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Jul 25, 2007, 08:01 AM
Thread OP
Discussion

how to cut engine off if...?


hello. i think lot of modellers have such problem, like weak throtile linkage on airplanes, which causes engine dying when ideling (even when idle is set ok) so i think to adjust idle screw the way, that it won't let enigne cut off due to linkage vibration during engine operation (especially 4 stokers and gassers). so I'm sure anyone has done this way, but how can i cut off engine in flight?
plz, don't ask me why i need cut it off in flight

thanks in advance
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Jul 25, 2007, 08:05 AM
Registered User
turk1's Avatar
Gospodin,you should use your transmitters throttle cut function or/and throttle trim function.
Jul 25, 2007, 08:54 AM
Most computer radios have an engine cutoff. You can shut it off anywhere
Jul 25, 2007, 09:02 AM
Thread OP
u don't understand me.
everything is set ok on my plane, but: when i adjusted EPA for idelign, rpm was more than when i hold throtile controll arm on carb with fingrs. so when this arm doesnt' vibrate, engine can run on lower RPM. i thought about using rubber holders for linkage, whick will work like demfer.
Jul 25, 2007, 09:29 AM
Registered User
Not sure I understand your problem. But set your idle trim to the top, adjust your linkage so that it idles with the idle trim (channel 3) set at the top. Then when you want to cut off the engine, move the idle stick all the way down and then move the trim down, it will cut off the engine. Most of us cut off the engine, that is stop the engine, by using the throttle trim button. Some transmitters do have a cut off button, that causes the engine servo to travel to the max cut off position and causes the engine to quit. Some transmitters have a programmed method of doing this too.

Any way, it appears to be a linkage problem, the amount of travel in the throttle arm on the engine. Vibration should not enter into the problem, it is there and will always be there. You may also use end point adjustment (EPA) to set the travel on the servo. I also use a screw stop on the servo arm so that I can move the linkage without removing the servo arm. On Futaba radios that is called ATV instead of EPA but it is the same thing. These features are found on the mid to up class radios. The simpler four channel radios do not usually have such features.

Good luck,

Chip
Jul 25, 2007, 10:40 AM
Zor
Zor
Suspended Account
Quote:
Originally Posted by Bako
hello. i think lot of modellers have such problem, like weak throtile linkage on airplanes, which causes engine dying when ideling (even when idle is set ok) so i think to adjust idle screw the way, that it won't let enigne cut off due to linkage vibration during engine operation (especially 4 stokers and gassers). so I'm sure anyone has done this way, but how can i cut off engine in flight?
plz, don't ask me why i need cut it off in flight I shall not ask. Big secrets?

thanks in advance
Bako Hi,

I am not aware that any modern (recent) transmitters have an engine cut off function in terms of a switch or other means that says "engine cut off" (or similar wording). Perhaps there is that I am not aware of.

Throttle control and throttle trim are used in a properly set up throttle.

The throttle stick comes all the way back for idling while the throttled trim is centered or has enough motion to fully close the carb. Bringing the throttled trim to minimum fully close the carb and shut off the engine.

If you read back in this forum you will find extensive discussions on setting the engine throttling set ups (akjustments).

Regards

Zor.
Last edited by Zor; Jul 25, 2007 at 10:48 AM.
Jul 25, 2007, 10:48 AM
Registered User
turk1's Avatar
Bako,that linkage normally never vibrates as much unless it is called glitching.Are you sure it is vibration but not glitching of servo?
Jul 25, 2007, 02:52 PM
Thread OP
o dunno waht means glitching, but i tell you, good people, 3-rd time: when i set up minimum ideling by radio, engine idels faster. and when i hold this linkage nead carburator arm, this way engine can idel on lower rpm-s. I think, that from the vibration linkage shekes, it's changing his length on axis X and this way carb arm rotates a bit from bit opened to bit closed, whcich closes the little remaining hole in drossel and whick provides endine dying.
Jul 25, 2007, 03:59 PM
S.A.D. member
ivanc's Avatar
Bako, sounds like you have throttle linkage problem - possibly slop somewhere between the servo arm and carb barrel arm. There's no way that simply engine vibration will close the throttle enough - if it vibrates, it shakes in both direction and the barrel will not only close but also open while the average setting will stay the same and that is what matters.

Another possibility is that your low end needle is set up too rich. As the engine idles it loads up with fuel and eventually dies. If this is the case adjust the low end needle for reliable idle and transition.

