Patrol/LSA Tail Spring Setup

[lsa140]

I'm at the point of deciding which tail spring mount to fabricate on my LSA. Plans call for a tapered rod spring with a welded in mount. The design looks very clean, light, and low drag. That being said, the only spring/suspension option for that setup is the round spring. A standard leaf spring mount would allow a bolted on stinger mount, a leaf spring, or something like the T3 suspension system. I would also have more options with the leaf mount if a field repair was required. I'm curious if anyone has some ideas or thoughts on the matter.

It looks like the tapered spring locates the tailwheel closer to the rudder. I can see where this reduces drag, and provides for a little better angle of attack. Is there sufficient distance from tailwheel to rudder to avoid interference on a gross weight landing on rough terrain? Obviously, you hit it hard enough, and things will conflict. Just curious if those flying the stinger type tail spring are finding they have sufficient clearance. It looks like the spring is shared between the Patrol and LSA, so I'm sure there is plenty of strength for my 1500 lb gross weight.

I think someone mentioned the stinger type of design can sometimes wallow out the bolt hole where it pins the spring to the fuselage. Is this something that could be improved by adding a little more material to that area?

It is tempting to stick with the plans, but it would be a lot easier to make a change at this stage of construction.

[Mark Goldberg]

I might suggest you trust Bob's engineering. My thought is the same as you said - with 1500 lb gross the same spring is very strong on an LSA if it is beefy enough for a Patrol at 2,000 gross. Mark

[lsa140]

Thanks for the input Mark, good advice for sure.

[stinger]

lsa 140: I bought my tail wheel system from Aviation Products Inc. 6" double fork,20* round tail wheel assy. Tail spring , round 7/8-5/8 taper. for $380.00 .There are two different degrees of mounts for you to choose from, depending on the degree you weld your receiver on. You will not have a problem if your receiver and taper stinger match good and tight . Hope this helps. Stinger

[lsa140]

Looks good stinger. Thanks for the info. I like your hangar, looks like a great space to work in.

[lsa140]

I do trust Bob's engineering, but also appreciate the freedom that scratch building allows. Cub parts are available everywhere in my area, so I seriously considered going with the leaf spring. I believe Steve Wittman pioneered the use of tapered, round steel springs for both the main gear and tail. The Tailwind uses a similar setup on the tail. I know some have experienced cracking of the receiver socket. I think the Tailwind plans call for the same size receiver tubing, but it doesn't have near the reinforcement Bob designed into the LSA/Patrol. Gross weight of the Tailwind is very similar to the design gross of the LSA. A lot of Tailwinds use tiny, hard rubber tailwheels. I imagine this transmits some higher frequency vibration through the spring. It also has a much faster takeoff/landing speeds.

I will be running the tundra tailwheel, and spending a lot of time on beaches and gravel bars. I've decided to go with the tapered spring, and incorporate a few of the thicker tubing sizes used on the Patrol in that area. I'm sure the LSA is plenty strong as designed, I just wanted to have a little more metal to resist fatigue and cracking. I'll also be paying close attention to the applied heat, and stress relieving that area.

Here is my tail spring socket. It uses a thicker 1-1/8 x 058 outer tube. There is a little more info on my build thread: http://bearhawkforums.com/forum/bear...40-build/page3