rc lifer

Hello guys. I have a Super Tigre X.11 that I need a head for. It is the blue anodized head I am in need of, or un anodized. I like the small power house engines and would like to get this one running. I bought it off feebay without a head, thinking I could use the head from my worn out ST X .11 BB, but it wont work. I found there is a difference between the BB and PB engines besides just the bearing, different case .So if you have one please contact me.Thanks

Mr Cox

I don't think that the plain heads, non BB, will fit either. They really changed the design a lot from the first blue head ones. The blue head protrudes a lot into the cylinder and there is no squish band. They were also very low on the compression ratio. The later plain head ones are better, while the BB ones are real gems...

Here are some images I had on my computer of the plain bearing ones, the blue head one is a little disappointing but the plain head one is very strong;

Mr Cox

I took the head off on one of my "spare" engines with plain head. It is very similar to the BB ones. The head does not protrude into the cylinder and there is a squish band etc. It looks like the first blue heads ones very abandoned completely. The performance was also very low and there were no engine reviews with actual running data. I have understood that the policy was to not publish really bad test data in order to not ruin the reputation or collaboration with engine makers, instead the journals would only write a preview where they didn't run the engine...

On the one Blue head engine that I have, I put the head in lathe to increase the compression ratio. It went from useless to possibly useful but nothing near the performance of the plain head ones.

rc lifer

Thank you Mr Cox, I had a blue head X11 in the early eighties and I broke the crankcase in a crash the first tine I flew it. I never did get to know the engine very well before that, just bench run-in. I have purchased three off ebay and the first two were completely worn out and useless, NO compression. Nice little carburetors though. I modified an OS FS .20 and a OS 26FS to run with the X11 carb. That made the little four strokes really stand up. Made a good thing even better. That's another story. Have you ever run an ASP.12, I found one on Feebay a few years back and have yet to run it. I got lucky with the ASP, its in great shape. Thanks again, the pics are helpful.

Mr Cox

Yes, the APS .12 are very nice engines, they are set-tup for low nitro and small props. The true ABC technology and dual needle makes them a little nicer than the OS .10 engines. The X.11 are a little stronger than both though, and they throttle very well with their midrange adjustment and all. It is just the blue head which they didn't make right, I think.

Here are some typical numbers on 10% nitro, stock mufflers, and an APC 7x4 prop:

APS .12 (one extra head shim); 16500rpm
ASP .12 (one shim under the cylinder); 17200rpm

ST X.11 (plain head); 16800rpm

The ST blue head is way too low on compression, it is only 7:1, and it was changed to 8.5:1 in the plain head ones.
But one can change it quite easily on a lathe. I removed 0.1-0.2mm (if I remember correctly) and then I got about 14000rpm on the same prop as above.

There is a test of the plain head in MAN (1985) where they also explain why they didn't publish any report on the earlier blue head (made around 1980);

rc lifer

Thanks again Mr Cox. That covered everything I wanted to know about the X.11. The MAN article was insightful. Also thanks for the stats on your running of the ST and ASP. I am not so much concerned about maximum performance, as reliable operation and good throttling. Sounds like the ASP is close in performance. May be I should use one of my Norvel 074 engines in the Jr. Skylark I have framed up, it would sure be lighter than the ASP or the ST.

hllywdb

Even the 074 is over kill for a jr skylark. They were built for rudder only and the power of an ok cub. An 061 or even an 049 will fly it fine. The 074 will work you will just be at 1/2 throttle most of the time. You will also want to set the wing and stab incidence at zero. They came with positive incidence to climb out under power then settle into a slow glide after the motor quit.

rc lifer

Ok thanks for that. I was wondering if changes would be necessary to make it a good flyer. I have a nice TD 051 with a Hiscot Trottel, I was thinking of using that but the Hiscot unit chokes the TD some. Not as much thrust as a straight TD. I dont want to be under powered. it would be simpler to make it electric, I have some fine fling e-powered planes. Running the little engines is a lot of fun though, and I have some I havent run for many many years, the Hiscot/TD being one. In fact it has been more than 20 years since I flew the H/TD in a little three channel trainer type airplane. It really did not have a great rate of climb, but once it got up it was fun. I put trike LG on it with a Dubro 1/2a steerable nose gear and it was fun making touch and goes and fun to taxi around.

