RE: GMS Engine Tuning Problem  
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RE: GMS Engine Tuning Problem - 4/13/2005 12:37:56 AM   
Flyer Freq



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

ORIGINAL: Harry Lagman
I recently tached a couple of GMS .47s with stock exhausts with the 12 1/4 x 3 3/4 APC prop while helping set them up. We got between 11,700 and 12,000 at sea level. Your 12,080 seems about right based on my experience with these engines. The 14,800 must have been a false reading.


I suppose it is possible it was a false reading. The only other factor that was different, was that the 14,800 was taken in 20 degree weather, vs 60 degree's with the 12,080 on my engine. I don't think that can account for the 4,720 RPM difference, though

Andy.

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       Post #: 201

RE: GMS Engine Tuning Problem - 4/14/2005 10:02:06 PM   
Keefer



Posts: 208
Joined: 6/15/2002
From: Santee, CA, USA
Status: offline
quote:

ORIGINAL: XJet

quote:

ORIGINAL: Wayne Miller

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.



On the GMS engines with a large-bore carb, the best source of pressure is the crankcase, not the muffler. My GMS76 crankcase puts out more pressure than the YS pressurized fuel systems. So the engine never quits by running lean after it warms up.

(in reply to XJet)
       Post #: 202

RE: GMS Engine Tuning Problem - 4/15/2005 6:24:56 AM   
Flyboy Dave



Posts: 13460
Joined: 3/20/2002
From: San Bernardino County, CA, USA
Status: offline
quote:

XJet....
I suggest those interested take a look at the following links for more information
(and note that air *is* a fluid that is often considered incompressible at subsonic speeds)



OK....air is a fluid....and can't be compressed....

...you need to go back to science class, son.

FBD.

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       Post #: 203

RE: GMS Engine Tuning Problem - 4/15/2005 7:53:00 AM   
XJet


 

Posts: 3462
Joined: 3/31/2003
From: Tokoroa, NEW ZEALAND
Status: offline 		Just follow the links I provided and see for yourself. I didn't invent the science -- don't kill the messenger :-)

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       Post #: 204

RE: GMS Engine Tuning Problem - 5/9/2005 4:14:47 AM   
Wayne Miller


 

Posts: 978
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline 		Hi,

Just an update, I just finished fighting a GMS .47 that had the modification.

It would die right after takeoff or prolonged wide open throttle. We checked with my 15% nitro synthetic/castrol blend fuel and it worked fine.

I forgot the obvious - the problem ended up being old fuel.

Just thought I'd pass it along.

Fly4Fun,

Wayne Miller

(in reply to XJet)
       Post #: 205

RE: GMS Engine Tuning Problem - 5/19/2005 6:30:17 PM   
Flyer Freq



Posts: 912
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline 		While my engine is running well, I am playing with a concept that might be helpful for the .47. I have set up a uniflo tank, which should help with fuel delivery. I am thinking it will especially be helpful when hovering. I tried it with a check valve between the muffler and the tank, and that was a disaster. While I know they recommend a check valve, so fuel can't flow back to the muffler, the fuel tank pressurized to much. After running at high rpm, the pressure forced too much fuel back through the carb, screwing up the idle and transition. I removed the check valve, and the engine running was consistant. It seemed as though I went through fuel faster though. Not sure how much fuel went through the muffler when throttling back. My buddy and I talked about setting up a tank with some sort of a pressure regulator, to keep tank pressure the same, no matter what the tank level or rpm of the engine. I am figuring it would have to maintain a steady 2.5 to 3 lbs. I have some idea's how to accomplish this, but maybe someone reading this knows of such a device that is already made,....

Andy

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Lose not thy airspeed, lest the ground rise up and smite thee!
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       Post #: 206

RE: GMS Engine Tuning Problem - 5/22/2005 4:40:53 AM   
Flyer Freq



Posts: 912
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline 		I flew the uniflo tank on my .47 today, and I couldn't believe the difference. It took a good running engine and made it great! I can't put my finger on it, but I think the difference was that the mid range was more linear and faster to respond. I had a whole new confidence in my plane. I would encourage anyone to try this tank configuration, especially if you like to hover!

Andy

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

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       Post #: 207

RE: GMS Engine Tuning Problem - 5/22/2005 3:03:40 PM   
Wayne Miller


 

Posts: 978
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline 		Hi Andy,

I'm interested in learning more about this tank - where can I find information on it?

Thanks for letting us know the results.

