RE: CRRC GF45i  
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RE: CRRC GF45i - 8/30/2005 10:47:37 AM   
RustyTumbles



Posts: 756
Joined: 9/8/2003
From: Townsville NTH QLD, AUSTRALIA
Status: offline 		CRRC,

Are these guys flying with or without the velocity stack on the motor? If my carb mod does not work the stack is the next place I'll be looking for the cause of the problem.

I have got the 22x10 3w prop balanced and bolted to the motor. I am hoping to fly again on friday if the weather is good. Fingers crossed it works this time.....

(in reply to crrcpro)
       Post #: 101

RE: CRRC GF45i - 8/30/2005 6:03:51 PM   
reynolds74


 

Posts: 196
Joined: 9/10/2003
From: Povoletto (Udine)Friuli Venezia Giulia, ITALY
Status: offline 		I've seen that the velocity stack for the Zenoah have a cylindric shape instead of the one used by CRRC that have a cone shape. Does this have any influence on the air pressure?
Anyway, for what I can see around, almost all the people who's using a gas engine to do aerobatics have the carb air inlet besides the firewall, to allow the carb breathing in a such of a calm airbox.
Maybe this modification, turning the carb 90 degrees backward, could be useful.

I have a question: does the carb position have any kind of influence for the engine running? I mean, if it's rotated left or right or upside down, does it matters?

Bye.

Andrea

(in reply to RustyTumbles)
       Post #: 102

RE: CRRC GF45i - 8/30/2005 8:05:58 PM   
Jim Branaum


 

Posts: 1669
Joined: 10/22/2002
From: Fair Oaks Ranch, TX, USA
Status: offline 		From what I was taught, the primary purpose of the velocity stack was to contain the small splatters of fuel when the throttle was opened suddenly. The various shapes used are attempts to get the theoretical additional benefit from the stack and its shape.

The position of the carburetor should have no influence on the engine operations if the static hole in the fuel pump is protected or piped elsewhere.


_____________________________

Jim Branaum AMA 1428

(in reply to reynolds74)
       Post #: 103

RE: CRRC GF45i - 8/31/2005 3:21:48 AM   
RustyTumbles



Posts: 756
Joined: 9/8/2003
From: Townsville NTH QLD, AUSTRALIA
Status: offline 		Some engines like the ram air effect and others don't. Also the static port for the diaphram pump can have a large effect on the mixture if is pressurises durring flight. I have done some research here on rcu and some people have the port routed to the carb inlet to sense the pressure at or near to the throttle butterfly. I will try that if the fuse routed pipe doesn't work.

(in reply to Jim Branaum)
       Post #: 104

RE: CRRC GF45i - 8/31/2005 10:16:43 AM   
reynolds74


 

Posts: 196
Joined: 9/10/2003
From: Povoletto (Udine)Friuli Venezia Giulia, ITALY
Status: offline 		Bigsport,

I've seen your mod to the carb, adding a line, but I still don't understand which effects this mod will have (due to my poor experience with gasoline engines). Can you explain me again?

Bye.

Andrea

(in reply to RustyTumbles)
       Post #: 105

RE: CRRC GF45i - 8/31/2005 12:24:19 PM   
RustyTumbles



Posts: 756
Joined: 9/8/2003
From: Townsville NTH QLD, AUSTRALIA
Status: offline 		Basically on the carb diaphram cover plate a piece of copper tube is soldered to it and sealed around the bottom of the tube, so no air from in the cowl can get in. Next a piece of tubing is attached to the copper tube and routed into the fuse. The idea is to prevent the pressurised air inside the cowl getting into the static port of the diaphram cover plate and forcing the diaphram onto the needle at increasing the fuel flow, and therefore making the engine run extremely rich. So the diaphram is now only subject to the static air pressure inside the fuselage. So in theory it shouldn't turn rich when the cowl becomes pressurised with ram air. If it does the problem is else where? And my guess would be the velocity stack. But we will see on friday when I fly again.

(in reply to reynolds74)
       Post #: 106

RE: CRRC GF45i - 8/31/2005 1:59:31 PM   
Jim Branaum


 

Posts: 1669
Joined: 10/22/2002
From: Fair Oaks Ranch, TX, USA
Status: offline 		Bigsport,
At a high level, your theory is correct. However most gas burneres I have used a simple elbow pointing to the rear of the air flow solved the over preassure problem on the diaphram. Your routing a line back to the inside of the fuselage is overkill, but it will work.



