CTSW Cruise Speed

[Ed Cesnalis]

1 minute ago, SkyrangerRich said:

Really interesting thread and timely for me. Bring a new CTSW owner I'm currently trying to baseline aircraft performance to enter into Skydemon (like a European Foreflight). 

Did a couple of runs yesterday, 7 degrees (C) at 1800ft asl, -12 degrees of flap. 

4400 rpm is 110knts IAS. 

4800 rpm is 122knts IAS. 

Totally non scientific, just me buzzing around the sky straight and level, no triangles etc. 

 

Those aren't good speeds to run a Rotax.  Can you flatten your prop pitch?

[FlyingMonkey]

1 hour ago, Ed Cesnalis said:

Roger, my engine doesn't have to struggle for power because of my altitude, that's silly. 

The higher the altitude, the less power put out by any non-turbo reciprocating engine...that's a fact.  "Struggling" might be a relative term, but your engine produces significantly less power at your cruise altitude than mine does at my cruising altitude.  Drag is also higher at lower altitude, so that offsets somewhat.  The crossover point where lower power overcomes lower drag happens at about 7500-8000ft.  That's why when you want maximum cruise performance over the ground, you should select 7500-8500ft as your cruise altitude. 

At your cruise altitudes of 10,000ft+ your engine *is* struggling for power, relatively speaking.  Even more so at the 14,000ft altitudes you regularly visit.  Your stall speed is also higher due to the less dense air, in ground speed terms.

 

[Ed Cesnalis]

1 hour ago, FlyingMonkey said:

The higher the altitude, the less power put out by any non-turbo reciprocating engine...that's a fact.  "Struggling" might be a relative term, but your engine produces significantly less power at your cruise altitude than mine does at my cruising altitude.  Drag is also higher at lower altitude, so that offsets somewhat.  The crossover point where lower power overcomes lower drag happens at about 7500-8000ft.  That's why when you want maximum cruise performance over the ground, you should select 7500-8500ft as your cruise altitude. 

At your cruise altitudes of 10,000ft+ your engine *is* struggling for power, relatively speaking.  Even more so at the 14,000ft altitudes you regularly visit.  Your stall speed is also higher due to the less dense air, in ground speed terms.

 

You have to put it into context. Roger seems to agree that 5,500RPM is the number, where Rotax dyno runs have demonstrated peak power happens within the continous power limitation. Then Roger encourages me to use a higher number like 5,650RPM because my engine stuggles at high altitude and some further nonsense about moment arm.

My plane, at 7,100' MSL elevation does not struggle to use 5,500, that's my point.  Yes there is less O2 and yes there is less drag but what's most important is my prop is flat enough to permit 5,500 RPM.  This same relationship exist in Georgia and Arizona just using different numbers that none the less result in 5,500 in either case.  I don't need extra RPM because of some high altitude 'struggle', that is silly.

[Ed Cesnalis]

1 hour ago, FlyingMonkey said:

The higher the altitude, the less power put out by any non-turbo reciprocating engine...that's a fact.  "Struggling" might be a relative term, but your engine produces significantly less power at your cruise altitude than mine does at my cruising altitude.  Drag is also higher at lower altitude, so that offsets somewhat.  The crossover point where lower power overcomes lower drag happens at about 7500-8000ft.  That's why when you want maximum cruise performance over the ground, you should select 7500-8500ft as your cruise altitude. 

At your cruise altitudes of 10,000ft+ your engine *is* struggling for power, relatively speaking.  Even more so at the 14,000ft altitudes you regularly visit.  Your stall speed is also higher due to the less dense air, in ground speed terms.

 

More simply put. I agree that my engine 'struggles' to produce power due to the high altitude.  The relevant point is my engine does not 'struggle' to produce or maintain RPM and the setting/limitation at issue here is RPM.

[Roger Lee]

HP increases as torque decreases after 5000 rpm.  You problem is not only are you loosing torque as you increase rpm you are loosing HP due to altitude. Your Warp is already inefficient and then add loss of HP and torque and you lost performance. 5500 is absolutely not the optimum pitch for you. 

