RE: GMS Engine Tuning Problem

RE: GMS Engine Tuning Problem
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RE: GMS Engine Tuning Problem - 2/21/2005 11:07:25 PM

Wayne Miller

Posts: 969
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline

Hi XJet,

I expect the muffler pressure will do the trick as well. I'll be interested in knowing the results of your test. I know that when I did my original modifications, and used muffler baffles (posted near the beginning of this thread), I lost a couple of hundred RPM, but the engine ran great. By just drilling the carb brass insert I didn't lose any RPM.

By the way, how do you measure the muffler pressure? I'd like to do the same.

Look forward to the results of your tests.

Fly4Fun,

Wayne

(in reply to XJet)

Post #: 176

RE: GMS Engine Tuning Problem - 2/22/2005 1:57:57 AM

downunder

Posts: 3171
Joined: 10/10/2002
From: Adelaide, AUSTRALIA
Status: offline

The easiest way to measure muffler pressure (and still use it to pressurise the tank) is to put a T piece in the pressure line, run a length of clear tubing from the T and drop the end into a tall glass of water. Start the engine and run it at whatever revs and you'll see the level of water in the clear tube drop. If the tube is taped to a ruler you could measure the exact amount the level drops. Now 30 feet of water is near enough 15psi so 1 foot is 0.5psi and 1" is about 0.042psi. You'll most likely see it drop about 6" which would mean the muffler pressure was 0.25psi. Another way is to just raise the tube out of the water until you start to see bubbles coming out the end.

(in reply to Wayne Miller)

Post #: 177

RE: GMS Engine Tuning Problem - 2/22/2005 2:41:58 AM

Wayne Miller

Posts: 969
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline

Hi Downunder,

Thanks for the explaination, I have used capillary action depth gauges a long time ago when SCUBA diving. This is basically the same principle except instead of forcing water into a blocked tube and compressing the air, you are pushing air down into water. The more the water is displaced by the compressed air, the more pressure you have.

I think I've got it! Thanks.

Fly4Fun,

Wayne Miller

(in reply to downunder)

Post #: 178

RE: GMS Engine Tuning Problem - 3/24/2005 3:49:28 AM

Flyer Freq

Posts: 906
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline

Hey Guy's!

I hadn't heard anything from this thread or any others on RC Universe in a long time. I decided to check and make sure there weren't any other remarks on any other forums about the GMS .47. Imagine my surprise, when I found that discussions were still going on in this thread and I wasn't getting notification. I hope RC Universe didn't black ball me or something

.

I ordered my replacement carb body from Tower, and received it a few weeks ago. The new body had the hole in the spray bar in the same place as my first spray bar. It is slightly off center, but none of the holes on either spray bar is hidden by the wall edge, as was the one in my friends bad runner. I have not run mine since putting all my old carb pieces on the new body, as I have retired my SE and ordered a 4D. I hope to get everything going in the next 3 or 4 weeks.

Wayne, by the way, thanks for giving me credit for solving the turbulance issue. I am eager to hear others that try replacing the carb body. I don't believe the hole has to be dead center, but you should definately be able to see the entire hole when you remove the nipple from the carb body.

Talk to you later!

Andy

_____________________________

Lose not thy airspeed, lest the ground rise up and smite thee!
If you want to make God laugh, tell Him your plans

(in reply to Wayne Miller)

Post #: 179

RE: GMS Engine Tuning Problem - 3/24/2005 4:01:12 AM

Wayne Miller

Posts: 969
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline

Hi Flyer Freq,

Funny you just posted, I saw Spicoli's name in another thread and just PM'd him to ask how he made out.

Since my last post I've modified 3 GMS .47's by just drilling out the intake nipple and making the hole in the brass insert as large as possible directly under the intake nipple - as shown in the previous pictures.

Keep us updated.

Fly4Fun,

Wayne Miller

(in reply to Flyer Freq)

Post #: 180

RE: GMS Engine Tuning Problem - 3/24/2005 9:56:45 AM

XJet

Posts: 3354
Joined: 3/31/2003
From: Tokoroa, NEW ZEALAND
Status: offline

Just another datapoint, after getting our club's GMS47 engines running okay with different mufflers, I went back to the original GMS mufflers and added a stainless steel restrictor/extension to the tailpipe, which is also a little longer than the original. I also welded the two muffler halves together (they never seal properly otherwise and we've had at least one through-bolt break so welding them solves both problems).

The pressure nipple was also replaced with one that allowed a 0.5mm larger hole.

I also ended up making inserts for the mounting threads because the original screws stripped out on two of the mufflers. I made the thread-inserts of brass with an M5 outside thread and M3 inside.

Now the engines run great, the planes don't get covered in black gunge from the two muffler-halves vibrating against each other, and you can torque down the mounting bolts without fear of stripping.

One of our guys is now actually able to use his GMS47 on a 3D ship and since we modified and re-fitted the original muffler, he's never had a single dead-stick and the engine runs/transitions perfectly despite all those G's and wild throttle control inputs.

So we've got them running great -- but is it worth it?

Well I've just ordered two more Thunder Tiger 46Pros -- they run sweet straight out of the box without all that messing around and the one on my 3D ship just keeps getting stronger and stronger (about 20 hours on it now). The rest of our club members are also buying TT engines -- life's too short not to :-)

< Message edited by XJet -- 3/24/2005 10:00:20 AM >

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Post #: 181

RE: GMS Engine Tuning Problem - 3/24/2005 2:02:15 PM

Flyer Freq

Posts: 906
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline

Hey Wayne!

Curious to see the overall feedback from elongating that hole. It resembles the rectangular cut made in the spray bar of some of the Super Tiger engines that had midrange issues. ST went back to a round hole now, from what I have heard. I don't think the shape of the hole is as important as where, on the needle, it falls. This may be a good fix. I can't wait to get back to flying again!

