Possibly needing prop adjustment

[gbigs]

Um...yes.  Yellow arc 5500-5800.  Green arc 1800-5500.  Why did you leave out that 5500rpm is also in the green arc?  That means 5500 is both the end of the normal range and the beginning of the yellow arc.  If it makes you feel better, run continuously at 5499rpm.  But I bet it would be fine at 5501rpm too.  

 

Oh wait, you can't run continuously at 5499-5501rpm anyway, because your prop is too coarse...

 

I left nothing out.  I gave the table.  The point was is 5500 included at the 5 minute run time restriction, it is...  If you chose to 'run all day' at an EXACT 5500 (doubt you can do that) go for it.  Following the guidance in the POH is not just prudent, its required by the FAA.

[Ed Cesnalis]

My TAS is 127kts, I got about 10kts and 300fpm climb increases from flattening my pitch.

 

The down side would be that I am no longer optimized for some low fuel burn/ low power setting that I never use.

 

Consider a trip from Mammoth to Van Nuys.

• Initial climb - 3,000' the optimzed cruise pitch works well, I do the climb at well over 100kts TAS.
• Cruise - 150nm 5,500 RPM @ WOT making 127kts TAS - optimized pitch gives great performance
• Descent 40nm, retard throttle for 500fpm descent, maintain speed, optimized pitch works fine 

Return Flight

• Initial climb - 9,000' the optimzed cruise pitch works well, I do the climb at well over 100kts TAS.
• Cruise - 150nm 5,500 RPM @ WOT making 127kts TAS - optimized pitch gives great performance
• Descent 10nm, retard throttle for 800fpm descent, maintain speed, optimized pitch works fine 

The optimized pitch works well at most altitudes.  If I'm at low altitude I need a flat pitch for climbs, descents work good with flat pitch and cruising fast at 5gph (CTSW) is my target.

 

As I said above by imposing a 75% power limitation for cruise I never need a coarse pitch.  I still vote for 5,500 RPM @ WOT @ 7,500DA as a target that works well at almost all altitudes and permits best speed.

[Tom Baker]

What is your prop set to?  Are you flying at sea level most of the time?

What my prop is pitched at or where I am flying is not important. What is important is setting the propeller pitch to have the engine operating in a desirable RPM range. This RPM number can be measured in a static run up like most standard category aircraft with a fixed pitch propeller, or at wide open throttle in level flight. Once this is set, operating in any other conditions is a compromise on performance like with any fixed pitch propeller.

[FlyingMonkey]

My TAS is 127kts, I got about 10kts and 300fpm climb increases from flattening my pitch.

 

 

As I said above by imposing a 75% power limitation for cruise I never need a coarse pitch.  I still vote for 5,500 RPM @ WOT @ 7,500DA as a target that works well at almost all altitudes and permits best speed.

Your results are nearly identical to mine. The only difference is mine is pitched for the lower altitudes that I fly at (3000-5000ft most often). I intentionally had mine set a little flatter than needed for those altitudes, so that when flying cross country I can climb to 7500-8500ft and still make 5500rpm. At WOT at 3000ft I hit about 5750rpm.

[Ed Cesnalis]

Your results are nearly identical to mine. The only difference is mine is pitched for the lower altitudes that I fly at (3000-5000ft most often). I intentionally had mine set a little flatter than needed for those altitudes, so that when flying cross country I can climb to 7500-8500ft and still make 5500rpm. At WOT at 3000ft I hit about 5750rpm.

 

How can you be both?

• pitched for the lower altitudes that I fly at (3000-5000ft most often)
• set a little flatter than needed for those altitudes ... 7500-8500ft and still make 5500rpm

How can you be pitched for 3-5000' and make 5,500 @ 8,500'?  

 

Perhaps its confusion between the 5,800 and 5,500 limitations?  If you can make 5,800 then you are already pitched for max cruise at > 7,500 DA.

[Tom Baker]

My point is a simple one.  Since the prop is fixed in flight ANY setting is static for all density altitudes for all flights made at that setting.  I contend there is no such thing as 'set right'.   Diddling with the prop pitch may allow you to tweek for a given density altitude but the gain is so small that risking doing it wrong outweigh leaving it at the factory setting.

People are not diddling or tweaking like a race car driver to get ever ounce of power out for every flight. What they are doing is taking aircraft that were delivered with a propeller pitch that was to coarse, and adjusting the pitch to get a RPM that is closer to Rotax's recommendations. While your airplane may have been OK when you took delivery, many aircraft were not set right.

 

Take a look at the TCDS for any aircraft that can use a ground adjustable propeller, and they will provide a RPM range that the propeller needs to be adjusted to for that aircraft's normal operation.