Remember the Grand Canyon flight and your increased rpm over mine? That should be more than enough that you should try 5600-5650 before you lose all that money. LOL

Try it then come back with a comment. The difference here is I have tested all this and you don't want to try it. Why not? You have nothing to lose.  You can always put it back.

p.s.

You could even fly at 5600 (better than 5500 for you)  all day if you wanted. You just didn't know it.

[Roger Lee]

Legally you can't go past -6 in the US. That said I do know several that have used -12 for many years. I would not go past this. Plus if you fly at high altitudes like ED it will cost you performance rather than help. I have experienced that first hand. I've had some instances I had to switch back down to zero flaps due to lift issues.

 

I used to fly side by side guys with one CT at -12 and one at -6 and so long as the WOT rpm was the same they flew side by side. If one plane got 5650 and the other only 5500 the 5650 will pull away. EVERY TIME. I've done so many test it was ridiculous. CTSW's or LS's it made no difference.  You really need two of the same planes side by side. Testing with one plane is fraught with too many factors you can't get rid of. That is why I used 4 CTSW's that were MFG'd within 4 months of each other and took off side by side and flew side by side..

Just a note. If you ever had an incident and they checked the flaps at -12 that would put you in a bind. 

[FlyingMonkey]

16 hours ago, Ed Cesnalis said:

The relevant point is my engine does not 'struggle' to produce or maintain RPM and the setting/limitation at issue here is RPM.

But the fact you can hit any RPM means kind of nothing.  You can hit 6000rpm if you pitch flat enough, or probably 10,000rpm with the prop removed.  But that doesn’t translate to more power or thrust through the air.  That you can hit 5500rpm means only that you can make the most amount of power for your altitude that Rotax says you can safely make continuously.  

But that will be a LOT less than at sea level, I’d guess something around 55hp at 12,000ft or so. 

[Ed Cesnalis]

4 hours ago, FlyingMonkey said:

But tye fact you can hit any RPM means kind of nothing.  You can hit 6000rpm if you pitch flat enough, or probably 10,000rpm with the prop removed.  But that doesn’t translate to more power or thrust through the air.  That you can hit 5500rpm means only that you can make the most amount of power for your altitude that Rotax says you can safely make continuously.  

But that will be a LOT less than at sea level, I’d guess something around 55hp at 12,000ft or so. 

Right, most of my flights I have less than 60hp available, no wonder I fly WOT.

The fact that I can hit the RPM means something.  It means the 5,500 limit is not special for me and I don't need another 150 RPM because of this struggle.  You just said it means nothing.

That 150 RPM reduction from WOT to the continuous limitation is huge and  I won't even try to see if it makes me go faster.  Retarding the throttle never does.

You can say after a certain point the reduction goes away, like at 12,000 and thats true but of little value because you need the prop to be even flatter yet so the 5650 setting still robs power because its so far from optimized up high beyond where the limitation applies.

[Roger Lee]

5500 is not optimized for ground adjustable and Warp Drive adds another factor you haven't experienced. You're debating from a weak stand point. Many of us have tried it. You haven't.  You need to do your own research. Right now you're debating with limited knowledge and from an idea you think is fact, but research has proven different.  Some of your analogies are wrong and that's why you need to do your own testing.

 

My eyes were opened on some prop types and 2 vs 3 blade props. Sensenich said the same thing. My research project was the only one like it in the US.

 

[Ed Cesnalis]

8 minutes ago, Roger Lee said:

5500 is not optimized for ground adjustable and Warp Drive adds another factor you haven't experienced. You're debating from a weak stand point. Many of us have tried it. You haven't.  You need to do your own research. Right now you're debating with limited knowledge and from an idea you think is fact, but research has proven different.  Some of your analogies are wrong and that's why you need to do your own testing.

 

My eyes were opened on some prop types and 2 vs 3 blade props. Sensenich said the same thing. My research project was the only one like it in the US.

