Prop adjustment revisited

[Rich]

Here are the numbers after removing 1.5 degrees of pitch from the DUC Swirl three blade inconel prop. Sting S-4, 100 HP ULS.

 

Previously I was getting only 4950 RMP during the take off roll and climb out with pitch at 23.5*.

Straight and level WOT 5300 RPM.

 

Now prop pitched at 22*

Groung roll at take off 5230 RPM---- 48*F-----Elevation 1350 MSL

Climb out 5000 RPM WOT

Straight and level WOT 5350/5380. Hit 5400 a few times at 5500 MSL with DA 3550. Turbulent air.

MP 13.8

 

There was a good RPM gain at take off roll with only 70 to100 RPM gained at altitude, Straight and level.

More testing on different days with diffrent DA's will be needed to get an accurate read.

 

I believe the DUC prop is working as advertised with the constant speed effect at cruise, therefore, limiting the WOT cruise RPM's.

 

What really seems strange is that for there is very little change in RPM from WOT to approx 3/4 throttle setting.

 

 

[Tom Baker]

What really seems strange is that for there is very little change in RPM from WOT to approx 3/4 throttle setting.

That is not strange at all, at least not if the carbs are set up like I was taught in Rotax class. The throttle cable is set up with free play when at wide open throttle. You should have to move the throttle lever some before the carb actually comes off the full throttle stop. On the CT the distance the lever moves is quite exaggerated, some other airplanes not so much.

[Ed Cesnalis]

Here are the numbers after removing 1.5 degrees of pitch from the DUC Swirl three blade inconel prop. Sting S-4, 100 HP ULS.

 

Previously I was getting only 4950 RMP during the take off roll and climb out with pitch at 23.5*.

Straight and level WOT 5300 RPM.

 

Now prop pitched at 22*

Groung roll at take off 5230 RPM---- 48*F-----Elevation 1350 MSL

Climb out 5000 RPM WOT

Straight and level WOT 5350/5380. Hit 5400 a few times at 5500 MSL with DA 3550. Turbulent air.

MP 13.8

 

There was a good RPM gain at take off roll with only 70 to100 RPM gained at altitude, Straight and level.

More testing on different days with diffrent DA's will be needed to get an accurate read.

 

I believe the DUC prop is working as advertised with the constant speed effect at cruise, therefore, limiting the WOT cruise RPM's.

 

What really seems strange is that for there is very little change in RPM from WOT to approx 3/4 throttle setting.

 

Rich, should the Duc exibit near constant speed effect at WOT?  I would think you would have to back off or unload the prop to get it to coarsen? 

 

If that were my prop I would want it flatter yet but with the Duc, dunno.  Take the prop out of it for a moment and you can see that if you can't make 5,500 than you can't access all or your engine's power.

[gbigs]

Have scheduled the sport upgrade for the 912iS I own.  The torque increase will be interesting to watch as I have a factory set Neuform prop...  the only real way to increase performance across all density altitudes and throttle settings is torque increase.  Flattening the prop does nothing more than trade climb for cruise.  Cruise and gas efficiency should be the first priority, but those flattening their props are sacrificing that performance.

[Ed Cesnalis]

Flattening the prop does not trade climb for cruise.  Flattening the prop from factory settings does trade economy at a lower power setting for climb/speed at that and higher power settings including WOT.

 

For the most part flattening from factory settings will increase economy but there will be one low throttle setting range where economy would be better at the coarse setting.

 

Torque is easy to measure but a poor substitute for measuring power.  You could have lots of tourqe but no movement and therefore no power.

 

Torque has a curve just like power so any increase in torque will be different at different RPM producing different results.  All and all any increase in torque will be similar to the increase in power and a pretty small increase at that.  

 

The upgrade increases power and power potential but if your prop is too coarse you can still be limited to under 90hp in cruise even at WOT where the less powerful ULS could be realizing more power with an optimized pitch.

