HELP trim model !

[Osni Renato]

Hello Friends!
I have some questions about the trim of the airplane:

1 - how to resolve the lack of traction in the maneuvers high? I had this problem in a model, good traction in level flight lack of traction at the top!(mainly hourglass)

2 - The rudder is a significant difference if it's adjustable?

3 - The belcrank should always be set in the center of gravity of the model? what happens if it is put forward or backward that point?

thanks !

Osni

[Randy Cuberly]

Hello Osni,
I have to assume by "traction" you are referring to Line Tension.  Please don't take this as a criticism of your english because it's much better than any language I speak besides English.
Assuming you mean tension there are several ways to increase tension overhead and above 45 degrees elevation.  The easiest and most effective is to add wing tip weight to the outboard wing.  This does come at a price because too much will cause the outboard wing to drop in hard maneuvers.  The position of the Bellcrank in the wing does not matter in the least as long as it's located where it provides free movement.  The exit point of the leadouts (tether point) at the wing tip are what's important.  They should be (The center point between the two leadouts) approximately 1/2 inch behind the center of gravity (CG) to begin. 
Rudder usually has little effect on tension overhead and can in fact cause a reduction in some cases.  Location of the CG can have some effect...more nose heavy more tension...also less maneuverability.
Available power can also have an important effect on line tension overhead.  More power means more tension if every thing else is equal.
There are other items that can certainly effect tension in general but these are the main ones to consider first.
Assuming you have an adjustable leadout guide, position the leadouts as suggested above, add some tip weight and try it again.

Let us know how it works out and we can provide more information.

Randy Cuberly

[Larry Cunningham]

(Now watch me get into trouble with this..  )

1. In spite of that 1G x sin(elevation angle) force detracting from line tension, proper
trim can make a big difference. Frequently the leadout guide can be moved FORWARD
with some improvement, contrary to what might be expected. You need to experiment
a bit to see the actual effects. Too far forward is not good either.

2. A common feature of many modern stunter designs is a "flat" rudder, typically without
an offset and a mild airfoil on its inboard surface. Many older designs had excessive rudder
offset (e.g. Twister, as shown on original plans), where none works better (in my personal
experience).

And the Rabe rudder or wiggly rudder, is favored by many serious competitors. It needs proper
setup and trim, too much movement can be counterproductive.

3. The position of the bellcrank relative to CG is NOT important, in spite of many opinions to
the contrary. All that matters is where the leadouts exit on the inboard wing tip. If you are
mathematically inclined, you can easily show that the bellcrank cannot produce a couple to
affect yaw.

There are two disclaimers here. First, I'm ignoring any frictional effects on the leadouts.
Second, I'm ignoring geometric consequences of moving the bellcrank with respect to the
flap control horn. Shortening the bellcrank to flap control rod link will increase distortions
associated with its 3D (non-symmetric) geometry.  (Try a thought experiment with a very
long bellcrank to flap control rod, and you'll see that such distortions are decreased..)

Often, line tension will be optimized when the ship is well trimmed, with minimal drag induced
by yaw. CG also affects it; a very nose heavy ship may exhibit good line tension (at the expense
of maneuverability).

It's all compromises, trim.

L.

"Against the assault of laughter, nothing can stand." -Mark Twain

[Randy Cuberly]

Hi Larry,
Hows tricks?

I thought I said all that!....

[rustler]

More power means more tension if every thing else is equal. Randy Cuberly

Is that saying more power = more speed or torque, or is it due to e.g. a more powerful engine turning a bigger prop slower but getting the same airspeed or maybe a smaller prop faster and getting the same airspeed or something like that?

Any explanations greatfully accepted.

[Steve Helmick]

I know that the propeller makes a tremendous difference in line tension. I've had very good experiences with APC, Thunder Tiger and Graupner plastic propellers. I've not had good results with wood propellers (old TF paddle blade, Zinger, BY&O, Master Airscrew wood), except for Rev-Ups, which are just too difficult to find for my taste. One that seems useful is the TF Power Point. CF props are still being stubborn with me...very little in the way of encouraging results. 

If this is for the Stalker .76, I'm interested in your propellers!!!    Steve

[Randy Cuberly]

Rustler,
Well certainly more speed will give more line tension, but what I was refering to was the ability to produce and maintain thrust from the propellor during different loading conditions.  The two-four break was one way of accomplishing that by allowing the engine to produce lower rpm for less speed under light loading conditions such as downhill or at straight and level flight and then produce more rpm to maintain more thrust going uphill or in higher loading conditions.  Properly regulated this produces more power to maintain speed when needed.
A more modern approach is with a tuned pipe that is designed to regulate power as a result of speed and load on the engine.
In simple terms yes a larger propellor turning the same RPM with less pitch can produce "more power" and more line tension at the same speed.
Most importantly "more Power" can refer to a flatter torque curve that does not "sag" or lose RPM when loaded in maneuvers.
I realize this is a simplistic explanation and I certainly do not intend to offend you.  Obviously the efficiency of the prop can also play a large part in this senario and different types can produce different results under different loading conditions both on the engine dynamics and on the aerodynamics of the airplane.

Randy C.

[Osni Renato]

Hello Friends!
Thanks for the explanations, I will test the suggestions that I have and report on these same topics! ok?
This problem is not on the plane with the STALKER!
I had this lack of Tension Line (sorry for writing wrong before) in a model that I'm doing repairs (a bird collided with the line down in level flight and the plane slammed into the ground)!
The plane is engined PA51 and has the configuration of the wing and elevator similar to the Trivial and weighs 57 oz!
The props that use it are made by myself in carbon fiber measures are twoblade 12.25 x4, 25 and TriBlade 12x4, 25 !
The two with good results but tension line  contunuer weak maneuvers high!
My plane is almost completed repairs and intend to test this weekend if not raining! Here it's raining is already two weeks without stopping!

Big hug to all

Pics of my props and landing gear!

[Derek Barry]

Tip weight like Randy said, and I would move the leadouts BACK (sorry Larry, moving them forward never worked for me). However, as you add tip weight you may have to move the leadouts forward to compensate. The 12x4.25 prop should be fine.

Very nice work on the props and gear!

[Osni Renato]

Thank you Derek!
I will test the plane tomorow !

Regards !

Osni

[Martin Quartim]

Osni,

I believe your problem has more to do with your engine setup then with trimming.

I am no Pipe engine expert, but I suggest you post how you made your pipe, what fuel you use  and how you run your engine. I am absolutely sure folks here can help you run your engine much better.

Last year I noticed you having a hard time flying in the wind in Limeira and Piracicaba with your other plane. You built very light and with a PA engine you shouldn't be having this kind of problems in the overheads.

I'd start examining your custom made pipe, you told me it saves a lot of fuel and that to me is a clear sign it is chopping the power.

Martin

[Osni Renato]

Hi Martin !

The plane you saw was flying with the wind is a PA65! This new plane is with the PA51! Power Supplies are not missing!
Power is enough! Fuel is what you buy with (Byron)!
I believe that the tips that friends suggested to solve the problem!
Let's try !!!!!!!!!!
Regards

[Osni Renato]

Hello friends.
The plane is ready for testing but not for the rain.
Today was not truce for 30 minutes.
Who knows the next Saturday.
Thanks for the tips some are already set in the plane

Regards