Questions concerning $* 40 kitbash
03-16-2003 | 12:54 AM
#1
Thread Starter
Junior Member
Joined: Jul 2002
Posts: 25
Likes: 0
Received 0 Likes
on
0 Posts
From: macon, GA
Questions concerning $* 40 kitbash
Hi Guys,
I need help/enlightenment about the nomenclature involved with aircraft design. To make a long story short, I am in the midst of kit bashing a 4*40 by replacing the tail feathers and ailerons with something extra parts and moving the wing to a mid fuse position. How does one figure where the thrust line is and what is the thrust line? The 4* is o degrees on stab 1/2 degree up on wing with 2 degrees dihedral and 2 degrees down thrust on the engine. The engine is setting high in the fuse and I intend to lower it to the mid point of the firewall. My questions are; how do I find the thrust line? Do I need the engine down thrust to counteract the semi-simetrical wing design and 1/2 degree positive angle of the wing. What is the result of moving the engine 1/2 inch lower in the fuse( does this effect the thrust line location)?
I need help/enlightenment about the nomenclature involved with aircraft design. To make a long story short, I am in the midst of kit bashing a 4*40 by replacing the tail feathers and ailerons with something extra parts and moving the wing to a mid fuse position. How does one figure where the thrust line is and what is the thrust line? The 4* is o degrees on stab 1/2 degree up on wing with 2 degrees dihedral and 2 degrees down thrust on the engine. The engine is setting high in the fuse and I intend to lower it to the mid point of the firewall. My questions are; how do I find the thrust line? Do I need the engine down thrust to counteract the semi-simetrical wing design and 1/2 degree positive angle of the wing. What is the result of moving the engine 1/2 inch lower in the fuse( does this effect the thrust line location)?
03-17-2003 | 09:26 PM
#2
Thread Starter
Junior Member
Joined: Jul 2002
Posts: 25
Likes: 0
Received 0 Likes
on
0 Posts
From: macon, GA
Questions concerning $* 40 kitbash
since you braiy guys find these questions to hard, can you direct me to a link that would give me the answers to my qestions? 
03-18-2003 | 03:51 AM
#3
Senior Member
Joined: Oct 2002
Posts: 1,406
Likes: 0
Received 0 Likes
on
0 Posts
From: St. Charles, MO
Not easy but.....
Since you are starting off with 2 degrees of downthrust you probably will end up with something between 0 and 1 degrees of downthrust. The thrust line is just a line drawn through the motor crankshaft so moving it 1/2 inch lower will change the thrust line a little but not all that much. There is a horizontal balance and a vertical balance of forces and moments that allow the airplane to fly in a straight line. The thrust angles and incidence angles are an attempt to balance these things. However the balance is usually good for only one speed, usually wide open as that is where most of us fly.
The reason you don't get many answers for this kind of question is that the numbers needed in the equations for the motor is a wild guess, they vary with motor, prop, fuel, etc. It is easy to deal with at the full scale airplane sizes as the motor characteristics are well tested and known.
The changes you are making are pretty small actually. I don't know if I would go to the trouble of calculating angles for the motor. It could be left the same as the original design and adjustments made after the first several flights if necessary. It is what most model designers do based on experience, not on any massive amounts of calculations.
The reason you don't get many answers for this kind of question is that the numbers needed in the equations for the motor is a wild guess, they vary with motor, prop, fuel, etc. It is easy to deal with at the full scale airplane sizes as the motor characteristics are well tested and known.
The changes you are making are pretty small actually. I don't know if I would go to the trouble of calculating angles for the motor. It could be left the same as the original design and adjustments made after the first several flights if necessary. It is what most model designers do based on experience, not on any massive amounts of calculations.
