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Gasser Model RC Helicopters > Need help.. engine starts at >50% throttle?!
 
 
nicklau
Heliman
Location: Hong Kong

Hi all, I bet topics in engine tuning have been discussed many times. But I read many and didn't find a common one similar with my case.

I am tuning Zenoah G26PUH for my heli. I set the throttle opens from 0 to 100% with the throttle curve, and set the pitch curve from -2deg at 0%, 5deg at 50% and 12deg at 100%.

The high and low speed needle are set at default settings stated in the manual, 1 7/8 and 1 1/8.

But the problem is that the engine starts only when the throttle stick at mid position (>50%). At 50% the throttle is half open. Is it too much fuel? Should lean the low speed needle??

More, when engine starts, the rpm develops quickly and suddenly when I set the stick at nearly 100% (fully open).. is it a high speed needle's problem???

Thanks~!
07-22-2008 04:35 PM
 
 
kcass518
Veteran
Location: Manhasset, NY - USA

I don't know anything about the Zenoahs, but it sounds to me like your mechanical setup is off a bit. When your throttle is at 50%, is the carb barrel half open? Can you see the barrel? My throttle has markings on its mount that show me when it's closed, half open, and full throttle and I make sure that when I'm at half stick, my throttle is actually 1/2 open, and the servo arm, pushrod and throttle arm are all at 90 degrees. You may have to adjust the carb barrel relative to the throttle arm position.
07-22-2008 05:35 PM
 
 
nicklau
Heliman
Location: Hong Kong

It doesn't have marks for the close-mid-full opening on the G26. And from the pictures, can you tell if it's off a bit mechanically??

I guess it's proper to set the throttle curve starts from 0% to 100% at the very beginning??

Thanks.
07-23-2008 07:13 AM
 
 
enahs
Veteran
Location: Valparaiso, IN

You might want to post this in the gasser section on here. You'd probably get more responses to help you.

---------
Shane Eagan
07-23-2008 01:35 PM
 
 
JuanRodriguez
Elite Veteran
Location: Rochester, New York

For starters........

You should NOT be using your throttle curves to adjust the initial travels while adjusting your linkage...... You should use your throttle ATV to do that.....

Go to your ATV program and adjust your throttle ATV so that the linkage does not bind at full throttle OR at low throttle. You should be FULLY closed with the throttle trim all the way down so that you can shut the motor off at low stick, trim down....

It is in this program (ATV) where you should be checking that your throttle is 1/2 open when the stick is at 1/2.......

Once you verify the above, then you would adjust your throttle curve to suit your needs.....

And here is why you may be having the problem you described.......

You have only three points "active" on your throttle curve.....0-50-100. The rest are "inhibited"......

You need to "activate" all of your points so that you can set up your throttle curve to read similar to this : 0-25-50-75-100.

Once you activate these points, then you can adjust any of those points up or down as needed....You SHOULD NOT be attempting to start the motor at 50 % throttle setting !! The motor should start nicely and idle nicely with the butterfly open just a crack, probably under 25%......Let me know if this all makes sense....

Lastly, please do yourself a BIG FAVOR and find someone locally to help you set up and test hover your machine......

PS-- Don't mess with the needles of the carburator. Leave them at factory settings for now...
07-23-2008 01:37 PM
 
 
Pistol_Pete
Elite Veteran
Location: Tampa Bay non-Buccaneer

Quote 
Go to your ATV program and adjust your throttle ATV so that the linkage does not bind at full throttle OR at low throttle. You should be FULLY closed with the throttle trim all the way down so that you can shut the motor off at low stick, trim down....

I have a question!

Do you gasser guys use fail safe?

Reason I ask is if you adjust ATV for low throttle rather than doing it mechanically, in fail safe mode, your servo will travel way pass ATV settings.

I adjust ATV for high throtle but never low.

Does it make sense?

<><>...the lunatic is in my head...<><>
07-23-2008 02:42 PM
HOMEPAGE  
 
 
nicklau
Heliman
Location: Hong Kong

Thanks all!

Quote 
Go to your ATV program and adjust your throttle ATV so that the linkage does not bind at full throttle OR at low throttle. You should be FULLY closed with the throttle trim all the way down so that you can shut the motor off at low stick, trim down....

