High Speed Turn Lean-out on Viper

High Speed Turn Lean-out on Viper
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High Speed Turn Lean-out on Viper - 9/18/2004 2:30:50 PM

Posts: 25
Joined: 10/7/2003
From: oak forest, IL, USA
Status: offline

Hi Guys.
I just installed a tuned pipe on my Viper. It will turn 15400 rpm on the ground with a 40FX and a 9x8 APC pylon prop. Before the pipe I was getting around 13000 rpm or so. Now I have a problem with leaning out in high speed turns. It really flies like a rocket. If I make a wide turn or climb vertical no problem. Only when I yank the stick for a fast turn. Any body know how to fix this problem? I am not really to familiar with racing set-ups.
Thanks
John

RE: High Speed Turn Lean-out on Viper - 9/18/2004 3:41:23 PM

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Joined: 9/22/2002
From: Avon, CT, USA
Status: offline

Hello,
You can run a small 1 or 2 oz header tank closer to the engine, that should fix it. I had that happen on an old Sig Cougar I had. The tank fixed the problem. I would also suggest you run a 9x7 and make the pipe just a touch longer

Crashin Mike

(in reply to jkidless)

RE: High Speed Turn Lean-out on Viper - 9/18/2004 6:45:34 PM

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Joined: 12/29/2001
From: Monroe, NC, USA
Status: offline

John,

Most everyone who races Quickies use what is known as a Bubbleless (aka Bubbless, or Bladder) tank.

These tanks have an inner liner that holds the fuel. You suck the air out and collapse the liner (bladder), then fill it with fuel, typically with a large syringe made for the job.

There is no clunk because the fuel pickup tube is always in the fuel.

You get much more consistent runs with the bladder tanks.

If you want to know where to get a tank and syringe, just let us know.

_____________________________

Don Stegall
RCPRO Chairman of the Board

(in reply to jkidless)

RE: High Speed Turn Lean-out on Viper - 9/18/2004 7:45:48 PM

Posts: 2855
Joined: 12/29/2001
From: Brantford, ON, CANADA
Status: online

Use the type of tank that Don suggested, it will solve nearly every engine/tank problem known to mankind. I do not know what you are using, but you should be using pipe pressure, not crankcase pressure.

Ed S

(in reply to jkidless)

RE: High Speed Turn Lean-out on Viper - 9/19/2004 10:31:39 AM

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From: oak forest, IL, USA
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Hi Guys.
I am using pipe pressure for the pressure. I would like to know more about a bladder tank setup.
Please let me know.
John

(in reply to Ed Smith)

RE: High Speed Turn Lean-out on Viper - 9/19/2004 2:26:12 PM

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Joined: 12/29/2001
From: Monroe, NC, USA
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John,

Check out Performance Specialties High Performance Accessories and scroll down to the Tettra "Bubbleless" Fuel Tanks area.

Also check out the Jett Engineering Bubble-Jett Fuel Tanks and Tankers page.

Read INSTRUCTIONS for BUBBLE-JETT TANK and BUBBLE-JETT TANKER for a primer.

The only JETT tank that I've been able to use on the Viper is the CG tank placed behind the former at the wing leading edge. This requires relocating the throttle servo, which is probably too much work if you used the provided throttle servo mount.

I have not tried it, but I believe that a Tettra 4 ounce tank may be able to fit in the forward tank area in a Viper, possibly with a little grinding on the front wing hold down plate.

Filling a bubbleless tank requires a large syringe like the JETT Tanker, or the H&M Racing syringe.

If you are the industrious type, you can also convert a standard tank using a baby bottle liner for the bladder.

I have heard that Sig has a less expensive syringe that can be used for filling the tanks.

You also need a pair of hemostats, or a fuel line clip. Unfortunately these Fuel Shutoff Clips appear to be discontinued.

_____________________________

Don Stegall
RCPRO Chairman of the Board

(in reply to jkidless)

RE: High Speed Turn Lean-out on Viper - 9/19/2004 10:31:03 PM

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From: Clarkdale, AZ, USA
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After the Bladder tank (i like to use the Jett tanks myself) if it is still bogging around tight turns, if u r not already doing this, when u r tweeking the needle pinch the fuel line for a second and c how much the engine picks up...if it doesnt pick up at all then u r to lean and around turns it will bog or even die...im sure u already do this but if not it will help...

