Thorp Air Command - T18.net

The trusty set up is lighter than most others.
Another data point. I can weigh it if you like.
Cubes

The best thing would be if someone could post an updated W&B that showed the actual change when the swap was made but, if I had the weight and the new arm, I could pull mine, weigh it and see what the difference is.

I was able to bring mine home today. My normal 9 hour drive was just a 2.5 hour flight today

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

I posted an Excel spreadsheet that you can put whatever weights and arms you like. Knock yourself out.

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Bob Highley
N711SH
SN 835
KLAL

Thanks but I have my own. Unfortunately the spreadsheets are useless without the numbers to plug into them and your spreadsheet does not provide the info needed.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

This is what got me asking questions. If the spring hasn't sprung then I expect I will be machining a shim to correct it.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Is this without pilot and passenger, luggage?

That is empty...maybe a half tank of fuel and 2 quarts of oil stashed under the seat! It should be vertical or even tipped the other direction a little. I am going to get another airport bum to climb on so I can see how it looks with some weight on it before I settle on a course of action but I like to know my options ahead of time. I will say I am not fond of the idea of switching to the tube spring. In addition to the CG question.... Spring+new TW assembly=$$$$$ I need for other things.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

The trusty tube spring although longer is I believe lighter. So the change in CG is probably slight. But I guess that is the information you are looking to verify with real weights to prove it one way or the other.

Do you have a shimmy problem with the tailwheel as it current is?

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Bernie Fried
N18XS

That depends on your definition of "problem". It hasn't tried to shake me out of the aircraft or caused a loss of control yet but it shimmies. Some of that has to do with landing technique. I wheel land and generally keep the tailwheel off the ground as long as possible because it can't shimmy when it is off the ground. That habit came from flying aircraft with serious problems (ruin cables kind of problems).

The spring doesn't appear weak with a load...not that I would know how much flex is too much or too little but it seemed reasonable.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

YEP! What is the most common method of tracking W&B changes when equipment is replaced or added? I would have thought anyone who converted to the Trusty spring would have simply updated an equipment list or did a W&B revision making the numbers easy to get but my expectations may be a little high (some might say anal) since all of my experience until a month ago has been factory built and military aircraft.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

So I measured my fat ass hanging on to a two leaf spring with a Maule tailwheel attached. Then I replaced that arrangement with the trusty spring, collar and an AP six inch double fork tail wheel. They weigh exactly the same!! I'm surprised. But I think that Maule was smaller than most commercial tail wheels. Maybe I'm wrong.
The trusty set up moves the axel 8.75 inches aft. I guess to be very accurate, you would have to include the weight of the additional sash chain as well- which is tiny.
Cubes

One more point. Since the spring uses existing attach points, the center of that tail wheel weight would not be 8.75 inches aft. It would be something less. I'd have to try to balance the set up to determine center of mass.
Cubes

Good info Cubes. Of course you are correct about needing the center of mass. If the weight difference is that close then it wouldn't make much difference on the CG. "Negligible" would be the FAA term with no W&B update required. I am guessing the CG shift would be 1 tenth (±.05) of an inch aft. Not enough of a difference to worry about but I am going to look into fixing what I have before throwing another $500 at the bird. Thanks

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Hey guys,

For another data point, I switched from the double leaf spring and Maule tailwheel to the rod-type tail spring from Cubes and the double fork Air Products wheel as well. Checked the numbers for W&B and I'll confirm: negligible difference. Very happy with this setup too.

Les Krumel
Albuquerque