Propeller pitch adjusting tool

[damiens]

Hi Damiens -Disclaimer - I am a "bush" mechanic of some 50+ years. I have a PPL 25 years, RAA Cert 9 years and have owned a Rotax 912 ULS motivated ATEC Zephyr for about 8 years also. I am far from being an expert on the matter you have enquired about but do have some experience (on my own aircraft) which may be of assistance.

 

My home strip (1,100 ft amsl ) is very demanding, so I have my two blade prop pitched toward a climb advantage (not max climb) - NOTE I do not take passengers into/out of my home strip but frequently carry max load (fuel & camping gear).

 

I get 5200 rpm @ well over 1000 ft/min climb out and about the same for a full power static run up. I believe this to the the Rotax minimum recommended rpm under climb load.

 

As airspeed builds, I have to either increase climb angle or throttle back to stay within Rotax recommended rpm (engine speed & time limits)

 

I like to cruise at 4800 - 5200 rpm. This gives me an indicated air speed of 100 - 110 knots (depending on altitude) and a fuel flow of from less than 13 - 14 LPH.

 

My aircraft can "loiter" 50-70 knots @ 7-8 lph with the engine doing somewhere in the 4000 +/- rpm range

 

I rarely go above the the cruise figures but every now and again we will do a 5400 or more rpm - air speeds can go over 120 knots but fuel burn is correspondingly higher in the 18 +/- LPH range.

 

My WOT is @ the top of the yellow arc, so can only be sustained for 5 mins or so - I dont go there except to do a brief test..

 

If my home strip had a flatter (500 fpm) departure and approach, I would adjust my pop accordingly for better (higher air speed for given rpm and possibly better trip economy) cruise performance.

 

Your aircraft has the "look" of a fairly high drag airframe so you may be optimizing its STOL performance - should this be the case your figures look pretty good. If you want to improve cruise there would appear to be room to "corsen" the prop a little.

 

I have found that using accurate devices (with good repeatability) and obsessive attention to detail (check, recheck & recheck again) to set pitch angle pays off with better performance, smooth running and ultimately hopefully longer lasting engine/prop.

 

Only you can decide what the objectives are regarding engine speed / aircraft performance and set your prop accordingly.

Thanks SkippyD for the above, it's all great info. I suspect my beast is a whole lot more draggy (big 26 inch tyres and leading edge slats) than others I am reading about, as my climb RPM is a lot closer to my WOT straight and level rpm (I still need to completely test my straight level WOT in calm conditions to be sure).

 

I think I will use it as is for now and get some solid numbers established and written down, then maybe fine up a half a degree if required/preferred.

 

Thanks

 

Damien

 

 

[Blueadventures]

To resurrect an older thread and for my education as I am new to Rotax engines.On Sunday we re-pitched our Savage Cub (Rotax 912 ULS with three blade DUC Helices ground adjustable prop). On climb we were getting 5,200 rpm max before making the prop 1 degree finer and now we are getting 5,400 rpm on climb (performance improvement was stunning). I am yet to test max throttle rpm at straight and level as the weather became unsuitable.

 

We want max takeoff performance and good engine safety as well. Do I have it right, that we are aiming for probably about 5,500rpm on take off and most importantly about 5,650 rpm WOT in straight and level? Airfield is about 800ft above msl, should the test be carried out at sea level to be sure? Does the 800ft make enough difference to be concerned about?

 

I have also read to cruise anywhere between 5,000 and 5,400 rpm, as below that you are labouring the engine (fine for circuits and landings but cruise, keep it higher).

 

Thanks in advance.

