Rocket and Missile Prop Governor Failure Mode

[Seth]

Erik has a beautiful new prop on his Mooney that saved about 30 pounds of weight and removed his ability to fully feather the prop for glide purposes.  However, it also removed a previously unknown safety hazard.

Evidently, on Mooney Missiles and Mooney Rocket conversions, the failure mode for the prop governor is automatically feathering the prop.  This makes sense on a twin, which is where the setup came from originally, but it is horrible on a single as that means if your prop governor fails when taking off, your engine is running great, and your prop feathers a few hundred feed off the ground.

With many singles, the prop governor failure mode is high RPM or low RPM.  I'd rather have that so I'd have some power or control the RPM by the manifold pressure rather than be forced to land with a smooth running engine.

So, here is my questions, is there a way to replace the prop governor with one that the failure mode is not automatic feather without taking away the ability to fully feather the propeller by mechanically engaging the nitrogen gas (which feathers the prop - you simply pull the prop control lever all the way out to feather the prop)?  Is there a modification that can be made to ensure this does not occur?  Did I get bad information?

 

The prop governor on my Missile is a Woodward, model B210444 and my prop is a Hartzall model:  PHC-C3YF-2UF

 

Thanks for your thoughts and suggestions.  I do not like the current and newly discovered failure mode.  I will also be in touch with Rocket Engineering about this.

 

***EDIT and UPDATE****

According to Rocket Engineering the failure mode should the Properller Governor lose oil pressure in both the Missile and the Rocket is automatic FEATHER.  An explanation of why can be found further down in this thread.  

Feel free to PM me.  Good to know for the Rocket and Missile operators with fully feathering props.

 

-Seth

 

 

Edited October 26, 2015 by Seth

[Houman]

Seth, let us know what Rocket tell's you, because I find this to be alarming as well. I will ask my mecanic if he can check my prop governor at my next oil change. 

On the other subject, hope the baby is doing great !!!

Thanks !

[aviatoreb]

I know - I am sorry to have found out about this failure mode but it is quite real.  If I had not been shopping for that whiz bang cool 4-blade MT I probably would never known and also never had a problem and lived on in happy bliss.  Instead, I fixed my unknown-to me problem in the process of getting the whiz-bang prop and left you all with something to worry about. :-(

I very seriously doubt it would be possible an inexpensive change.  That there would be a prop governor that could control that same mcauley prop requiring only a change of prop governor.  Furthermore, even if there were, it would also require at minimum a field approval.  So then you would need to hire someone who knows how to navigate the field approval process unless you are VERY aviation-law savy yourself.  But really, I don't think it exists, a prop governor that is not full feathering to control the full feathering props.  Then if want to replace the prop anyway, might as well get what I got because at the end of the day it is a super setup, even if it is expensive - not more expensive than other props by the way.  Props are expensive when you buy them new.

I suppose if someone were building something from scratch, I bet a prop - prop governor setup could be engineered from scratch that would have a failure mode that would be idea for this application, meaning it would fail to fine pitch instead of full feather but still be a controllable full feather prop.  I bet that does not exist though since full feather props are made primarily for twins where fail to full feather is the desired way.

[Hank]

I thought the reason your Rockets have full-feathering props is because the engine and prop were taken from the Cessna 340? or 414? One of their big twins. Fail-to-feather is very desirable in that application. It has always been my understanding that this is how Rockets operate, but Missiles fail to flat like the rest of us. That's not part of why I would like a Missile, it's mostly cost, complexity, heat and operating expense difference between the two. But for now, my C is doing fine . . . just lower and slower.

Don't know if it's even possible to have a full feathering prop governor made that will fail-to-flat instead of auto-feathering; it's all about how the oil is pushed. Rockets use oil to flatten the blade angle; we use oil to steepen the blade angle. Thus when the engine fails and oil pressure falls, the blade moves on its own. My blade range is only 13º ± 0º to 29º ± 2º, which is a mere 61º from fully feathered    . . . although feathered is probably not a simple 90º rotation when you take into account the airfoil and twist in the blades.

[aviatoreb]

I thought the reason your Rockets have full-feathering props is because the engine and prop were taken from the Cessna 340? or 414? One of their big twins. Fail-to-feather is very desirable in that application. It has always been my understanding that this is how Rockets operate, but Missiles fail to flat like the rest of us. That's not part of why I would like a Missile, it's mostly cost, complexity, heat and operating expense difference between the two. But for now, my C is doing fine . . . just lower and slower.

Don't know if it's even possible to have a full feathering prop governor made that will fail-to-flat instead of auto-feathering; it's all about how the oil is pushed. Rockets use oil to flatten the blade angle; we use oil to steepen the blade angle. Thus when the engine fails and oil pressure falls, the blade moves on its own. My blade range is only 13º ± 0º to 29º ± 2º, which is a mere 61º from fully feathered    . . . although feathered is probably not a simple 90º rotation when you take into account the airfoil and twist in the blades.

