Alternative Engines?

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sgilkey
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Post by sgilkey »

Eric decided he'd rather go apple picking than fly but I got several test flights in with the GMS. It ran well on the 5% diet, smooth, no leaks, needled well, no dead sticks or blown plugs, throttled smoothly and reliably. Power looked respectable but i didn't have another plane in the sky for direct comparison. Overall though it was very well behaved. I'd still choose a good second hand FX over the GMS but if you don't have an FX i'd say the GMS has potential, so far....only "problem" was that it would not shut off all the way with the throttle closed, it kept running at a tick-over till I belly landed. Regular idle speeds were steady and reliable.
Cross Check

Post by Cross Check »

Hi Scott,

Thanks so much for the GMS reports.(It is our Thanksgiving WE here, so I will thank you again !)

Great to hear the GMS is basicly 'Bolt to bolt' compatible to the OSFX.25, we can live with the 1.5oz extra weight.(we can move the Rx batts aft)
Reliability is the key issue as far as 'selling' most newcomers to our sport.
( I keep finding that the 'newbies' are more smarter and better flyers than me ! )

A few RPMs down won't matter. If they have problems on the flightline though...
We NEED a decent engine close to an FX.

Scott, I'm sure you met Matt'Maverick' flying HOB Texans back pre-Y2K.
He was the only one who could actually get the 'old' GMSs going close to the then new OSFXs.
(They hit their peak, just as the muffler resonated off !)
He was the only one out of 5/6? that could actually get one going. I remember the carb barrel air leaking as a problem.(same throttle closed/can't shutoff you mentioned)

I know Matt was a friend of the Great Victor'Thunder' who loved getting the most out of every engine he ran. Vic could get an OSFP close to a stock OSFX.
Mabee they did some timing changes on the old GMS?

Don S, a Pylon racer, thinks the newer GMS.25 timing might be improved on the second page here:
http://www.rcuniverse.com/forum/m_88908 ... e_2/tm.htm

I know without a good/easy replacement for the OSFX, the great FUN we are having here will just fizzle away in a few years...

I'm Pissed Off at O.S.
Not because they did not Ever sponsor my Onslaught events. ( I've tried every year!)
Just because,
They discontinued the Best .25 engine, and replaced it with a lesser/more expensive one.

I wonder if anyone involved with engine development actually flys model airplanes?

Consumers, (and how can you not consume more engines than with Combat or Pylon?), will eventually win.

Is there anyway we can collectively get together and approach every engine manufacturer with 'OUR' COMBAT/PYLON WANTS ?

I nominate our/my most respected Engine Guru, the one and only Great Scott G (so Great he 'IS' his own 'Nickname'!!!)to be our 'R/C COMBAT FLYING' Representative.

(That means Scott will have to fly a Round to get the Job ! ! ! HeHeHe)

Sorry Scott,
I've been fortunate to pit next to Don 'Hollywood' a couple of times, and his type of infectious humour has ruled my life ever since !

Take care,
Have fun,
Dave'crosscheck'Fallowfield
Maac 6437
Unabashed Combat Team
sgilkey
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Joined: Mon Mar 19, 2001 8:26 am

Post by sgilkey »

Eric and I took advantage of a beautiful Fall afternoon to get several flights in on the two test planes. Both the Mag 28XL and the GMS25 performed very well. Power and in-air performance were essentially identical, no discernable difference. Both ran consistently throughout the whole tank, throttled well, blew no plugs, etc. Overall both ran great and seem interchangeable.

The next step in the test plan was to replace one of these engines with a 25FX and do some more comparison flights. Time did not permit this today.....
Cross Check

Post by Cross Check »

Hi Scott,
The Mag/GMS info is much appreciated.

One of the pilots here sprang for an OSAX.25 and flew it against our stock OSFXs in our Onslaught over Ontario, Oct.18th. It is very nice, if you like 'looking' at pretty/heavy engines...
Performance was very equal to an FX as far as we could tell. The big muffler was quieter.

The one thing the rest of us agreed on is paying the price for an AX.25...NO !

Some pilots here have been able to wear out their FX P/Ls over the years and are looking for some replacements ... OUCH ! in $CDN ! Doah !

Our discussions at the OoOMatch favored the cheaper GMS/etc. engines just to keep costs down for new pilots. (Once you get pilots to enter a Match, they all get Hooked...All of us know that !)

Scott, all the info you are giving us is great. Thanks allot.
Have you compared the porting/timing on the cylinders of FX vs GMS?
(Take your engines apart...What are friends for?..HeHeHe)

Thanks for your time and expertise Scott, we all appreciate it.

A $160 OS.25engine?

I'm hoping for an equal Magnum 'FU'.25 at half the price...

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

CC,
Im still waiting too hear from Magnum rep, on there ongoing development.
Once I hear there shipping too dealers I will let the forum KNOW.
Our rep understands our concerns with Combat pilots.
I am hoping too hear something by the end of the year, if not sooner.


Scott, Thanks for the info on the GMS.
As for the Magnum brand of engines the onls good ones are the XLS new breed.
The others are subpar at our elevation.
Cross Check

Post by Cross Check »

Hi Frank,
Much appreciated.
Tell all the Magnum reps/engineers that my old GP/PRO.25 Magnums work great at 600ft ASL. After many, many, gallons of fuel. ( I still run them in sport planes)

Tell them we are all 'drooling' on an XLS'Combat'.25...

And they should 'try' not to exceed the performance of an OSFX.25... by much ! ! !

