cliff600

My Feedback: (3)

I need a little help here again guys, I have a busted up Cub that I am trying to rebuild. I am trying to check the engine incidence using just the plane and a level, I don't have an incidence meter. I set the level on the elevator and leveled that. I put the level on the engine hub, and it was still pointing down several degrees. Can anybody tell me where it needs to be and how I can set it with the tools that I have.

Lnewqban

I don't know how many degrees of down-thrust your specific model needs to have.

Two degrees is usual for many models.

Once the stab, or even better, the central line of the fuse, is level, place the prop in a vertical position.

Then measure the distances from the top and bottom tips to a vertical string holding a plumb directly in front of and in line with the fuse.

With the diameter of the propeller and those two dimensions, we can solve the angle using some trigonometry.

cliff600

My Feedback: (3)

I get what you are saying, but I still don't know if it needs downthurst on the engine line and if so what degree.

Square Nozzle

My Feedback: (1)

I'm building a 1/4 scale BUSA Cub and the plans call for 2 degrees right thrust and 1 degree down.

sidgates

My Feedback: (2)

Cliff600
I eyeballed my Sig 1/4 Scale cub and the thrust line looks like it is lined up with the center line of the fuselage. The flat bottom wing is up about 2 degrees from the fuse center line. These settings should be close enough for test flight.

LesUyeda

"I get what you are saying, but I still don't know if it needs downthurst on the engine line and if so what degree. "

That depends completely on the aircraft, and the power plant. The ONLY way to know is to fly, and see what happens.

Les

Rodney

Most high wing planes require more down thrust (that is not incidence) than mid or low wing planes. A Cub often requires more than 2 degrees down thrust and almost always flys best with about 3 degrees right thrust. On my 1/4 scale with 1.2 cu. in. engine, it needed about 5 degrees down thrust.

cliff600

My Feedback: (3)

Mine is a 1/4 scale too, but I am putting a Brisson 40cc on it because it is gonna be a tow plane. It seems to have about 4-5 degrees of down in it now, I have not checked for right thrust yet. I know this is alot of engine for this plane, but it is gonna be a workhorse too. It had an Evo 26 on it and it seemed to fly ok as far as all the downthrust and right thrust, but I bet this 400 is gonna torque it around on takeoff. Maybe I will leave it where it is now and see how it goes.

David Bathe

BMatthews

The amount of downthrust also depends on where you put the balance point. If your Cub is setup to be more a trainer then you'll want a fair amount of downthrust.

The downthrust should not be set to the tail section. Instead if the wing is a flat bottom section set the lower surface level and then set up the engine or motor so it has 2 to 3 degrees of downthrust relative to that lower surface line. Even 4 would not be a bad thing, espeicially if the model is intended for beginners and has a more forward balance point as a result. While you're at it build in 2 degrees of right as well.

These are purely guess angles based on past experience. As mentioned each design and each trim setup of any given design will set the best amount of down and right thrust. But setting it up as I mentioned should keep you "in the ballpark". From there you can shim the engine or motor mounts with washers to fine tune it to your flying style desires.