Prop pitch and RPM

[Aero-Nut]

Have a Neuform 3 blade prop. In level flight and at full throttle with-6 flaps I am pushing 5650 RPM at 115 knots. Anyone know how many degrees I should add to the pitch to get my RPM down to where it should be?

[Anticept]

That's fine, leave that alone. It's supposed to be 5600-5800 WOT

[FlyingMonkey]

If that is WOT with the throttle all the way open, as Corey says it's just about perfect.  If you still have throttle left, you need to determine what the RPM is at WOT (give it a minute to stabilize), then we might be able to suggest a change.  Roger has set the most props here by far, so I'd take his recommendation. 

 

If you need to back it off, I'd guess it will be less than a half degree change.  I have had mine set a few different ways, IMO and it's *definitely* better to be a little too flat than too coarse.  These are high-rpm engines and need to be able to get those upper band rpms to make full power.  I had mine set to make 5700rpm at my cruise atltitude WOT and it was about perfect.  It could operate at higher altitudes all the way to 10,000ft+ too and the engine would not run out of breath in the climb.  

[Ed Cesnalis]

Altitude plays a role.  Below 7,500' optimizing for top speed doesn't make sense because cruising above 75% power is too noisy and probably not a good cruise setting.  Optimizing for 7,500' gives you best available performance but it might be too low for many.  Optimizing for 10,000' seems perfect for the western US.

 

Optimizing cruise for a given altitude means 5,500 RPM @ WOT when level.

[Roger Lee]

Leave it. It is where it should be and 5600-5650 rpm in flat and level flight is your BEST PERFORMING BALANCE point for cruise, climb and fuel economy. I've done more testing and research with this than I ever want to do again. This optimal rpm should be at your AVERAGE altitude.I would bet I've set well over 200 props in my time and 125+ in the last 10 years so I have a pretty good handle on this. 

 

Anything below 5500 rpm at WOT is absolutely counterproductive.

 

 

p.s.

Don't worry about what anyone says about the few knots of speed on their plane. Our instruments and especially the pilots are not that accurate to nit pick speeds. Not to mention weather difference.

[Ed Cesnalis]

Roger,

 

The OP is located near a lot of high terrain.  Is he 5650 near sea level at his home or when crossing the Sierra at 10,000'+?

 

If the former he is probably good but the latter would be too flat.

[Aero-Nut]

Thanks for the info. I will leave it as it is. I thought I saw it needed to be lower. Probably did as there seems to be many different thoughts on the subject. I am happy with the climb and cruise speed as it is. Thanks again!

[Roger Lee]

Whether you live at sea level or Mammoth, CA and depending on where you fly set the pitch for your average altitude. Everyone will at sometime fly higher and lower than their average. If you live at sea level and never go above 2K then set it for there. If you live in Mammoth, CA and always fly 10K-13K then set it for there. Since we don't have in-flight adjustable props you have to draw a line in the sand (your average altitude) somewhere.

[Ed Cesnalis]

If you live at sea level and never go above 2K then set it for there. 

 

That seems like such a waste to me.  The one benefit I could see is racing but who races CTs?

 

If I did live near sea level and I did optimize for best speed at 2K I would never use that extra power that is only available at WOT and at 2K.  That would be like 90hp, too loud and too high a setting for cruising.  If you were optimized for 7.5K or higher you could still cruise as fast as you want to at 2K simply by throttling back.

 

I continue to see 7.5K as the lowest altitude to optimize for as you would not be giving up anything until you were cruising higher than 7.5. 

[Roger Lee]

Hi Ed,

 

But your flatter pitched prop set for high altitude would be a waste at sea level flying. It would climb great, but be terrible for cruise and fuel consumption.

If I was running there with you and was flying let's say at 5200 rpm you would have to fly at 5300-5350 just to keep up and my fuel consumption would be less. Plus my top speed at WOT would be faster.

 

I've tested this side by side other CTSW's and more than once over the last 8 years.