Hi Damiens

In my thread of 21 june 17 I am happy with the pitch setting. Experienced rotax persons say to aim for WOT straight and level max 5,600. That is so if throttle linkage fails and engine goes to full throttle you can keep engine going. Therfore they like to get between 5,500 and 5,600. If you have a pitch setting that gives 5,200 WOT straight and level then you must reduce rpm after take off by 100rpm as if you continue to fly / cruise at the 5,200 you have the engine working hard at max. Re DUC props you know they like the rpm at takeoff roll brought on slower than just ramming the throttle to full power. From your post I believe that on your next flight you need to observe the WOT straight and level rpm so you can fully verify prop pitch is with rotax engine rpm specifications. Pm me if you want to give me a call. Cheers Mike

 

 

[Downunder]

Do I have it right, that we are aiming for probably about 5,500rpm on take off and most importantly about 5,650 rpm WOT in straight and level?

So you found out the Rotax loves to rev? Great isn't it!!

 

You won't get 5500 take off AND 5650 WOT I think. You have set the pitch "fine" for better take off which is OK, but you will probably see more than 5650 WOT. It just means you throttle back.

 

This is the compromise of a fine pitch. You can go a bit finer to get that 5500 rpm but but each increase also increases WOT rpm. I think 5400 is a good "fine" setting , personally.

 

The 5650 WOT aim is for those wanting "all round" performance. I'm getting about 5300 climb/60 kts and 5650 (or higher at times)WOT/sea level. Gives an alright climb and good cruise for a thick wing, high drag aircraft..

 

Stay inside Rotax specs and all is good.

 

Max continuous rpm 5500

 

Max rpm 5800 (5 mins).

 

And an important one, max WOT 5200 rpm.

 

You will find weather/temperature plays an important role in these figures. The 5400 now (in summer) may creep up to 5450 or higher in winter with more oxygen/denser air, leaning the engine and making more power.

 

 

[crashley]

HI I have also used a laser pointer fixed to the blade to scribe an arc on the floor which I mark with a texta then I rotate it to the other blade and mark that arc if the lines are on top of each other the blades are at the same angle but that only works if there is zero run out on the blades if there is any run out it will give large errors

 

I also remove 4 plugs and check it several times to ensure that the whole lot hasnt moved

 

 

[Downunder]

And an important one, max WOT 5200 rpm.

Made a mistake there. Should be MINIMUM WOT 5200 rpm.

 

 

[skippydiesel]

HI I have also used a laser pointer fixed to the blade to scribe an arc on the floor which I mark with a texta then I rotate it to the other blade and mark that arc if the lines are on top of each other the blades are at the same angle but that only works if there is zero run out on the blades if there is any run out it will give large errorsI also remove 4 plugs and check it several times to ensure that the whole lot hasnt moved

Hi Crashley - I have read about this technique but never actually tried it so please take the following comments in the spirit of enquiring they are made ;

 

• It seems to me that there are to many variables, on top of your "run out" concerne - aircraft suspension, tyre wall flex, engine mounting flex, movement of the entire airframe when you apply the rotational force (even with plugs removed there must be some resistance) to move the prop.
   
   
  
• You could eliminate a lot (but not all) of these by having the laser pointer "target" on the airframe (rather than the floor) - this would increase your accuracy & repeatability.
   
   
  
• You must measure the pitch angle of one blade in the first instance - Why not just repeat this for subsequent blade adjustments?
   
   
   
  

 

 

 

 

[Head in the clouds]

..... It seems to me that there are to many variables, on top of your "run out" concerne - aircraft suspension, tyre wall flex, engine mounting flex, movement of the entire airframe when you apply the rotational force (even with plugs removed there must be some resistance) to move the prop. .....

It's easy to assume there's a problem with the method, and to assume that there's enough resistance with plugs removed, that the airframe will move and that the method therefore won't work.

 

However the fact is, if you're careful, the method works very well. I've assisted quite a few times using the "laser attached to the back of blade projected onto floor" method, and it's simple, quick and very accurate. And results in a smooth-running airscrew provided the blades are of equal weight, balanced end-for-end, and track reasonably well. If you do happen to bump the plane or if it moves during the pitch-setting process, then it's very easy and quick to go back to the first set blade and check or re-do the other(s).

 

For the last one I made up a holder for a laser pointer that clips onto the blades, it has an adjustable rod that can be hooked over the blade tip or rested against the hub to ensure it locates similarly on each blade.

