Thorp Air Command - T18.net

Loose chains are for Champs, etc. Thorp's require a snug chain. I've got 1267 hours on N30WW and the chains (cables) have always been tight

I've mentioned my little theory on steering springs before. There weren't many comments, but I thought I saw some rolling eyes between the lines.

FWIW, in January I did a little experiment with the ACS so-called "compression" springs which came with MLM-P. In my humble opinion, they are a little stiff for my taste, so I wanted to see how stiff they actually were. They measured roughly 90 lb/in for spring rate, but interestingly they had A LOT of hysteresis.... basically because of the friction with the square wire bales that encapsulate the spring.

I also measured the hardware store tension springs that I bought for my taxi trials. The measured spring rate on those was about 14 lb/in, with no hysteresis that I could measure. I liked the feel of the softer springs much better, and maybe they were even a little on the soft and spongy side.

My theory is that there is an OPTIMUM spring stiffness for the T18 to get a good steering response whenever the tail is on the ground. Consider the extremes: First, no springs, just cables... I think everyone would agree that this configuration would be ... twitchy, to say the least. (Especially in a cross wind when the tailwheel touches. Ouch.) Now consider the other extreme: No cables, no springs, just the aerodynamics of the rudder to steer. I think we'd also agree that this would be a painfully unresponsive steering configuration. The best feel (which also has a subjective aspect) is somewhere in the middle. So, again, I think there is an optimum spring rate for steering springs, and in my no-thorp-time unqualified opinion, it is less than 90 lb/in.

Feel free to disagree.

Before I get comments regarding compression springs vs. tension springs, from the safety point of view.. not to worry, when I finally get MLM-P to an airworthy condition, I will make sure I address the problem of a broken spring somehow. I sure don't want to ever lose steering on a roll-out.

Cheers!

D

I have the "stiff" ACS springs and the cable/turnbuckle setup. I find the 90lb springs just fine, not twitchy at all.

In contrast Wendell's airplane has softer springs (still from ACS years ago but noteably softer). I find his airplane spongy at times even though the chains are tight enough to compress the springs 1/4 on the ground.

That tailwheel is your friend, I like as direct an input as I can get.

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD

Well, I kinda agree with Dick from a standpoint of having something too tight - case in point was after having tightened up the turnbuckles on Dick's plane at one time during the experimental stage of tailwheel rigging, I had the springs compressed just s sniglet and a clip break off as I castered the tailwheel pulling up to my hangar after a flight - had that happened during rollout, I'd have been eff bombing my way back to the hangar and off to the licker store for a good sound drinking lesson.
Hence, I just tightened them up to take the load off the clips and the spring after that. Tight gives ya good quick feedback, but no need to compress the springs at all. IMHO.
That setup has allowed me to land in an approx 25 direct X-wind in Mesquite NV.

Good luck with those sloppy chains guys! I can tell you I've personally been in a Thorp that ended up in a ditch due to sloppy tailwheel linkages and that was at a slow taxi.

The way I understand things landing in a 25 kt direct crosswind is due to your Scottish pilot skills and rudder. The tailwheel comes into play after the plane is no longer being controlled aerodynamically. I don't think you can attribute the non-tight chains to your success there. IMHO if that little clip broke because it had a few lbs of pressure on it ... it was defective, I don't really like those little links anyhow, hence the SS quick link mentioned above.

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD

Not sloppy, Lee - just not putting any load on the springs in the neutral position. And you are prolly correct - a defective clip.

Well here's how I see things (gravity). If you have no tension on the springs with no one in the airplane, as soon as you put one or two 170 lb humans and maybe be some luggage in there; you end up with sloppy chains.

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD

Good point Lee - I had forgotten about that