 

Been there and done that in my research. Rotax is very RPM dependent for performance right after fuselage design.

[Ed Cesnalis]

Think back past those 8 years to the one CT at the first Page fly in.  Remember the yellow one that could walk away from the others?

 

In 2006 I saw that my factory prop pitch wouldn't permit me to realize all available power and pitched for 5,500RPM.  It took you guys a little longer to find a flat enough pitch.

 

I don't think you heard my point.  You say you could outperform with with a coarser pitch at 2,000' and I say its not power that would be useful due to the noise or wise due to the almost 90% power setting.  

 

I don't think the economy difference would be large.  If your setting is optimzed for 2K but in fact you cruise partial throttle you are no longer optimized but would need an even coarser setting for best economy.  I would expect to be close to you even at a slightly different throttle setting.

 

I hear you say Rotax are RPM dependent but they are no different than any other engine that requires both MP and RPM to determine power. How would a Rotax be different?

[Roger Lee]

We only have so much to work with in our present setup and anything outside that isn't applicable to our discussion.

 

"Think back past those 8 years to the one CT at the first Page fly in.  Remember the yellow one that could walk away from the others?"

 

I do all the time. You're my poster child to all those over pitched owners I have adjusted.

 

Your chant was "Woodstock comes alive"

 

At the first Page, AZ Fly-In;

That's because I was pitched for 4.5K and you were set up for over 10K. This is exactly my point. We had this discussion. I was the one that got you to flatten your pitch when it was too course for your altitude, but was probably good down around sea level - 4'K. You could get 450 rpm more than me with the flatter pitch it that altitude.

Noise and power use of 90% isn't an issue in this. You are one of the very few that always fly's at 5500 rpm. Most others fly between 5000-5300 rpm during cruise. We only set the prop pitch o 5600-5650 to get a balanced state at 5000-5300 rpm with the knowledge that we still have good performance for take off.

 

I pitched my prop this year to get 5650 at 10K, but I had to fly more rpm at the lower altitudes than others pitched for lower altitudes and I lost fuel economy on top of it. At lower altitudes I had to fly 150 rpm more to keep up. At high altitudes I could develop more rpm than the low lander and could out climb them and had a higher top end. Plus my fuel burn at high altitude was less because I could throttle back where they had to add throttle to keep up. Just like you and I the first year. 

 

.

 

Without an in-flight adjustable prop you can not be optimal for all altitudes. With carbs you suffer HP loss with altitude and torque along with it. 3% for every 1'K.

This is also why the 912iS shines at altitude over our carbs. It can make some adjustments.

 

Forget MAP as it is useless to us in our present configuration. MAP pressure is worthless to us with the carbs and ground adjustable prop. We really can't influence it in the air for better performance. It will always be 1" - 1.5" lower than outside air pressure. We can only work with what we can influence in flight in all flight situations. (climb and cruise).

 

You have to have HP and torque to turn any given prop pitch. Too little pitch and you waste performance. Too much pitch and it gets even worse.

 

So we balance for our everyday general flying setup and average altitude set point until you can get the FAA to allow us in-flight adjustable props and then we can influence in-flight pitch, MAP and overall performance.

 

My guess is at sea level you can get at least 5800 rpm if not over? 

 

If all you can get out of your prop pitch setup where you fly is 5500 rpm WOT then it will be better at 5600-5650 and then throttle back to 5500 rpm for cruise.

[Ed Cesnalis]

Roger,

 

Memory is a funny thing, which of us has gotten old enough to loose it?  I don't remember if you were at the 1st McMiinnville fly-in?  While the others were flying the Gorge to Troutdale Yossi and I were touring the glaciers, ski areas and summit of Mt Hood.  We were checking out my early synthetic vision and marveling at the optimized performance.

 

I have always flown at high altitude with limited power.  Pilots here were and are of the opinion that flying without the throttle wide open is like flying with a dirty partially clogged air cleaner.  Above 7,500' power and performance are limited and WOT is called for.  I had Gary Annas (RIP) flatten my prop to give me max allowable cruise RPM resulting in the fastest CT around for 2-3 years.  I had a power curve that confirmed max power was at 5,500.

