low wing plane with no ailerons

[John Bright]

I have a 36" wingspan scratch built Pilatus PC-9 that is powered by a geared speed 400. It has 2 1/2 inches of dihedral at each tip. What I am wondering is can you fly a low wing plane on rudder and elevator, or does it need to be aileron and elevator. I have flown slope and thermal gliders for several years but this is my first power plane. I am mainly concerned about weight. I am at 22 ounces with out the two aileron servo's. I had planned on using them in flaperon mode, but with the weight of the two servo's and linkages that puts me at almost 24 ounces.

[Lon Enloe]

John,

Welcome to the E-zone! This is the location that keeps me in the air and having fun.

You might want to peruse the "Modeling Science" forum--there are some very knowledgeable folks who hang out there who can help you with this--they have been very helpful to me.

There are some threads running there on this topic, and I'm sure these folks would be more than willing to engage with you on this as well.

Lon

[CSI]

John,
You sure CAN fly a low wing plane with rudder and elevator only. Matter of fact, you will have to fly it MORE! I mean the low wing plane is not as stable at the high wing. The low wing generally has less tendency to return to a wings level attitude after being disturbed. Basically the pendulum effect where the fuselage is hanging at the bottom for a high wing is lost with a low wing. Making turns with rudder only requires slipping and skidding the airplane with the rudder. This will force a turn by creating uneven lift on each of the wings. The low wing's "problem" is that it will take more control of opposite rudder to bring the airplane out of the turn, thus you will have to fly it more...meaining more positive/constant control. The high wing generally helps you level the wings with less opposite rudder needed.
All airframes are different and may take a little more or less control input, but Yes, you can do it without the ailerons.
If I remember correctly, the Kyosho Spree Sports is a low wing with rudder control.
Hope this helps,
Ken

[flieslikeabeagle]

John, I have no personal experience with this, but my understanding is that it is quite possible, though you will need more dihedral angle in a low-wing Rudder/Elevator/Throttle model than in an equivalent high-wing model, for the reasons CSI explained.

How much wing area does your model have? With 22 oz on a 36" wing span, it will likely have a pretty high wing loading, making for a high stall speed and less maneuverability.

-Flieslikeabeagle

[BMatthews]

2 1/2 is probably enough to get away with it. 3 inches would be better and give you a snappier roll response. 3 1/2 would definetly be enough and would make it fly very snappy even if it looks a little odd.

The wing of the PC9 is quite small in scale so you're right to worry about weight. In fact I suspect that 22 oz may already be too much unless the design cheats and has a larger than scale chord.

[vintage1]

I make that 7 degrees each side. Shoul be enough unless it has a LOT of side area in the nose, or above the wing. Or a teeny weeny itsy bitsy tiny polka-dot.... fin..:D

36" and 22oz is OK. Will be fast. Probably need to go to direct drive on that 400 to get pitch speed up. Probably will land at over 20mph.

[John Bright]

Flieslikeabeagle I am not quite sure on the wing area and loading. The wing was scaled up about 15% the center section has a 7" chord and is 8.75" long which should be 61.25 sq. inches. The tip panels are 7" and the root and 4.5" chord and each panel is 13.75 " It has been a looong time since I have been in any math classes but as close as I can figure the is 79.0625sq inches, so with the two tip panels and the center section I come up with a total 219.375 sq. inches. I am not positive on the area of the tip panels since there is a double taper, hopefully I am in the ball park. I am not sure how to calculate wingloading but the weight is 22 ounces right now.
Any math wizards that can check my calculations?.

If I need to move this thread to the "Modeling Science" forum how do I go about that?

[vintage1]

Seems to be IN modelling science.

I've got a 30" plane of slightly less wing area that used to fly at 22oz oin a DD speed 480.

no rudder, only ailerons on that one. It was a bit hard to launch - needed a HEFTY chuck.

Motocalc reckons yours will stall at 19mph. If your figures are correct.

If at all possible use 3s LIPO to get weight down. And thrust up. You will need not too much gears on that - pitch speed needs to be well over 40mph.

8 cells and 8x6 prop and 2.33:1 is as low as you dare go.

I think you are in trouble even then.

I'd go no more tha 1.85:1 and a 7x5. Even that is pretty marginal.

Direct drive, more cells or a speed 480?

[John Bright]

I realized it had been moved about the time I hit post. Thanks for the info. I think I will strip it back down and try again. The wing was foam with a carbon spar, then sheeted, and covered with monokote. The fuse had lightening holes on the bottom and sheeted on the turtle deck and monokoted. I think I'll move the tail servos to the back and eliminate the linkages, and ditch the monokote. I can cut a new wing, I think I over built the wing any way. I can probably get by with out sheeting it, old habits die hard. I have 2s 7.4/1500mah Kokam li-po and a 10 amp esc and a speed 400 that is currently on the mini-olympus gear box with a 8x4 prop. I would like to get this plane to a weight which would make that combination work. What kind of weight would I need to make that happen.

[vintage1]

Well..we can work backwards with a 2s LIPO, 2.33:1 box...you need around a 8x6 I'd say.

Even then pitch speed is not ging to be much over 30mph...

Something has to give. The size of the wings, the gear ratio or the pack voltage.

Guessing that the motor and box are pretty much givens, can you go to 3s LIPO and a 7x5?

If you then keep the weight below 20oz, I think it will fly very well. 17oz should be achieveable.