_____________________________

Jim Branaum AMA 1428

(in reply to RustyTumbles)
       Post #: 107

RE: CRRC GF45i - 9/1/2005 6:04:05 AM   
RustyTumbles



Posts: 756
Joined: 9/8/2003
From: Townsville NTH QLD, AUSTRALIA
Status: offline 		I guess will see tomorrow when I fly it!!!! I'll get some more numbers on the 22x10 prop as well.

(in reply to Jim Branaum)
       Post #: 108

RE: CRRC GF45i - 9/1/2005 6:16:43 AM   
aiken779


 

Posts: 3
Joined: 8/27/2005
From: shenzhen, AE, AFGHANISTAN
Status: offline 		hello bigsport,

how your edge 540t price? and where can buy it cheap on yous.
I hope make a friend of us, can't we?

regards

(in reply to RustyTumbles)
       Post #: 109

RE: CRRC GF45i - 9/1/2005 11:50:21 AM   
RustyTumbles



Posts: 756
Joined: 9/8/2003
From: Townsville NTH QLD, AUSTRALIA
Status: offline 		Try the PA web site www.precisionaerobatics.com or www.troybuitmodels.com for the edge. It think they are about $850 AUD.

(in reply to aiken779)
       Post #: 110

RE: CRRC GF45i - 9/1/2005 4:07:53 PM   
reynolds74


 

Posts: 196
Joined: 9/10/2003
From: Povoletto (Udine)Friuli Venezia Giulia, ITALY
Status: offline 		Thanks Bigsport,

now I've understud.
I'm only thinking that if the cowl is opened to insure enough cooling effect, that means more than the front inlet area, there should be no air in pressure inside the cowl, only air that is passing by, so the effect is not noticeable.

Anyway, please let me (us) now what about your next runs...

Thanks.

Andrea

(in reply to RustyTumbles)
       Post #: 111

RE: CRRC GF45i - 9/1/2005 9:42:38 PM   
Jim Branaum


 

Posts: 1669
Joined: 10/22/2002
From: Fair Oaks Ranch, TX, USA
Status: offline 		Normally, we want two times as much exit area as inlet area to insure proper engine cooling. Many baffle the engine reasonably tightly to reduce the excess air being brought into the cowl. This insures that there is no high pressure area within the cowl. Some of us go as far as to provide three times the exit area as inlet area to insure cooling even at low throttle settings on hot days.



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Jim Branaum AMA 1428

(in reply to reynolds74)
       Post #: 112

RE: CRRC GF45i - 9/2/2005 6:42:54 AM   
RustyTumbles



Posts: 756
Joined: 9/8/2003
From: Townsville NTH QLD, AUSTRALIA
Status: offline 		I have finally got the GF45 going nicely. I took it out today. The first flight was the same as sunday so the carb mod didn't improve anything. However when I landed I grabbed the plane on did another run up. It was reving out nicely but then I put my hand in front of the carby to block the prop wash and it dropped a few hundred rpm. So the I put my hand behind it and it picked up a few hundred. So back to the pitts we went to make a scoop. I found some cardboard in the car and cut it to size and cable tied it to the velocity stack. Started it up again and tached it. We got an extra 400rpm static!!! So I taxied back out and took off, it ran well and had more power than before but was still a little rich. I have since been leaning the low end needle after each flight and it is coming on nicely. Even got some prop hang time from it. But my day came unstuck when I ran out of fuel. I almost got it back to the strip, just caught the edge of the long grass and it flipped over stripping both elevator servos. I was just having a ball and forgot how long I'd been flying.

All flying today was done on the bolly 21x10 as the engine wouldn't spin the 22x10 any more than 5500rpm. It may spin it at 6000-6500rpm once fully run in but I won't try it again for a while.

I will be removing the cardboard scoop and filing the velocity stack so the fron't edge is lower than the rear. I will report again once I fix the plane, make some adjustment, and fly her again.

(in reply to TooLy)
       Post #: 113

RE: CRRC GF45i - 9/2/2005 10:46:14 AM   
reynolds74


 

Posts: 196
Joined: 9/10/2003
From: Povoletto (Udine)Friuli Venezia Giulia, ITALY
Status: offline 		Tooly,

already done, but no reply...

Bye.

Andrea

(in reply to TooLy)
       Post #: 114

RE: CRRC GF45i - 9/4/2005 9:41:53 AM   
RustyTumbles



Posts: 756
Joined: 9/8/2003
From: Townsville NTH QLD, AUSTRALIA
Status: offline 		Here is a few pics of the mods I have done to get the engine running sweet. I have filed the velocity stack to scoop the air in. I have repaired the muffler again with quick steel metal expoxy for the auto parts store. It is able to withstand 260 degrees C so it should hold up better than the silicone sealant. I hope to fly again next weekend if I get my new servos by then.

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