 

You argue that noise and an almost 90% power setting isn't an issue yet you point out that others fly at lower power settings than I do.  I believe you are proving my point, you guys don't fly at lower power settings because you don't like going fast you do it for 1) a comfortable noise level, 2) economy, with the drag near sea level you don't get much extra speed at the higher setting, 3) 90% power is a dumb setting for cruising an aircraft.  Rotax may have a simple RPM limitation but that doesn't make it smart to cruise at 90% plus as you point out no-one does it.

 

I don't see 5,800 even in Death Valley.  That's the funny part is over time you came up to the same setting that I use.  You explain it quite differently but we end up at the same pitch.  Years ago you were advocating coarser than 5,650.  At 5,650 and low altitudes cruising at 5,300 or less makes sense and its what I do when and If I cruise down low.  When you guys do the Grand Canyon tour I"m sure your throttles are open and your RPM are up just to keep up with the others.  That's how it went when I was there the 2nd time and some of you could keep up.

 

Does the iS shine at altitude?  From what I have read it is too dumb, above 93% throttle it just goes full rich like our carbs do.  It could be smarter and actually lean for the high altitude at full throttle but its not there, not a priority for Rotax apparently.

 

You say to forget MP its useless to us.  Actually we control MP with the throttle just like in a 182, its prop pitch that we have to forget about and live with the setting achieved on the ground.

[FlyingMonkey]

The problem we are all trying to work around is that we can only have a setting optimal for one altitude. I see what CT is saying, in that overall piston airplane efficiency is generally best around 7500ft because drag goes down faster than engine performance up to that altitude.

 

But if you never cruise higher than 4500ft, I'd have to believe you'd be better off setting the prop to be optimized lower, where you are actually doing your flying. That's how mine is setup, and I had no trouble making full RPM or speed over the Grand Canyon at 11,500ft.

 

Certainly this is a great discussion. I wish we had a panel of aeronautical engineering PhD experts on here to give us a definitive answer. Sadly we just have to rely on experimentation and observation in our own local flight conditions.

[Ed Cesnalis]

But if you never cruise higher than 4500ft, I'd have to believe you'd be better off setting the prop to be optimized lower, where you are actually doing your flying. That's how mine is setup, and I had no trouble making full RPM or speed over the Grand Canyon at 11,500ft.

 

 

 

If you have no problem 'making full RPM or speed over the Grand Canyon at 11,500ft.' then you are not optimzed for 4,500'.  Both can't be true.  At 11,500' full RPM and speed means WOT and 5,500RPM.  At that setting you would have to throttle back to cruise at 4,500' without overspending.  When you throttle back you reduce your power setting and the resulting speed.

 

The longstanding definition of optimzed is optimized for speed not climb.  Optimized for cruise speed means WOT and 5,500RPM.

 

Using this and the previous CT forums the definition may have evolved to 5,650, which is neither optimized for climb or cruise but a compromise.  Another way to see it is 5,650 is optimizing for speed for a higher altitude, probably above 7,500' which is what I am advocating.

[Ed Cesnalis]

Certainly this is a great discussion. I wish we had a panel of aeronautical engineering PhD experts on here to give us a definitive answer. Sadly we just have to rely on experimentation and observation in our own local flight conditions.

 

Rotax publishes a power curve that shows both hp and torque.  Max cruise is ~92hp with max climb(5-min) ~98hp (max torque is similar RPM). We also know that best performance is at 7,500'DA. What else do we need to know?

[Roger Lee]

This is so long I should have started it Once Upon a Time or made it into chapters.

 

 

"Memory is a funny thing, which of us has gotten old enough to loose it?  I don't remember if you were at the 1st McMiinnville fly-in?"

 

We are the same age within a couple of weeks I believe and of course I was there. That's where I met Erin.  You're making me think it isn't my memory issue.  I have pictures of us standing together and we talked extensively. Roger Heller, Roger Fane and Tom P. and FD Germany came. We roasted a pig and ate at the Museum.