 

Roger,

Please read and consider what I write this time. It defeats your contention that I should have a pitch setting flatter than WOT @  5,500 PM ( at an altitude that I pick that is typical for my mission and at least 7,500' )

The only way you are right / could be right is if I ignore the 5,500 limitation and begin cruising at 5650.  Then you would be right, I would now be optimized for best speed.  I don't think thats the argument.

Here's where you are defeated so pay attention: Flying at 5,500 now means a significantly retarded throttle.  When I pitch for my upper altitude range and comply with your pitch recommendation my max available continuous horse power will be down around 45.

On the margins, like my high altitude mission, prop efficiency's performance matters less becuase  the IAS and HP are significantly less. 

[Roger Lee]

You won't know what many others know until you try it. While you're at it try another prop to. That will be an eye opener for you in climb.

[Tom Baker]

Speed is a factor of prop pitch, RPM, and prop efficiency. While setting prop pitch to run wide open at 5650 should let the engine develop more power it doesn't mean the airplane will be faster at 5500 RPM, when compared to one that is set to turn 5500 RPM at full throttle. With both engines at 5500 RPM, the power should be fairly close to the same for both engines. The airplane with the higher pitch angle in theory should be faster than the other, because it is moving more air. The only way this wouldn't be true is if the propeller efficiency happened to be reduced because of the increased pitch.

[Tom Baker]

7 minutes ago, Roger Lee said:

You won't know what many others know until you try it. While you're at it try another prop to. That will be an eye opener for you in climb.

Roger, while I agree that setting the prop as you suggest will help in climb, I don't agree that the prop with less pitch will be faster at the same RPM. The only way this can be true is if the propeller loses efficiency because of the increased pitch setting because of too high of angle of attack. I see that as unlikely.

[FlyingMonkey]

9 hours ago, Ed Cesnalis said:

Right, most of my flights I have less than 60hp available, no wonder I fly WOT.

The fact that I can hit the RPM means something.  It means the 5,500 limit is not special for me and I don't need another 150 RPM because of this struggle.  You just said it means nothing.

That 150 RPM reduction from WOT to the continuous limitation is huge and  I won't even try to see if it makes me go faster.  Retarding the throttle never does.

You can say after a certain point the reduction goes away, like at 12,000 and thats true but of little value because you need the prop to be even flatter yet so the 5650 setting still robs power because its so far from optimized up high beyond where the limitation applies.

I agree you are at the best prop setting you could be at for your altitude to maximize power/thrust.  Climb might be better at 5650rpm.  Not sure if you'd give anything up in cruise by doing that.  Roger says no, it might be worth a try.

[FlyingMonkey]

5 minutes ago, Tom Baker said:

Roger, while I agree that setting the prop as you suggest will help in climb, I don't agree that the prop with less pitch will be faster at the same RPM. The only way this can be true is if the propeller loses efficiency because of the increased pitch setting because of too high of angle of attack. I see that as unlikely.

I agree.  The big question is whether the increase in climb is worth it vs the decrease in cruise.  If you gain 200fpm and lose 2kt, it might be a good trade for you, but it's really a subjective question.

[Roger Lee]

This goes for fine tuning your engine. Ed's 5500 isn't terrible, but could be better.

Here is a good example. I have flown with my CTSW right next to a CTLSi. I'm cruising at 5200 rpm and the LS is cruising to keep up with me at 5300 rpm. What is the difference? My WOT is set to 5600-5650 and his is set to 5500 WOT. And because he is at 5300 rpm he is out of economy mode and using more fuel than me. What people are failing to see is HP increases with rpm increase (Ed needs all he can get) and torque goes down. You need both to turn a prop efficiently and to get the most out of the fixed pitch prop. At Ed's altitude he could use better climb. Ed is handicapped in 2 places. He normally fly's at extreme altitudes compared to the majority of LSA users. He is also handicapped with the Warp Drive prop (borrow a different one and at least try it) . If he changed to a different prop and set it to get around 5K rpm on takeoff he'd see a huge difference in climb. (I have already tested this with the Warp up to 12K). The top end speed would be a little less remarkable compared to climb. It would also be a little less stressful on his engine because it wouldn't work quite as hard to try to turn 5500. This helps decrease engine temps to.

