In flight Adjustable Prop

[facthunter]

You are getting more effective thrust from your engine by having a "variable " pitch. That's the reason for having it. so you will go faster and take off more quickly, with that set up... For POWER you need MP and RPM's.. Pressure altitude minus the drop through the carb gives you the available MP. It's probably about 2 inches .

 

In Flight "adjustable" is like having gears in a car. If you increase speed in a given gear your RPM's rise. This doesn't happen in a "constant speed" which is actually "Constant RPM" within the limit of the stops which Must be there to control the limit of the range of pitch available. You don't want a situation to happen where it goes too fine in the air, or you could have it over revving and the plane stalling. Nev

 

 

[nathan_c]

I’ve just deleted and re written my reply as I have just done some research on how your system works and my reply wasn’t quite right.

 

Everything I wrote above is more applicable only to a constant speed system as I understand it now.

 

As I understand your in flight adjustable system now, I believe that in some ways it works like a fixed pitch, and as fact hunter says just like in a car, as your speed increases your rpm will also increase so as this is happening, that would be when it is appropriate to coarsen your prop so that the rpm sits at the appropriate range.

 

I admit to knowing little about what settings you should use, so if rotax suggests 5300 then that would be the best advice to follow. The main point to take out of all of this would be to make sure that if you need to increase power to begin a climb, increase the pitch on the prop before adding power, and reverse if you are reducing power, make sure you do power before prop.

 

 

[BirdDog]

Thanks Nathan,

 

Yep! My Motor RPM has direct connection to how fast my prop spins. Might is not constant speed. Just the pitch is adjustable.

 

Cheers

 

John

 

 

[Camel]

I’ve just deleted and re written my reply as I have just done some research on how your system works and my reply wasn’t quite right. Everything I wrote above is more applicable only to a constant speed system as I understand it now.

 

As I understand your in flight adjustable system now, I believe that in some ways it works like a fixed pitch, and as fact hunter says just like in a car, as your speed increases your rpm will also increase so as this is happening, that would be when it is appropriate to coarsen your prop so that the rpm sits at the appropriate range.

 

I admit to knowing little about what settings you should use, so if rotax suggests 5300 then that would be the best advice to follow. The main point to take out of all of this would be to make sure that if you need to increase power to begin a climb, increase the pitch on the prop before adding power, and reverse if you are reducing power, make sure you do power before prop.

Hi, not saying your wrong but from first hand experience, from cruise to commence a climb I would power up first adjust attitude and climb then as load increases adjust prop finer ! If I did it the other way I could over rev and slow the plane down as well prior to climb ! Just my opinion from experience ! I have used IFA and CSU and prefer IFA !

 

 

[nathan_c]

Hi, not saying your wrong but from first hand experience, from cruise to commence a climb I would power up first adjust attitude and climb then as load increases adjust prop finer ! If I did it the other way I could over rev and slow the plane down as well prior to climb ! Just my opinion from experience ! I have used IFA and CSU and prefer IFA !

You could well be right, like I said I know little about IFA's, and this thread has actually lead me to learn a bit about them myself. I only have CSU experience, and on a CSU you would fine up the prop first in that situation.

 

It is a shame I can not edit my posts above to reflect the incorrect information.

 

 

[Downunder]

Maybe hit the "report" button on the posts Nathan. Just so they don't linger with the incorrect information.

 

The Rotax engines are a little bit different than other GA engines in that they are high reving and geared.

 

And as stated generally IFA and not C/S.

 

 

[facthunter]

You don't want to make this harder than it has to be. Constant speed. is easy. set the revs and it stays there unless you close the throttles at low speed.

 

Variable pitch is an angle of the blades just like you may have been able to do on the ground but now you can do it anytime. with your In flight adjustment capability.

 

If you leave it in fine it's like being stuck in first gear. The engine will over rev as your speed increases,. so what would you do in a car ? Change into a higher gear.. Move the pitch to a higher figure which is within the makers recommendations for rpm.

 

In cruise essentially the same,. as your speed increases control the RPMs by pitch adjustment to below the limit revs, but don't' go ridiculously low. with the revs . You will over prop it and you should be able to sense that. Don't go there..You will find the position and revs with practice . If you want to reduce cruise speed just reduce power( MP) initially. If it's a large MP change you might like to load the motor by reducing revs a bit to make it pull a bit more. You will have to experiment. On descent you might increase speed or hold it steady where it was roughly for cruise. If you are power off that's OK, just close the throttle,. like any fixed pitch set up the motor will pick the revs it will on descent.

 

. You do have other options . You might do a drift down with lower revs and some power on to keep the engine warm and use your height to save a bit of fuel.. Hope this helps . It's so much more difficult than CS but see it as a lot of quick change fixed pitch options. Some (at the extremes) are not useable. Like if you fitted a prop with pitch too fine you would exceed the desired revs during the take off.. You don't want to be adjusting things during the take off and climb. That's dicey. Nev

 

 

[skippydiesel]

Y...............Like if you fitted a prop with pitch too fine you would exceed the desired revs during the take off.. You don't want to be adjusting things during the take off and climb. That's dicey. Nev

First the disclaimer - I have no experience with an in flight adjustable prop and only limited experience of constant speed.

 

I have however experimented with my ground adjustable - current setting is my best effort at getting good climb performance with acceptable cruise (I have to get in/out of a very marginal strip).

 

Based on the above it would seem to me that you would set up your prop to give excellent climb out at full fine, with wide open (full) throttle (WOT) with your engine delivering near or full power and little chance of an overspeed. As with any fixed or ground adjustable prop you would use your aircraft attitude & speed to govern engine rpm. (Rotax advise no less than 5200 rpm in climb and in full power static run up). On reaching a safe/acceptable altitude you would level out to cruise or cruise climb - air and engine speed will start to increase, you can either adjust your prop (corsen) to manage your rpm and / or reduce throttle setting. This is when your manifold vacuum gauge will assist you to achieve the correct balance between engine speed and vacuum (as advised by Rotax) for the desired aircraft performance.

 

Decent can be managed by simply reducing power ( I always carry some power to reduce than chance of shock cooling and carbi icing) but you must remember to change your pitch to full fine at or before down wind, as you must in a position to make powered corrections to the landing profile and do a go round if necessary.

 

I suspect that in an engine failure, full course would tend toward a slightly better glide performance.