Alternative Engines?

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Cross Check

Post by Cross Check »

Hi Scott,

Thanks for the great 'combat worthiness' review of the GMS. Looking fwd to the flight performance results.

The Q-25 Pylon racers also use the OSFX and are looking for a replacement. Here is a link to the OSAX performance with some comparative #s on the second page for the GMS:
http://www.rcuniverse.com/forum/m_8890850/tm.htm

If you don't mind some questions:
-How do the mounting bolts/distance to prop match up between the GMS and the OSFX?
-Are the mufflers interchangable?
-What makes the GMS 1.5oz heavier than the OSFX? (Muffler? Heavier crankcase?)

Your LSneedle experience reminds me of a 'fix' on the old (Y2K era)GMSs that we had a hard time with...(the then $160 FXs would have been allot cheaper in the long run !!! HeHeHe)
The LSneedles would vibrate in/out and play havock with the HSneedle. Fix was to set the LSneedle, then CA/Goop it in so it would not move.

Thanks for taking the time to check out the GMS Scott. Much appreciated.

Anyone have any news of the possible Magnum replacement for the OSFX?

They did a great job with the MagGP.25 vs the OSFP.25...
(fingers crossed, touch balsa...)

Take care,
Have fun,
Dave'crosscheck'Fallowfield
Maac 6437
Unabashed Combat Team
Vapor
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Post by Vapor »

Nice report Scott!
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dirko
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Post by dirko »

Thanks for sharing, Scott.
Hat Trick
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Post by Hat Trick »

Sounds promising. All the GMS's I've seen other guys run could barely get out of their own way!
Yankee Samurai
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Post by Yankee Samurai »

My friend has one, it has been modified. Will turn a 8 x 5 19K on 25% nitro and mousse can.
sgilkey
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Post by sgilkey »

weather cooperated so i got some test runs in. all runs are with OS plug, temp about 60 degrees.

1) baseline 1x.004 shim, 5% nitro, MA 10x4 G/F3 13.6k

2) remove shim 13.7k

3) go to 15% nitro (still no shims) 13.9k

4) change to OS .32 carb (still 15% and no shims) 14.2k5) 9x4MA G/F 2, 15%, no shim, 32 carb 18.6k I'm guessing this would be maybe 18.3k on stock carb

Overall the power on a 10x4 is not quite up to most FX but it's fairly close. Hard to say since the air temp was cold. My typical 25FX LimB/2548 setup all this year has been OS plug, 5% PowerMaster and on that I usually get a solid 14k, which is perfectly adequate. In these classes you can be 500 rpm down from peak and still get excellent performance, and it's so much easier to not have to worry about juggling fuel, breaking out, etc. Plus the 5% is cheap, and the fuel economy is impressive! (as a side note, Brian was flying his FX-powered Open B planes on 5% at our last meet and was using less than 4 ounces.) Anybody who's had to chase, or been chased by, Eric or Brian at Lim B meets may have noticed they are generally a little slower than most other planes. That's not been a real problem and they still score well. It lightens my workload as pitman and that's the real beauty of these two classes- you can be 500 rpm off and still do well! Whereas in SSC if you are 500 rpm down you will see a noticeable drop in pulling power.

Anyway overall the engine behaved nicely, ran clean and smooth and seems like a decent prospect. I'd start with no shims and 15% nitro next time around....
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Post by sgilkey »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by ptsullivan</i>
<br />I wonder if at least there should be at least one shim to maintain the
seal between the head and the sleeve over the temperature range?
Perhaps that is a myth, I am definitely curious.
Please keep posting results. How do you evaluate vibration/balance?
I am especially concerned with how well it maintains a tune. I have
often found the make or break from one engine type to another was not
the outright performance, but the repeatability.