Andy

_____________________________

Lose not thy airspeed, lest the ground rise up and smite thee!
If you want to make God laugh, tell Him your plans

(in reply to Wayne Miller)

Post #: 182

RE: GMS Engine Tuning Problem - 3/24/2005 2:11:27 PM

Flyer Freq

Posts: 906
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline

XJET:

I have looked at a few of the latest engines from GMS. It looks to me like they have corrected the hole alignment problem. While the hole is not dead center, it is not so far out that the fuel has to make a 90 degree turn to get through it. I am back to recommending the GMS again. With the problem solved, they make a great 3D engine.

Just a word of caution on the TT engines. There are some quality control issues and poor customer service issues with ACE RC. I hope I can say that without getting slapped. Our local hobby shop discontinued the entire TT line, because they couldn't deal with ACE anymore. You can read on many threads within RCU to back this up. I have always liked the TT line also, but they have their issues, just like everyone else, I guess

.

Andy

_____________________________

Lose not thy airspeed, lest the ground rise up and smite thee!
If you want to make God laugh, tell Him your plans

(in reply to XJet)

Post #: 183

RE: GMS Engine Tuning Problem - 3/24/2005 2:57:47 PM

Wayne Miller

Posts: 969
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline

Hi Flyer Freq,

Thanks for the information on the hole alignment on the new engines. It looks like they are agreeing with the fix.

Although I doubt if it will ever be acknowledged, I bet we had a lot to do with getting the problem fixed.

Fly4Fun,

Wayne Miller

(in reply to Flyer Freq)

Post #: 184

RE: GMS Engine Tuning Problem - 3/24/2005 4:49:44 PM

Flyer Freq

Posts: 906
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline

quote:

ORIGINAL: Wayne Miller

Hi Flyer Freq,

Thanks for the information on the hole alignment on the new engines. It looks like they are agreeing with the fix.

Although I doubt if it will ever be acknowledged, I bet we had a lot to do with getting the problem fixed.

Fly4Fun,

Wayne Miller

I would like to think so!

Andy

_____________________________

Lose not thy airspeed, lest the ground rise up and smite thee!
If you want to make God laugh, tell Him your plans

(in reply to Wayne Miller)

Post #: 185

RE: GMS Engine Tuning Problem - 3/24/2005 11:49:00 PM

rlbrobst

Posts: 30
Joined: 3/14/2005
From: Muncie, IN, USA
Status: offline

Wayne, I have a gms .40 and am having the exact same problems! The only difference is that I have a pitts muffler on mine. I found today that Tower recommended the wrong muffler for this motor. If you put your finger over the muffler exhaust partially covering the outlet it would rev up fine and not stall out. So I called them. The muffler that I have does not give enough pressure back to the tank to pressurize the tank due to it having 7/16" tubing for the exhaust as the correct muffler has 3/8" tubing for the exhaust. They told me I could return the muffler but it has already had the tubes cut to fit my corsair. So I would have had to buy a new/correct size muffler. WRONG! Not for another 40 bucks! I am going to slip some copper tubing inside the too large of exhaust tubes and cut the exhaust down a bit. This motor was starving for back pressure. Yours sounds like the muffler you are using is causing yours to starve for back pressure also. You might want to try what I said about partially closing off the exhaust with your finger as someone holds the plane and you run it up to full throttle.

Rick

(in reply to Wayne Miller)

Post #: 186

RE: GMS Engine Tuning Problem - 3/25/2005 1:10:51 AM

Wayne Miller

Posts: 969
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline

Hi Rick,

Thanks for the input.

You will notice at the beginning of the thread, (there are pictures) I had experimented with putting baffels in the muffler body to increase back pressure, this worked well. However, in the end we found that if we fixed the fuel draw by drilling out the carb input nipple and brass insert (see previous picture in an earlier poast), that we could elliminate the baffles. Since then I have done several engines just by drilling out the carb fuel nipple and carb brass insert - all worked well after that.

Since the time when I had inserted the baffles, I was looking at some of my older K&B engines and I noticed the muffler pressure nipple is on the extension between the engine and the muffler I was wondering if this may be a better tap for muffler pressure?

I have never played with the GMS .40, so I'm not sure what would fix it. Please keep us up to date when you get the problem fixed.

Fly4Fun,

Wayne Miller

(in reply to rlbrobst)

Post #: 187

RE: GMS Engine Tuning Problem - 3/25/2005 6:40:31 AM

XJet

Posts: 3354
Joined: 3/31/2003
From: Tokoroa, NEW ZEALAND
Status: offline

quote:

ORIGINAL: Wayne Miller

Since the time when I had inserted the baffles, I was looking at some of my older K&B engines and I noticed the muffler pressure nipple is on the extension between the engine and the muffler I was wondering if this may be a better tap for muffler pressure?

No way -- that's exactly the *wrong* place to put a pressure nipple.

The exhaust stack has gases flowing at very high speed through it during most of the engine's operating cycle.

Mr Bernoulli dicovered that the faster gases travel through a tube, the lower the pressure becomes inside that tube.

This means that a pressure nipple placed at the point of highest gas velocity will produce *very* poor results and may actually end up sucking as much (if not more) than it blows.

The *best* place for a pressure nipple is at the point in the muffler where the gasses are travelling at the lowest velocity (and therfore the pressure is highest). This is typically (although not always) at the point where the nuffer is widest.

< Message edited by XJet -- 3/25/2005 6:41:21 AM >

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Post #: 188

RE: GMS Engine Tuning Problem - 3/25/2005 1:17:19 PM