 

If you want a double-check that the airframe hasn't moved during the process you could just add a second laser pointer to the firewall or engine mounting frame and mark the point on the floor where it projects. If that doesn't change, nothing else has ...

 

 

[skippydiesel]

It's easy to assume there's a problem with the method, and to assume that there's enough resistance with plugs removed, that the airframe will move and that the method therefore won't work......................................

No worries mate! It's not that I think your method is wrong as such, it's just not for me.

 

I will stick to my masking tape, pencil, metric steel rule, builders level, digital protractor (for fine adjustment) and Warp Drive protractor (for course adjustment)

 

 

[Blueadventures]

To resurrect an older thread and for my education as I am new to Rotax engines.On Sunday we re-pitched our Savage Cub (Rotax 912 ULS with three blade DUC Helices ground adjustable prop). On climb we were getting 5,200 rpm max before making the prop 1 degree finer and now we are getting 5,400 rpm on climb (performance improvement was stunning). I am yet to test max throttle rpm at straight and level as the weather became unsuitable.

 

We want max takeoff performance and good engine safety as well. Do I have it right, that we are aiming for probably about 5,500rpm on take off and most importantly about 5,650 rpm WOT in straight and level? Airfield is about 800ft above msl, should the test be carried out at sea level to be sure? Does the 800ft make enough difference to be concerned about?

 

I have also read to cruise anywhere between 5,000 and 5,400 rpm, as below that you are labouring the engine (fine for circuits and landings but cruise, keep it higher).

 

Thanks in advance.

I aim for 5,500 WOT straight and level; I do not accept above 5,600 WOT straight and level. (I'd re-pitch off your 5,650 WOT S-L) My DUC prop setting is giving 5,580 so I have left it there. The DUC propellers do not have a big variance between climbs reduced rpm at full power and WOT straight and level. I have done plenty of reading up, asking persons running DUC props and get this confirmed. I always ready to learn more though. I believe this is due to the resin mixture used to manufacture the props. They also say you need the bring on the rpm to full power at a nice rate so the prop can flex under the load and if you takeoff like a short field style and hold the brake and get to full power quickly cavitation will / may occur and unsettle the prop. Hopefully you have already read about this. As posted earlier happy to have a chat about the DUC props and rpm any time so pm your contact if you want.

 

 

[Blueadventures]

HI I have also used a laser pointer fixed to the blade to scribe an arc on the floor which I mark with a texta then I rotate it to the other blade and mark that arc if the lines are on top of each other the blades are at the same angle but that only works if there is zero run out on the blades if there is any run out it will give large errorsI also remove 4 plugs and check it several times to ensure that the whole lot hasnt moved

Agree with the laser pen idea. I fitted a laser pointer pen to the pitch measuring tool posted in post 1 after 'Jetjr' told me about the idea and its a great tool now. Cheers

 

 

[xair1159]

Adjusta-Prop - a hi-tech accessory for adjusting pitch angles.

 

Two x 2 ft lengths of 2"x1" timber (for the non-metric parts of the world )

 

Two bits of foam pipe insulation

 

Two penny washers

 

Long bolt, bit of plastic tube and a wing nut

 

Clamp over the root end of the blade, gives much finer adjustment and is kinder on the blades

 

 

 

[skippydiesel]

Adjusta-Prop - a hi-tech accessory for adjusting pitch angles.Two x 2 ft lengths of 2"x1" timber (for the non-metric parts of the world )Two bits of foam pipe insulation

 

Two penny washers

 

Long bolt, bit of plastic tube and a wing nut

 

Clamp over the root end of the blade, gives much finer adjustment and is kinder on the blades

You might find that a smear of carnauba wax/polish on the "hubs" will give a smooth rotation to help with fin adjustments.