 

 

This discussion does not take into consideration an in flight adjustable prop and only a ground adjustable or fixed pitch prop because that's all we have to work with. The huge majority of Rotax owners do not have MAP and you don't fly by MAP pressures, but RPM since they don't have MAP. Although MAP is certainly influenced by the prop we don't fly by the MAP, but by RPM or we wouldn't be taking about RPM now and all forums wouldn't talk rpm, but how much MAP do you fly. MAP isn't part of our discussion.

 

"I had a power curve that confirmed max power was at 5,500"

 

​You don't have max power if all you get is 5500 rpm at WOT. HP, torque and prop pitch have to be in sync and balanced at any given time to get max performance and if you have influenced one or the other too much in either direction you can loose performance.  If we are propped for let's say 5'K and you get only 5500 rpm at WOT and I get 5650 RPM at WOT I will always pull away from you and be able to fly at less fuel and throttle setting if we pull back to cruise at 5200 rpm. I've had 8 CT's at my field and have done more in flight testing side by side than anyone in the US and most likely the world. I'm the only one in the world that has done extensive prop testing with pitch and 12 different props on CT's and with at least 4 flying side by side at one time during the testing for a more accurate comparison. I'm the only one who set the props and documented all my findings and gave them to the MFG's. They chose not to publish them and I can only speculate that because the Rotax is rpm depended on its performance regardless which prop you put on it. So any MFG can't claim this prop or that prop is great and wonderful. They couldn't sell lots of different models and would only be relegated to a couple of them because performance is so close the average individual couldn't tell.

 

You are still one of the few that fly WOT at 5500 rpm above 7500". Most do not do that. The over whelming majority fly between 5000-5300 at any altitude. This is strictly a personal choice item.

 

"You argue that noise and an almost 90% power setting isn't an issue yet you point out that others fly at lower power settings than I do."

 

Noise rarely ever is the main consideration for RPM cruise setting. You could count those people on one hand. Who basis their performance of their aircraft and prop pitch settings on noise? No one I have ever known.

 

 

"You argue that noise and an almost 90% power setting isn't an issue yet you point out that others fly at lower power settings than I do.  I believe you are proving my point, you guys don't fly at lower power settings because you don't like going fast you do it for 1) a comfortable noise level, 2) economy, with the drag near sea level you don't get much extra speed at the higher setting, 3) 90% power is a dumb setting for cruising an aircraft.  Rotax may have a simple RPM limitation but that doesn't make it smart to cruise at 90% plus as you point out no-one does it."

 

 

None of the majority fly at 5000-5300 solely based on noise levels. (maybe a few depending on their headset)

We don't fly at 90%. I'm not sure why you keep saying that. We set the prop pitch to achieve the proper balance between HP, torque and fuel economy and then throttle back because the reward between 5500 rpm in cruise verses 5200 rpm in cruise is very little except the 5500 person is burning more fuel and gets little speed/distance increase in return.

 

"Years ago you were advocating coarser than 5,650."

Never happened from me. That was FD. I have always advocated the 5600-5650 area. We don't have the HP or torque to turn most props efficiently at anything below 5500 and you get negative returns in performance for doing so. I've been testing and working with the 912 long before LSA. I've been doing testing and research on aircraft since 1980. It's what I enjoy.

 Inquiring minds want to know.   

 

" When you guys do the Grand Canyon tour I"m sure your throttles are open and your RPM are up just to keep up with the others.  That's how it went when I was there the 2nd time and some of you could keep up."

 

Exactly!

Thank You. This is exactly why we set our prop pitch for our average altitude. Some that live at sea level may rarely fly over 2'K while you almost always fly above 9'K+. If you want your BEST BALANCED performance you set your prop pitch for your specific needs.

 

 

"Does the iS shine at altitude?  From what I have read it is too dumb, above 93% throttle it just goes full rich like our carbs do.  It could be smarter and actually lean for the high altitude at full throttle but its not there, not a priority for Rotax apparently."

