earl williams

My Feedback: (27)

WITH THE ENGINE ANGLED DOWN A COUPLE OF DEGREES, WHAT AFFECT WOULD IT HAVE ON THE PITCH? WOULD THE PLANE TEND TO FLY DOWN OR UP?

Richard L.

My Feedback: (24)

Most planes have built in down thrust and right thrust for a reason: "TO KEEP THE PLANE FLYING STRAIGHT AND LEVEL." Without down thrust, the nose will tend to pitch up.

hookedonrc

I ran into too much down thrust on my trainer when I was learning. The engine wanted to pull the nose wheel into the ground. I actually learned landings before take off till my instructor and I found the problem. The engine had 4* of down thrust in it. After shimming the motor mounts to a 0-1* down angle, the plane flew great.

Airdale CPO

My Feedback: (3)

I would like to re-open this discussion if I may. When I mounted my engine on my Sukhoi, I noticed that it had no right thrust of any kind. It does have down thrust but no right thrust. Matter of fact it looked as if it had left thrust. Since I am not an expert by no means, I need to check myself and ask what I did was right. I ended up having to put three washer under the forward mount of the engine (mounted 90 degrees) to give me right thrust. Now it is very secure but I do have space between the mount and the engine. Is this a bad thing? Or should I retry and put something under the actual engine mount on the firewall?

bearmech

My Feedback: (1)

Between the firewall and mount wold be better, less stress on the engine mount lugs.

ghendrix01

My Feedback: (1)

Several years ago I acquired a small twin complete without radio equipment. I installed the radio gear but didn't check the thrust angle of the engines. After the first flight (a handful with the plane climbing at different rates depending on the throttle setting) I checked the trust angle of the engines which I found to be 1 degree up. It was suppose to be 2 degrees down. After shimming the engines with plywood wedges to the proper thrust angle, it flew great. Hope this indicates the need for down thrust.

George

vinnie

My Feedback: (1)

Try these Airdale.

http://www2.towerhobbies.com/cgi-bin...?&I=LXE953&P=7

3DFanatic

My Feedback: (5)

It sounds like a Goldberg Sukhoi? According to their website, it's not suppose to have any down/right thrust. Though mine has several degrees of right. No down, however.

Airdale CPO

My Feedback: (3)

vinne-RCU, I have thought about buying the thrust plates but if I install them they will cover the fuel opening, so I will have to shim from the firewall like "bearmech" has said. I have already started to make them and will give them a shot. I went to the Goldberg site and the plane there is much bigger my wing span is only 56". I am still looking who makes the kit though, but I do see about the engine thrust. The plane was given to me with a busted tail and I am putting it back together and recovering. I thank you all for your inputs and I will re-post my fixin's. Hopefully I will have pics as well.

Brian

HangerBum

What is the most accurate method for measuring engine thrust angles? Point to point off the Horiz stab corners? or try to get a line off the fuse.......

HangerBum

And another one, if I may...... my (arf) instructions do not mention thrust settings. Is there a rule of thumb setting for thrust? or do I just fly the plane and adjust according to the way it flies?

feihu-RCU

earl williams -

The purpose of downthrust is to prevent the airplane from pitching up when power is applied. The need for downthrust depends on the particular airplane, as some configurations may even require upthrust; however, most high wing trainer types require about 2 degrees downthrust to fly level when the throttle is set at about 1/2 to 2/3 power.

feihu

feihu-RCU

Hangerbum -

Measuring downthrust has always been a controverisial subject. Downthrust with respect to WHAT? Some say the fuselage longitudinal axis (where is that((wit)))), a horizontal reference line (wit), the wing incidence line (wit), or the stabilizer incidence line.

What matters is the location of the engine with respect to the vertical CG of the airplane; that is the location of the CG on the side view of the airplane where the mass of the airplane is concentrated. (A high wing airplane may be considered top heavy whereas a low wing airplane may be considered bottom heayy). The engine thrust line should be adjusted so that it passes thru or slightly above the this CG to minimize pitching moments caused by speed and power changes.
How do you find the vertical CG? Hang the airplane by the prop, and hang a plumb line from the prop alongside the fuselage. The verticle CG is where the plumb line and the longitudinal (30% or so) CG line crosses.

feihu

flyerdude

I have the same question as HangarBum.

What is the best way to adjust for 3 degrees right thrust for example. How do you know you have 3 degrees?

feihu-RCU

flyerdude -

To measure right thrust for example, assume your fuselage has no warps, set your propeller horizontal and measure the distance from the right tip of the prop to the rudder hinge line on top of the rudder. Lets say you have a 10" prop, and you measured 29and 7/8 inches. Now measure the distance from the left tip of the prop to the rudder hinge line and lets say you measured 30 and 1/8 inches. You have measured a right triangle of a (using half a prop blade) 5" leg and a 1/8" leg, the Tangent of which is .125/5 = .025. The Tangent angle for .025 is 1degree and 25 seconds.
So for 3 degrees right thrust, you will need to shim the engine right so that the right tip of the propeller will be offset about 1/4 inches. Got it?

feihu