 

 

[Flow]

Hey folks, I am about to launch on a prop/crank indexing, blade tracking, pitch matching, spinner centering, dynamic balancing, further tweaks to the relative pitch and then Fourier transformations on the wave form to help with building some custom engine mounts mission and wondering if people could post some photos of any uber accurate tools they have used or built to measure prop pitch down to 0.01 degrees repeatable.

 

Maybe something like this with a proper 0.01 repeatable digital something (?) maybe mems base reliable digital somethings just don't exist for less that one metric moon beam...

 

Or maybe just adding an engineers bubble to my warp drive protractor and mold the protractors face to the back of the prop profile at the measuring spot.

Or maybe after dialing in the tracking attach a laser to something like this and match the arcs on the floor?

 

I really need a reliable, repeatable pitch tool before I launch down this rabbit hole.

Very interested to see what folks have created.

 

[skippydiesel]

Flow - your photo's dont appear (for me)

[IBob]

Flow, I made a mount for a laser pointer that allows me to hook it onto the back of the blade.

I use a stick to get each blade to the same height off the floor. I use a sliding square to measure in exactly the same distance from each blade tip ( and mark that position with masking tape).

The pointer projects onto the floor, where I also put a bit of masking tape. With this arrangement, 1 deg of pitch = approx 26mm (as I recall) of pointer movement on the floor: it's not hard to get all the blades within about 2mm on each other, so accurate to about 0.1deg.

Obviously it's important that the aircraft doesn't move during this: mine has park brakes, and sits at the top of it's suspension travel.

It's also essential to check blade tracking, which will throw this out.

 

I have done this 3 times on my own aircraft, and once on another, it's not difficult.

I get very smooth running.

 

A digital protractor (inclinometer) on the back of the blade would probably give the same result and be simpler, with one proviso: just because something reads to one decimal place does not mean it is accurate to one decimal place. And most low cost inclinometers carefully make no claims about accuracy: they just say they read to 0.1deg, or whatever.

 

Finally one way to check how evenly your blades are pitched is to fly so that the sun is reflecting off the blades: with perfect pitching, the blade flash will appear always in the same place.

[Flow]

Thanks Bob, I am pretty sure we met a Hood a while back 🙂 Do you have a photo of your contraption per chance?

 

[Blueadventures]

Hi Flow. The laser pointer is the way to go to lessen the degree difference, less than .01 for example.  Re the tool I made I modified it somewhat. I find you need it to have a bit of mass weight to it so it holds onto the blade when fitted, so I added a piece of flat alloy bar to the tool.  As the back of my DUC blades are slight concave I plan to add an adjustable pimple point so it sits square on any blade type.  Mine sits flat against the back of my blades even though the blade has a gap at on side.  However I have been adjusting two E-prop sets and they have a pronounced curve on back of blade and need to be careful.  
 

I’ll post an image later for you.

[Kyle Communications]

There isnt a real way to get the type of accuracy you are talking about achieving.

 

A digital protractor is usually about 0.1 deg as Bob said. The laser pointer would be a more accurate way as Bob said as you get the expansion arm. Sort of like a zoom lens on a camera or a scope sight on a gun.

 

usually the digital protractor is the quickest and easiest and realistically once you get to that level you are not going to be able to feel any further differences

 

[kgwilson]

A good straight edge is as good as a laser pointer, just a little more difficult to use. I used a bit of aluminium angle as the straight edge

Edited November 14, 2020 by kgwilson

[Kyle Communications]

The Eprop device has a holder on the digital protractor that sets its position the same on every blade provided its planced at the same spot on each blade. its easy on the Eprop as you set it at the edge of the titanium LE. Measuring blade angle can only be done on one particular point out from the centre..change that point and the angle is different.so knowing what degree you set the blade is only relative to that point. Its a starting point the only true way is by the rpm and increasing and decreasing the pitch to achieve the rpm range you want...the only other requirement is to get whatever that pitch angle is exactly the same on each blade. This is done with the protractor or the laser...the laser will allow you to better make smaller fine adjustments

You will see the Eprop protractor in this video

 

[IBob]

KGWilson, you are not wrong in theory. But I found a straight edge much more difficult to use in practise......it is hard to position it repeatedly so it is just touching the floor....and I found it less accurate.