If you lived and flew at lower altitudes 5500 isn't terrible, but can be made better for best overall performance. If you have a Warp Drive it is good for rough fields, but not near as good for short fields or high and or hot altitudes. It can be made better. Like I tell mechanics with their documentation, don't strive for mediocrity because there is an abundance of that, but strive to be a cut above.

I have done the largest prop test in the US and have changed pitch on over 100+ LSA's and not a single pilot wanted to go back to their old prop settings and I never lost a single bet. Maybe I need to make my bets larger then I could retire again, but then Tim and John-Olav would be mad at me. LOL

[FlyingMonkey]

I don't understand how what you're saying could entirely be true Roger.  How are you flattening the pitch and getting higher speed at lower rpm?  Flattening the pitch *should* increase rpm at a given throttle setting and increase rate of climb.  Assuming the same HP at a given RPM, it should not be possible to go faster at flatter pitch for identical airplanes, unless I'm missing something.  

Are you sure the 200rpm difference was prop pitch and not just that the CTLSi was certainly a much heavier airplane?  Or that the injected engine doesn't have a different hp/torque curve that peaks later?  Both?  I think there are too many variables in your scenario to pinpont the flatter pitch as clearly superior in this exact circumstance. 

[Roger Lee]

29 minutes ago, FlyingMonkey said:

Are you sure the 200rpm difference was prop pitch and not just that the CTLSi was certainly a much heavier airplane?  Or that the injected engine doesn't have a different hp/torque curve that peaks later?  Both?  I think there are too many variables in your scenario to pinpont the flatter pitch as clearly superior in this exact circumstance. 

No because I've done it with many CT's.

 

Was yours better when I advised you  it was better to change?

[Skunkworks85]

Rodger,

I know you are a respected member of the community, and I do like hearing your information, as some of the things you claim can only be learned from lots of experience. but,

It is really hard to follow you, 

Would you agree with,

There is an optimal pitch for climb, and on the other end of the spectrum there is and optimal pitch for cruise?

These 2 pitch settings are at the opposite ends, and any change in one will directly and adversely effect the other?

IF that statement is true,

How can you claim that there is a magical pitch that will improve both speed and climb performance relative to whatever current pitch is on the aircraft?

Saying "I tested it" does not prove the theory. Although I am convinced you believe you are correct. The physics of the matter say otherwise. And for this reason alone, is why in-flight adjustable props were invented.

There is probably one universal pitch on the CT aircraft that averages the cruise and climb of the 95th percentile of all CT's made. And that maybe the pitch you use. Does it make it the right one for everyone? 

What was your control group for all your testing? What kind of metrics did you record? When comparing aircraft to aircraft was there more than just One variable changed? Or is is possible one weighed a little more? had more aft cg? had some glider tape in different locations? trimmed differently? ect?

Being and engineer, I subscribe to,  "In god we trust; all others bring data"

 

[Ed Cesnalis]

2 hours ago, FlyingMonkey said:

How are you flattening the pitch and getting higher speed at lower rpm?

with a prop change it could make sense.  Roger wants me to do it with the same prop, I don't even have to try.

[Ed Cesnalis]

3 hours ago, Skunkworks85 said:

There is an optimal pitch for climb, and on the other end of the spectrum there is and optimal pitch for cruise?

These 2 pitch settings are at the opposite ends, and any change in one will directly and adversely effect the other?

wrong comparison.

for the opposite ends of spectrum, (flat vs coarse) the comparrison is:

flat (climb/speed) vs coarse (fuel economy)

There is in fact an adjustment that improves speed and climb and its to flatten the pitch.

My CTs have been delivered with a coarse pitch which is good for economy cruise when you are throttled back but not for speed or climb.

You are right that Roger is wrong on this when he claims a setting that requires a retarded throttle to comply with the continuous limitation would lead to any speed or climb improvement over a flatter pitch.

[Skunkworks85]

That is the benefit of the adjustable pitch prop. and mostly what it is used for today. But if you have an engine that can maintain a set RPM regardless of how coarse the prop gets, you will in fact, increase in speed. 

