What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Prop Hunting and Surging

MarkC

Active Member
Hi All,

I just started flying my RV-7 (first flight was on Sunday 12/02). It flies great except for a little issue I'm having with (I think) the prop governor. At certain speeds the RPM's vary by up to 100 up and down from where the prop is set. it smooths out after a while and flies just fine but when I change power, off it goes again. Anyone had anything like this happen? The governor is an MT from Van's. The only real advice I've had thus far is "pull it off and send it back to van"s". As I'm only about 7 hours on the plane now the idea of taking the plane down for a month while Van's gets around to shipping me a new one is not too appealing.

Just wondering if there is anything I'm missing.

Thanks,

Mark
RV-7 - N234C - 7 Hours and counting.
http://websites.expercraft.com/markc
 
I know the solution. 100 hours now and I'm on my third governor.

What you need to do is look at the serial number on the governor. It must end in -C or -D. Yours is probably -B.

I have -D in mine and its perfect. Talk to Jeurgen at MT in Florida. MT was fantastic helping me sort this out.

Don't talk to Vans about it. I relayed the info to them but they were unfamiliar with the problem. Deal directly with MT.

In the meantime MT and I decided the airplane was ok to fly while waiting for the new governor. You'll notice if you pull back the power a bit after about 500 AGL, it will do away.

Steve
RV7A
 
Humm good info above

Third time I have heard of prop rpm issues with a MT gov. Woodward govs seem to not do this, last longer and are rebuild-able. I am told MT govs are worn out after getting to TBO from a prop shop? Can't verify that. Not saying they are bad, but they are more lightly build. Brand new Woodwards are priced too high, so the MT is an attractive buy.
 
Last edited:
PCU 5000 Governor

I spoke with Bob Honig at Copperstate about Ameritech Industries in Redding - they do lots of engines and props, Superior, ECI, MT, Hartzell, they pretty much cover the spectrum. Bob appeared to be extremely knowledgeable.

He very stridently recommends a PCU 5000 governor, PMA'd, shorter and more compact than MT, 3 year warranty or engine TBO, $1,450 new. They claim that is less than most overhauls.

I'd sure look into this if I were you. http://www.americanpropeller.com/

George
 
Last edited:
sjhurlbut said:
I know the solution. 100 hours now and I'm on my third governor.

What you need to do is look at the serial number on the governor. It must end in -C or -D. Yours is probably -B.

I have -D in mine and its perfect. Talk to Jeurgen at MT in Florida. MT was fantastic helping me sort this out.

Don't talk to Vans about it. I relayed the info to them but they were unfamiliar with the problem. Deal directly with MT.

In the meantime MT and I decided the airplane was ok to fly while waiting for the new governor. You'll notice if you pull back the power a bit after about 500 AGL, it will do away.

Steve
RV7A

Ahh, that sounds exactly like the issue I'm seeing. I'll give the guy at MT a call and check the serial number next I'm down there.

Thanks for your help,

Mark
 
Started seeing +- 300 RPM today...

So, with almost 50 hours on the plane my prop started hunting and surging as well, I was very lucky to be at an airport that has a prop rebuild shop on site. Apparently they heard my plane going around the pattern and said they hadn't ever heard one surge so much. This has never been an issue before but today it was quite apparent. I am working with one of the MT distributors who was very helpful. I will let you know how this goes, I hope this is a simple issue of replacing the governor but it could be something else.

- Galen
 
This thread is starting to concern me. I just installed an MT governor with a 'B' serial number on my 320. What is MT saying about these. Are they freely swapping them out or only after we see +-300 rpm (dangerous in my opinion)?
 
You guys have my attention as well. My plane only has 10 hours on it, and the "B" MT gov has worked great so far. Is this something that will just start happening one day? Are these "recalled" by MT, or just when you have problems?

Thanks,
Rusty (used to be happy to get a B)
 
grjtucson said:
I spoke with Bob Honig at Copperstate about Ameritech Industries in Redding - they do lots of engines and props, Superior, ECI, MT, Hartzell, they pretty much cover the spectrum. Bob appeared to be extremely knowledgeable.

