VO wrote:

Paul,
Which rubber mounts I need to use in case 20B for Velocity?
Any suggestions for bolt size as well?
FYI - firewall is playwood with TRIAX on both side and
reinforcement TRIAX points for suggested five points of attachment.
Thanks.
Vlad
N1UT

What is the distance from the bottom mount hole on the firewall to
the top mount hole on the firewall? If it is at least 12 inches
a Barry 22003-14 should work. More is better. Separate these holes as far
apart vertically and horizontally as possible. 24 inches apart vertically
is way better. In that case you can go down to a 22003-13. You might need 
to beef up the skin near the top holes with several additional layers 
of glass cloth.

Copy Perry's design as close as you can. You will really need the 
22003-14 at the 860 pound axial rating. The radial rating is
385 pounds each which is more than enough for a 20B. The fire wall 
thickness must be built up to 0.875 inches thickness with glass and 
plywood in the area of the mounts. Say three or four inches in diameter. 
The center of the mount hole  should be as close to the fuselage skin as 
possible. Say not more than about two inches in on the inside.

The bolts are 5/8 with the 22003. You can reduce this to 7/16 as per Bulents
trick of a bushing. Bulent used Delrin but I would use steel. Or you can drill
3/8 holes in the bolts stopping short of the threaded portion if the weight
seems too much. Use these types of fittings shown in the drawing where the 
mount goes through the firewall to keep the length of the bolts reasonable.
These are for the 22002 size so you will have to scale them up slightly.

Don't forget the large diameter thick washers on the inside of the firewall.

Paul Lamar
 
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