like the Norvel "whine" even if that's a hard motor to finger start. I want something that will land on its belly and not bust props, so maybe some kind of pusher or pod-mounted engine model? All my nitro planes have wheels and that doesn't work too well on a hay field. I was looking at a plan built A-10 that uses twin ducted 049s that may work, especially if I can run them off a common fuel tank.

Anyway, it's a nice day here in Oregon so I am going to give the Devil Plane another whirl with some mods (engine alignment, elevator throw/sensitivity). Maybe I will tame that beast and that then solves the problem. Of course once mastered, boredom creeps in!

Hi!
Your plane is tail heavy!!!!

Hi!
Most likely your plane is tail heavy!!! Simple as that...and a Cl-plane is often very short coupled...that's no good in R/C!

Well I flew it 3 times. First time, take off not too hairy, engine died on climb out, turned and landed dead stick with good control.

Second time it immediately did a space shuttle roll and plowed into the grass upside down. Spectators laughed. Fortunately nothing broke as the grass is now 8" high.

Third time off it went, reasonable straight climb-out, made 3 circuits of the field, it's still twitchy in the up/down plane and it's fast, but once you get used to it you can control it, more or less. After a few minutes, it ran out the fuel, engine died and it glided right in and landed like a seagull into the wind which surprised me. If anything it glides better than it flies. It seems that the minor changes (engine alignment, reduced elevator throw) have tamed the Devil Plane. I am going to give it a little more weight in the nose and adjust the elevator sensitivity one more time. It's still too darn nervous.

I also finally figured out how to start and needle the engine so it doesn't die 10 seconds into the flight. it needs a good squirt of prime because with the carb on the side, it won't prime itself even if you cover the inlet and turn the prop 10 times. And it needs to be set good and rich initially and then it won't lean out when it climbs or the gas gets low.

Hardest part is you can't see whether the darn thing is upside down or not, when it's flying between you and the sun, even tho the underside is red and the topside white. You have to "test" the controls and deduce what it's doing.

Well I think I have my belly lander! Thanks to all for the suggestions. I am going to leave the decollage for the moment, next time I have to reglue the tail I will fix that.

Well congratulations vh2 and glad to see you have had some success with the project and hope there is much more.

I do completely understand the desire to work through some of the challanges of projects sometimes like these even if they may not be the most practical. That makes the successes so much better

Thought you would get a kick out of this picture made in the late sixties at my fathers house and with an airplane I flew in the same way with the same engine, a bottle carb OS Pet 099 it was just a simple thing I made up and use to toss it off a walk bridge over a gully at his place in the desert when I visited him. It to had no landing gear and was flown with just ailerons and elevator, I just wired the throttle open.

John

Well I can relate to the crutches as well, I am recovering from knee surgery thoughout this project and have been hobbling around in a knee brace for 7 weeks. I set up a little table and a seat in the hay field so I can sit while I fiddle with the planes, and of course I now try to land them as close to me as I can.

I have grown fond of that PET and kinda like the noise it makes with no exhaust muffler ... Thanks for the picture ...

A C/L flite streak balanced on the spar is a wild ride and doesn't need much throw at all. To reduce twitchiness, most people would prefer a C/G about halfway between the LE and spar.

Check the incidence of the fixed horizontal stab too. Negative incidence would be very bad. A touch of positive incidence (droopy tail) is acceptable and is often used to equalize inside/outside turning performance.

Cutaway, sounds like you have "been there done that".

Yes the further forward I move the CG the more control I have. I started just on the leading edge of the main spar and that was unflyable. Plus I compounded the problems by mounting the motor with too much down attitude and I had the throws set quite aggressively to start. When I painted it red and black, I had no idea it would turn out to be the Devil Plane.

I took the advice and adjusted my throws to 50% and my exponential to 33%. Added a little lead in the nose. I had already put the control rod on the longest hole in the horn. The elevators are now quite "sluggish" in comparison to where I started out. Perfect flying weather today. Engine sure starts easier with a starter vs. finger. Surprise, I actually enjoyed the flight! Plane obeyed my control inputs, still quite spirited, but for the first time I felt I was in full control vs hanging on for dear life. The plane is still quite sensitive to elevator as well as ailerons. Enjoyed it so much I flew it again. The plane zips around smartly and it glides quite well provided you give it some nose down. Then I quit because I have a rather small battery in this plane, to get it to fit in the wing root I had to use a 220 maH NiNM glider battery, and I had quite a bit of time on the battery since I last charged it. Turns out I needn't have worried, 3 full tanks and two aborted launches and all the battery needed was a squirt of juice ... about 50 mah. I have tamed this Devil and it belly lands on the grass quite gracefully. Next flight I plan to do some loops and rolls.

Now I wonder if anyone has a small 1/2A starter they would like to swap for a full size one. I have two full size and I fear too much power for the little motors. This 09 is just big enough to give you a nasty finger cut.

Decades ago when I flew flite streaks in slow combat, I'd shave the rear of the stab mount on the fuselage down about 3/32"- 1/8" when building them so the tail had a droopy look. Without it, the inside turns were much better than outside. With it, I noticed no visible degradation in inside performance and outside was helped a lot.

I flew a Jr. Flitestreak in control line precision aerobatic events, It was powered by a TD 09 and was fast on 57 ft lines. I had it balanced closer to the leading edge than to the spar, and about 20 degrees either way on elevator throw. It was very smooth and still flew squares and triangles nicely. Control line Flitestreaks with the single wheel gear as shown will really grease landings on hard surface. Glad you got yours sorted out.

So cutaway, are you saying the plane has too much decollage ... that's my observation of it.