He very stridently recommends a PCU 500 governor, PMA'd, shorter and more compact than MT, 3 year warranty or engine TBO, $1,450 new. They claim that is less than most overhauls.

I'd sure look into this if I were you. http://www.americanpropeller.com/

George


See also www.pcu5000.com for the company website.

:) CJ
 
13brv3 said:
You guys have my attention as well. My plane only has 10 hours on it, and the "B" MT gov has worked great so far. Is this something that will just start happening one day? Are these "recalled" by MT, or just when you have problems?

Thanks,
Rusty (used to be happy to get a B)

No they are not "recalled" and it doesn't happen to all -B mods. If you get surging however call MT and get it swapped out. The current mod is -D. This is what I'm using, and its perfect now.

Steve
RV7A
 
gshipman said:
So, with almost 50 hours on the plane my prop started hunting and surging as well, I was very lucky to be at an airport that has a prop rebuild shop on site. Apparently they heard my plane going around the pattern and said they hadn't ever heard one surge so much. This has never been an issue before but today it was quite apparent. I am working with one of the MT distributors who was very helpful. I will let you know how this goes, I hope this is a simple issue of replacing the governor but it could be something else.

- Galen

Exact same thing as mine. Call MT and ask for -D mod. In the meantime pull the power back a bit after the initial climb and the surging will go away. I also found that it was worse when the oil was hot (overshoots, touch and goes, enroute climbs). With the power pulled back I was still able to get 1500 fpm without surging.

Steve
RV7A
 
MT Prop Gov

Have MT gov model P-420-3 Installed on RV-6 with O-320D2B, and since 2004, 150 hrs now, and has operated normally. Serial number does not have any letter suffix. Prop is Hartzell 2 blade via Van's. Ditto. Ops normal. Non AD prop.
 
Some MT govenors don't have a dash leter on the serial number, what can we determine from this?
John Adams
 
Governor Installed

Just finished installing the new replacement governor from MT. It was late so I didn't get a chance to do a runup and test everything out. Hopefully I will have good news to report tomorrow!

Thanks,

Galen
 
prop surge

I just flew my official first flight this morning and after about an hour I felt like testing some things. Level at 4000 MSL, 2400 rpm and 23 inches, I was showing 180 deg. oil temp with the Van's oil shutter full open. OAT was 53 deg.. I then closed the shutter and the temp slowly rose to about 205 deg. after about 10 minutes. At 206 deg.'s the prop began to surge by about 50-60 rpm. Oil pressure also correspondingly went from 80 to 75 psi with the temp increase. I opened the shutter again, temp went down, pressure went up and the surging abated. I'll have to go search for my MT dash #.

Jon RV8 N484JT #82473 2.4 hrs
I just found my paperwork, I have an MT part #P-860-4 serial #06G077-B
 
Last edited:
I'm certainly NOT very knowledgable about the mechanics of prop governors or hub controls - so someone please educate me here. This sounds like the prop hub has a small (intentional or not) leak-through of oil and the changing viscosity changes the rate of flow - but that would also dictate that high-temp oil is reaching that leak-through point, meaning it's most likely in the controller, not the hub. Do the hubs have a single control line with spring return, or is it a balanced piston arrangement with dual control lines? Or does this depend on the prop/controller used? If there is a small leak-through factor in the controller on the final output line to the hub, the oil temp/viscosity changes will certainly affect the leakage quantity there, causing the output pressure to bleed slowly and inducing the hunt/surge behavior. Please enlighten me....
 
Last edited:
Prop servo oil pressure/leakage

All,

Here is my understanding of the problem as I've seen it before...

The props on your airplanes are what we call "single-acting." Oil pressure from the governor works in one direction; oil pressure is used to increase pitch only. It works in the opposite direction on counterweighted/feathering props. On pressure-to-increase single-acting props like yours, a return spring, blade centrifugal twisting moment and aero twisting moment - depending on conditions - work against oil pressure and returns the blades to low pitch. Without oil pressure the blades will move to low pitch.

One important fact, the pressure required from the governor increases with increasing blade angle (either higher speed or lower RPM).

