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Thinking inverted engine

Post  score15 on Fri Jan 02, 2015 12:16 pm

Hi.
I have a reed valve cox 049 with an air restricting carb. I was planing to mount it inverted in a small warbird but i read that this is a bad idea as at lower rpm it gets rich, floods the glow plug and the engine quits. would i have the same issue if i mounted it on its side, its just it would look awful with a cylinder sticking out through the top of the cowl.

Thanks and happy new year.
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Thinking Re: inverted engine

Post  balogh on Fri Jan 02, 2015 1:13 pm

I think with a properly set needle valve the engine, when throttled, should not quit/get hydraulically locked no matter where the cylinder points.

It is true though in principle the engine would get hydraulically locked less-likely when running rich with the cylinder positioned horizontally. I personally like even this engine position as it reminds me of a Boxer type engine.
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Thinking Re: inverted engine

Post  Surfer_kris on Fri Jan 02, 2015 1:49 pm

If it is the Cox sure start with intake choke, then I guess it will not run well inverted. That contraption is not a carburator, it merely chokes the engine to reduce the rpm and I don't think it will work well inverted as the fuel will cool down the glow-plug.

Rotated to the side (horizontal cylinder) might work similarly to the upright position though. The best thing is to check all of this during bench running before you install it into the plane.

You cannot expect to get any real throttling with these contraptions, it is merely a way to vary the rpm somewhat.
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Thinking Re: inverted engine

Post  roddie on Fri Jan 02, 2015 1:57 pm

Some throttle types (such as the Ace-venturi-style for the Cox Bee's) recommend the use of a muffler to hold heat in the cylinder at lower engine speeds... but if you have a cylinder/piston-set that has sub-piston induction (SPI), it won't run well with a muffler.

You can check to see if the engine has SPI, by positioning the piston at top dead center, and check to see if the bottom of the piston-skirt raises above the exhaust ports on the cylinder. (it helps to hold the engine between a bright light source to see if there's a gap) If you can see light below the piston skirt, you have an SPI cylinder/piston.

If your planned (inverted) cylinder arrangement is totally cowled-in.. then the engine may run hot enough without a muffler to use the throttle. You might try experimenting with fuels having a different nitro content, to see if you get better performance. You can also set your throttle-trim for the best reliable idle before the engine starts to load-up. A really low idle is a cool scale-like effect if you can reliably achieve it.. but the reed-valve engine's power-band is pretty narrow.. and you may not want to go below 6K rpm anyway. For ground-handling; you may find that you need at least 6K to get the model rolling.. depending on it's weight.

I hope this has been of some help. I like the scope of this project!! Best of luck!!



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Thinking Re: inverted engine

Post  GallopingGhostler on Fri Jan 02, 2015 2:48 pm

My observations of at least the Ace exhaust choke throttle sleeve, which a similar one Bernie has, even though non-linear really doesn't make much of a difference on a half-A plane of nominally 36" (915mm) wingspan. There isn't much difference in speed between glide and power up climb for a Cox reedie. So, the non-linear response of the choke tube throttle might not have a great impact for concern.

Kris has a good point. I'd bench run it in the various positions to see if it will run reliably. That will help resolve that issue prior to mounting in the plane. It is easier to hydraulic lock an inverted engine, although it may look cooler. A hydraulically locked engine is easily damaged. Given me sometime insistent stubborness in starting a difficult engine, it would be easy at least for me to damage it. At least a side winder allows fuel to drain, especially if exhaust slits are to the sides of the engine.

I think a problem may occur if idle is extended, engine might quit. Bench running would verify that. Don't mean to offset the cool factor of an inverted engine. If you can get it to run reliably inverted, then by all means do so. I just know my propensity to damage things.

My Cessna 177 CL build with Enya .09-III TV (throttle wired wide open) is an inverted engine build for cool factor. Laughing

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Thinking Re: inverted engine

Post  rsv1cox on Fri Jan 02, 2015 3:00 pm

I run a pair of almost fully housed, inverted but unrestricted Golden Bee's on my P-38 with zero problems.
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Thinking Re: inverted engine

Post  GallopingGhostler on Fri Jan 02, 2015 3:29 pm

rsv1cox wrote:I run a pair of almost fully housed, inverted but unrestricted Golden Bee's on my P-38 with zero problems.  
I hear you, surmise that running inverted is nothing new. Many of Walt Musiciano's Scientific half-A CL kits show inverted OK Cubs and Babe Bees. I guess the issue is how it runs with the choke tube throttle, as it would tend to run richer at idle.

Today would be an ideal day to do engine runs in the garage, given the sub-freezing weather. Unfortunately I don't have a choke tube throttle to play with. One thing I do need to investigate is how well A.C. Gilbert engines run as sidewinders. I am told they prefer upright running with venturi above the tank. Just hate drag out all the stuff (motorcycles, car, etc.) so they don't get coated with Castor oil fog. lol!

