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01-27-2013, 10:43 AM
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Join Date: Oct 2005
Location: Independence, OR
Posts: 396
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Prop Governor Spring Is Too Powerful
In my RV-8A project I find that the spring in the prop governor is so powerful that it puts the prop into the full high RPM setting unless I set excessive throttle friction (one setting affects all three levers on the quadrant). At any reasonable setting of the throttle friction, the prop control won't stay put; it moves forward.
The governor is a Hartzel S-1-0 bought from Van's and the throttle quadrant is the "deluxe" model (there's nothing deluxe about it) from the accessory catalog.
I'm not interested in converting to a separate control for the prop governor. And I think I understand the reason for the spring (high RPM in case of cable breakage).
So what does that leave me for an acceptable method of dealing with this? Is it permissible to "unwind" the torsion spring mounted around the cable-connect arm of the governor to effect less force on the cable?
Thanks,
Joe
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Joe Dubner
RV-8A
Independence, OR
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01-28-2013, 02:03 AM
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Join Date: Mar 2006
Location: Gilbert, AZ
Posts: 1,628
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You are dealing with an experimental airplane. You can do anything you want with the spring. I had a similar issue with the "deluxe" quadrant. The single friction lock would bind one control before it added a bit of friction to another. I ended up using a separate vernier control for both prop and mixture controls. (I know, you don't want to do that. I must ask, why not?) Most modern aerobatic aircraft use this set-up. I'll never go back!

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Ron Schreck
IAC National Judge
RV-8, "Miss Izzy", 2250 Hours - Sold
VAF 2021 Donor
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01-28-2013, 07:04 AM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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Quote:
Originally Posted by ronschreck
...I ended up using a separate vernier control for both prop and mixture controls. (I know, you don't want to do that. I must ask, why not?) Most modern aerobatic aircraft use this set-up. I'll never go back....
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+1 on the entire post. Do what you want with the spring... And the vernier on the prop and mixture is the only way to dial in RPM and LOP temps... And they stay that way no matter how loose the throttle lever is.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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01-28-2013, 07:31 AM
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Join Date: Oct 2005
Location: Independence, OR
Posts: 396
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Thanks for both of your replies. Sure, I can do what I want with the spring but I'm looking for "accepted methods"; I'm loathe to capriciously toss out a safety feature.
OTOH, the push-pull cable is highly unlikely to break, so maybe removing the spring really is the answer. After all, there are no springs on the throttle and mixture controls.
This is yet another part of the RV-8A build that falls into the category of "if I had known then what I know now ...". :-(
--
Joe
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Joe Dubner
RV-8A
Independence, OR
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01-28-2013, 07:48 AM
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Join Date: Apr 2006
Location: Vancouver island, BC Canada
Posts: 385
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I've come to the same point. With a 3 lever quadrant, I need too much friction to keep the prop lever steady. I also spend way too much time fine tuning the power. Time to change to vernier prop and mixture.
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Jim Green
RV7 tip up
IO360 Whirlwind 200RV
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01-28-2013, 11:27 AM
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Join Date: Mar 2006
Location: Gilbert, AZ
Posts: 1,628
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Quote:
Originally Posted by Joe
Thanks for both of your replies. Sure, I can do what I want with the spring but I'm looking for "accepted methods"; I'm loathe to capriciously toss out a safety feature.
OTOH, the push-pull cable is highly unlikely to break, so maybe removing the spring really is the answer. After all, there are no springs on the throttle and mixture controls.
This is yet another part of the RV-8A build that falls into the category of "if I had known then what I know now ...". :-(
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Joe
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Joe,
I would never bypass a safety feature without giving it a great deal of thought. Look at it this way. If your prop control cable breaks and there is no spring to drive the governor to fine pitch what are you left with? At worse a prop in coarse pitch. Not feathered or in reverse pitch! So what do you do in that worse case? Land without incident and fix the cable. You will have ample power at coarse pitch to do a normal landing. Maybe even a go-around!