The governor serves two purposes; an oil pump to boost engine oil pressure and a flyweight/spring/valve arrangement to port oil to the prop or to case/return depending on how the pilot biases (sets RPM) the spring. The flyweights move the valve/spring to increase oil to the prop if RPM increases over the set-point, or ports oil back to the case if it drops below the set-point.

The governor is a simple oil pump; it has a capacity limit. It can pump only so many qts/min before it reaches a maximum capability at each RPM. When the oil warms (viscosity drops), the leakage through the crankshaft transfer bearings and the governor itself increases. If the leakage is too high, it might exceed the governor's capacity to pump enough oil to maintain RPM. If it does, the RPM will increase, the pump speed increases, pump capacity goes up a little, the oil quantity needed is restored, the RPM drops back down to the set-point, the pump capacity is exceeed again, the RPM increases, etc. This cycle/oscillation may continue or just stabilize at an elevated RPM.

I've heard this problem crops-up on high time (high leakage) engines or when ambient/oil temps are high.

The only way I know of fixing this problem is decrease leakage or use a higher capacity governor.

The other possible scenario is the governor relief valve pressure is set too low, thus bypassing oil to the case (increasing the flow rate demand on the pump). If the pressure required to maintain the blade angle reaches or exceeds the relief valve setting, it may be bypassing back to the case instead of going to the prop? This might be how MT is fixing the propblem with the same governor? They may be increasing the relief valve setting to a higher pressure?

Be safe,

Les Doud
Hartzell Propeller Inc.
 
Gary Bricker

Sounds like this applies to mine. It go's +300RPM's on take off but is fine if I pull it back. I have 2+ hours on it. Has anyone seen this.
 
Replacement Governor working

Sorry I didn't post earlier,, anyway, the prop governor is working now. I worked with Juergen at MT-USA, they shiped me a replacement right away.
 
Gary Bricker said:
Sounds like this applies to mine. It go's +300RPM's on take off but is fine if I pull it back. I have 2+ hours on it. Has anyone seen this.
Does it surge through +300 or go up to that and stay there? If it stays there then you just need to adjust the stop on the governor down, if it surges, then there could be something wrong with it.
 
Things that will exacerbate this issue are the propeller pitch limit settings. Generally, new Hartzell propellers shipped from Hartzell come with a manual. My guess is that most purchasers never even open it and fail to realize that there are propeller "pitch limit" adjustments that should be made during the flight testing. If these settings are not correct, then no governor will "act" correctly.

The propellers I have used indicate for the RV:

C2YL-1BF/F7663-4
150hp: low pitch 12.1----high pitch 37.5
160hp: low pitch 12.7----high pitch 37.5

C2YK-1BF/7666A-4
180hp: low pitch 11.1----high pitch 38.5
200hp: low pitch 13.5----high pitch 38.5

What you see here is that the stop limits are somewhat a function of horsepower. The problem in many RV applications arise when someone has a "hopped" up engine. The factory pitch settings (or the ones of the previous application if it is a used propeller) simply may not account for the increase in horsepower.

I doubt any governor can be effective if it alone is used in an attempt to regulate "max rpm" particularly at full throttle at sea level.

Unfortunately, Hartzell probably does not issue settings for the myriad of engines that don't fall under the "stock" horsepower. In fact, I doubt they would approve their propellers for use on any engines other than "stock".
 
I resurrected this thread because having MT modify the governor from the original -B to a -D did not cure my surging problem. Only evident at full power from a standing start with a hot engine (e.g., a stop 'n go), the surge limits are 2600 - 2700. Going to high rpm in cruise doesn't seem to excite the surge, and all other rpms are stabile. I'll post Juergen's comments after I talk to him and Hartzell.

Chickenlips' comments are interesting because the engine can put out well over 200 hp instead of the nominal 180 at sea level, but there doesn't seem to be a problem holding rpm except as noted. Airport elevation is 2,500, rpms are stabile at 6,500, so maybe I'm on the cusp of "critical horsepower" for the 72" C2YR.

John Siebold
Boise, ID
 
John
I too had my MT -B changed to a -D and saw little change in the surging.
Juergen sent me another governor and it works great.
It appears that they sent me an overhauled one because the data sheet showed it with 26 total hrs. After 20 hrs. of flying with the hunting it's nice to fly without it now, so I don't care about the used gov.
Get them to send you another gov.

