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Propeller pitch adjusting tool

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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

 

 

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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

 

 

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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.

 

 

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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

 

 

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And an important one, max WOT 5200 rpm.

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

 

 

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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?
     
     

 

 

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..... 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 ...

 

 

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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)

 

 

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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.

 

 

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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

 

 

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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

 

Adjusta-Prop.jpg.132a84f80827ddd4ccc155f914021860.jpg

 

 

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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.

 

 

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