Thorp Air Command - T18.net

John Evens, do you have any specs on that Inertia ring you carvred out, OD ID Thkness and such, I believe you said you just used a-36 cold steel to cut it from. Seems I got a hankerin to do some cuttin. Good show on the Sedona Flyin Rich! from what I hear I really missed out and all had a jolly time. You also did a good job on the write up!! Dan

Cubes has dimensions from the steel ring I recently sold. It's 11 lbs finished. I placed the ring on a Manila folder, traced it- he should be able to give you the sizes.

T

I'd have to measure it next time I'm at the hangar. I didn't make a drawing, and just made it from some notes... I copied it from one sold by Mark Landoll. It was so long ago that I'm a little fuzzy about the dimensions, but 11 lbs. sounds about right. It was just a hunk of steel plate I bought at a salvage yard - they sawed it into a square for me & I took it from there. Man, that was tough to rough out in a circle with my homemade bandsaw, before the lathe & mill work. Probably should have cut it with a torch.

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

Thanks John, I have a buddy that will make quick work of it with his water jet, holes and all. I will do finish on it with the lathe. Yours worked out so I figured if I done one like yours all will be good...Dan

Danny,
I'll send you Terry's trace if you make me one.
Cubes

Does this damper mount on to the ring gear or the crankshaft flange? I would imagine that it has to be machined very precisely to avoid an imbalance condition. If it's on the ring gear, what is the plan to compensate for the clearance that is present in the ring gear bolt holes?

Just wondering.

Jim

I can make a couple of them I just wanted them to be just like Johns to try and match the performance that he gets, John didnt you have a Pic of your install there are some questions here about clearances......if your trace is the same as Johns Cubes it should be fine..Dan

Yeah. Mine is from the mark landoll ring as well. He no longer produces them. Was looking into making some to sell. Not sure of the market.
When I had the balancer installed (16lbs) it gave me an additional 100rpm.
Cubes

I'll see if I have any pictures in the morning... I'd sure like to take some measurements & write them down/keep them this time, so if it's not too late for you, I'll try to do that - probably this weekend. I had no clearance issues whatsoever. Yes, the ring bolts to the flywheel/ring gear assembly on the back side, and utilizes the existing holes. Some older flywheels may not have the holes (my engine is a little over 30 years old). Yes, it's very important that it be machined true, and the holes located very accurately... after the lathe (it takes a pretty big one - bigger than my little guy) I used a milling machine/jig bore & an indexing table to do that. I also balanced my entire assembly dynamically with my ACES balancer. Like Cubes, I picked up RPM, and hence usable horsepower by adding the ring. The Lyc likes the additional angular momentum over that with just the lightweight Aymar/Demuth prop. It also idles a little more reliably & smoother at a lower RPM.

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

I'm not sure what clearance you're talking about, Jim.

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

Thanks John! That will be fine can wait till next week no biggie. Cubes I will take the info that you have also if you want to send it as many woodie props that we have out there I would assume that there will be a few other folks that would not mind having one also. Im just trying to get all of the info on this ring that I possibly can before I start the process of building a couple. I have done some research and found that what John & Cubes have to say on this subject is spot on, myself, I am looking for a smoother Idle, and if there are other benifits well that is ok too.....many thanks Dan

John,

I was refering to the holes in the ring gear. I believe they are clearance holes for a 1/4" bolt.

Jim

Forgive my confusion, but when you say clearance holes, do you mean that they are oversize or a loose fit for a 1/4" bolt? I'm just not sure what the concern is... please try one more time, Jim.

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

Hi John,

On my ring gear there are 1/4" holes around the outside of it. I believe there are 12 of them. These holes are slightly larger than 1/4" to allow for AN4 bolts to fit. With a regular AN4 bolt in any of these holes there will be clearance between the bolt and the hole. This will allow the damper to be slightly off center and hence will result in an imbalance. This can be balanced out but if the damper is ever removed and re-installed it will have to be balanced again. The balancing process usually involves drilling holes on the heavy side to attain balance. Subsequent re-balances may result in a damper that can't be balanced.

Jim

OK, I've got it Jim. I just couldn't imagine exactly what you thought the issue was. Your holes may be larger than normal, but I just haven't seen that issue. It is true that they are not close tolerance holes, but I haven't had any problem with that in many hundreds of hours (close to 1000) with my installation. There are many others also using those holes for the same purpose, & I haven't heard of any related problems. A couple of points: Once I got it mounted with bolts in every hole, I don't remember any discernible possible movement before everything was tightened down. I could be wrong. While it is true that the ring gear assembly is balanced by the manufacturer by drilling material off of the heavy side, that is not how we balance in the field. Those holes & bolts are ideal for adding balance weight in the form of washers. Just as with my propeller, I indexed the ring to the ring gear assembly with some marks. I don't really expect to ever have to take it off anyway, & never have, but it is easy to re-balance if necessary. Of course you should try to choose bolts with the best fit for your particular parts. SAE grade 8, or even grade 5 would be fine, strength wise, & if you find some that fit better for you, then so much the better. That is just my opinion, and you have to make your own choice about those things of course. I believe I did use AN bolts... I'll take a close look tomorrow, & also take some pictures for the group.

One other point... the steel ring is not a "damper"... it is merely a weight which adds to the rotating mass. The direct drive Lycoming with the light weight propeller likes that.

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