C G on Bi-Plane
07-21-2011, 06:41 PM
#1
Member
Thread Starter
Join Date: May 2003
Location: blair,
NE
Posts: 31
Likes: 0
Received 0 Likes
on
0 Posts
C G on Bi-Plane
Bought a bi-plane from a friend but don't know what kind it is. stagger wing on top straight on bottom. Top wing 47", bottom wing 43"
I don't know how to figure C G on this type of plane.
Could some one help?
[img][/biplane002][img][/biplane003]
I don't know how to figure C G on this type of plane.
Could some one help?
[img][/biplane002][img][/biplane003]
07-21-2011, 09:39 PM
#2
RE: C G on Bi-Plane
I will take a shot Midwest.
Actually the top wing is a sweptwing and the lower a straight wing. Stagger just means the topwing is forward or rearward of the lower wing. If the upper such as yours is forward its called positive stagger. If the upper is rearward of the lower then its called a negative stagger.
Actually balancing is quite easy on that airplane. Look at your photo from above it looks for all the world just like a single wing with tapered leading edge and a straight trailing edge. Now for balance purposes we can treat it just like a single wing with a tappered leading edge.
All we need to do is find the half way point from the centerline and the wingtip and measure this planview chord at this point. Remember we are actually measuring the distance (in this case) from the leading edge of the top wing rearward to the trailing edge of the lower wing and this is half way out there to the wingtip.
If we make the assumption that 25% mean aerodynamic chord is the target CG and I do strongly suggest using 25% for this type airplane then just marking one quarter of the distance back from the leading edge out there at this half way point to the wingtip will be your target CG to balance to.
John
Actually the top wing is a sweptwing and the lower a straight wing. Stagger just means the topwing is forward or rearward of the lower wing. If the upper such as yours is forward its called positive stagger. If the upper is rearward of the lower then its called a negative stagger.
Actually balancing is quite easy on that airplane. Look at your photo from above it looks for all the world just like a single wing with tapered leading edge and a straight trailing edge. Now for balance purposes we can treat it just like a single wing with a tappered leading edge.
All we need to do is find the half way point from the centerline and the wingtip and measure this planview chord at this point. Remember we are actually measuring the distance (in this case) from the leading edge of the top wing rearward to the trailing edge of the lower wing and this is half way out there to the wingtip.
If we make the assumption that 25% mean aerodynamic chord is the target CG and I do strongly suggest using 25% for this type airplane then just marking one quarter of the distance back from the leading edge out there at this half way point to the wingtip will be your target CG to balance to.
John
07-22-2011, 05:33 AM
#4
RE: C G on Bi-Plane
I don't disagree with the previous posts completely, but I would use the area method in this case, which geometry is a little complicated.
1) Make a copy of both half wings (top and bottom) in cardboard.
2) Find the centroid of each. The MAC will be over that centroid. In order to find where that centroid is, hang each cardboard from a pin in a wall. Pin it from different points along the edges and draw plumb lines from each point down. The centroid of each half wing is the point at which the different lines cross and meet each other.
3) Over that found point, draw a line that should be parallel to the fuselage centerline. The length of that line (from LE to TE) is the MAC for each wing (Mean Aerodynamic Chord). Divide that line into four equal segments. Mark the forward 1/4 of the chord.
4) Place the cardboards on a table and overlap them in the same way the wings are staggered. Pin each 1/4 of the chord points. Draw a line between those two points.
5) Calculate the ratio (Area top wing / Area bottom wing) x 100. That is the percentage on which the CG should be over that line. CG should be closer to the wing with bigger area.
6) Pin that point, so you can transport and mark the location on the bottom surface of each top halfwing. Extend a line between both marked points. Balance on any points along that line.
1) Make a copy of both half wings (top and bottom) in cardboard.
2) Find the centroid of each. The MAC will be over that centroid. In order to find where that centroid is, hang each cardboard from a pin in a wall. Pin it from different points along the edges and draw plumb lines from each point down. The centroid of each half wing is the point at which the different lines cross and meet each other.
3) Over that found point, draw a line that should be parallel to the fuselage centerline. The length of that line (from LE to TE) is the MAC for each wing (Mean Aerodynamic Chord). Divide that line into four equal segments. Mark the forward 1/4 of the chord.
4) Place the cardboards on a table and overlap them in the same way the wings are staggered. Pin each 1/4 of the chord points. Draw a line between those two points.
5) Calculate the ratio (Area top wing / Area bottom wing) x 100. That is the percentage on which the CG should be over that line. CG should be closer to the wing with bigger area.
6) Pin that point, so you can transport and mark the location on the bottom surface of each top halfwing. Extend a line between both marked points. Balance on any points along that line.
