In flight Adjustable Prop

[BirdDog]

Hey all,

 

So my Sportstar has an inflight adjustable prop, and up to now have not had much need to move from full fine (no X country Endo) but now that I am about to start venturing out, I thought it best to start researching its appropriate use.

 

There is little to no info in the manual (It's factory fitted) and can't really find much online. I emailed Evektor some time ago, but no response either. :(

 

Any tips, hints, do and don'ts would be much appreciated.

 

Cheers

 

John

 

 

[poteroo]

inflight adjustable prop

Find an instructor who holds the endorsement and have him/her conduct your endorsement. You need to do this to be legal, and to satisfy your insurers that you have attained competency in handling the IFA prop. happy days,

 

 

[Camel]

Where are you located Birddog ? Is your prop a Kaspar ?

 

 

[Downunder]

100hp rotax I imagine.

 

Minimum rpm at WOT 5200.....

 

 

[BirdDog]

I have the endorsement and I know how to use it. Take offs, landings etc etc.

 

What I want to know is how to get the "Best" out of it. Easy to say... course her up in the cruise. Fine for landing and takeoff etc etc. But I am looking for the finer details.

 

@Camel - I am in Yass, NSW. My prop is factory fitted woodcomp.

 

@Downunder - Its a 912 - so yep. 100HP at 5800

[OZJohn]

You need to go by manifold pressure so as not to overload the engine, and to get best economy.

 

The numbers are in the Rotax manual for constant speed prop.

 

Let me know if you need further info. John.

 

 

[BirdDog]

OK... So having a look through the manual (Rotax 912ULS) I have found the following image.

 

Now from flying around at cruise (around 5000rpm) my Manifold Pressure sits at around 23 to 25.

 

So according to this image, I could course the prop up to 27. Am I reading that right?

 

[GALLERY=media, 4045]Rotax-Cyl-Pressures by BirdDog posted Dec 30, 2017 at 7:39 PM[/GALLERY]

 

 

[skippydiesel]

"...............I could course the prop up to 27. Am I reading that right?"

 

Hi BirdDog,

 

You could, but I would suggest a more conservative 55-75% setting, using tacho & manifold pressure.

 

It a long time since I did my training in constant speed but I think you will get better fuel consumption, quieter operation, lower vibration and longer service life from your engine if you cruise at conservative power settings.

 

I would be inclined toward "Take-off power" 5800 rpm only for only as long as it takes to achieve a minimum safe altitude - followed by a reduction to "Max continuous power" 5500 rpm to consolidate the climb out. If cruise climb is required, do not go below go to 5200 rpm. Once cruise altitude has been achieved further reductions to between 4300 & 500 rpm depending on mission/preference should be selected.

 

It is common to achieve desired rpm by leaving throttle wide open (WOT) & changing prop pitch, until desired engine speed/manifold pressure is achieved (see DownUnders comment). In this way you are using the prop pitch to act as an engine speed (rpm) governor at a given load on the engine.

 

As your system in not a CS prop you will have to work out how best to manage it in the variose phases of flight from start up, to shut down. I agree with Poeteroo - try and find an instructor or at least a genuinely knowledgeable/experienced person to assist you (try a gliding club - some self launch gliders use in flight adjustable props).

 

 

[Downunder]

MANIFOLD PRESSURE

 

I think the allowable mp is variable with rpm and altitude too. You should be able to find chart for it....

 

My friend uses rpm and fuel consumption to set his cruise.

 

Says it works for him....

 

 

[BirdDog]

Thanks Guys,

 

That's pretty much what I am going trial on my next flight. Get to the cruise, and then adjust the prop and throttle to get the RPM sitting at around the 5000rpm mark, and get the MP to around the 26 mark. Then do some experimenting to find the best result.

 

Cheers

 

John

 

 

[skippydiesel]

MANIFOLD PRESSUREI think the allowable mp is variable with rpm and altitude too. You should be able to find chart for it....

 

My friend uses rpm and fuel consumption to set his cruise.

 

Says it works for him....

Mp will vary with altitude.

 

I would suggest that fuel consumption is a secondary effect of rpm/manifold setting. It would work but is less than ideal.

 

A VDO manifold gauge is not expensive is easy to fit & connect (balance tube already has a "connection" point) why not just fit one and use it to "set up/adjust" the engine.

 

 

[BirdDog]

I’m confused. I have an MP gauge.

 

Was the 2nd part of your comment mean for me Skippy?

 

 

[Downunder]

I would suggest that fuel consumption is a secondary effect of rpm/manifold setting. It would work but is less than ideal.

I agree. I'ts not my aicraft but and I never flown the type...

 

I believe the previous owner told him that's how it's done (rpm/fuel).

 

Every aircraft I I've seen with an IFA/CS has a mp gauge, so it probably has one.

 

Be careful with 5000 rpm John. Over coarse at that rpm you are "low speed loading" the engine out of rotax operating spec.

 

One of the reasons they changed the crankcase in 2006 was because of exactly this reason. Eg WOT/full coarse at 4800.

 

This loading was splitting the crankcases open, so not insignificant damage.

 

I would advise min 5200 until you know exactly whats going on and what loading is happening.

 

Also take a look at the power and torque charts...... my personal opinion is 5200 is the perfect economy cruise.