 

you are referring to the efficiency of the prop. adding coarseness to the prop to reduce engine RPM to save fuel.

 

My original statement is true. if a prop stays at one speed, a fine pitch will be better for climb and coarse will be better for speed.

[Tom Baker]

48 minutes ago, Ed Cesnalis said:

 

flat (climb/speed) vs coarse (fuel economy)

 

Ed, saying that flat increases speed is only true if you can allow the engine to turn that faster speed. With the 5500 rpm limit the fastest speed is going to come from the coarsest pitch setting that allows the engine to turn 5500 rpm. Any coarser you lose power because of the lower rpm, and any finer you move less farther forward with each revolution of the propeller. Again the only thing that would make this not true is if the angle of attack of the propeller blades is getting close to stalling and they are losing efficiency.

Also as you flatten the pitch you get to a point where the increase in rpm compared to the decrease in effective pitch will cause the airplane to slow down.

[Roger Lee]

We'll have to discontinue here because the nay sayers aren't  willing to do the research.

Here's an easy question. How many here had WOT rpms under 5500  (FD started at 5200 years ago) and changed the pitch to get higher rpm? Ed was one of them right after he got his CT. Like I said I have reset over 100 LSA props and hundreds more have done it on other forums with this info. This 5600-5650 WOT rpm is all over the net and on almost all LSA forums for best BALANCED pitch / rpm at your average altitude. 

"These 2 pitch settings are at the opposite ends, and any change in one will directly and adversely effect the other?"

Remember my post: Best Balanced pitch / rpm at your Average altitude. You are right that too far in either direction will impinge on the other sides performance. The one but here is if you fly out of high, hot, short runways or fly heavy you may want to tune towards the flatter side at 4700+ for better climb over your cruise. So this side is a personal choice. Anything under 5500 WOT in flight in flat and level flight is over pitched and you start to lose it all. Cruise speed, climb, fuel economy and higher engine temps.

 

"Saying "I tested it" does not prove the theory. Although I am convinced you believe you are correct. The physics of the matter say otherwise. And for this reason alone, is why in-flight adjustable props were invented."

This research was done with 14 props, 4 almost identical CTSW's, 4 months of time, one person setting pitch and take off parameters and these aircraft taking off side by side and flying side by side. The only research project of its kind in the US. The results were all documented and sent to the prop companies that participated and told they could publish them if they wanted. 

None did because it showed that all the prop companies that swore their props were better was disproved and that rpm  and flying technique showed they did not have the best thing since sliced bread, but they all performed about the same except for climb in the Warp drive which was far behind climb from the others.

The best thing here is for someone to get their hands on 14+ props, 4 aircraft the same, a single mechanic and have pilots take off and fly side by side and repeat the research project. Then and only then would anyone here have hard confirmable facts. I have several research projects with CT's and Rotax that test the limits, but was ask to not put them out to the public. I have hinted at some along the way, but like the prop research not sure who is paying close attention.

p.s. A flatter prop does not increase speed past its optimum pitch. For us anything past 5650 will start to increase climb, but decrease speed. Once past 5800+ you start to lose it all.

"You are right that Roger is wrong on this when he claims a setting that requires a retarded throttle to comply with the continuous limitation would lead to any speed or climb improvement over a flatter pitch."

Remember what they said about the horse.

 

[Ed Cesnalis]

1 hour ago, Tom Baker said:

Ed, saying that flat increases speed is only true if you can allow the engine to turn that faster speed. With the 5500 rpm limit the fastest speed is going to come from the coarsest pitch setting that allows the engine to turn 5500 rpm. Any coarser you lose power because of the lower rpm, and any finer you move less farther forward with each revolution of the propeller. Again the only thing that would make this not true is if the angle of attack of the propeller blades is getting close to stalling and they are losing efficiency.

Also as you flatten the pitch you get to a point where the increase in rpm compared to the decrease in effective pitch will cause the airplane to slow down.

That's why we say 5,500 @ WOT.