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Ron Schreck
IAC National Judge
RV-8, "Miss Izzy", 2250 Hours - Sold
VAF 2021 Donor
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01-28-2013, 12:03 PM
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Join Date: Nov 2006
Location: Perham, MN
Posts: 350
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Joe,
Did you contact the governor manufacturer? I know my PCU-5000x governor is available with different torsion spring configurations. Maybe they can provide a weaker spring.
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Paul Winkels
RV7 Standard Build - First flight 4/16/2016 - Now Flying!
Last edited by Sparky : 01-28-2013 at 04:06 PM.
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01-28-2013, 04:40 PM
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Join Date: Apr 2006
Location: Ottawa , Canada
Posts: 224
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Joe,
I had a similar concern with my Hartzell governor during installation. I had the following email exchange with Hartzell support:
I asked:
I am installing the throttle quadrant in my RV-8, and I noticed that the spring force from the governor to return to 'fine' position is faily large, and will require a lot of friction locking on the quadrant to hold a prop setting.
Is this spring force reduced when the engine is running due to oil pressure?
Les Doud, from Hartzell replied: (a member on these forums BTW)
Yes, the spring force is reduced with the engine running but not from oil pressure; the flyweight reaction is what reduces the spring force.
If the spring force is still considered unacceptable after you start flying, let us know and we should be able to provide a spring with lower force.
I have been flying for a year and a bit now, and I find the tension on the quadrant acceptable (ie: smooth to operate, and it doesn't drift) with the stock spring.
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Chris Hepburn
Ottawa, ON
RV-8 C-GOGO FLYING
Renew 12/20
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01-28-2013, 05:20 PM
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Join Date: Oct 2005
Location: Independence, OR
Posts: 396
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Quote:
Originally Posted by chepburn
Yes, the spring force is reduced with the engine running but not from oil pressure; the flyweight reaction is what reduces the spring force.
If the spring force is still considered unacceptable after you start flying, let us know and we should be able to provide a spring with lower force.
I have been flying for a year and a bit now, and I find the tension on the quadrant acceptable (ie: smooth to operate, and it doesn't drift) with the stock spring.
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Thank you, Chris; this is the best news yet! I had not considered that the net force of the spring would be different under operating conditions.
I had taken Sparky's suggestion and called Hartzell. The nice lady in tech support had actually heard of this situation before but said they didn't have any other springs. They did have some different lever arms (at $27.50 apiece  ) that I could experiment with. F'getaboutit!
But for the archives and for anyone who cares, here are the Hartzell lever arm part numbers and their hole-to-hole distances: - 102309 1.3 inches (came with the governor)
- 102551 1.5 inches
- 102368 1.637 inches
- 103568 holes at 1.3, 1.713, and 2.125 inches)
Later I spoke with Gus at Van's and he acknowledged the problem. Some RV-10 builders (who occasionally also use the quadrant) have been running into the same issue. Gus suggested adding a tension spring to counter some of the force of the Hartzell torsion spring. One end of the new spring could easily be anchored on the cable attach bracket but the spring rate and length would still require calculation and testing.
"Unwinding" the tension spring is not a very good idea; nearly all of the force probably comes from the last turn. It would have to be "unwound" a fraction of a turn which would necessitate a new attach tab.
So plan A is to do like Chris (I will re-evaluate after flying) and plan B is to contact Les Dowd about a new spring if needed.
--
Joe
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Joe Dubner
RV-8A
Independence, OR
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01-29-2013, 03:56 PM
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Join Date: Sep 2010
Location: Redlands, Ca.
Posts: 1,458
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Simple Fix!!!!!
....You could add a small helper spring to cancel off part of the other spring and adjust it to what ever it takes to keep everything happy. Simple and not costly and very easily removed if you desire. 
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Allan Nimmo
AntiSplatAero.com
Innovative Aircraft Safety
Products, Tools & ServicesInfo@AntiSplatAero.com Southern California (KREI)
RV-9A / Edge-540 
(909) 824-1020
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