 

 

 

Have scheduled the sport upgrade for the 912iS I own.  The torque increase will be interesting to watch as I have a factory set Neuform prop...  the only real way to increase performance across all density altitudes and throttle settings is torque increase.  Flattening the prop does nothing more than trade climb for cruise.  Cruise and gas efficiency should be the first priority, but those flattening their props are sacrificing that performance.

 

[Ed Cesnalis]

I can't find power/performance/torque curve(s) for the sport upgrade.  The upgrade reportedly results in a higher/improved torque curve but remember the original 912i suffered from some lack of torque compared to the ULS, it has some ground to make up.

 

If anyone finds charts please post.

[ctfarmer]

CT, within practical limits, flattening the prop does have the effect of improving takeoff whilst limiting cruise performance. That is the principle behind why a variable pitch props works.

 

As well, what is a factory setting? - each to his own here depending on what they are trying to achieve.

 

FD published a CTLS performance supplement but many have finer settings than that from what I can see.

[Rich]

CharlieTango, on 28 Dec 2014 - 12:39 PM, said:

Rich, should the Duc exhibit near constant speed effect at WOT? I would think you would have to back off or unload the prop to get it to coarsen?

If that were my prop I would want it flatter yet but with the Duc, dunno. Take the prop out of it for a moment and you can see that if you can't make 5,500 than you can't access all or your engine's power.

 

 

CT,

 

I don't see why it wouldn't.

 

DUC states “the effect of 'constant speed' is not related to the deformation of the blade but its geometry and its particular profile".

“Extra flat profile and narrow cord length gives better aerodynamic and acoustic performance with less fuel consumption"

DUC also states that “there is very small engine speed difference between the aircraft on the ground and in flight." That seems to hold true with my experience yesterday.

 

I don't think that I should flatten the pitch any more at this time until I've made a few trips with it. I'll be flying to the Sebring Expo, Jan14-17th. That will give me a better idea of the new pitch change and related performance. My plane will be on display at the Sport Air USA booths. I hope to see some of you there.

[Ed Cesnalis]

CT, within practical limits, flattening the prop does have the effect of improving takeoff whilst limiting cruise performance. That is the principle behind why a variable pitch props works.

 

As well, what is a factory setting? - each to his own here depending on what they are trying to achieve.

 

FD published a CTLS performance supplement but many have finer settings than that from what I can see.

 

ctf,

 

To have this conversation there needs to be a definition of cruise performance.

• Best speed at highest throttle setting limited by 5,500RPM?
• Best speed at 92% throttle where econo mode or needle jet leaning begin?
• Best speed at 75% power at x DA?

or - because you say cruise performance is limited you mean economy?

• Best average economy at x% throttle?
• Best average economy at x DA?

For many years at least 'factory settings' meant CTs were delivered with pitches that limited RPM to < 5,300 in many cases a lot less.  From 5,300 and a definition of cruise performance relating to speed not economy then it remains true that flattening the pitch improves both climb (rate) and cruise (speed).

 

If your definition of cruise performance relates to economy then your statement becomes true with reason for caution.  We wouldn't fly our constant speed equipped planes with high power settings and a coarse prop setting and likewise we shouldn't run our CTs with coarse props and high power settings.  Given this negative it makes more sense to optimize for climb and speed (flat) vs economy (coarse) because you are stuck in that setting for all phases of flight.  If you are stuck in coarse than how do you take-off / climb at full power?

 

I find few times when a coarser pitch would benefit me, If I cruised the beaches that would be one exception.

[Ed Cesnalis]

I knew a guy that raced formula 1 and I saw him changing props so I asked what's up?  He was getting ready to race at Reno and that entailed changing from his cruise prop to his climb prop.  That's when I got it  race prop = climb prop.

 

Whether you are looking for best climb or best speed you need to access the maximum available horse power, which tends to be at maximum RPM and manifold pressure, which means a flat pitch.  The O200 powered formula 1 racers go round them pylons at very high RPM.