Yes I used ATV to set the throttle to fully close and fully open, and not by the throttle curve.

Quote 
PS-- Don't mess with the needles of the carburator. Leave them at factory settings for now...

Ar.. I think it's a bit too late. I already adjusted the needles. But when I start with the 'default' condition, the engine doesn't start. So I follow the manual and set the H and L needle to 1 7/8 and 1 1/8.

Can someone tell me how to tell where is the start point of each needle? Fasten it until I get some 'resistance'? I can't see any marks.

Quote 
You SHOULD NOT be attempting to start the motor at 50 % throttle setting
Yes I think it's quite abnormal. But my engine ONLY starts when throttle is half open. Is it too much fuel? The low speed needle is too rich, and need to lean by fastening it?

Thanks again.
07-23-2008 05:39 PM
 
 
nmrs
Senior Heliman
Location: Austin, TX

Quote 
You have only three points "active" on your throttle curve.....0-50-100. The rest are "inhibited"......

You need to "activate" all of your points so that you can set up your throttle curve to read similar to this : 0-25-50-75-100.

Inhibited just means the point will fall mathematically exactly between the points that are activated. On a five point curve 0-25-50-75-100 is identical to 0-inh-50-inh-100. (The same would apply to his 7 point curve; I was just lazy to do that 7 point math...)

450 se v2
07-23-2008 05:43 PM
 
 
rbort
Elite Veteran
Location: Franklin, MA - U.S.A.

Reset needles

To 1 3/8 on each.
Set ATV so you get 120/120 to 140/140 from fully closed to fully open with idle trim on kill.
Enable throttle curves and cut them down - should not be 50% at midstick, try 25% to start there.

P.S. Engine will start/run at different throttle settings depending on L needle. High needle can be fully closed and engine will still start and idle, run up to hover. NOT SAYING close the high needle, just saying to make it clear which needle does what. High needle comes in after 1/2 throttle to full throttle to assist low needle with more fuel flow.

-=>Raja.

1005 Xcell Gas, BHH G26 3D Plus, Jewel Generator
Spectra-g, BHH G26 3D Plus, Jewel Generator
07-23-2008 06:19 PM
 
 
doorman
Elite Veteran
Location: E.Berne, NY

I Think You Have Nailed It!!!!!!!!!!!!!

Hi Raja.

I was about to post the same thing, but read yours first.... you "beat" me this time!!!!!
Going to IRCHA????? We will be there Thurs-Sun...
See you soon....Stan

If there is a cure for this, please don't tell me about it!!!
07-23-2008 09:10 PM
 
 
rbort
Elite Veteran
Location: Franklin, MA - U.S.A.

No IRCHA for me...too far unfortunately

Hi Stan!

But going to Delaware tomorrow. Are you coming down there? Will PM you too!

-=>Raja.

1005 Xcell Gas, BHH G26 3D Plus, Jewel Generator
Spectra-g, BHH G26 3D Plus, Jewel Generator
07-24-2008 02:03 AM
 
 
sean911sc
Senior Heliman
Location: San Diego, CA

There are some great post on throttle setup. As mention above - get the mechanical setup first. I'm new to gassers, but I'm flying curcuits with my Vario trainer with 4-blade 2-bolt head.

ATV's as Raja stated to as a start.

What worked for me: Set TX: T-curve to 0/100 linear curve only for initial mech setup. Throttle trim at 0% is engine cut, 50% is engine start (low idle) or about 6% on curve when all is said and done.

During my mech setup I used what looked to be 50% open butterfly based on control horn travel. Match to TX 50%. TX 0% with T-Trim fully down - butterfly closed. TX 100% - butterfly fully open.

Now with that set, I zero all throttle points on T-curve and set all points to 5% (roughly my idle/engine start position). My pitch curve is also set to allow only a hover at most (low to mid stick is a pitch range of -2 to +6).

I now step thru all seven points with a spotter on tach and bring the throttle curve up at each point until target RPM is reached.

Once throttle curve was set and flyable I added GV1 and Stator Gator. Works very well and now have about 5 gallons on the meter.

Sean
07-24-2008 05:03 AM
 
 
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Gasser Model RC Helicopters > Need help.. engine starts at >50% throttle?!
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