Ivan
Jul 25, 2007, 07:48 PM
Loose engine mount or engine? pulls forward at WOT, and settles back at idle? Just something to look at. Re-adjust so no fast idle with radio setting, forget about holding with fingers. probable servo set-up problem EPA not right. FOUR strokes normally run just fine. One last thing I can think to check, The carb has a screw that retains the carb barrel " the whole part that rotates" and can also set the mininum idle. Too far in gets higher idle, too far out gets sloppy, side shifting motion that can cause high to low idle at one radio setting, which would disappear if you held it with your fingers. GOOD LUCK REPORT BACK IF YOU GET IT FIXED. WE WANT TO KNOW CAUSE. The screw I,m referring to normally sticks upward and has a set nut to keep it locked in place. It is not an idle or high speed needle.
Jul 25, 2007, 08:07 PM
Suspended Account
I suspect you have the fuel mixture set too rich at idle. When you hold the throttle arm you might be pushing in the throttle barrel leaning out the mixture. If there is any slop in the throttle cam it will allow the throttle barrel to move in and out this will also allow the low speed (idle) mixture to change (this is for twin needled and tube and barrel type carbs) as these idle mixture adjusters are usually carried in the throttle barrel. This motion will have a greater effect on the fuel mixture (Fuel flow) than the air flow (carb throat opening). I would also look at what is known as an Ackerman effect. This is what happens when changing linear motion (push rod) to radial motion (the carb barrel).

Please let us know what type of engine you have. Can you get us a photo of your installation?

Friends don't let friends fly nickel,
Konrad
Jul 25, 2007, 08:18 PM
How much slop (play) do you have in your linkage? If you can move the throttle arm on your carb hardly any without your servo moving, that may be too much. If you can noticeably move the servo without moving its drive motor (and thus hearing gear noise and feeling resistance), you should change the servo out.

As far as your original question: Cut the fuel. You can sometimes close the needle valve (remembering where you had it). If you have a fuel button, inserting the fuel probe to fuel the plane should stop fuel to the engine. (these can be troublesome though). The RC car guys pinch the fuel line closed to stop the engine. Some stop the flywheel using their shoe, but a whirling prop is a bit harder, and more painful. Don't use the shoe method!
Jul 25, 2007, 10:36 PM
Quote:
Originally Posted by Zor
Bako Hi,

I am not aware that any modern (recent) transmitters have an engine cut off function in terms of a switch or other means that says "engine cut off" (or similar wording). Perhaps there is that I am not aware of.

Regards

Zor.
Where the heck have you been the last 10 years? Most computer radios have a functional switch as mine used to shut the engine off without having to fool with the throttle trim as in most cheap 4ch tx's. To please you, it may not specifically state "engine cutoff" but 99% use it as such.
Jul 25, 2007, 10:56 PM
Suspended Account
On second reading I have to ask, are you stalling the servo against the idle stop screw? Is this an atempt to gain a steady idle speed? Are you using a soft mount system?

A photo would help.

Friends don't let friends fly nickel,
Konrad
Jul 26, 2007, 01:48 AM
Thread OP
ok.
I have magnum 91rfs
haitec eclipse TX (with throtile cut off function...... whicj i use wery well)
I don't miss low and high speed needles, no idle stop screws.
my engine idels perfectly, steady, it can idel more than minute with no proplem.
when i'm holding throtile arm on carb with fingers, i don't push it in ( i know, that will chenge mixture). I think, that all this problem is caused with looooong controll linkage from center of the plane to carburator. it's about 30cm in length and it's made from 1mm steel wire. there is no slope in controll system.
one reason can be:linkage is diving on carb arm and the mixture is changing a bit.
second: due to vibration linkage is bendin, which causes closing drossel a bit.

"If there is any slop in the throttle cam it will allow the throttle barrel to move in and out this will also allow the low speed (idle) mixture to change (this is for twin needled and tube and barrel type carbs) as these idle mixture adjusters are usually carried in the throttle barrel" >>>>>>>>> lcarb throat will newer open more, than i adjusted by radio. it can be closed eventually due to linkage bending.

I think this problem can be solved installing linkage in tube, which full provide this wire from servo to throtile arm. and also i'll try to let the linkage near carb go thrue rubber (about 3mm), whioch will work like demfer.

and about cutting the engine off. yes, i'm using tuc off funktion, which rotates serv arm more and closes carb throat. but i asked u, how can i cut engine off if i adjusted minimum rpm by idel stop screv, this screw won't let carb throat close completely.
now my screw is loosed enought to let engine die in flight if i want.

and at last, i think i must apologise for my english


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