However, I have just taken delivery of a Hoffmann propeller for which the torque value is given as 15 - 17Nm = 1.5 - 1.7 m/kg = 10.8 - 12.3 lb/ft). I don't know the material used in the Hoffmann but assume it's probably a dense hardwood like beech.

Hoffmann's torque value is quite a drop from the flight manual figure and given my remark about crushing I'll probably start with that but what torque values do you people use for your props?

I have a Hercules propeller on my RF4D and these are the torque figures specified by Hercules. Like yours, my bolts are actually metric, but I believe their diameter is very close to 5/16" so I think I use 13 lb ft, but I would check bolt diameter with a vernier caliper before actually torquing them up.

http://www.hercprops.com/wp-content/uploads/2018/01/PROP-INSTALLATION-MANUAL-REV-2.pdf

All the best, Bob

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On the Clubs SF25C that has had both a Limbach 2000 engine with Hoffman prop and is equipped with a Sauer 2100 with a MT-prop there has been and is the same torque values for the propellerbolts.

25Nm sounds too high and equivalent with the torque setting for the sparkplugs in Limbach engines (The Sauer has a little lower torque setting of the plugs of 20Nm).

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I'm now using the Hoffmann figures of 15 - 17 N/m. I was just interested to know what other people were doing especially since the difference between what Hoffmann say and what is written in the Flight Manual is not a trivial difference.

But as I said, I had used the Flight Manual figure simply because it was written in the manual and I had no other reference even though, from observation, it produced slight crushing of the hub. Mind you, there are other numerical errors in the same manual so perhaps it was written by an innumerate. Yet the Flight Manual is supposed to be the definitive source of information, is it not?

Quote:

Originally posted by Donald Thank you Frederik. I'm now using the Hoffmann figures of 15 - 17 N/m. I was just interested to know what other people were doing especially since the difference between what Hoffmann say and what is written in the Flight Manual is not a trivial difference. But as I said, I had used the Flight Manual figure simply because it was written in the manual and I had no other reference even though, from observation, it produced slight crushing of the hub. Mind you, there are other numerical errors in the same manual so perhaps it was written by an innumerate. Yet the Flight Manual is supposed to be the definitive source of information, is it not?

I'm not sure that i agree with you about engine/propeller figures in a flight manual. Yes the flightmanual is supposed to be the definitive source of information about the plane but in the lovely world of aviation that means that it is the definitive source about the planes fuselage, wings, stabilisor, flight characteristics, speedrestrictions etc. It is however not the definitive source of information about the engines maintenance, propeller, magneto etc. (if of course it's not the airplane manufacturer themselves that has made the engine, propeller, magneto etc).

The enginemanual is the only correct source of information about the engine and the prop manual is the only correct source of information about the propeller since they are certified to the different manufacturer of the separate components, compare it to the fact that all TB:s for eg. our Sauer engine is produced and validated by Sauer and not Scheibe. Scheibe doesn't even give a notice about a TB from Sauer, it's yout own responsibility to find and perform it.

It's not comparable to a car where the carmanufacturer takes the responsibility of the whole car and every piece of true and correct information is supposed to be in the cars manual.

If i bought a brand new SF25 with a Rotax engine and got a problem with the engine itself, i would not consult the flightmanual for the SF25, instead i would consult the enginemanual. The same goes (in my world) if i make a mistake in the maintenance that breaks the engine, i would bet you that neither Scheibe or Rotax would help me out if it turns out that i used the flightmanual and not the engine manual for service of the engine.

With that said, if you didn't have any other source of information regarding the torque setting of your porpellerbolts i would probably have done the same thing you did .
Though because i am the glider service technician in my club with soul responsibility for our TMG i would have questioned the numbers though but that would have been due to experience of fixed pitch wooden propellers on similar types of planes and engines.
If i had not had that experience i would have gone along with the settings specified in the flight manual.

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First impression was that it is a lovely looking prop. On installation the drilling most perfectly matched the bolt pattern in the hub of all the props I have had and with all the bolts torqued to exactly the same value the tracking was absolutely faultless. Never seen that before, always having needed a little more or less torque on a couple of bolts to get it just right.

In flight it seems smoother and gives about 3 knots more at max continuous cruise throttle, so all in all I'm pretty impressed with it.

On the matter of bolt torque which started this thread I have initially set it at the minimum value given by Hoffmann, 15 N/m. My reasoning, with which my inspector agreed, being that the wooden cored prop will have come from a climate controlled factory in Germany to live in a moister climate in the North of Scotland so, despite the apparently impervious finish I expect the core to absorb moisture and expand. And yes I know to check and re-torque at different times of the year.

Anyway, it's good to get BP back in the air after such a long lay off and discover I have not forgotten how to do it. It sure put a grin on my face today.

I'm sorry that it took you so long and cost so much to get back into the air, but very glad that your Fournier's smoothness and performance have both improved.

May you now have many more happy hours in the air in 'BP

And have a very happy Christmas and Hogmanay, Bob

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