Flying Saucer Repairs - "Gravity Resistant Flying Machine"

Thanks, got it all together and ready to test. So turns out every one of those choke style back plates is cracked where the spray bar is inserted. Even the 2 new ones I bought from cox international were cracked. So I motosealed it all together, hope for the best. If it works it works. From now on its only non chock style backplate. Engine has amazing compression. 2 head shims installed. Probably needs more run in.

Hope to have a flight report soon.

The original "290" engines, the "postage stamp" back (engines and replacements for the RTF's) were molded out of DuPont Delrin, which was almost indestructible. My 290's from the early 1970's are as good now as they were then, IMO. It appears that the earlier horseshoe backs were also made of the same material. The latest plastic of the horseshoe backs is of a different plastic, appears brittle. Since the stocks could be as old as 25 years, it is possible that the plastic became age hardened. I attempted to remove the NVA to repair a Testors McCoy Rotomatic engine from a new horseshoe back I bought a couple years ago, and it cracked.

(A common practice before was to remove the NVA and drill out the venturi to allow more air to pass, increasing the engine's power. With the back cracking would make this maneuver impractical.)

Seems that since this is a common occurrence, may be if someone in the community could make either a metal or plastic collar band that would wedge the crack shut and hold it firm, (say 0.001" undersized for tight fit) might be a good way. I don't know if the choke tube is sufficient along with cracked edge sealed with sealant to help salvage the situation.

Someone here already fixed this crack in the horseshoe backplate using a coper tube or aluminium one Not sure cant rember cool flying saucer i never se one of those

Cool deal I like the way you made your own bushing and spacers to fit , Good luck on the flights with the Kids!!

I like the idea of the tube/ring to close the cracks. Thanks. I remember reading about that on here for TD venturi bodies. I gotta get that old metal lathe going to bad about the quality issues over the years.

See if the janky fix will holds up enough, my goal was to seal the airleaks. The choke does cover the venturi nicely. Now thinking about how that engine will be freewheeling around the tank will probably apply a load the spray bar, cracked area. I do have a non choke backplate I can bolt on, might be a good idea to bring it to the field.

Here's the fixture I came up with to hold the dowel bushing for "machining." I new there was no chance I could drill the hole dead center. So I drilled the hole first, incerted the fixture with a drop of ca. Then held the rod with the drill press chuck to turn it. That way I could use a file and square off the drill press table to "true" it up, file to dimensions. According to my caliper I got it with in .1 mm good enough.

If you wanted or needed actual dimensions of the missing bearing, I can get those for you off of my UFO.

Flew the saucer today! It was a big hit with the kids. Had a few issues starting it, no fuel draw. Put it to the side for a bit then tried again and it was good to go. My guess is the read was sticking a bit or something.

It's so darn cool. It even sounds like a alien ufo. And kinda hovers around. This model needed to be run at near peak to fly properly, I thought wet 2 cycle would be good but not enough. Fun morning and all. Lots of flights, the engine should be near broken in now, and looks like my janky fix is working so far.

Thanks NEW222 appreciate the offer. Illreach out if I need to make some more.

Surestart backplate fix:

https://www.coxengineforum.com/t14591-surestart-engines-with-cracked-backplate-housings?highlight=Surestart+crack

Cool Man I bet the kids were all in to it , Never seen one but seem to bee cool for the time period .

To fix cracked venturi you can try different round ballpoint pen barrels for a snug fit on venturi. A piece of ballpoint pen barrel is enough to fix it. Sanding inside of pen barrel piece with rolled sandpaper can bring it to snug fit size. I didn't try yet, but I think that it works.

Levent Suberk wrote:Surestart backplate fix:

https://www.coxengineforum.com/t14591-surestart-engines-with-cracked-backplate-housings?highlight=Surestart+crack

MauricioB wrote:I have seen that problem on gray plates. Therefore a while ago I made this solution. You can even make it long and also place an air valve if it is of your interest. The aluminum alloy tube is the permanent and definitive solution to this problem that comes from the source.




and if you want you can place an additional air valve

Mauricio came up with a deluxe fix, plus enhanced it with a choke style throttle. Back in the mid 1970's, I worked a year in the shop of Research Corp. of the University of Hawaii's Geophysics Department. As a student help at minimum wage (cheap student labor), I helped Bert, a german immigrant watch maker, who as their machinist made parts for the UH Geo's ocean bottom seismometer project, having access to very nice Bridgeport milling machines and lathes under Bert's helpful eyes. Then they found I could do electronics, soldered components onto custom printed circuit boards for the seismometer instrumentation package.

A bit of a pragmatic practical realist   , at this later stage in retirement, affording a $500 miniature modeling lathe/mill might be quite a stretch to repair a $7 engine from the Cox Surplus Sales outlet (April 12, 2008).



But again, I am flabbergasted by the excellent workmanship done by Cox Engine Forum craftsmen.

Levent Suberk wrote:To fix cracked venturi you can try different round ballpoint pen barrels for a snug fit on venturi. A piece of ballpoint pen barrel is enough to fix it. Sanding inside of pen barrel piece with rolled sandpaper can bring it to snug fit size. I didn't try yet, but I think that it works.

Levent, that is a good bit of practical thinking on an inexpensive solution to the gray horseshoe cracked venturi problem.

Brainstorming (a lost art these days   ), I do wonder though if a ball pen plastic, probably the least expensive in the world would be be able to stand up to the high frequency vibrations and residual temperatures of a Cox .049. My initial thoughts are probably using "right sized" available aluminum or copper tubing, with gentle round filing to snug fit and a touch of Epoxy glue to lock into place.

Ballpoint pen handles are made from polystyrene or polypropylene as like as Bic ballpoint pens. Because they are seamless they are very resistant to crack. Aluminum is better perhaps. Need to try

Wow there is some excellent repairs done on this issue.

I reached out to Cox International to see if they have any good backplate left. If not may try one of these fixes if the engine acts up.

Here's the crew from Sunday Funday. All 3 generations were out.