 

I have an FD CTLS 912iS at my field. I get to fly along side and take off side by side all the time. We constantly get to compare notes.

He just like us is RPM dependent on performance. At lower altitudes and when I'm at 5200 he is at 5300. There is a slight prop pitch difference between us. BUT when we get about 7500' I have to start adding throttle to equal his speed so then he is at 5200 and I'm at 5300, plus he is burning 1.1 GPH less and the higher we go like up to 10K the bigger the fuel difference and rpm spread and up to 1.5 gph.

 

You should come back to the Page fly-In as many have taken care of the over pitched issues from earlier FD distribution and we are more set up for higher altitudes. 2007 McMinnville and 2008 Page are so yesteryear.

 

I don't have to read all these things, guess or interpolate. I get to do it for real all the time. I have MFG's sending me products for testing and I get to fly side by side the same aircraft for comparison. This last part is more critical than most think because it helps reduce the pilot error factor, but it can never make it go away. Pilot's and the worse part of any testing because of the human factor so all you can do is set things up to help reduce that issue. Only one mechanic also helps reduce error factors.

 

I think you need more of that California Yoga.  

 

This is all about balance with the aircraft and not max or noise anything. 

 

 

[FlyingMonkey]

If you have no problem 'making full RPM or speed over the Grand Canyon at 11,500ft.' then you are not optimzed for 4,500'.  Both can't be true.  At 11,500' full RPM and speed means WOT and 5,500RPM.  At that setting you would have to throttle back to cruise at 4,500' without overspending.  When you throttle back you reduce your power setting and the resulting speed.

 

The longstanding definition of optimzed is optimized for speed not climb.  Optimized for cruise speed means WOT and 5,500RPM.

 

Using this and the previous CT forums the definition may have evolved to 5,650, which is neither optimized for climb or cruise but a compromise.  Another way to see it is 5,650 is optimizing for speed for a higher altitude, probably above 7,500' which is what I am advocating.

I did not claim "optimal" at 11,500. I claimed acceptable.

 

And IIRC the engine does not make full power at 5500rpm, but at 5800rpm. If you are set for WOT at 5500rpm, I'd think you'd be leaving some hp on the table that you could use for climbing, even if only for 5min at a time.

[Ed Cesnalis]

I do remember the pig on the grill at the FBO, yum.

 

We had the same argument before regarding MP.  You argued that high RPM caused engine wear and I argued you had to multiply RPM by MP to get power/work/wear.  MP matters and the throttle sets it within available range even if you can't read it on your panel.  Rotax power is no more RPM dependent than Lycoming, Continental, ...etc.

 

You don't have max power if all you get is 5500 rpm at WOT

 

That is exactly where max [continuous] power is, 5,500 @ WOT.

 

HP, torque and prop pitch have to be in sync and balanced at any given time to get max performance and if you have influenced one or the other too much in either direction you can loose performance

 

We don't sync torque and hp, just refer to the power curve.  Max power is only available at one DA determined by your pitch. Max performance is only available at 7.5K DA and then only if your pitched for 5,500RPM WOT @ 7.5K DA.

 

We don't fly at 90%. I'm not sure why you keep saying that

 

You say if you only fly at 2K then optimize for 2K.  I say that doesn't make sense because you won't use it.  WOT @ 2K DA @ 5,500 is almost 90hp. If you don't fly at 90% why would you optimize for that?  Optimze for 7.5K DA or higher and you can have about the same speed / economy at 2k as the plane optimized for 2k but your plane will be optimized for best performance which is something that you can use.

 

You are still one of the few that fly WOT at 5500 rpm above 7500". Most do not do that. The over whelming majority fly between 5000-5300 at any altitude. This is strictly a personal choice item.

