Thorp Air Command - T18.net

Thanks. I'm getting ready to make the logbook entry and am considering a statement that the the CG change is negligible. I will return the airplane to phase I testing and complete the 5 hr test period, however.

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Scott Hinton
Elizabeth City, NC
N78WG

My scales and calculator would not compute the difference between the Scott and ACS. I found I needed more ground time than air time to get use to the "new" steering.

Negligible it is. Bill I agree, but we don't want reality to impact the rules...

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Scott Hinton
Elizabeth City, NC
N78WG

Scott: working in the Canadian Air Force we often do several modifications a year. Most are fit form function types with upgraded components. Often these are negligible moment and weight changes and are recorded as nil changes. Our airworthiness authority allows for this. DND weights all of our aircraft every 5 years and in most cases these Nil changes change the 4th decimal place to the C of G. You have more effect on C of G by washing a CC-130 Herc than most modifications. Also painting a aircraft significantly changes the C of G. While I do beive in recording all changes in the weighing records negligible moment and weight changes are just that.
Food for thought.

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Victor J Thompson
C-GIRQ
"In Memory Of Dad"

BFinny & Rick Brazell : Noticed your great tailwheel assembly and would like to know where you acquired it ?? I have a basic homebuilders tailwheel ( LANGS )at the end of my short leaf springs. The centering cam hardly works at all and has alot of play in it making for a difficult landing rollout. Would love any input anyone has on making my Thorp easier to handle on landing rollout. I'm thinking the tailwheel would make a difference ??
Please let me know what yours is and where you got it....I'd like to copy it if I may !!

Thanks; Stluke

stluke,

Get tailwheel setup here... http://finetuneflight.com/Page_1.html

Tail wheel rod came from Tom Hunter. Not sure if he has anymore ? Tail wheel is the Aviation Products twin fork. See the vendor page. Spruce also sells it or you can order it direct from AP. Linkage set up is from Bill Williams. Search the Thorplist archieves and he has a parts lists...about $50.00 worth of parts....less the springs ? [8D]

RB

Save that Lang tailwheel (discarding the rest of the mechanism) and put new sealed bearings in it. Then install a Van's tailwheel mechanism and rod, using the Lang tailwheel. I have done this on 3 airplanes now--Tailwind, Pitts, and my Thorp. Great setup.

I made a front adapter from an aluminum block, and a rear adapter from 4130 heavy wall tubing. Both bolt up to the same places that the spring mounts did.

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Dave M
Sacramento
ex-T-18 owner

While Dave could be praised for his adoption of a straight round tail spring to the Thorp,instead of the bent leaf spring, or the bent rod spring; I suggest that the adoption opens the door to a greater failure mode than the Trusty mod or John Thorp's leaf spring design.

Lyle Trusty was very specific in his plans that the rear mount heavy wall tube be tied to spring via a bolt...not welded. Otherwise the rod spring is free to rotate in the rear bracket and can cause failure of the front attach point...which of course will ruin your day.

In Dave's picture, not only is the spring not tied to the rear bracket, the rear bracket is held at some distance off the bottom of the fuselage which would give more of a lever arm to any side loading the tail wheel might encounter in a cross wind.

In addition the RV tail spring is shorter than the Trusty design.

The rebound rate of the Trusty spring was engineered to match the rebound rate of the main gear...unlikely that the designer of the RV rod spring took that into consideration.

Lastly the tail wheel shown on Dave's plane has less ground clearance than the twin fork aviation products tail wheel. Obviously if that vertical face where the tail wheel mount pivots falls into a hole or hits something, the assembly is going to be subject to very real sudden stresses.

Dave, the fact that you have made this modification work on other planes in no way ensures that is is a safe long term design for the T-18.

Failure of the tail wheel on the T-18 can result in loss of your life.

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Tom Hunter
805-202-4261