 

Below this the power/torque drops away and trying to keep up a good speed loads the engine unnecessarily...

 

They love to rev, so don't be shy....

 

 

[Yenn]

The normal way to get best performance ie fuel use, is to run full throttle at low rpm.

 

This of course depends upon what Rotax say. Usually with a normally aspirated engine, above about 5000 feet it would not damage an engine to run full throttle and very low revs.

 

 

[skippydiesel]

I’m confused. I have an MP gauge.Was the 2nd part of your comment mean for me Skippy?

Nope! - I was commenting on DownUnders contribution.

 

 

[BirdDog]

UPDATE...

 

So had a good play with prop yesterday, and very pleased.

 

I managed to speak to a ROTAX tech and get some advice etc, and after getting her up and cruising I had to back off when she hit 115, as it was too lumpy to be going that fast!

 

Anyways... More playing to be done! Means more flying! LOL! :) That can't be a bad thing!

 

 

[OZJohn]

BirdDog from your description I am guessing your Woodcomp Prop is a SR3000. If so I can send you the operators manual (PDF) if you don't have it.

 

Pitch stop adjustment is critical to stop over revving in fine or propeller stall flutter in full coarse and full power. John.

 

 

[BirdDog]

Yes it. And yes please that would be great. Do you need an email address. I can PM to you.

 

Cheers

 

John.

 

 

[planesmaker]

I think it important to adjust in correct sequence ie after T/off to reduce power decrease mp with throttle then adjust prop for revs. When increasing power such as going into a climb increase revs with prop adjustment then add mp with throttle. That way you have less risk of overloading the engine. My 2 cents

 

 

[BirdDog]

Yep. That’s what the rotax guy told me.

 

Get up and into cruise. Backing to get stable, then course the prop, increase throttle, then prop, then throttle etc etc until ten desired result is achieved.

 

 

[Cosmick]

Most important to reduce revs prior to changing pitch to fine so as to not over rev the engine.

 

 

[planesmaker]

Just to be clear

 

Want to increase throttle? Prop finer first

 

Decreasing throttle? Throttle back then prop coarser

 

 

[BirdDog]

The sequence would be...

 

Take off - Full fine - After climb, reduce power to bring the RPM back from max (Say 5300rpm) Increase prop pitch a couple of clicks. This will bring RPM down as it courses up. So increase throttle to get RPM back in range. Repeat and rinse!

 

Then once cruising and you want to come down.... Decrease throttle, and reduce prop pitch. As the prop is reduced in pitch, the RPM will increase. Repeat and rinse!

 

Take off = Full fine.

 

Landing = full fine.

 

Cheers

 

John

 

 

[nathan_c]

I’m not familiar with the system on your plane, but if it is the same as regular constant speed units or in flight adjustable (and as you have a manifold pressure gauge im assuming it would be), I just want to clarify a few terms and procedures that relate because there is a few posts here with wrong or ambiguous wording.

 

Most importantly (vs a fixed pitch), your throttle is now controlling power (i.e manifold pressure), and not your RPM’s. Your propellor rpm is now controlled by your pitch control. You should be setting your power setting based on the manifold pressure gauge, and not the rpm gauge with an adjustable system.

 

In full fine mode, you are effectively using the prop in a fixed pitch like configuration, and the RPM will rise and fall correspondingly with power changes, however it’s important to note that you are still directly changing the manifold pressure with throttle position changes and not prop RPM.

 

Importantly you need to be aware in what order you change things depending on your phase of flight. Let’s assume you are already stable in the cruise, if you wish to increase power and climb, the correct technique is to increase propellor RPM first to the desired setting, and then increase MP second and begin the climb. When you level out, the procedure is reversed. Level out, decrease the MP first to your desired power setting, and then reduce the prop RPM second.

 

In a constant speed unit, for a descent a reduction in MP is sufficient with no pitch change, however in your manually adjustable system you may need to bring the RPM back (after the MP reduction) to avoid overspeeding the prop ( you would need to have a play and advise on that point).

 

If you make sure that you follow the correct technique and try and avoid lugging the engine by having a high power setting with a far too coarse setting like you said, you should not have any issues with damaging the aircraft. An hour with a qualified instructor may also be beneficial if you still are unsure of how to approach the system and get the most out of it safely.

 

I mainly wanted to write this post because some comments have been referring to reducing RPM by reduction of throttle (only relevant on the full fine stops), and some other phrases have been thrown about which havnt been quite correct, so I felt it beneficial to point out exactly what controls are changing what in an adjustable system, and the difference between fixed vs adjustable re. What the throttle is actually doing.

 

Hope that was helpful to people out there

 

 

[BirdDog]

Thanks Nathan,

 

Great info.

 

I have been talking direct to ROTAX and they have been a great help, and he put more emphasis on making sure I kept the motor RPM around the 5300 mark. I guess, if as you say, the prop RPM falls with an increase in pitch, so does the motor RPM fight? Hence the need for more power (more throttle)

 

Roger (Rotax) has recommended 5300 RPM on motor, with 26-27 on the MP. And that's pretty much where she sat last flight, but had to back off, as it got too quick for the conditions I was flying in. It was not full pitch nor WOT, so not sure what she would actually do at full beans! LOL!