 

I don't believe that for a second.  When the DA gets high enough and your hp drops low enough you will advance your throttle even all the way to full.  A flight over Yosemite on a bumpy day will get any CT pilot up to 13k or higher.  100% of us would advance the throttle (probably already there long ago) before we get down to 40+hp and can't maintain altitude.  Above 7,500'DA is where mountain pilots of normally aspirated planes equate a partially closed throttle to a clogged air cleaner.

 

This is where both the ULS and iS are lacking.  Your examples of flying with both have both leaned.  The ULS self leans at the carbs and the iS leans with the fuel injection.  Your examples show the better efficiency but on both planes it changes at WOT where they both go full rich.  Its funny if you ask me, WOT is needed at high altitude as well as leaning but in a ROTAX you can't have both at the same time.  A real weak point in the design.  The iS could have been smarter its just not in the code.

[Ed Cesnalis]

I did not claim "optimal" at 11,500. I claimed acceptable.

 

And IIRC the engine does not make full power at 5500rpm, but at 5800rpm. If you are set for WOT at 5500rpm, I'd think you'd be leaving some hp on the table that you could use for climbing, even if only for 5min at a time.

 

Actually you claimed 'full' RPM [and] speed.  That would be like 5,500RPM and 123kts TAS.  You can't be speed optimzed for 4.5K and make numbers like that.

 

Max cruise/continuous power is not 100%.  It is often limited to 75% which is max power at 7.5K DA if optimized for there.

[Roger Lee]

"You argued that high RPM caused engine wear and I argued you had to multiply RPM by MP to get power/work/wear."

 

I did and it still stands. Running at 5500 rpm all the time has more wear attributed to it than running at 5100 rpm. That part is fact and has nothing to do with our rpm prop pitch for balanced performance discussion.. Wear is wear and you choose where you want to run. That's why I said it was personal preference. That was true then and it is now. 

Over pitching adds even more wear below 5500 rpm WOT. It stresses the engine components and they were never designed for that. That's why guys with a prop pitch set at 5200 and lower and running WOT were cracking the crankcases.

 

"That would be like 5,500RPM and 123kts TAS"

 

Sure he can and so can I. You are a different animal due to the fact you always have to fly so high and when you do come down towards sea level your not pitched for that. Your performance at your altitude will always be less than ours.

 

Sync was a bad choice of word.  Balanced was what it should be.

 

"You say if you only fly at 2K then optimize for 2K.  I say that doesn't make sense because you won't use it.  WOT @ 2K DA @ 5,500 is almost 90hp. If you don't fly at 90% why would you optimize for that?"

 

Because it puts less stress and wear on the engine. you don't need to use it unless you need to climb.  You also want a balanced prop pitch for cooler engine temps during the warm months. Again at your altitude it would make a huge difference because you run richer all the time. If I only flew where you do I would change the needle position and jetting. Think a larger picture. 

 

This is still not about noise, max power and always being at WOT in cruise.

 

 

"You are still one of the few that fly WOT at 5500 rpm above 7500". Most do not do that. The over whelming majority fly between 5000-5300 at any altitude. This is strictly a personal choice item.

 

"I don't believe that for a second"

 

You should it's true. You need to fly at higher rpms because of where you live. Take a poll if you want. I talk to people from all over the world up to 10 times per day. RPM is a constant discussion. I don't have a single client that fly's at WOT in cruise and have only met 1-2 in any of my classes.

 

I fly at 5200 rpm at sea level and I fly at 5200 rpm at 10K.

 

Your sample group for all this is just around where you live, reading and a few comments from people. I eat and live this stuff everyday. I work on more than 30 Rotax engine aircraft a year and interact with people from all over the world with direct feedback.  There are no suppositions, it is real world in flight numbers.

 

I don't have to guess or figure it should be, I get to see real results plus years worth of testing. I get to fly all kinds of LSA and see their performance and prop choices.

[Ed Cesnalis]

I know you have a lot of experience working on CTs and other very light aircraft but things still have to make sense to me.