[FlyingMonkey]

How can you be both?

 

• pitched for the lower altitudes that I fly at (3000-5000ft most often)
• set a little flatter than needed for those altitudes ... 7500-8500ft and still make 5500rpm

How can you be pitched for 3-5000' and make 5,500 @ 8,500'?  

 

Perhaps its confusion between the 5,800 and 5,500 limitations?  If you can make 5,800 then you are already pitched for max cruise at > 7,500 DA.

My understanding is that the higher the rpm I can reach down low, the higher it will be as I climb up. Instead of pitching for 5500 WOT, I am pitched for 5750rpm WOT at ~3000ft. As I climb up I will lose some rpm as the air gets thinner, but can still get close to 5500rpm at the best cruise altitudes. I may have given up a little efficiency at my normal lower cruise altitude to buy a little more flexibility in higher alt cruise when I use it.

 

It may be this is exactly how yours is set up, and you just cruise more at that optimal altitude for that setting. Either way, I'm very happy with my settings both at lower level and higher cruise altitudes.

[Ed Cesnalis]

My understanding is that the higher the rpm I can reach down low, the higher it will be as I climb up. Instead of pitching for 5500 WOT, I am pitched for 5750rpm WOT at ~3000ft. As I climb up I will lose some rpm as the air gets thinner, but can still get close to 5500rpm at the best cruise altitudes. I may have given up a little efficiency at my normal lower cruise altitude to buy a little more flexibility in higher alt cruise when I use it.

 

It may be this is exactly how yours is set up, and you just cruise more at that optimal altitude for that setting. Either way, I'm very happy with my settings both at lower level and higher cruise altitudes.

 

 

To compare apples to apples you need to qualify some points. For the sake of this discussion I assume that we optimize for speed using 5,500 limitation.

 

Given that you cannot cruise at 5,750RPM then I wouldn't call that pitched for 3,000'.  In order to cruise at 3,000' you would have to significantly retard the throttle. A lot of available cruise performance becomes unavailable due to the 5,500 RPM limitation.  If I'm pitching for a target altitude that can only mean 1 of 4 things:

1. Best speed
2. Best climb
3. Best economy
4. Compromise

Our pitch discussions over the years have focused on #1 with the 5,500 limitation.

 

The reason we run similar pitches at our quite different locations is the practical envelope isn't very large.  Pitching for best speed at 3,000' will exceed 75% power (not an optimum cruise setting) and won't be comfortable. Pitching for DAs above 12,000' is a loosing battle due to loss of power.  There is about a 4,000' DA window where you can pitch for best speed. 8,000'-12,000'  Keep your target low in that range if you want every last knot or if you fly low and keep it high if you fly high or want to compromise speed and economy.  If you want to compromise speed and economy than target a throttle setting that is 92% or below.

[FlyingMonkey]

To compare apples to apples you need to qualify some points. For the sake of this discussion I assume that we optimize for speed using 5,500 limitation.

 

Given that you cannot cruise at 5,750RPM then I wouldn't call that pitched for 3,000'.  In order to cruise at 3,000' you would have to significantly retard the throttle. A lot of available cruise performance becomes unavailable due to the 5,500 RPM limitation.  If I'm pitching for a target altitude that can only mean 1 of 4 things:

1. Best speed
2. Best climb
3. Best economy
4. Compromise

Our pitch discussions over the years have focused on #1 with the 5,500 limitation.

 

The reason we run similar pitches at our quite different locations is the practical envelope isn't very large.  Pitching for best speed at 3,000' will exceed 75% power (not an optimum cruise setting) and won't be comfortable. Pitching for DAs above 12,000' is a loosing battle due to loss of power.  There is about a 4,000' DA window where you can pitch for best speed. 8,000'-12,000'  Keep your target low in that range if you want every last knot or if you fly low and keep it high if you fly high or want to compromise speed and economy.  If you want to compromise speed and economy than target a throttle setting that is 92% or below.

 

Roger has often stated pitching for at least 5600rpm WOT at cruise altitude, instead of 5600rpm.  When I reported my results after the re-pitch he mentioned he though it was a very good setup.

 

Also, since engine power is related to rpm, it seems that if I can get 5500rpm at whatever altitude Im at, I'm making full power.  If I get 5500rpm at 3000ft, even if I have to retard the throttle a bit, aren't I getting max engine performance?  Of course, the prop might be slightly flatter than optimal and I might lose a little bite there, but it doesn't seem to be hurting me much.