I think the Missile has the same engine as many other single engine IO550 applications so it was the choice of rocket engineering to put a full feathering prop on it as a matter of philosophy.  I wouldn't sell Conrad too short - maybe his risk management is better than mine?

I don't think a fail-to-flat full feathering governor exists since there has not been a perceived need.  But I bet one could be invented.

But maybe this is why we don't see full feathering props on ALL single engine airplanes.  

 

[jetdriven]

Is it he governor or the prop? Many twins and aerobatic props use oil pressure to decrease pitch.  So it's really the prop that feathers itself upon loss of oil pressure.  The governor simply supplies oil under pressure. 

Edited October 20, 2015 by jetdriven

[Yooper Rocketman]

The way I understand it, lack of oil pressure causes the prop to seek feather.  The reason it doesn't feather upon every shut down is due to a centrifugal latch that locks the prop a few degrees off the stops when losing oil pressure at a lower RPM.  I looked at numerous prop governor sites, including McCauley's website, and many failure modes are discussed.  The prop gov totally cutting off oil flow to the prop doesn't seem like a viable failure mode.  One site even implied it couldn't happen; any failure mode of the prop going to full feather when the engine was developing oil pressure was likely another problem, not the gov.  

I find it hard to believe if this was a realistic failure mode for this prop, on the Rocket conversion, that Darwin could have ever gotten the STC approved.  In addition, I've never heard of this failure mode (prop going to feather when the engine was producing power/ oil pressure), either by operators of twins, or in any of the hundreds (maybe thousands) of accident investigations I have read over the last 30 years.  This very scenario that sounds scary in a single engine, prop going to feather on take-off, would be almost as scary in a twin on take-off.  It also begs the question, why in twin training is identifying and feathering the proper engine (upon one quitting) such a drilled in procedure, if the props go to feather all by themselves.  I've never heard in the twin training syllabus a procedure to deal with this issue.

I think we are fearing the sky is falling here guys.

Tom Sullivan

[Seth]

I'll call back Rocket Engineering and have them look back into the files to figure this out.  I didn't think it would be approved this way either.  Even if the failure is low RPM, that's better than failure.

It's not "the sky is falling" it's I need to know and understand the risk inherit in the aircraft I fly.  I don't like to put off maintenance, but if my prop governor ever starts hunting or not holding RPMs exactly (which is exhibited 400 hours and 4 years after it's overhaul in the last few weeks) I need to know that if it fails, it's not going to cause me to have a forced landing.  Re-reading Erik's post was very timely.

I'll report back one what the different prop/governor shops state as well as Rocket.

-Seth

[Shadrach]

I think this failure mode is unlikely if it's even possible.  The other thing to note is that in a full feather, hi power situation, it's likely that the engine would begin detonating almost immediately.  

Edited October 21, 2015 by Shadrach

[aviatoreb]

I think this failure mode is unlikely if it's even possible.  The other thing to note is that in a full feather, hi power situation, it's likely that the engine would begin detonating almost immediately.  

That might be the key - maybe aerodynamically even with no mechanical stop to the full feather, it would still maintain a small heavy pitch since it is aerodynamically more costly to go full feather under full power.

I can say btw that if you put the engine in idle and then put the prop in full feather - guess what happens - the engine shuts off - ask me how I know...

[aviatoreb]

I'll call back Rocket Engineering and have them look back into the files to figure this out.  I didn't think it would be approved this way either.  Even if the failure is low RPM, that's better than failure.

It's not "the sky is falling" it's I need to know and understand the risk inherit in the aircraft I fly.  I don't like to put off maintenance, but if my prop governor ever starts hunting or not holding RPMs exactly (which is exhibited 400 hours and 4 years after it's overhaul in the last few weeks) I need to know that if it fails, it's not going to cause me to have a forced landing.  Re-reading Erik's post was very timely.

I'll report back one what the different prop/governor shops state as well as Rocket.

-Seth

I am very curious what they say - although it is not directly my concern anymore I am still very interested.  The MT engineer said he was surprised that this prop configuration was certified for the reasons I repeated.

[M20F]

Singles and twin prop/governors operate backwards of each other as a general rule.  Singles use oil pressure to increase pitch while twins work opposite the oil pressure decreases pitch and it is the spring which increase pitch (big spring in the nose of the prop on a twin which you don't see on singles).  Pins come out at an RPM threshold so it doesn't feather when you cut the power.  End result is loss of oil pressure in a single means it goes to low pitch and in a twin it goes high pitch into feather which is what you want in both cases, thus the reverse design.