Cole

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SAM-RAI Racing

(in reply to PylonWorld)

RE: High Speed Turn Lean-out on Viper - 9/20/2004 12:11:32 AM

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Joined: 1/19/2004
From: Victoria, AUSTRALIA
Status: offline

quote:

ORIGINAL: Ed Smith

Use the type of tank that Don suggested, it will solve nearly every engine/tank problem known to mankind. I do not know what you are using, but you should be using pipe pressure, not crankcase pressure.

Ed S

Ed,
Am curious about the "not crankcase pressure" advise. Why doesn't CCP work?

This will be an issue for me as I'm building an AJ2(QM15) up for use in the Australian QM class (.21 size engines in QM15 size airframes), and the only pressure fitting on my engine/pipe combo (Cyclon with Magic Muffler) is in the middle of the backplate.

Cheers,
Dave

(in reply to Ed Smith)

RE: High Speed Turn Lean-out on Viper - 9/20/2004 1:06:06 AM

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From: oak forest, IL, USA
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Cole,
After I get my bladder set-up I will see how things go. I did do the pinch test, but I guess the G's are too much.Thanks for your help.
John

(in reply to ColeThornton)

RE: High Speed Turn Lean-out on Viper - 9/20/2004 2:07:44 AM

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Joined: 12/29/2001
From: Brantford, ON, CANADA
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Dave,

Two things. None of our racing engines, Q500, Q40 or F3d with tuned pipes use crankcase pressure. So that should tell you something.

I started off F3D with crankcase pressure and thought I was doing OK. Then I went to pipe pressure. the difference was truly amazing. With CCP I was forever fiddling with the needle and pinching the line at the same time to get the engine to the first stage. With pipe pressure, assuming everything else was set up correctly, the engine needled up to full tune with no effort. The engine started, needled to the first stage, needled up to where it jumped on the pipe and final setting.

I can only guess it has something to do with CCP being pulsed by the piston stroke while Pipe Pressure is smoother and constant.

Ed S

(in reply to Shackas)

RE: High Speed Turn Lean-out on Viper - 9/22/2004 5:29:13 AM

Per_N

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Joined: 9/4/2002
From: Stockholm, SWEDEN
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John
Just turn the needle out 1 or two clicks, this is a standard problem. Here we are not allowed to use bladder tanks, so this problems happens if you lean out too much.

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Per
Sweden

(in reply to Ed Smith)

RE: High Speed Turn Lean-out on Viper - 9/22/2004 5:41:23 AM

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Joined: 3/2/2003
From: Over da rainbow, KS, USA
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Have you tried moving the tank up in the fuselage? The old Formula one's were critical of tank position, and you "tuned" the tank position so that the engines could pull the gee's without going lean. Usually 1/8 to 1/4" change in height was all that was required. Also, if your fuel line is too small or long it is restrictive of flow. Running on pipe pressure is easy, the pressure is low, while CCP is sensitive to the size of the port on the engine. Too large and it becomes very touchy, but when sized right it works OK with unthrottled engines.

(in reply to Per_N)

RE: High Speed Turn Lean-out on Viper - 9/25/2004 3:04:45 PM

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Joined: 10/7/2003
From: oak forest, IL, USA
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Hi Don
I will be trying out my new tank today.
I will let you guys know how it works.
John

(in reply to PylonWorld)

RE: crankcase pressure on .21 - 9/28/2004 5:03:23 PM

DHG

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Joined: 4/24/2002
From: Arvada, CO, USA
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Dave,

We used to use crankcase pressure on the .15s in the original Quarter Midget class. As long as you're not trying to throttle the engine, it works OK. Finding the needle the first time is a bit tricky, since the crankcase generates a lot of pressure and it's easy to flood the engine if your setting is too rich. On the Quarter Midgets, the exhaust system was a simple tube extractor that didn't create any pressure, so the only way to pressurize the fuel system was to tap into the crankcase.

If the Australian rules require/allow use of a muffler or pipe, I would recommend blocking off your crankcase pressure tap and installing a pressure tap on the muffler or pipe. This will allow you to manually prime the engine at startup by blocking off the tailpipe with your finger.

If you're using an extractor, you'll need to stay with the crankcase pressure. Use trial and error to find the correct needle setting. After that, startup is a simple 2-step process:

1. Insert earplugs.

2. Hit it with the electric starter until it runs.

Duane Gall
RCPRO

(in reply to Shackas)

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