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Throttle spring reversal

steve wyman

Well Known Member
I mentioned reversing my throttle springs on the after flight mods thread, and I seem to have opened up a can of worms and I don't want the thread to drift from the original subject. In answer to you folks that object to my reversing the springs, you should also realize that I'll also be reversing the actuation direction at the same time. This means that when you push the throttle to full power, you are actually, physically pulling the throttles open ( the springs will, then, only aid in pulling the throttles back to idle). I used this same setup for 3 years on my RANS S-7, with no problems. In fact, RANS has you make this mod, in the build.
 
Isn't one of the purposes...

...of the throttle spring to make the engine go to full rpm if the throttle cable or a linkage breaks?

Your system would give you an idling engine if a throttle cable failure occurs.
 
When I built the Zenair CH601HDS, I did away with the springs altogether and used pushrods to control the throttles.
I never liked the "cable" approach.
 
...of the throttle spring to make the engine go to full rpm if the throttle cable or a linkage breaks?

Your system would give you an idling engine if a throttle cable failure occurs.
You are absolutely right, but tell me what you think the chances are of both throttle cables breaking simutaneously? If only one breaks( as is most likely), you will have a situation wherein one half of the engine is at full throttle, and the other half at something less, unless you open it up to match. In this scenario, you are then flying at full throttle, while managing an emergency situation, controlling power with the ignition switches? I think I'd rather just accomplish an engine out procedure, and maintain a good glide speed. I practise this on almost every flight, just for drill. Steve
 
Fail safe

The springs are supposed to open the throttle in case of linkage failure. I think the most likely point of failure is where the cable connects to the throttle lever. Some airplanes have crashed after a throttle cable failure and the throttle closed. I think that the springs used on the Rotax are too strong. The throttle will creep forward unless the friction wheel is very tight. And the springs will pull the throttle right out of your hand if you are not careful. There should be a throttle design that is easy to operate and stays where you put it. While flying, failing open is better. On the ground, failing closed is better. I would like to see a failure mode that keeps the throttle in the last position selected by the pilot.
Joe
 
I think I would rather have....

You are absolutely right, but tell me what you think the chances are of both throttle cables breaking simutaneously? If only one breaks( as is most likely), you will have a situation wherein one half of the engine is at full throttle, and the other half at something less, unless you open it up to match. In this scenario, you are then flying at full throttle, while managing an emergency situation, controlling power with the ignition switches? I think I'd rather just accomplish an engine out procedure, and maintain a good glide speed. I practise this on almost every flight, just for drill. Steve

...more power that can be controlled on/off, than no power (or idle power) that is fixed...:(
 
I have to agree. Having no power over hostile terrain = dead. Having choices in an emergency is good.
 
My CT has a throttle lever design which has not required friction adjustment in the 230 hours I have flown it. It is smooth, easy to move and stays put. It is spring loaded to full throttle in case of cable failure.

So, to answer Joes comment, there is a design that will do as he asks but I think it would be difficult to adapt to the 12. Then again, I don't have the talant to do something like that.
 
I had a scary issue a few years back with my 6A using a vernier throttle. I took out the vernier feature and loved it thereafter. I am not crazy about the Rotax setup with the spring to full on failure altho I can appreciate the practical aspects of the theory. If a separation of only one carb cable occurred on landing however that could be interesting. My vote goes with Mel's idea of push rod control . I wonder how difficult that would be to install on the Bings?
Dick Seiders 120093
 
My vote goes with Mel's idea of push rod control . I wonder how difficult that would be to install on the Bings?
Dick Seiders 120093
On the Zenair I installed a "belcrank" on the firewall consisting of a horizontal shaft running in nylon bearing blocks. Welded to that are vertical rods aligned with the throttle levers. Ran a pushrod from each of these to each of the throttle arms. It's been flying for 1300 hrs without problems.
 
I cannot wrap my mind around having a throttle go closed if a control breaks. I can always kill the engine running full throtle, but cannot bring it up to power when at idle. I like control!
 
You'd be pushing on a rope

or at least on a flexible cable. I looked at this since I don't like the excessive throttle creep either, but if you reverse the spring attachment than you'll be trying to push the throttle arms with a pretty flexible cable. I don't thik you could ever keep the carbs in synch. I WOULD like to find some softer springs-- does anyone know the specs on the Rotax-supplied springs?

Wayne 120241 143WM 10 hours now.
 
or at least on a flexible cable. I looked at this since I don't like the excessive throttle creep either, but if you reverse the spring attachment than you'll be trying to push the throttle arms with a pretty flexible cable. I don't thik you could ever keep the carbs in synch. I WOULD like to find some softer springs-- does anyone know the specs on the Rotax-supplied springs?

Wayne 120241 143WM 10 hours now.
Wayne, you not only reverse the springs, but you reverse the throttle actuation brackets, also. This way when you push the vernier knob to full power, you are actually physically pulling the arms on the carbs to full power- the springs, then, only aid the throttles in coming back towards ide. Steve
 
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