aspeed

I still haven't tried my Jr. Skylark. It came with a Queen Bee .074. I think that is about right for it. It wouldn't run when I bought it. It does now though. Maybe I'll try it tomorrow in the garage, its only been sitting for about 8 years. Sounds like your .11 would be a good candidate for a completely new head with a turbo plug. Probably take a couple/few hours with a lathe.

rc lifer

Aspeed. Yes a new head would fix it up for sure, but I don't own a lathe. If I had one I could probably get a head hacked out. I would like to find a Sherline hobby lathe that was affordable, have not as yet. I need a good drill press and a band saw, a bench grinder and a 4 or 6 inch belt sander and then I could make most anything I need. Thats why I posted a request for a head, thanks for your input. Your Skylark Jr with a Queen Bee sounds like a good combo. I had a Queen Bee and was not able to get it idle well, I gave it to a modeler friend and he used high temp silicon sealant on the carb parts and that fixed the motor right up. It ran pretty fair after that. That was about 30 years ago. Cox never did come out with a good carb for the small engines, not that I know of anyway.

aspeed

I tried to run the QBee today. It was about freezing out, and the crank seized up a few times. It doesn't idle down much either. It ran ok on the test stand a couple years ago with no muffler. Maybe the muffler is the problem, I need one at the field where I fly, I guess I could drill it out, or replace it with a Norvel, or leckie (oh noooo) Tried the TD head, and the regular 1/4 -32 plug head, which seemed faster oddly enough. about 13,800 with a 6 - 3.5 prop. and muffler. It was 15,300 with no muffler a couple of years ago.

Mr Cox

You might have to check the reed valve if it has been sitting for a long time without being used.

The carb needs a low end-compensation and then it works okey at least. You can do this by making a fixed airbleed and/or enlarging the top orifice in the carb. The muffler didn't hinder it much, when I tested without, but I got the best results by using a Turbo plug rather than the regular glow plugs.
On glow I have the following numbers written down (10%Nitro);
graupner 6x3; 17000rpm
graupner 6x4; 15800rpm

It runs much sweeter though as a diesel engine, the RJL head is a direct drop-in;

https://www.youtube.com/watch?v=KLFfH1vQKSY

aspeed

It didn't run at all when I first got it. Then I took it out of the plane and freed up the reed etc, and it worked ok on the stand with no muffler. I don't remember how the throttle went then. Right now the throttle is more of a shutoff. I wrote down 15,400 with no muffler, and was kind of happy with that. Now the crank seizes up. I think I have to take the motor out of the plane again and remove the screen to try what you mentioned with the carb, maybe opening up the plastic bore on the top, right? Maybe I can open the muffler a bit too, and lap the crank. Not sure if I want to continue flogging a dead horse. Maybe I'll check to see what else fits on the motor mount. Norvel, or one of the TT .07's maybe. Sorry for hijacking the thread, but I have been looking at this plane for so long, and want to see it go, even if it is only once. I have a lot of planes like that from swap meets over the years.

Mr Cox

Here are two mods that one can do, I thought it would be too much to do them both but it turns out that the description is pretty accurate;

Mr Cox

There is another problem I had when bench running, the throttle will go well past full throttle...

Once in the airplane with the screen off, one can easily use the servo endpoint to adjust for full throttle (rather than the throttle stop).

aspeed

Yes I will have to take it out of the plane and do that. 3/16" is good to know, thanks. Not sure I will put it back in the plane though. Screens are good and bad. The Norvels are hard to see through as well. I kind of like to leave them on, but never do because you can't see anything. Just an update, It works fine now, squeaked up to 16,000 with the TD head, and idles nice with a .040" airbleed, .187 top hole and no screen. Had to use a flashlight to get a tach reading in the garage at night. Tried to scare the possum out unsuccessfully with it. It just played possum. I think I will use it too in the spring.