Prop governor question

Widow · Post by **Widow** » Sun Sep 16, 2007 9:49 am

Looking for a little education please!

I have a basic understanding of what the purpose of the prop governor is ... but would appreciate further edification! Also interested to know what the effect would be of using the "wrong" governor, e.g. DHC-2, R-985, Hamilton Standard 2-blade prop, Hartzell governor ... ?

xsbank · Post by **xsbank** » Sun Sep 16, 2007 10:20 am

I'll try - A propeller is not most efficient at one pitch setting, its much better at fine pitch for take-off and coarse pitch for cruise. There is an optimum setting for climb, etc. In addition, the engine will not be able to reach its rated horsepower unless the pitch of the propeller is fine enough for the engine to be able to reach take-off rpm. It will also be very noisy and gobble fuel unless you can coarsen the pitch for cruise.

The prop governor does 2 things - it allows the pilot to select the appropriate, best-pitch for the regime of flight he needs i.e. fine for take-off and coarse for cruise (there is a continuum) and the governor keeps the rpm selected by automatically making changes to the pitch of the prop to maintain the selected engine rpm. E.g. close the throttle in cruise and the engine rpm will not change as the prop governor will make the prop pitch go fine to keep the rpm the same as selected.

There are governable limits, too, that the propeller cannot go beyond, as in this example, eventually the prop could not go 'finer' and the rpm will decay.

As far as manufacturer goes, many companies construct parts for aircraft and you may find a mixed bag of manufacturers on one engine - what is important is the part number. At various times a manufacturer will call for tenders to make various parts and companies bid on the right to supply the part. Hartzell and Sensenich and Rotol and Hamilton-Standard (etc.) likely all made the appropriate governor at one time or another.

As an example, an RJ has its tail section made by Mitsubishi, control surfaces by Avcorp, navigation by Collins, gear by Dowty, engines by GE (and GE sources its fuel control systems, governors, oil pumps etc. etc.

The 985 was built in such large numbers for so long and largely for war production that many companies were involved.

Part numbers are very important!

Hope that is accurate enough and answers the question? I'm sure that I'll be upbraided if I missed something!

Ref Plus 10 · Post by **Ref Plus 10** » Sun Sep 16, 2007 11:27 am

Hey XS,

Just a minor correction to a pretty damn good explanation, the prop governor does not maintain engine RPM, it will control the prop RPM regardless of power setting (excepting power settings which will not supply sufficient oil pressure to push the blade angle to a fine position). Aside from that, well said!

+10

oldtimer · Post by **oldtimer** » Sun Sep 16, 2007 11:56 am

Widow - You have had some simple explanations of how a propeller works. I, unfortunately, have had very little to do with single engine airplanes of late because when I was flying singles, all that was required was to know in very simple terms how and when we were supposed to change pitch.
If memory serves me, there are two basic design differences in propellers. All propellers use engine lubricating oil, pressure boosted by a prop governor oil pump as and if required, delivered through the crankshaft into the propeller to change pitch. One very basic difference between some models of Hamilton Standard props and Hartzell Props is the way they change pitch. Ham Stands use engine oil pressure to force the piston in the hub, mechanically attached to all blades, to both increase and decrease blade angles. Hartzell and others use a system of external counterweights and blade twist to increase blade angle (High Pitch - low RPM) and engine oil pressure to force the blades to Low Pitch, High RPM. (I hope I do not have this backwards). There is, of course, a large list of approved propeller/governor combinations and a list of propeller/airplane combinations. To find out what is available to the Beaver, you would have to go to the original Type Certificate. Look on the tombstone data on the first page of any DHC-2 journey log. I do not know where to find the type certificate on line but it must be available because it is public knowledge. Also, just to muddy the waters, there are many STC's, or approved changes to the engine/propeller/airplane so some digging may be necessary. Hope this helps.

xsbank · Post by **xsbank** » Sun Sep 16, 2007 1:10 pm

Looking at your pictures again, the prop is in fine pitch, which means the pilot selected fine pitch or the engine was not making any power. Is there any indication from the prop control lever? I suppose any impact that would have destroyed the a/c may have moved the levers...

Widow · Post by **Widow** » Sun Sep 16, 2007 2:41 pm

Here's a pic from when it was first recovered:

The TSB letter to the coroner said the prop was set to fine pitch.

4blue · Post by **4blue** » Sun Sep 16, 2007 6:00 pm

generally speaking, you'll use a finer pitch setting (higher RPM) for times when you want high power, or high power available.

For example, take-off, climb, approach, landing.

black hole · Post by **black hole** » Sun Sep 16, 2007 8:46 pm

As far as I know there are 2 propeller hubs that are approved on the Beaver 2D30 a counter weight prop, and the 22D30 that is a hydromatic prop controled both ways by oil pressure. Many different blades are approved on either.
Both props use a different governor. Sorry I don't know what happens if you use the wrong one. I should expect the results would be noticed on the first run up.

BH

Spinner · Post by **Spinner** » Mon Sep 17, 2007 7:07 am

I see the picture is of a 2D30 prop I do believe. It uses oil pressure to hold/bring the prop to fine pitch and counterweights to coarsen the pitch.

The prop governor has a set of flyweights in it that are spinning at a related speed to the engine rpm. If the speed of the engine drops the flyweights move (drop) and increase the flow to the prop giving a finer pitch and more rpm. When the rpm reaches the set position the flyweights are neutral and the oil is slowed/cut off. If the rpm goes too high the flyweights move up and allow oil to drain from the prop hub coasening the pitch and slowing the engine/prop down. The flyweights return to neutral once the speed decreases.

The cycle happpens very quickly as the flyweights are continuously adjusting. It is not noticable to the human eye though.

Without pictures it probably doesn't make a lot of sense but hope that this helps a bit.

regards

Widow · Post by **Widow** » Mon Sep 17, 2007 7:23 am

Lot's of helpful answers here ...
thanks all ...

We did send the governor (recovered with fuselage and accessory section), I think there's a pic in the engine slideshow ... http://www.youtube.com/watch?v=D-_dJY_1upo