Thrust line maximum degrees.
 

Hello, I would like to know if there is any way to know how many degrees of engine thrust or power line change is required for some specific model in order to get a better flight.I flew a Richmodel Long EZ 160, which comes with the engine fixed in a "rectangular square" area on the rear part of the fuselage, but had lots of trouble trying ti keep it flying straight and level, with a strong nose down tendency, this situation were reduced in proportion of engine power reduction, means the less engine power the less nose down tendency, I even had to use full trim up and fly the model with half elevator up stick.There were no problems at idle power.So I was told to change the engine thrust line by rising the bottom part of the engine mount about 2 to 3 degrees. That's will help to lower the tail and keep the nose level then with some minor trim changes in flight.I am using a OS MAX 1.60 FX glow engine, a MA 16x10 3-blade pusher propeller, and the model weights about 18 pounds.In all scenarios the model was well balanced.

Thanks, Isaias G.

RE: Thrust line maximum degrees.
 

lechusa, adjust the thrust line so that the engine is not trying to lift the tail of the plane UP. It is a big model, but it is possible to feel for neutral equilibrium with a helper as the engine is running and with the model in both your hands.

RE: Thrust line maximum degrees.
 

Well the LongEze has a high thrust line and is a pusher to boot. So if it is pitching down at higher power you want to angle the thrustline upwards to induce some tail down and nose up torque.

It's pretty tough to figure out how much change you need without a really BIG amount of fancy math and knowing the drag centers of all the stuff and how your stability margin is set and likely the phase of the moon to boot. The big boys at Boeing and Mcdonald Douglass would do it that way (without the moon bit) but for us simple modelers it comes down to a "try and see and then do it a bit more or take some out" sort of deal. Just don't patch up any alterations to the cowl until you're done. Or better yet run it without a cowl or with a test cowl if it requires the cowl for proper airflow around the engine. Get the thrust line set up correctly so the tendency is to slightly climb as you add power. Then fix up all the pretty bits so it looks nice again.

RE: Thrust line maximum degrees.
 

Another thing to look for is if you use a soft mount, like the Dubro isolation mounts, is that the rubber gromlets are not going soft. I was having trouble with a 3D plane I built a few years back, when I punched full power on the ground, it would snap right and do donuts on the runway. The issue turned out to be that one of the aluminum spools was short by 2.5mm so the motor was basicly setting on a chair with one short leg. As soon as it came up to about 3/4 power, the chair tipped to the short leg, giveing a bunch of right thruts. I'm holdig right rudder, the engine is set for 2 degrees rignt and suddenly there is about 5 degrees of right. What a ride.

Don

RE: Thrust line maximum degrees.
 

Heck, even with all the math and computer time in the world, the fullscale designers still approach test flying new designs with an understanding there is a good chance there will be changes needed.

I think we modelers have it better. We don't have the math (usually) nor the wind tunnels and just go test fly. Saves a bunch of time, methinks.

RE: Thrust line maximum degrees.
 

Hello again, and good news.Finally my Richmodel Long EZ 160 flew as expected by changing the angle of engine power line, raising the lower part of the engine mount(using some washers) up to 4 degrees.You can take a look at the video I took at youtube.com, then seach as: long ez 160.With the OS MAX 160FX and a 3-blade MA 16x10 propeller, this model is very fast and with good response; In the video as soon a left the ground just a few feet, I reduced the engine power a bit less than half throtle an see how it flies.

Thanks all for your advises, best wishes: Schaye G.

P.D.: Now just a couple of days left for my new project to arrive: The World Models Spitfire Giant Scale!