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

Eric and I headed out tonight for more test flights. I replaced the Mag 28Xl with a box stock (no muffler baffle) 25FX, and put it up against the GMS. On the ground, the FX tached about 400ish rpm more than the GMS. I expected it to walk the GMS in the air, but to my surprise the performance was very similar. Eric was flying the FX plane and claimed to have no speed advanatage (he was chasing me) but to my eyes he had a very tiny advantage. But hardly noticeable. IN vertical climb, again, maybe a slight advantage. The numbers would imply more of an advantage, but in the air they were virtually identical.

I did not try running the FX with no head shim (I was running 5% nitro) tonight but on a test stand run, there was no measurable difference when running 5% with no shim. Which also surprised me.

Maybe in the air the GMS unloads a bit more, I dont' know.

We flew wide open, and we did some low and slow chasing (yes, some folks might be surprised to learn you can actually PRACTICE flying low and slow!!!). The GMS throttled well and accelerated cleanly from extended low-speed running. No leaks, no blown plugs.

Overall I of course like the FX, who doesn't??? But if you have a GMS, set up per the way I did it, at least, it seems to be very competitive and reliable. We probably have the equivalent of 2-3 complete meets worth of time on this GMS and it has not given us a bit of trouble and has been very reliable. I'd say it has potential!

This concludes my test reports on the GMS, I don't plan to do any further alterations to the engine in search of more power.
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Ed Kettler
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Post by Ed Kettler »

Thanks for your great contributions on this important topic, Scott. We really appreciate your effort!

Ed
sgilkey
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Post by sgilkey »

My pleasure! This kind of stuff is fun. The proof of the pudding will be subjecting it to an actual contest! That won't happen till next spring. On our test planes the tanks are big enough for "heats" to last maybe 8 minutes so the engines get a workout and the GMS has been doing fine.
AIM
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Post by AIM »

Just to clarify.. You are running a different carb? right?

I wonder what would be needed to make the GMS run LimB 14000+ w/10/4 using the stock carb.
sgilkey
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Post by sgilkey »

No, all the testing including flight testing was with the stock GMS 25 carb. I did a few test stand runs with the .32 carb and those are noted in the previous posts, that carb did net a few hundred rpm increase.

So if you remove the stock head shims and run 5%, at least according to my engine, you're basically there in the 14k range. Running 15% will give a couple hundred more rpm. The test flights with no shims, stock carb, 5% nitro were very competitive with a 25FX (also running 5%).
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boiler
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Post by boiler »

I flew against a GMS this last weekend in CA. It kept up with my fx. Of course it had a can on it. It was mounted on a coro plane. Maybe the pilot can give you guys a picture.
spaddawg
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Post by spaddawg »

Hey Bob, glad to see you made it back home safe and sound.
I have been running the GMS .25 I think the longest of anyone in the RCCA and I can tell you this. I have taken one of my engines out and tried to blow it up on one of my planes. I put it in the air running 30% with a 9X4 MAS prop turning 19,800 at the leanest setting I could get it in 115-deg Vegas weather. It got hot, it faded out a little over the course of a 5-min run. Ran it out of fuel landed it. Took it home to check the internals and everything still intact even the Teflon inserts on the wristpin. Bolted it back up and put it back on the plane and have flown it for the past 5 years in combat. Ran it at the Pearl Harbor classic this month against Bob and it was turning 18,600 on 15% with a KY can. On a 3-lb Spad with a 48" wing it was holding its own against Mako's, Axe's, and Mig's all day Sunday.
I have found that the best thing to do is to seal up the area around the card with clear silicone and to set the low end needle a little on the fat side to the point where it loads up and dies after about 10-sec. with the throttle fully closed. I run the OS plugs. I have planted them nose first into some of the hardest of hard soils and even one engine to engine hit and never bent a crank. I keep the single head shim in and the stock carb. I break my engines in with a 8X6 MAS and 15% fuel with it running on the fat side. (4) 5-min runs with a couple of lean pinches in each run with a 20-min cool down between runs. 5th run switch to 9X4 MAS a little on the fat side still for a full 5-min. run in the air. Then I lean it down to normal running mode just fat of lean and run it for a good 4 to 5 flights. After that I take the engine and pull the carb off. I take the back plate off, and the head and submerge it all minus the carb in to a can of Slick-50 for a good 48 hours. Pull it out let it drip dry. Bolt it back up and seal the carb and go flying. Now when I am done for the day of flying I put 4 to 5 good drops of Tri-Flow down the carb and hand prop it through a couple of turns and put it away till the next time. After the first run of the day I can start my GMS by hand by just giving a quick back spin to the spinner nut with a snapping of my fingers motion and they will fire right up. For RC COMBAT the GMS .25 is a Cheap $59.99 Work Horse that will keep running and running time after time with little effort. I ran one on a 2548 ME109 a few years back and it held its own against the OS's. If you want the best bang on a cheap budget, this is it!
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boiler
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Post by boiler »

Thanks for sharing James.
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boiler
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Re: Alternative Engines?

Post by boiler »

Here is another one to try. It is made by magnum and looks like it would work for 3548 and limited B. Don''t know about Open B. Price is great.

http://www.himodel.com/sort.php?sub2=CH
Bob (Longhaul) Loescher
rcca# 621 RC Combat Geezer
Bring those planes in closer where I can see them.
[url=http://www.rccombat.net/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=11380][img]http://www.rccombat.net/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=11381[/img][/url]
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