[Ed Cesnalis]

...  it seems that if I can get 5500rpm at whatever altitude Im at, I'm making full power.  If I get 5500rpm at 3000ft, even if I have to retard the throttle a bit, aren't I getting max engine performance?  ...

 

You only have full continuous rated power when you realize 5,500 RPM at max(manifold pressure) or at WOT.  5,500RPM @ partial throttle is a lower power setting.

 

RPM = speed not power.  Does it take more power to make a dump truck go 55mph than it takes to make a harley davidson go 55? 

[Roger Lee]

It's just an average balance.

 

Balance is what we are looking for. No pitch is perfect at sea level and 10K too. Pick your normal and average altitude, set it and leave it. If your WOT rpm is around 5600-5700 then walk away and feel good. A few rpm this way or that isn't worth hassling trying to tweak it constantly. Splitting hairs with a prop pitch will put you in a mental institution.  Here is part of the difference. This morning with two CTSW's I went flying. One could get 5800 rpm WOT at 3500' and the other 5650. When he was flying at 5200 rpm flat and level I had to fly 5400 rpm to match his speed not to mention I was burning more fuel. Too flat is counter productive (unless you need great climb)  just like too course. Too course cost you everything. There is nothing good to be said for over pitching.

[Doug G.]

100H, "fixed pitch" has an actual aeronautical meaning. So does "ground adjustable", "in air adjustable", and "constant speed."

Put them on your list of things to look up.

[Marco01]

Marco01where exactly do you have the 20° ?I assume it is 20° from the centerhubasking because I have to reajust my Neuform for the 100hp (from the 80 )merci

20° are taken ay 20 cm from prop blade tip. Make sure to have the nose wheel up in order to have engine horizontal axis // from the ground, and the blade // to the ground as well...

[gbigs]

100H, "fixed pitch" has an actual aeronautical meaning. So does "ground adjustable", "in air adjustable", and "constant speed."

Put them on your list of things to look up.

 

You miss the point.  While the prop rotates on a CTLS it is FIXED PITCH.   Again, I doubt FD is miss setting the prop on it's own product.  And do doubt those twiddling their props with the idea they are gonna eek out a few more knots or ounces of gas efficiency are doing little more than swapping climb for cruise or the reverse.

 

Some of the same guys chasing the prop pitch fantasy are the ones that fail to see the performance difference between the older 912ULS and the 912iS.  And that difference is far more pronounced than anything you get changing prop pitch.

[FlyingMonkey]

You miss the point.  While the prop rotates on a CTLS it is FIXED PITCH.   Again, I doubt FD is miss setting the prop on it's own product.  And do doubt those twiddling their props with the idea they are gonna eek out a few more knots or ounces of gas efficiency are doing little more than swapping climb for cruise or the reverse.

 

Some of the same guys chasing the prop pitch fantasy are the ones that fail to see the performance difference between the older 912ULS and the 912iS.  And that difference is far more pronounced than anything you get changing prop pitch.

 

Roger already mentioned exactly why they set the props for less efficiency, fear of LSA speed breakout.  Which do you doubt more, that FD would dumb down their prop a little bit or that they would risk losing the entire US market because of a prop set too efficiently?

 

We have already pointed out this does *not* swap climb for cruise or vice versa.  It allows the airplane to make closer to full power, improving climb AND cruise.  Both myself and CT gained ~10kts and 300fpm, and Roger has dozens of similar anecdotes.

 

This is not a Continental engine with a 2600rpm limit with a torque curve that peaks at 1800rpm.  It's a motocycle-style engine that needs high rpm to make its power, and keeps making power right up to the redline.  If you don't get the rpm up, you don't make full power, plain and simple.

 

And there is no performance difference between a 912ULS and a 912iS, other than in fuel economy.

 

Your steadfast refusal to listen to or even acknowledge logic, even from Roger, Tom Baker, CharlieTango, or other highly experienced forum members can only mean one thing... 

 

[Ed Cesnalis]

If you don't get the rpm up [and the manifold pressure (i.e. 5,500@WOT)], you don't make full power, plain and simple.

 

 

In my experience, in this regard the Rotax behaves exactly the same as a Lyc or Conti.

[Ed Cesnalis]

You miss the point.  While the prop rotates on a CTLS it is FIXED PITCH.   Again, I doubt FD is miss setting the prop on it's own product.  And do doubt those twiddling their props with the idea they are gonna eek out a few more knots or ounces of gas efficiency are doing little more than swapping climb for cruise or the reverse.

 

Some of the same guys chasing the prop pitch fantasy are the ones that fail to see the performance difference between the older 912ULS and the 912iS.  And that difference is far more pronounced than anything you get changing prop pitch.