Fly4Fun,

Wayne Miller

(in reply to Flyer Freq)
       Post #: 208

RE: GMS Engine Tuning Problem - 5/23/2005 12:10:32 AM   
Keefer



Posts: 208
Joined: 6/15/2002
From: Santee, CA, USA
Status: offline 		Try the July 2005 issue of Fly RC Magazine. Good description in there, with a simple drawing.

(in reply to Wayne Miller)
       Post #: 209

RE: GMS Engine Tuning Problem - 5/23/2005 3:35:09 AM   
Flyer Freq



Posts: 912
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline 		Keefer is right, Fly RC Magazine is where I got it. The instant throttle response and consistancy of RPM at different stick positions has me wanting to change all my planes to this setup. If you would like, I will try to describe the hookup. Unfortunatley, the Great Planes tanks, with the two built in nipples and one nipple in the rubber stopper, are not candidates for this hookup. I am bummed , because that is my favorite tank.

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       Post #: 210

RE: GMS Engine Tuning Problem - 5/23/2005 3:46:15 PM   
Dean in Milwaukee


 

Posts: 35
Joined: 2/6/2005
From: milwaukee, WI, USA
Status: offline 		Found this thread last night, pulled apart my first gen. .47 motor and found the offset hole just like all the others.

This morning I disassembled and used the nipple as a guide for the biggest drill bit I had that spun freely inside the nipple, drilled, then blew out with brake cleaner and reassembled and ran it, on the ground only so far.

Seems to have worked! Before, to ensure good running with the nose pointed up, both at 1/2 throttle and full required a overly rich mixture, both on low and high speed needles, which of course hurt power. Now, I'm only slightly rich sitting level, ( couple of clicks), and the motor will actually pick up a bit of rpm when nose up from the inherent lean out in this position, just like its supposed to.

Importantly, it only took just a few minutes of fiddling to get it running right, where in the past it was much more difficult to get right.

Throttle response is improved as well, importantly as this is installed in a tufflight 4d. It'll be nice to actually try some hovering without worrying about lack of power or a flame out.

I'll report back after a test flight.


Dean in Milwaukee

< Message edited by Dean in Milwaukee -- 5/23/2005 3:50:01 PM >

(in reply to Flyer Freq)
       Post #: 211

RE: GMS Engine Tuning Problem - 5/23/2005 3:54:46 PM   
Wayne Miller


 

Posts: 978
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline 		Hi Dean,

Thanks for the input, I look forward to your first test flight report!

If you still have difficult adjustments on the carb, you may want to drill the intake nipple and brass insert one size larger than you did.

Fly4Fun,

Wayne Miller

(in reply to Dean in Milwaukee)
       Post #: 212

RE: GMS Engine Tuning Problem - 5/23/2005 3:58:13 PM   
Flyer Freq



Posts: 912
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline 		Hey Dean!

Add the uniflo tank to that equation and you will even get better consistancy. The uniflo tank allows you to set the carb for best running on the ground. That setting is not supposed to change in the air, because gravity, for all practical purposes, is removed from the equation. Gravity affects the force of fuel flow without muffler preasure. The more fuel in your tank, the more gravity feed. If you get your preasure line and carb line at the same reference point, gravity is no longer the factor it once was. I set mine up on the ground to scream, and expected it to go real lean when I pointed the nose up. To my surprise, there was no noticeable difference. I didn't tach it, but my calibrated ear didn't notice anything.

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

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       Post #: 213

RE: GMS Engine Tuning Problem - 5/23/2005 6:22:50 PM   
Dean in Milwaukee


 

Posts: 35
Joined: 2/6/2005
From: milwaukee, WI, USA
Status: offline 		"Hey Dean!

Add the uniflo tank to that equation and you will even get better consistancy"


I will probally try that out too. Anything for better throttle response during a hover.

Now if I can only get some more stiffness into my 4d's tail control linkages to stop the flutter at medium speeds. Maybe a pull/pull setup will do it.


Dean in Milwaukee

(in reply to Flyer Freq)
       Post #: 214

RE: GMS Engine Tuning Problem - 5/23/2005 6:32:06 PM   
Flyer Freq



Posts: 912
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline 		Dean:

I am putting a 4D together right now, also. The only way you will get rid of the flutter is to make the high speed modifications they show on the Tuff Flight website. It is basically the addition of counter balance weights for the elevator and rudder. The setup appears easy.

Andy

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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 Dean in Milwaukee)
       Post #: 215