McFarlane Throttle springs

by Sean Lillico in General Tech Discussion 8 years ago

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Re: McFarlane Throttle springs

by James Ott » 8 years ago

James Ott

22 323 359

I have a question about throttle springs. I am now using the lightest McFarlane springs on my 912uls and am much happier than with the original Rotax springs. However, I would really prefer to remove the springs entirely and operate springless, or maybe with just one very light spring on one side only. My question is: has anyone experienced any carb sync problems when operating springless? Since the springs always urge the throttle cable towards WOT it seems to me that this would remove any tendency for slight slop in the cable to affect the carb sync. Without springs your cables would need to be absolutely free of any slop (hysteresis). Anyone have any experience or thoughts on this?

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Re: McFarlane Throttle springs

by Roger Lee » 8 years ago

Roger Lee

127 5.2k 4.78k

Hi james,

No springs can make carb syncs harder. Nothing there to stretch and pull the cable all the way out. No springs also means you are going to land right below you if a cable broke or for some reason the cable quit on one or both sides. Having the carb go WOT on an affected side will allow the user to go WOT on the unaffected side. Then you could fly where you need to be to a field and land. You wouldn't want a carb doing it's own thing while flying in an emergency situation. I follow the Vans website. They have too many broken springs and the cause of the problem should be resolved not just throw another spring at it.
The guys who reversed to springs to close the throttle makes no sense to me and they are going to land right under themselves too. I see no redeeming qualities to reverse the carb spring. McFarlane has so many broken springs I think it is the spring metallurgy being too brittle. A softer metal would have more give and less vulnerable to brittle vibration breakage.

Nothing wrong with lighter springs.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: McFarlane Throttle springs

by James Ott » 8 years ago

James Ott

22 323 359

Thanks Roger.
Just curious though about losing a cable on one side or both and then the springs go to WOT. Yes, this allows you to fly towards a better landing field, but you can't fly at over 5500 rpm for more than 5 minutes. Then you would have to shut the engine down for a while and then restart. Will the engine restart OK at WOT or will it just flood?

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Re: McFarlane Throttle springs

by Roger Lee » 8 years ago

Roger Lee

127 5.2k 4.78k

I know I'll regret putting this in print.

Yes the engine could flood at a WOT setting on a restart. You could how ever help that in a shallow dive to get the prop up to speed and try it. I have not tested this so this is pure conjecture. It would not how ever bother me to fly at 5700 rpm to a field more than 5 minutes away. My engine turns 5650 rpm at WOT. I would fly 15-30 minutes to a field if it meant not crashing and destroying me or the plane. In an emergency sometimes you have to step outside the normal day to day operational box.
There is a safety and liability factor there and I personally wouldn't worry about the 5 minutes.

This has to be a personal choice if you want to cross this line.

Maybe Rob or one of the other experienced guys here will chime in and we can get their take.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: McFarlane Throttle springs

by Rob Seaton » 8 years ago

Rob Seaton

3 1.32k 240

Remember that the certified and non-certified 912/914 series engines are the same; same parts, same production line, same dimensions. (paperwork is the big difference)
Here is the EASA CS-E 440 Endurance Test endurance run that all the engines have passed to earn certification.
After the endurance run the engine is torn down all parameters must be within serviceable limits.

Part 1 A 30-hour run consisting of alternate 5 minute periods at Take-off Power and speed
and Maximum Best Economy Cruising Power or Maximum Recommended Cruising Power conditions.

Part 2 A 20-hour run consisting of alternate periods of 1.5 hours at Maximum Continuous
Power and speed and 0.5 hour at 75% Maximum Continuous Power and 91% Maximum Continuous speed.

Part 3 A 20-hour run consisting of alternate periods of 1.5 hours at Maximum Continuous
Power and speed and 0.5 hour at 70% Maximum Continuous Power and 89% Maximum Continuous speed.

Part 4 A 20-hour run consisting of alternate periods of 1.5 hours at Maximum Continuous
Power and speed and 0.5 hour at 65% Maximum Continuous Power and 87% Maximum Continuous speed.

Part 5 A 20-hour run consisting of alternate periods of 1.5 hours at Maximum Continuous
Power and speed and 0.5 hour at 60% Maximum Continuous Power and 84.5% Maximum Continuous speed.

Part 6 A 20-hour run consisting of alternate periods of 1.5 hours at Maximum Continuous
Power and speed and 0.5 hour at 50% Maximum Continuous Power and 79.5% Maximum Continuous speed.

Part 7 A 20-hour run consisting of alternate 2.5 hour periods at Maximum Continuous
Power and speed and Maximum Best Economy Cruising Power or Maximum Recommended Cruising Power conditions.

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McFarlane Throttle springs

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