 

Even if your sport upgrade increased your hp over the ULS it is a very small increase and you cannot realize any increase above ULS speed if you can't cruise at 5,500.

[gbigs]

You may find language from the Neuform propeller operators manual helpful in understanding why the prop is set by the factory the way it is:

 

When the propeller was designed, special attention was paid to the attempt to transform

the engine’s power in the quietest possible way. One aspect of this concept is to operate

the engine with reduced propeller revolutions and rather big angles of incidence of the

blades.

 

We recommend to stick to this concept and to use the appropriate reduction gears in

order to gain the maximum propeller performance. A higher number of revolutions

increases the noise emissions, leads to losses during the cruise and has therefore no

advantage.

 

Neuform also warns against damage over-revving the prop.

 

http://www.neuform-composites.de/_downloads/pdf/propellermanual.pdf

[Ed Cesnalis]

with a 2.34:1 reduction ratio, the 5,500RPM needed to realize max(ratedContinuousPower) translates to 2,350RPM for the propeller. 

 

Neuform provides this table for limits:

 

Limits of numbers of revolutions:

 NEUFORM S: n max = 1950 min -1

 NEUFORM T: n max = 2300 min -1

 NEUFORM TX: n max = 2600 min –1

 NEUFORM C: n max = 2600 min –1

NEUFORM D: n max = 2600 min –1 

 

3 of 5 Neuform props appear to have power limits that would permit 6,084RPM and 2 would limit below 5,500.

 

Which Model is on your CT?  I don't have a Neuform.

[Tom Baker]

You miss the point.  While the prop rotates on a CTLS it is FIXED PITCH.   Again, I doubt FD is miss setting the prop on it's own product.  And do doubt those twiddling their props with the idea they are gonna eek out a few more knots or ounces of gas efficiency are doing little more than swapping climb for cruise or the reverse.

 

Some of the same guys chasing the prop pitch fantasy are the ones that fail to see the performance difference between the older 912ULS and the 912iS.  And that difference is far more pronounced than anything you get changing prop pitch.

Filling the trunk of your car with manure for the flower bed doesn't make it a truck, just like rotating a ground adjustable propeller doesn't make it fixed pitch.

[Tom Baker]

You may find language from the Neuform propeller operators manual helpful in understanding why the prop is set by the factory the way it is:

 

When the propeller was designed, special attention was paid to the attempt to transform

the engine’s power in the quietest possible way. One aspect of this concept is to operate

the engine with reduced propeller revolutions and rather big angles of incidence of the

blades.

 

We recommend to stick to this concept and to use the appropriate reduction gears in

order to gain the maximum propeller performance. A higher number of revolutions

increases the noise emissions, leads to losses during the cruise and has therefore no

advantage.

 

Neuform also warns against damage over-revving the prop.

 

http://www.neuform-composites.de/_downloads/pdf/propellermanual.pdf

Rotax says just the opposite. http://legacy.rotaxowner.com/si_tb_info/serviceletter/sl-912-016.pdf

 

This document from Rotax is why I adjust the propellers to a flatter pitch. Since the engine is 10 times the cost of the propeller, and the propeller is operating within limits I will continue to do it this way.

[Anticept]

 

Prop Stuff

 

CTs ship now with CR3 type props.

[Doug G.]

100H, here, I looked it up for you. I repeat we do not have fixed pitch propellers! You are wrong!!

 

https://answers.yahoo.com/question/?qid=1006042020364

[gbigs]

 

with a 2.34:1 reduction ratio, the 5,500RPM needed to realize max(ratedContinuousPower) translates to 2,350RPM for the propeller. 

 

Neuform provides this table for limits:

 

Limits of numbers of revolutions:

 NEUFORM S: n max = 1950 min -1

 NEUFORM T: n max = 2300 min -1

 NEUFORM TX: n max = 2600 min –1

 NEUFORM C: n max = 2600 min –1

NEUFORM D: n max = 2600 min –1 

 

3 of 5 Neuform props appear to have power limits that would permit 6,084RPM and 2 would limit below 5,500.

 

Which Model is on your CT?  I don't have a Neuform.

 

 

All CTs are shipped with a Neuform prop from the factory - the prop is an FD standard.

[gbigs]

100H, here, I looked it up for you. I repeat we do not have fixed pitch propellers! You are wrong!!

 

https://answers.yahoo.com/question/?qid=1006042020364

 

Again, it matters ZERO what the prop is called (of course it's a ground adjustable three-blade prop). 

 

What matters as far as this thread is concerned is that the prop is FIXED PITCHED in flight (as opposed to a Constant Speed, Controllable Pitch, Two-Position, Full Feathering etc).