 

Flow, I cobbled my contraption together from what I had lying around. It is so crude, I hesitate to post pics...but eh well:

The laser is a cheap gift I had but never used. It sits below the edge of the blade when in place. Any laser that made a fine point or line would do.

It's screwed to a block of wood that I put over the planer.

The hook for hanging on the blade is aluminium strip screwed in place.

And the screw you can see is so that the thing sits with the RH edge of the wood flush to the blade, the LH edge of the wood is held up by the screw head. This is because the back of the blade is not a flat plane, but has a long twist in it: if I was making it again, I think I would arrange for it to sit on 3 points. As it is, it sits on one straight edge and one point.

 

It's quite heavy, and as Blueadventures suggested above, this is an advantage: it sits snug to the back of the blade under it's own weight.

 

The acid test with most measurements is repeatability: you should be able to go round the prop a minimum of 3 times and get the same reading for each blade. If you can do that, you can be confident in your system.

I can readily do that with this contraption, so I've never felt the need to refine it.

 

Do however be sure the aircraft sits still.

And do carefully check the blade tip tracking.

[IBob]

(PS. Ignore the fact that my laser can rotate: I just set it in one position and leave it there.)

[Blueadventures]

16 minutes ago, Kyle Communications said:

The Eprop device has a holder on the digital protractor that sets its position the same on every blade provided its planced at the same spot on each blade. its easy on the Eprop as you set it at the edge of the titanium LE. Measuring blade angle can only be done on one particular point out from the centre..change that point and the angle is different.so knowing what degree you set the blade is only relative to that point. Its a starting point the only true way is by the rpm and increasing and decreasing the pitch to achieve the rpm range you want...the only other requirement is to get whatever that pitch angle is exactly the same on each blade. This is done with the protractor or the laser...the laser will allow you to better make smaller fine adjustments

You will see the Eprop protractor in this video

 

Thanks Mark.  Good video shows more on the adjustment than the E-prop people show and English speaking (Not meant to be complaining about E-props video).  I would like to suggest that people using the E-prop digital protractor place a piece of carpet on any cement hangar floor as I have seen them brak when they fall onto the floor as its a hard plastic mount the cube fits into; or have 5 minute epoxy handy.  Cheers.

[Blueadventures]

7 minutes ago, IBob said:

KGWilson, you are not wrong in theory. But I found a straight edge much more difficult to use in practise......it is hard to position it repeatedly so it is just touching the floor....and I found it less accurate.

 

Flow, I cobbled my contraption together from what I had lying around. It is so crude, I hesitate to post pics...but eh well:

The laser is a cheap gift I had but never used. It sits below the edge of the blade when in place. Any laser that made a fine point or line would do.

It's screwed to a block of wood that I put over the planer.

The hook for hanging on the blade is aluminium strip screwed in place.

And the screw you can see is so that the thing sits with the RH edge of the wood flush to the blade, the LH edge of the wood is held up by the screw head. This is because the back of the blade is not a flat plane, but has a long twist in it: if I was making it again, I think I would arrange for it to sit on 3 points. As it is, it sits on one straight edge and one point.

 

It's quite heavy, and as Blueadventures suggested above, this is an advantage: it sits snug to the back of the blade under it's own weight.

 

The acid test with most measurements is repeatability: you should be able to go round the prop a minimum of 3 times and get the same reading for each blade. If you can do that, you can be confident in your system.

I can readily do that with this contraption, so I've never felt the need to refine it.

 

Do however be sure the aircraft sits still.

And do carefully check the blade tip tracking.

Not crude; purpose made.  Cheers.

[Kyle Communications]

Hi Mike

 

I have spares of those clips now as they are only 3D printed. The meter isnt anything too great but for what actually makes any difference its well good enough to get the blade angles all the same. The laser method to me is far more accurate than any memms device around that someone can afford