Friction Torque direction query

Hello Byron

Given that the crankshaft is locked for this check the direction of rotation on the 30 degree freeplay is not moving the crankshaft or oil pump.  Because of this it makes no difference.  I however always like to pull on the leading edge of the propeller for this as the trailing edge is rather weak in comparison.  

Cheers. 

Rotax Wizard wrote:

Hello Byron

Given that the crankshaft is locked for this check the direction of rotation on the 30 degree freeplay is not moving the crankshaft or oil pump.  Because of this it makes no difference.  I however always like to pull on the leading edge of the propeller for this as the trailing edge is rather weak in comparison.  

Cheers. 

Thank-you, good point about there being no risk from engine rotation with the locking pin installed.

Very good point about distributing the force during the measurement on the larger surface area of the leading edge. The ROAN video uses inch-pounds and says to use a length of 30”. The Rotax line maintenance manual uses newton-metres and just says to define your own length (in metres of course)

At 30” of length on a composite prop you do feel like you should be closer to the propeller hub for risk of damage to a blade. Noting that the further you are from the hub (as L increases) the force required to take the measurement declines.

Cheers,

Byron.

I agree to pull against the leading edge of the prop, but you're right that either way should produce the same reading. Remember the engine comes from Europe and NM are the standard metric measurement, but you can use inch pounds. Even in the checklist for this procedure it has the place where you write in the number in NM or inch pounds.

30" is a standard, but you could use 28" if you wanted. You just don't want to be too close inward say less than 24" because the pull will be so stiff getting a good consistent reading doesn't work very well.

I usually pull it through three times because the gauge can fluctuate some as you pull. I prefer a digital gauge too. They are around $12 - $15 on Amazon. It's basically just a fish scale.

So if you measured out from the center of the prop shaft to lets's say 30 or 28" then hook up the gauge and pull it through and get a reading of 17 ft/lbs then you multiply that reading times the distance you measured out on the blade. i.e. 28" x 17 ft/lbs =476 in/lbs. or  i.e 30" x 16 ft/lbs = 480 in/lbs

The final number doesn't have to be an exact number. It is a range. Most I see are around 460 in/lbs to 485 in/lbs. Some are higher and some are lower. I see 440 sometimes and 500 sometimes. The 500+ is rare.

The scale, of course, just reads pounds.  It's multiplying by the distance from the center that makes it foot-pounds, inch-pounds, or whatever.

Roger Lee wrote:

I agree to pull against the leading edge of the prop, but you're right that either way should produce the same reading. Remember the engine comes from Europe and NM are the standard metric measurement, but you can use inch pounds. Even in the checklist for this procedure it has the place where you write in the number in NM or inch pounds.

30" is a standard, but you could use 28" if you wanted. You just don't want to be too close inward say less than 24" because the pull will be so stiff getting a good consistent reading doesn't work very well.

I usually pull it through three times because the gauge can fluctuate some as you pull. I prefer a digital gauge too. They are around $12 - $15 on Amazon. It's basically just a fish scale.

So if you measured out from the center of the prop shaft to lets's say 30 or 28" then hook up the gauge and pull it through and get a reading of 17 ft/lbs then you multiply that reading times the distance you measured out on the blade. i.e. 28" x 17 ft/lbs =476 in/lbs. or  i.e 30" x 16 ft/lbs = 480 in/lbs

The final number doesn't have to be an exact number. It is a range. Most I see are around 460 in/lbs to 485 in/lbs. Some are higher and some are lower. I see 440 sometimes and 500 sometimes. The 500+ is rare.

Hi Roger,

Thanks for your reply, I ended up with an eBay scale (picture) attached, digital one that lets me select Newtons, pounds or Kilos, accuracy was acceptable for a cheap scale based on the checks I did with some known weights.It also has a ‘hold’ feature that is somewhat useful for storing the maximum force, digital ones seem pretty easy to read when pulling through the stroke.

I also found standing on a small ladder helped with my ‘angle of attack’ while pulling or maybe I am just short! I placed some small pieces of tape then put some marker pen points on the tape on the spinner backing plate and gearbox housing as reference points so I could see how far I was through the stroke.

Cheers!

Byron