 

To repeat, we now have the same prop pitches.  If I descend to one of the lower valleys and then cruise I have to throttle back.  We can argue about why, I maintain its noise, lack of much additional speed due to drag (economy), and overspeeding (5,650 RPM range ).  Our pitches and therefore available power are now very similar.  Our biggest difference is that I use all available power when available power falls below 75%, that means above 7.5K DA my throttle is wide open.

 

More RPM only means more wear at the same MP.  A higher RPM with a lower MP produces less wear not more, assuming the MP is low enough to result in a lower power setting.  It doesn't matter if we are talking wear or power the result will always be determined by both MP and RPM never by RPM alone. Giving more weight to RPM because its a Rotax or because you don't have a gauge is silly. At least we agree that a high power setting at a low RPM is the worst case for wear. That alone indicates I'm right, lower RPM in that case cause more wear not less.

 

I will agree with you that needle and jets are a consideration for me but it would come at a price.  In order to use needle circuit leaning I have to throttle back and give up speed and power just to get into leaning range, not a great compromise.  A leaner main jet would give me some leaning but I would be compromised when climbing out at sea level. A mystery to me is why does my Rotax work so well at full rich when leaning is needed?  My Lycoming wouldn't do that, it demands leaning for cruising above 10k.

 

You may be able to claim that people don't fly WOT above 7.5K and you might be correct but that doesn't mean it makes any sense.

 

I fly at 5200 rpm at sea level and I fly at 5200 rpm at 10K.

 

Okay, but why?  I too would use that power setting at sea level (remember according to me we fly the same prop pitch) but why would you fly at a much lower power setting at 10K?  At 10K you have 30% less power than at sea level.  Economy at 5,200 has leaning from the needle circuit as well as less volume from the altitude so your fuel burn is lowered.  There usually isn't much reason to cruise a CT at 10K unless there is high terrain.  Granted flying on top could be another reason but LSA are probably flown on top less than Cessnas, Pipers, ...etc.  When terrain is an issue its a good idea to keep your speed up so you have more options when things aren't working out.

 

The only reason I can see to fly partial throttle at 10K in a CT would be if I was low on gas and needed the extra range to make a fuel stop. Apparently YMMV.

[FlyingMonkey]

Actually you claimed 'full' RPM [and] speed.  That would be like 5,500RPM and 123kts TAS.  You can't be speed optimzed for 4.5K and make numbers like that.

 

Max cruise/continuous power is not 100%.  It is often limited to 75% which is max power at 7.5K DA if optimized for there.

 

Don't recall my TAS, but I was making (barely) 5500rpm.

[Ed Cesnalis]

Don't recall my TAS, but I was making (barely) 5500rpm.

 

Sounds like you were speed optimized (barely) for over 11k DA?

 

We do tend to be pitched the same these days, at least once we are optimized.  That's very close to where I am at.  One other reason that ball park makes sense is that when utilizing sport pilot privileges my cruise altitudes tend to be 1k-2k lower.  In the old days flying a 180 Cherokee or a 180 Skyhawk I would most usually cruise at 10.5 or 11.5 where these days I do much of it at 8.5 and 9.5 stepping higher for the Sierra Nevada.

[FlyingMonkey]

Sounds like you were speed optimized (barely) for over 11k DA?

 

We do tend to be pitched the same these days, at least once we are optimized.  That's very close to where I am at.  One other reason that ball park makes sense is that when utilizing sport pilot privileges my cruise altitudes tend to be 1k-2k lower.  In the old days flying a 180 Cherokee or a 180 Skyhawk I would most usually cruise at 10.5 or 11.5 where these days I do much of it at 8.5 and 9.5 stepping higher for the Sierra Nevada.

 

Well that's the other possibility...we could all be talking around each other, but once we use whatever accepted methods and we seem to be optimal at our altitude, we could all be about the same because that is as optimized as we are going to get, regardless of altitude.  I think that *might* be what Roger is saying. 

 

You optimizing for 5500rpm WOT at 10,000 is probably not far off from me optimizing to 5650-5700rpm at 3000ft.

 

Maybe we're *all* right!