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Thinking inverted engine

Post  score15 on Fri Jan 02, 2015 5:22 pm

Thanks for the replies.
i figured that it might not be the best idea to run it inverted but i think on its side is the way to go. The plane is intended to fly until the fuel is all gone, but i would like throttle control as the plane is at the smallest end of the recommended wing span range,
i don't want a rocket ship. Could i set the throws so flat out is only 3/4 throttle and then the difference in mixture change is smaller.

please ask if i said something you don't understand.

i will bench run the engine at different angles and throttle positions.
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Thinking Re: inverted engine

Post  rsv1cox on Fri Jan 02, 2015 5:24 pm

Let us know how those Gilberts run at 90 degrees. I have a couple that I have to find the proper plane to mount them on.

Bob
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Thinking Re: inverted engine

Post  Surfer_kris on Fri Jan 02, 2015 5:33 pm

I run inverted engines too, one can simply turn the plane upside down while starting in order to avoid hydrolocks etc.

During running though the idle is more sensitive to a correct fuel ration compared to an up right position. It can also be a little tricky to get the fuel tank at the correct height. A horizontal orientation is very easy to use and looks good to. Don't know how/if that is different in CL applications.
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Thinking Re: inverted engine

Post  GallopingGhostler on Fri Jan 02, 2015 5:45 pm

rsv1cox wrote:Let us know how those Gilberts run at 90 degrees.  I have a couple that I have to find the proper plane to mount them on. Bob

Bob, I'll provide an post run report when I do it. It's snowing now and looks like weather will be less than optimal next few weeks, so may have to do that sometime in Spring. Got several NOS discontinued Hayes long engine mounts for the Gilbert .11 and .074. This will simplify mounting to an engine bulkhead and routing fuel plumbing. The high mounted venturi has kind of stumped me, makes all sorts of challenges involving fuel tank installation. These Hayes mounts resolve a lot of that. Also got the Sig two part long "T" engine mount for .15-.25's, which would also work. - George

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Thinking Re: inverted engine

Post  Oldenginerod on Fri Jan 02, 2015 9:01 pm

It would seem that the Gilberts prefer to draw fuel from below, so as long as the fuel level is below the veturi, I don't believe it will cause any issues which way they point.
I had the discussion a while back over on .049 Collectors about which Cox (and other) horizontal cylinder orientation works best for C/L, inboard or outboard.  There were very mixed opinions so I think the jury's still out on that issue.

The melting Rod. Hot
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Thinking Already done!

Post  dinsdale on Fri Jan 16, 2015 8:26 pm

I've been running a couple of them inverted for about a year now.  With very little modification to the plastic back plate you can invert the engine but still have the "carby" and mixture screw poking up.  It works a-treat!  I went further on one of them and reduced the height of the induction tube, reamed it out to size and refitted the carby.  I also shortened the mixture screw.  My bench testing (which only consisted of rpm measurements) showed no measurable change in performance.

I forgot to add that I use the standard glow plug adapter heads with short plugs with idle bars (I like idle bars on all of my r/c engines. Most people reckon they're a waste of time, but they've always worked for me.). One is a pusher and one is a tractor. I didn't even think of most of the things mentioned above. I just did it and haven't had a moment's angst since.

Disclaimer:  I use my 2 on r/c airboats (swamp buggy style of thing).  I wanted to lower the CoG (inverted engine) but still be able to prime the engine easily for starts and to have easy access to the mixture setting (upright mixture needle).  I also bought a couple of choke tubes and carbies, as separate items from Bernie so that I could play around with them.  I'd have to go up the the shed to remind myself exactly what I did to the back plates, and that ain't gonna happen just now - sorry Sad
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Thinking Re: inverted engine

Post  GallopingGhostler on Fri Jan 16, 2015 10:18 pm

dinsdale wrote:I forgot to add that I use the standard glow plug adapter heads with short plugs with idle bars (I like idle bars on all of my r/c engines.  Most people reckon they're a waste of time, but they've always worked for me.).  One is a pusher and one is a tractor.  I didn't even think of most of the things mentioned above.  I just did it and haven't had a moment's angst since.

I've used those too. They work fine, if one doesn't mind a slight drop in RPM. In fact, I wouldn't have any problems using a glow plug head on a Sure Start to power an RC plane that used a Cox Tee Dee .020 on it, like Ken Willard's Virus. Used it on a Norvel .061 when I lacked a proper head button.

I also bought a couple of choke tubes and carbies, as separate items from Bernie so that I could play around with them.  I'd have to go up the the shed to remind myself exactly what I did to the back plates, and that ain't gonna happen just now - sorry Sad

If like me, you probably put it in a safe place. It will pop up sooner or later. Then you'll be amazed or embarrassed where you put them. Very Happy

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Thinking Re: inverted engine

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