Thorp Air Command - T18.net

I see a lot of info on the tube springs (Trusty, Van's...) and some on the 862 steel leaf spring. Is anyone using or have information on the 589 aluminum spring? Was there problems with 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

My aircraft had one when I purchased it, it now has a Trusty spring and AP tail wheel. It is a spring in name only, I don't think that mine moved at all.

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Bruce Finney
N18JF T-18C #262
Yelm, WA USA

They are heavy, hard to make and expensive.
Cubes

What Cubes said plus this from the "Old Forum." Great resource , more people should use it .

RB

BOOM , CHICKY BOOM !

I hadn't seen the "old forum". I had seen references to it but posts about issues with corrupt files and such with the "move" had me under the impression it was gone. I originally got here through the thorpcentral.com "support" button. I found the "retired" forum this morning on thorp18 site and will make use of it.

Thank you everyone for the input.

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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

Rich,
Good find, I had forgotten about my previous post on this subject, particularly the info from Tom Hunter. The archives hold a wealth of good info.

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Bruce Finney
N18JF T-18C #262
Yelm, WA USA

Thanks Bruce . Remember I am always right at least 50% of the time !

RB

If there is an option that is lighter than the 862 gear and keeps the tailwheel in the original location, I would like to hear about it. Before anyone suggests putting one of the long spring tubes on it let me remind you my bird is already tail heavy and extending the arm of the tailwheel will not help me pull the lead off the engine.

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

What tail wheel are you using? There are some very light tail wheels out there, A/S has one at 3 Lb's

Tailwheel assembly is the homebuilders double fork from Spruce and it has caster angle issues. Quick measurements of the spring have me believing the wrong angle was purchased and installed in 2014 (I was probably the first to fly that set up last month). At 5.2 pounds it is one of the lighter options I have seen without dropping down to a 4" tire but I mostly fly off of grass strips and not all of them are kept mowed short nor are they as smooth as paved. I am not as concerned with removing the weight as I am with not making the balance worse. I just thought I would explore some options since I have to fix the caster angle anyway.

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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

Jeff: So at this point we don't know what the tail weighs on the scale ? Something just doesn't smell right with this set up . Can you take a pic of the entire tail wheel assembly , including what type of spring you have on it . It may be a "non-standard" spring on it packing some addition weight ? You said this had a V-6 engine on it so is there any chance some addition lead weight was added internally to the horizontal stab or maybe the horizontal mast has a larger weight on it ? Just thinking out loud while sitting on the round throne waiting for the election results !

RB

I will have to search through the old receipts to see if I can find what the original tailwheel was. Judging from the way the aircraft was built I would guess it was the Scott 3-24. The existing tail spring is steel leaf and meets the dimensions on drawing 862. The airplane was tail heavy when it was built and had an O-290 installed. The V-6 actually improved the CG but now the re-installation of an aircraft engine has returned it to being tail heavy. No, I have not actually weighed it. I wasn't having any luck getting the scales down so out of curiosity I took a bathroom scale to the hangar and learned the tail is ~100 pounds in the 3-point attitude with about 15 gallons in the fuel tank but that is as close as I have gotten to actually weighing it. After looking through the drawings I have come up with a couple of theories about the extra tail weight but I am currently 520 miles from the aircraft and cannot verify them. Lead added to balance the control surfaces is one of the theories.

After reading Rich's post about the mast I went looking for that drawing to see what was there. Drawing (510) is currently MIA (not in the "horizontal tail" folder). So I guess I will be doing a drawing by drawing search this evening (possibly reorganizing by number in the process). I did a pretty good look for ballast in the tail and did not find any but I must admit did not look for extra weight added to the mast. I wouldn't have realized it was extra if I had noticed any there anyway.

Fixing the TW caster angle is at the top of the list... right next to replacing the broken spinner bulkhead and removing the radiator mount. I don't think there is a problem with the current W&B sheet so borrowing scales isn't as high of a priority. If scales were handy it would have been done already but the aircraft flies fine so I will get to it when I get to it. If I do solve the W&B puzzle I intend to post the findings.

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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 have been checking with as many thorps as I can, and have found 45 Lb's for the tail is about the norm. My tail weight is about 38 Lb's and is to light (o360 and C/S) I have done a lot of work on the plane and need to re weight it and check the W&B before the next flight.
Phil
118BC

I found the same thing when I looked into it. Assuming mine was properly leveled at the last weigh-in (I believe it was), it is 67 pounds. Since it is within the CG envelope and there are an unbelievable number of possibilities to account for it. I decided to not worry about it for the time being... other than to avoid making it worse.

Binder made a post that made it sound like his T-18 is heavier than mine in the back.

I may not actually do it but, I have been thinking about calling Grove to see what they might have to say about an aluminum tail spring. They have main gear legs made out of much thinner material than the 3/4" called out in drawing 589 supporting a lot more weight on a longer lever than would be required in this application.

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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

Here's a couple for you.

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Bob Highley
N711SH
SN 835
KLAL