-Pete

<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Pete I agree, I've had engines run well on the stand and perform erratically in the air. I'm anxious to do some test flights but the weather is really on the downward slide around here. Should get at least one more outing, though.... All I can say is on the bench it has a nice broad needle, throttles well, is clean and leak free and runs pretty smoothly. I'm more impressed than I expected to be, though I wish it made a few humdred more r's!!!
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Post by sgilkey »

Crosscheck, I still have to check weight and mounting bolt spacing. the muffler spacing is the same as the FX, as is the carb neck diameter. I have to weigh the base engine yet, but as I said earlier the muffler is very beefy, it's probably almost an ounce heavier than the OS. BUt is appears to be well-constructed. Longhaul turned me on to them as replacements for FX mufflers, they are well built and cheap! BUT they are slightly shorter in the header than the FX muff, so for scale planes you may not have enough offset to the fuse (don't ask me how I found out!!!)

The GMS has a nice big head which MAY (?) help cooling in partially-cowled installations like 2548???

I plan to keep an eye on that LS needle, it seems to stay put for now (better than a Magnum carb) but I am concerned about it over time....

OH, one other thing on my engine, that I noticed when playing with the shims- when you torque the head, the piston pinch gets tighter at TDC. This usually means something is out of square, or a piece of foreign material is present at the liner flange. Well, I checked and checked and could find no dirt, and I lapped the top of the cyl flat on a piece of glass. I've been running it with the head bolts just snugged, which reduces the binding, and the seal seems OK, even with no shim. So far....
Cross Check

Post by Cross Check »

Hi Scott,

Thanks for your time and efforts. Much appreciated. You are really great at 'explaining' engines over the internet. I do remember you in person,(you actually FLEW back then !!! HeHeHe) Telling me how I could get 'more' out of my MagGPs and MagPROS when the OSFXs came along... I can still get over 12.5K out of most of them old relics(10-3)for WW1 !!!

The 'Easy' selling point for us, (Maac Scale Combat is just modified 2610) was 'Buy an OSFX' and take the baffle out. 9-4 or 10-4, the thrust is equal. 15% fuel is all we run/want to afford. Easy for anyone new to join in. Cool.

Now we NEED another engine. To replace the OSFX. The Q-25 Pylon racers are in the same boat.

Even if the GMS is down a bit on power, I sure hope it will turn out to be Reliable. The cheaper price will help. (we can 'detune' our existing OSFXs by sticking the baffles back in) The beauty thing about OSFXs is they are easy to run and very consistent. I'm wishing and hoping Magnum can/will clone the OSFX, at a reasonable cost. That would be Great for all of us. (And They WILL SELL MORE than OS ever didn't even dream of...I'M SURE) I am personally freaked out that OS dropped, if not, the best model engine I, (We) have ever run.

In the meanwhile, I'll be asking Santa for a GMS. (I've been a good boy...I swear by it ! ) And try it out next year against/with the pilots I fly with.

Like Scott says... what's a few measly RPMS when pilot skill is the most fun part of the Combat Game...(Unlike Scott, I still love flying combat, and have a very hard time trying to limit my increadible flying skills to mid/back half of the pack ! ! ! HeHeHe) You gotta admire/respect Scott, for Not overwhelming/intimidating all of the rest of us...HeHeHe (Don 'Hollywood'V is the best I've ever encountered at hillarious 'pitside' banter, and I've tried my best to learn from him)
Humor/humility is one, if not, the best thing I like about R/C Combat...

Anyways, Back to the GMS/alternative engines...

Scott, good news on the muffler bolt spacing. And that the newer GMS mufflers are better. ( There must be more than a few of the old GMS mufflers buried deep at the Lennox field that we could not find back in Y2K.) Those $75 aftermarket semi tuned 8in long pipe/mufflers didn't help the old GMSs afterwards!