Good luck

Jon RV8 O-360A1A Hartzell blended 74"
 
Nix on MT

You can read more of this saga at

http://www.vansairforce.com/community/showthread.php?t=15451&highlight=prop+surging

The third MT governor I installed simply wasn't doing the job. In prior posts I thought that I might live with the mild surging it still allowed. So much for that daft thought.

I installed a PCU5000X and the prop RPM is now rock solid, all flight regimes and temperatures. This is the same experience of several other buddies flying all manner of engines/airplanes at my home airport. The PCU5000 is the Jihostroj governor once sold by Van's, now certified (PCU5000) and marketed in this country by Aero Technologies.

Sorry, MT, good customer service doesn't make up for an unsuitable design. Count your blessings, those of you who are using an MT governor and don't get surging of your Hartzell. Maybe you just got lucky. Or it could be the original Jihostroj labeled MT. Current MTs are their own design governor and it looks a lot like the Jihostroj, but the internals are quite different. There's obviously sufficient variation from one unit to another to reveal its borderline performance.

John Siebold
Boise, ID
 
Add another to the list of surging governors. New recent new MT unit from Vans on my freinds new RV7 with a Hartzell is surging bad....
 
Prop surging seems to be very common at the moment!

Hello,

A couple of months ago, when I visited Steve Arnold in the UK (first RV9A with WAM120 Diesel) he could not take me up for a test flight because he had a problem with sucking in air through a faulty fuel line connection and......... the prop was surging! He had 7 hours on the clock at that time. Sorry, do not know what governor he is using.

Regards,

PilotTonny
 
Ping!
Yep, mine surges too when the oil temp is high (195+ deg.). My craft now has a restriction for no takeoffs when oil temp is above 190 until I get a new governor.
MT
P/N: P-860-4
S/N: 06G097B
 
Thanks, too, to you, Chickenlips, for your explanation of the limit settings with power! That's a very important cosideration when using used equipment. You and Les have added to the wealth of knowledge we need to possess with our experimentals!
 
Governor Hunting

Hi all, I have been through this with my MT/Jihostraj governor and -390 engine, though not +/-300rpm! For those not familiar with the previous thread on MT governors and their pedigree, do a search here and you will find some good info.

The relief valve pressure can be set on a test bench, and is often different for each type of prop, as I understand it. Different relief valve springs are also available for some governors if there is insufficient adjustment.

The speeder spring can also be varied, and shims fitted or removed, to tailor the governor so that it won't (or is less likely to) hunt with your engine/prop combo.

I had surging with commensurate oil pressure fluctuations initially, and couldn't get 2700rpm. Adjusting the governor pitch stop wouldn't get me 2700, I had to change the relief valve spring (acro prop, pressure to decrease pitch). The hunting occurred at all rpms, but was worse with hot oil (185?F+). I got the speeder spring changed and things have improved, though in stable cruise with hot oil hunting can still be induced (+/-50rpm, noticeable note and vibe change). I haven't been back to further tailor it to see if I can get rid of it altogether.

I dealt direct qwith the Jihostraj factory and found them helpful and willing to impart knowledge. They are frustrated at the MT/Jihostraj/PCU5000 governor confusion and similar numbering system. I got the parts fitted and tested locally.
 
governor surging

Had the same problem with surging after 13 hrs called Juergen at MT in Florida,They had just come out with the -E version and sent me one to try before sending the old one back,My old one would surge up to 300 rpm unless I kept rpm below 2400,New one stays within 10 rpm on the Dynon.I have 48 hrs tt so far with no other problems. Bob in East TN.
 
I just finished test flying my MT prop governor upgrade from -B to -F. It isn't good enough for me. The surging at takeoff with high oil temps is still there but not quite as severe as before, "only" about 120 RPM. This modified governor isn't nearly as stable in basic cruise either as it wonders 30-40 RPM every now and then. I'm done messing with the MT and will be ordering a PCU5000 on Monday. Just another data point for the record.
 
Back
Top