I would think it would be reasonable/easy enough to adjust the pins so that the propellor couldn't feather in a single engine installation at loss of oil pressure.  Somebody more mechanically inclined then me would have to comment though.  

I can definitely attest though that low/no oil pressure above RPM threshold will put a twin engine into feather having seen it first hand on a T-Bone with some intermittent oil pressure issues.  

 

[Yooper Rocketman]

That might be the key - maybe aerodynamically even with no mechanical stop to the full feather, it would still maintain a small heavy pitch since it is aerodynamically more costly to go full feather under full power.

I can say btw that if you put the engine in idle and then put the prop in full feather - guess what happens - the engine shuts off - ask me how I know...

OMG, you did it too?  Hope your situation wasn't as butt puckering as mine was!

[Yooper Rocketman]

That might be the key - maybe aerodynamically even with no mechanical stop to the full feather, it would still maintain a small heavy pitch since it is aerodynamically more costly to go full feather under full power.

 

One of the sites I researched last night noted that exact fact; that the prop needed to be unloaded to go to feather.  In other words, if you were in a climb, it couldn't go to feather unless you lost power, pulled power or pitched the airplane into a descent.  It will be interesting to hear what Seth finds out.

[carusoam]

Trying to find data about the specific govenor model that Seth mentioned, I have found...

The company...

http://www.woodward.com/Applications-Aircraft.aspx

The sales company that handles sales of new and OH'd Governors...

http://www.qualityaircraftaccessories.com/products/aircraft-prop-governors/woodward-propeller-governors/210444-woodward-governor

Family and company history...

http://www.encyclopedia.com/topic/Woodward_Governor_Co.aspx

Have yet to find a spec sheet for the gov...

The STC is sure to have a statement regarding the operation and emergency operation of the engine with this prop.  Expect Rocket engineering has put together a complete package.  See where your STC documentation is.  It usually goes directly into the POH for your plane.

The documentation has to exist somewhere.  This is the premiss of having a factory built airplane with official modifications.

Best regards,

-a-

thoughts that come to mind...

Edited October 22, 2015 by carusoam

[aviatoreb]

OMG, you did it too?  Hope your situation wasn't as butt puckering as mine was!

Ok - I will tell my story if you tell yours.  :-)

Shortly after I got N10933 about 5 years ago, I was practicing an emergency engine out landing.  It was a cream puff scenario since I was like a 5000 ft and there was a big runway maybe 10 mi away.  In fact it was necessary to scrub a bit of altitude - So I was all line up and on like maybe 6 mi final for the runway and thought gee I will try full feather and see what happens.  2 things happened.  1st wow - the glide ratio increase so dramatically it felt like we jumped up.  Its a major increase in glide ratio.  Then the engine started sputtering since in idle there is not enough power to turn over the full feathered prop.  And it shut down. Yikes!  And I pushed in the prop control that stopped the engine instinctively before I had even a chance to think much about how I was flying with the engine turned off - and it came back to life just like that.  So I didn't have more than a moment of pucker.  More like I was thinking after the days flight, gee I don't think I will do that again.

[carusoam]

Erik, 

What happens during an ordinary shutdown?

I am thinking the big spring tries to feather, or at least rotate the blades towards the high angle.

Or is there a reason that doesn't get a chance to happen.

Best regards,

-a-

[aviatoreb]

Erik, 

What happens during an ordinary shutdown?

I am thinking the big spring tries to feather, or at least rotate the blades towards the high angle.

Or is there a reason that doesn't get a chance to happen.

Best regards,

-a-

I don't know why the prop on a rocket does not go to full feather on shut down, like you see on a turbo prop.  What is different?  I don't know.  Seems important to this discussion.

[jetdriven]

The way I understand it, lack of oil pressure causes the prop to seek feather.  The reason it doesn't feather upon every shut down is due to a centrifugal latch that locks the prop a few degrees off the stops when losing oil pressure at a lower RPM.  I looked at numerous prop governor sites, including McCauley's website, and many failure modes are discussed.  The prop gov totally cutting off oil flow to the prop doesn't seem like a viable failure mode.  One site even implied it couldn't happen; any failure mode of the prop going to full feather when the engine was developing oil pressure was likely another problem, not the gov.  

I find it hard to believe if this was a realistic failure mode for this prop, on the Rocket conversion, that Darwin could have ever gotten the STC approved.  In addition, I've never heard of this failure mode (prop going to feather when the engine was producing power/ oil pressure), either by operators of twins, or in any of the hundreds (maybe thousands) of accident investigations I have read over the last 30 years.  This very scenario that sounds scary in a single engine, prop going to feather on take-off, would be almost as scary in a twin on take-off.  It also begs the question, why in twin training is identifying and feathering the proper engine (upon one quitting) such a drilled in procedure, if the props go to feather all by themselves.  I've never heard in the twin training syllabus a procedure to deal with this issue.