Several of us here are using a Bisson (OSFX).25 Pitts style muffler. It is lighter, more compact, which is less drag, and less prone to dirtnap damage. And fits into a 'pop bottle' cowl better. There is no RPM difference we can tell. Best thing is we can get the engines mounted 90 deg rather than 45 up to clear the std muffler for landing. The tank/carb at 90deg works great for even runs over 5minutes. The 45deg engines are not bad at all, but can tend to go lean last minute or so. My upright engines with the tank as far up as possible need a rich launch and it takes me 2-3 Rounds to get the needle set so I'm not too lean for the last minute of the Round.

Here should be a picture of my latest ride, a 'Bissionated OSFX, simulating a Griffon powered Spitfire MkXIX:
http://www.rccanada.ca/rccforum/attachm ... 1244475083
(It was a test flight, normally, I always land with my intact streamer, HeHeHe)

Bonus with the Bisson Pitts type muffler is the twin pipes go straight down. With an underhand launch, the plane and myself do not even need cleaning !
My upright engine planes give me a facefull of oil on my glasses, 75 seconds before Start Combat ! Doah !

One of the guys here, 'Buzz' could not get a std muffler to fit outside his radial engine planes he was building. Contacted Bisson and worked things out for a 'Combat' .25 (OSFX) 'Pitts type' muffler that is perfect. The two pipes seem small, but have the same restriction/muffler pressure as the stock/non baffle OSFX muffler.

I believe they are around $30 CDN, and contact Bisson (Google them) about the '.25 Combat' Pitts muffler. I dare anyone to bust/break one. Don't get the std .25 Pitts Bisson that is available.

I don't work for Bisson, just sharing what is 'new' around here.
The coroTech here freaks me out everytime. The best ones do not know what the internet is ! ! ! They are coroArtists too.

We are still having a laugh here, getting Heats in, trying to keep our streamers, while trying to cut some. First to Last seems the last anyone cares about here for
the Spectators or Pilots alike here.

Will not be the same game, with uneven power engines...

Thanks for the GMS report Scott,

Take care,
Have fun,
Dave'crosscheck'Fallowfield
Maac 6437
Unabashed Combat Team

P.S. Sorry for my long windyness, Beans and Beer for supper...HeHeHe
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Post by sgilkey »

I should comment that the GMS is clearly no FX. I'd take an FX over a GMS any day- better made and more power, and I'd gladly pay the extra. But the question was what are the alternatives now that the FX is dinscontinued. If you CAN'T get an FX, the GMS seems to have potential.

Also regarding running with no head shim, the Webra 25GT comes with no head shims, the anodized head seals directly on the liner flange.
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Post by sgilkey »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Hat Trick</i>
<br />Sounds promising. All the GMS's I've seen other guys run could barely get out of their own way!
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Mike, do you know what they were running for head shims? My engine has .015" head spacing with no shims, plus it came with 2x.008 and 1x.004 installed, giving a total head spacing of .035". I didn't run it like that but I would guess that would REALLY sap the power!

Crosscheck, I checked the dimensions. Mounting pattern and muff spacing are identical to the FX. The prop driver is a few mm further forward than the FX relative to the mounting holes but it's very close. the base engine weighs .8 oz more than the FX and the muffler is .8oz heavier also, total gain 1.6oz over the FX.

I have mounted the GMS and a Mag 28 XL in two practice planes so Eric and I can do an airborne comparison test. My vastly superior piloting skills aside, I hope we can assess speed and pulling power. Then after determining the "winner" powerwise I plan to put an FX on one of the planes and do another comparo. That is if the 50 degree rainy weather ever lets up.....
combatgoblin
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Post by combatgoblin »

To bad your not in central Florida we are having record heat waves in the 90's
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boiler
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Post by boiler »

Been there, done that, glad I'm back in the cooler temps but it needs to stop raining. Did I say that after complaining about a severe drought???
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Post by Hat Trick »

Don't know Scott but my guess is they were ran as they came in the box.
Papabear1
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Post by Papabear1 »

Thanks for the great info Scott. Keep up the testing. I will need this kind of info next season.
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