Thorp Air Command - T18.net

I hit a little snag with my Homebuilders tailwheel assembly today during the condition inspection. The bearings were bad so I elected to replace them with the advertised replacements that came with the airplane. Unfortunately, I didn’t catch the fact they are not the same inside diameter until after I had pressed them into the wheel. I checked my collection of emt and 4130 but I don’t have what I need to make a bushing. The only choices I see is to figure out the correct bearing (I don’t have a local bearing store and the numbers on the old bearing are not legible), order some steel to make a bushing or retrofit a cone bearing. Since I am on hold for parts anyway and I know others are using the same wheel, I thought I would ask and see what they had done to correct the issue.

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

I'd call Aviation Products and see what they have to say.

http://apitailwheels.com/
Aviation Products, Inc.
114 Bryant Street
Ojai, CA 93023
(805) 646-6042
apitailwheels@gmail.com

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

I believe I got my spare set from Spruce . Let me see if I can locate my set . They should have a P/N on the side of the bearing . Stay tuned .

RB

Spruce P/N 06-00060 . KSK/499502H roller bearing . Made in Japan . 5/8 axle bolt .

RB

That’s what I have. AP told me those fit the single fork model. The double fork uses a 1/2” bolt. Thanks for checking.

I went to town this morning to see if NAPA could help and ended up buying a steel nipple at the hardware store to make a spacer. I reamed it to fit the 1/2” bolt and turned it down to fit inside the bearing. When this set fails I favor converting it to cone bearings. The same bearings, races and seals found in a Scott or Alaska Bushwheel would fit. The wheel would need a slight modification to ensure wheel stayed centered on the races. Once converted the zerk fitting would actually serve a purpose and it is likely the bearings would outlast the wheel... maybe several wheels.

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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 think it would be a pretty good trick to convert that wheel to a tapered roller bearing. Even if there is enough material to allow machining the wheel to accomodate the outer races and probably grooves for a grease seal snap ring, it would be silly to do so in my opinion. The “good” bearings for these wheels will outlast the non-replaceable tire, which is what is going to dictate replacement of the tire/wheel assembly, and I think that one of these replacement industrial wheels would probably be cheaper than a set of Timken roller bearings, seals, etc. Just a thought.

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

I don’t know if I had the “good” bearings or not. Since they actually fit the application, I suspect they came installed in the wheel when it was new in 2014. They didn’t last 70 hours. My experience with sealed wheel bearings on certified airframes is that a person is better off converting to cones. I have never encountered snap rings to hold the seals in a tailwheel but Cleveland(McCauley) and ABW are the only ones I have worked having a double fork. The cup needs something to hold it though. Machining snap ring grooves there would be one option. I was thinking a press fit sleeve with a little “Bearing Mount” or other structural adhesive would get it done quicker and easier while being just as strong. The sleeve would need a hole to allow grease to travel to the bearings.

The wheel assy is a cheap caster riding on a hardware store bolt so, even though I consider them to be the best, Timkens would probably be overkill. Then again, Timken bearings and cups (2 of each) can be had on Amazon today for $75.24. One other brand is $25.99 for the same set. The Aircraft Spruce price is $239 for the same parts. I didn’t price the grease seals but they should be around $10 each. By comparison, it is $23 for the replacement bearings I used that didn’t fit. That doesn’t seem like a huge price difference for an improvement that could conceivably be transferred from one wheel to the next.

AP does stock the correct sealed bearing if you call them direct.

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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

A good set of the proper sealed ball bearings are available for that wheel from multiple suppliers. We may be luckier here in Denver than some places, as there are a number of local suppliers for the right bearings. Even the wheel assemblies themselves are available from independent wheel suppliers. They are a relatively common industrial wheel. In any case, they should be readily available on the internet. My only real point was that the proper ball bearings are just fine on this wheel in my opinion. I used to run a Scott on my T-18, and I cleaned & re-packed the tapered bearings every year. When I went to the Aviation Products dual fork wheel, the bearings lasted the life of the wheels... they lasted over 500 hours both times I replaced them. I could’ve gotten more time out of them but the tires became worn down to a diameter that I didn’t like.