I think we are fearing the sky is falling here guys.

Tom Sullivan

There's feathering stop pins which retract due to centrifugal force at around 800-1000 RPM.  below that the prop stops against that pin in a high pitch position.  Above that RpM the prop will feather if the oil pressure is lost. Aerobatic airplanes do this during violent maneuvers, the oil pickup gets uncovered and the prop surges in pitch, the prop RPM jumps to 1800 or so then recovers.  

Singles overspeed when they lose oil pressure.  I can verify this first hand.  Actually the twins increasing pitch with loss of oil pressure I can verify too.....

Edited October 22, 2015 by jetdriven

[MB65E]

On our Super Legacy we had a TSIO-550-E with larger turbos and manual waste gates on it. The prop was a counterweighted Hartzell Semitar with an accumulator set at 41psi. The governor is the weak link in the 550, besides the starter set up. The pins on the flyweights can one free thus causing oil pressure loss thus feathering the propeller on a perfectly good engine. Knowing the failure modes of our governor, we elected to put stops on the propeller. We experimented what RPM was needed to have a "limp home" mode. I believe it was around 1700 RPM that we could maintain level flight. With that data we went to the prop shop and told them to set the high pitch stops at 1700 rpm. However, this condition would only allow level flight. A 500fpm decent rate could not be overcome if the govenor did fail.  American propeller and wings west (Governor Larry) did the set up.

Not sure if the rocket  STC had any data on it but American propeller and Wings West might be able to help. 

Sure beats loosing the aeroplane (jk regarding Aircraft) on take off because a roll pin in the governor came loose. With all that in mind they still don't like 3300 RPM, but sure sound great!

-Matt

[N231BN]

Jetdriven is absolutely correct.

As far as rocketman's comment, it MAY be correct on a McCauley with the spring but I know for a fact a Hartzell with counterweights will go into feather at full power.

The only feathering prop that will go to low pitch with a governor failure is a Hamilton-Standard. It uses an electric pump to feather the prop since the governor loses the pressure required as the RPM drops. The smallest one I know of would be about two feet underground if hung on a Mooney though...

[KevinR]

timely discussion- I just bolted on a freshly overhauled prop governor to a freshly overhauled engine, prop, engine mount, exhaust, etc. 

I've gotten to know a few guys at Rocket & Palm Beach Propeller throughout the process. If we don't have a consensus answer yet, let me pose the question to the guys who just did the work.  

[Seth]

No need to post the question.  I just got off the phone with Rocket Engineering who verified the information.  I can have a PM or phone conversation with anyone wanting details of who I spoke with but since this is public forum, I'm not going to list the individuals name.

OFFICIAL WORD:  In the event of a governor failure (meaning loss of oil pressure to the prop governor) the prop on both the Missile and Rocket will indeed FEATHER - even with a working engine (the engine will shortly quit as well as we learned from Erik's test).

So, the true danger zone is a governor failing at takeoff or very low altitude, as then you are in a 16:1 glider a few hundred feet off the ground.   Takeoff, get to 700+ feet, more likely 1000 feet AGL as fast as possible so in the event of a governor failure (or engine failure) you can make the impossible turn and land.  The good news is that you're in an airplane with a full feathering prop.

 

The reason for this feature is due to the setup taken from a twin Cessna (which Rocket used as a blueprint for the setup - either the 340 or 414).  They had to make it feather or the flat pitch prop at failure would have been a 1:1 glide ratio (or something like that - huge amount of drag).  This way, should your governor die at altitude, you'll be a glider with a 16:1 glide ratio and hopefully miles of options to find a suitable landing destination. 

 

So  Erik, your change is that you no longer get a full feathered prop, and thus slightly lower your glide distance, but your airplane weighting balance is better with 30 pounds off the nose and a four blade prop.  

 

Hope this clears up information about our Missile and Rocket conversions.  

 

-Seth

Edited October 26, 2015 by Seth

[carusoam]

Great follow-up, Gentlemen!

Best regards,

-a-

[aviatoreb]

Huh - no kidding Seth.  I was kind of hoping I was wrong because it doesn't seem right.

I do see why they are using the prop-engine combo from he C340 on the rocket, but what about the missile?  That prop does not come from a twin does it?

What is it you were saying about 1:1 glide with an otherwise flat prop?

Yes, I know I have lost the full feather 16:1 glide. And as I said I decided to trade that for also loosing the extra failure mode of loss of thrust at the most vulnerable time which is first 700-1000ft of flight.

So as for me - stop the prop.  I wonder what my glide ratio actually would be if I stop the prop? I hope I will never know because that is something I will not test in practice.  I would think my glide would otherwise be the same, or slightly worse, than a standard mooney.