Down Thrust and Sidethrsut
06-06-2002 | 05:51 PM
#2
Member
My Feedback: (1)
Joined: Jan 2003
Posts: 39
Likes: 0
Received 0 Likes
on
0 Posts
From: allen,
KY
Down and side thrust
most planes have the down and side thrust built into the firewall so you can use a regular engine mount. Of all the kits I've built I can't remember a single one that didn't have the angle set this way. I have built some profiles that needed washers added to get the side thrust set correctly, I would imagine that you could set some small washers between the rear engine mount holes and the mount to get a few degrees of down thrust.
What plane are you using your mount on? ARF or Kit?
What plane are you using your mount on? ARF or Kit?
06-07-2002 | 05:39 AM
#3
Thread Starter
Member
Joined: Feb 2003
Posts: 39
Likes: 0
Received 0 Likes
on
0 Posts
From: Du Bois,
PA
Down & Side Thrust
Its a Modletech Magic ARF. No where in the building instructions does it tell you to PUT this in, but in the back of the book it says that they have settled on 2 degrees of Down and 1 degree of side. The firewall is completed by them.
06-07-2002 | 07:45 AM
#4
Banned
Joined: Jan 2003
Posts: 4,923
Likes: 0
Received 0 Likes
on
0 Posts
From: gone,
Down Thrust and Sidethrsut
You can put a wedge shaped shim between the mount and the firewall to refine the thrustline. Your hobby shop can order the correct shims (they come in sets)
Unless the aircraft shows a need for the thrust line to be changed... don't worry about shimming the mount. As stated above... the angles should be built-in.
Also.. without use of a thrust line indicationg jig... you really won't know where the eninge is pointed. You can't "eyeball" closer than about 3 degrees discrepancy. And even with the device to measure WHERE the engine is pointed... you have to have the plane rigged into a jig so that it's level by its "Datum" line. (which is what all angles on the plane are referrenced to.) The wings will be at some number of degrees + incidence (normally... I've seen -3 in one case) the tailplanes will be at some - incidence, so you can't depend on measuring them to get the plane straight.
However, after trimming the plane, you can correct for "ballooning" with increased throttle or turning with diferent throttle settings by shimming the engine. (that's why you have the side and down thrust. If the plane is over-powered (like most people seem to want now...) the thrust line may need adjustment for greater than 70% throttle to not need trim changes.
To check side-thrust, fly high, turn off the engine and ttrim for a straight glide. Now if you need to correct with rudder to fly straight with engine on, you need side-thrust adjustment. (and even then... you may see a different amount needed at different throttle sttings...)
The check for downthrust is to set the plane for a 1/2 to 2/3 throttle level hands-off. Add power. If it balloons (noses up) it needs more downthrust. Note that the plane SHOULD climb with added power... it shouldn't have the nose point up sharply immediately on increasing throttle. (but any flat bottom, high wing trainer type will have the nose rise a bit no matter what you do.)
Unless the aircraft shows a need for the thrust line to be changed... don't worry about shimming the mount. As stated above... the angles should be built-in.
Also.. without use of a thrust line indicationg jig... you really won't know where the eninge is pointed. You can't "eyeball" closer than about 3 degrees discrepancy. And even with the device to measure WHERE the engine is pointed... you have to have the plane rigged into a jig so that it's level by its "Datum" line. (which is what all angles on the plane are referrenced to.) The wings will be at some number of degrees + incidence (normally... I've seen -3 in one case) the tailplanes will be at some - incidence, so you can't depend on measuring them to get the plane straight.
However, after trimming the plane, you can correct for "ballooning" with increased throttle or turning with diferent throttle settings by shimming the engine. (that's why you have the side and down thrust. If the plane is over-powered (like most people seem to want now...) the thrust line may need adjustment for greater than 70% throttle to not need trim changes.
To check side-thrust, fly high, turn off the engine and ttrim for a straight glide. Now if you need to correct with rudder to fly straight with engine on, you need side-thrust adjustment. (and even then... you may see a different amount needed at different throttle sttings...)
The check for downthrust is to set the plane for a 1/2 to 2/3 throttle level hands-off. Add power. If it balloons (noses up) it needs more downthrust. Note that the plane SHOULD climb with added power... it shouldn't have the nose point up sharply immediately on increasing throttle. (but any flat bottom, high wing trainer type will have the nose rise a bit no matter what you do.)