I did a lot of playing around with tailwheels in the 28 years that I flew my Thorp... even built a mold & made some solid urethane tires, as well as machining a couple of wheel halves patterned after the Scott wheel for those tires, to use with the Aviation Products fork assembly. We thought the tire would last “forever”, but the problem was that the urethane would take a set and have a flat spot after sitting in the hangar for a week or so. The “thump, thump, thump” for awhile when taxiing drove me crazy. So, I understand, and appreciate the desire of some of us to improve the little wheel in the back. Just wanted to say that I came to believe that the AP wheel was actually pretty good for what it has to do.

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

I got bushings from the bearing store that go from 5/8 to 1/2. Also made spacer out of tubing to keep the bushings from working in.

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Bob Highley
N711SH
SN 835
KLAL

Hey Jeff,
Like John, I found direct replacements locally. Perfect fit, precision bearings. Been running them a while.
I can look for them if needed.
Cubes

Guys,

I have the Aviation Products, double fork system and I switched from the cast iron wheel to a Matco wheel which is much lighter and has very good quality sealed ball bearings.

Jim

Guys,

I forgot to mention that i have the solid 6" Matco wheel. I tried the pneumatic one and the tire is not very robust.I haven't been able to find anything that fits and is more durable. The part number for the 6" solid tire is: WHLP406-WD. It comes with the bushings to adapt the 5/8" bearing ID to the 1/2" axle bolt.

regards,

Jim

I learned today that Aircraft Spruce does not currently stock replacement parts for the Homebuilders Heavy Duty Double Fork tailwheel assembly. No wheels, no bearings. The bearings they sell for Homebuilders line can be used in conjunction with a spacer but they are not a direct replacement. They seem to carry wheels for every other model.

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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

Hi Jim,

FWIW - The wheels on the Aviation Products T/W's are not cast iron... they are some kind of what appears to be an aluminum alloy. The lightweight versions of the Matco wheels are lighter, being purpose-built and machined with lightening holes, etc. (starting with the 8" & up wheels) - the 6" wheels are some kind of plastic/composite material I believe. The 8" aluminum ones are MUCH more expensive than the A/P wheels also. You can get a replacement 6" wheel/tire direct from A/P (if they are still in business). I noticed that Jeff J. said they were currently unavailable from Aircraft Spruce. I also found them one time at an industrial wheel supplier here in Denver. Aviation Products is in Ojai, CA, and their phone number is 805-646-6042. They don't have a website, but an older catalog I have from them lists the 6" replacement wheels at $35, and they are available with 1/2" or 5/8" bearings. To my knowledge, the bearings that they now have are a higher quality bearing than what originally used to come on those wheels. The part # for the 6" wheel (1/2" bearings) is 6138.

By the way, the 6" light weight Matco dual-fork tailwheels (WHLT-6D) weigh 4.8 lbs. and the dual-fork 6" Aviation Products wheel is 5.2 lbs., and the A/P 6" single-fork wheel assembly is only a hair over 4.6 lbs.

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

If you search for 6138 on tha Aircraft Spruce site the wheel will come up but there is no link to follow. Just the option to add it to the cart (currently no stock). The good folks at Spruce were unaware there are 2 different axle sizes so they may decide to add replacement bearings specifically for the dual fork models or a spacer to use what they already offer. At a minimum I believe they will update the bearing description to inform people of the bearing size and/or intended use (single fork models).

R&K Industrial Wheels has almost no internet presence. Their own website doesn’t show this wheel in their product line. I don’t have convenient access to an industrial supply store so I have to rely on outfits like Grainger, Zoro, Amazon and the like. They have zero presence anywhere I have looked which makes me question how “common” R&K is. Could they just be regional?

Bearings are sold everywhere but you have to know the specs. I do not know what makes one flanged bearing “heavy duty” versus regular. I have yet to find any advertised as “heavy duty”. 120 pounds is the max load rating I have found and I believe that matches the stock bearings.

The Matco option is interesting but, looking at the Matco website, it doesn’t appear Matco makes anything in a 6” dual fork.

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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