Weight in a wing tip??

[fli48rc]

I'm converting a Veron Fokker Dviii from Gas to Electric. I am puttng an AXI engine into it, and this engine needs to be mounted through a firewall. The cowling on the model is such that I am not really going to be able to give the down right orientation to the engine. I am wondering about putting some weight in the right wing tip. Good idea, bad idea? Would this at least help in the pull to the left during flight?

 

[Malcolm Fisher]

I'm converting a Veron Fokker Dviii from Gas to Electric. I am puttng an AXI engine into it' date=' and this engine needs to be mounted through a firewall. The cowling on the model is such that I am not really going to be able to give the down right orientation to the engine. I am wondering about putting some weight in the right wing tip. Good idea, bad idea? Would this at least help in the pull to the left during flight?[/quote']Don't like the idea myself - any imbalance in an airframe is a recipe for problems - potential disaster with a heavy wing tip.

Wouldn't it be possible to make the hole in the firewall offset to give the required side and downthrust?

From what I remember of the shape of the front of this plane, it shouldn't be difficult to do this for an electric power plant. Electric motors are far less bulky than glows and the necessary offset thrust can be accommodated for those engines.

Having said that, I have no direct experience and am just making my observations and drawing conclusions from what I have read in magazines and on news groups.

As far as I know, no full size aircraft has any down or side thrust. Torque induced turns are usually corrected for by judicious use of control surface deflections.

Malcolm

 

[duncan]

Bad idea to weight one tip,when power is reduced you have the potential for a spin to the heavy side. One of the old dethermaliser systems carried a small weight in the fuselage at CofG , a nylon thread tied to the weight and the other end of the thread pinned to the wing tip. When deployed to end the flight the weight was released and swung on the wing-tip like a pendulum causing a spiral dive. The theory was that if the thread was long enough the weight would hit the ground first and aircraft would recover slightly and not spin into the ground with a thump. Lateral balance is one of the most neglected aspects of trimming a model aircraft. It is not uncommon to see a couple of screw-nails in the tip of a model`s wing as a last minute "fix". As Malcolm says dont be scared to modify the nose to get the essential sidethrust, 3 degrees typical, and some downthrust to counter that high wing. Doubtful if anyone will notice.

 

[wonwinglo]

Agree on everything said here about wingtip weights,not a good idea,I doubt whether you will need very much sidethrust really,could you incorporate the motor into a tube of some kind that could be slightly adjusted and then permanently fixed when you have sorted out the thrustline for your model ? my own D.7 had downthrust but no sidethrust with a small 15 size motor she pulled away with a slight turn but nothing drastic,I know tha any thrust adjustments tend to look untidy inside a radial type cowl but subtle adjustments are hardly noticeable.

Being a parasol with a noticeanble pendulum effect about its axis unfortunately the D.8 does need some downthrust,you could assist things with a trailing edge strip of wood a few inches long to counteract any turning tendencies,but lay off the weighted wing idea,a recipe for disaster.

Hope that you get it sorted.

 

[fli48rc]

I can appreciate all the advice... I guess I will look at adding washers to the bolts I use to attach the engine to the firewall and attempt to tip it through enough to attain the 3 degrees. The problem is the length of the prop adapter, the size of the prop, and the cowling. It is going to be a tough fit. I will update everyone once I get it figured out. Thanks again