CTSW Cruise Speed

[Ed Cesnalis]

7 minutes ago, Roger Lee said:

"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."

 

Will you ever address, that cruising with a retarded throttle isn't best speed or climb?  Do you ignore the continuous limitation?

[Roger Lee]

First the 5500 continuous is just a liability rpm. It makes sure you will never have an issue worldwide. The truth is far above that. The 5800 max is also a liability safe rpm. So if you liked 5600 it could do that all its life to. I ne don't.ver had to fly at 5500 rpm because I don't live and fly at your altitude. Just like the other 95%.

"Will you ever address, that cruising with a retarded throttle isn't best speed or climb?"

The answer is no. Best speed or top speed. Top speed will be at WOT, but cost fuel and the extra rpm don't warrant the extra fuel and the few extra knots. Best fuel economy or worse fuel economy. WOT is always worse fuel economy. WOT is  always better to climb faster than retarded or you wouldn't use it at takeoff.

Wear at WOT all the time is more than reduced throttle. Over pitched at WOT can and has cracked many a 1500 hr. (pre mid 2006) crankcase on top with a 2" crack.

You may want to reword your question.

 

[Roger Lee]

Andy,

Chime in on what you did to your prop.

 

p.s.

I did a 2008 Tecnam 2 months ago. He thinks he got turbo charged. His rpm was only 5200 WOT and lots of fuel use and high engine temps. Set his at 5600 WOT. Had another Tecnam owner call me a week ago with the same issue.

[Ed Cesnalis]

23 minutes ago, Roger Lee said:

You may want to reword your question.

I don't have a question.  I'm just once again reacting to you saying my prop is pitched wrong.  I don't agree, I haven't changed it in years because its working so well.

[Roger Lee]

"I haven't changed it in years because its working so well."

Because you haven't tried anything else.  

We all know what we know, but there is always more out there to know and it's up to each to know there is more to know and to never stop realizing we really don't know all we thought we knew.. LOL

Anything less stunts our personal growth. I'm a hardcore researcher and always have to know why and more. That's why we have Matco's and know what happens and at what rpm the engine runs with a fuel pump failure and why we have a number of LOA's for the CT or we can now put a Sensenich on CTSW's. Causes and cures for over heating. Using a K&N on the SW or wheel pant mods. header wrap, the Odyssey battery instead of the SB and the list goes on......  Research and testing it never stops. Remember what Yoda said....:)

You have to be willing to try it to rule it in or out otherwise it's just speculation no matter what you think you know.

If I came over there and put on a different prop and set the WOT rpm to 5600-5650 you'd give me a hug and wouldn't need that big bore kit. LOL

p.s.

Big bore kits have had their own issues. I know a few that wish they hadn't gone there.

[Scrapman1959]

Your GPS based true air speeds flying a triangle or a box won’t be accurate unless you actually split the 360 degrees evenly into 3 reciprocating courses such as 180, 300, and 060 or if flying a box, split 4 courses evenly, such as 360, 090, 180, and 270. 

[Skunkworks85]

11 hours ago, Scrapman1959 said:

Your GPS based true air speeds flying a triangle or a box won’t be accurate unless you actually split the 360 degrees evenly into 3 reciprocating courses such as 180, 300, and 060 or if flying a box, split 4 courses evenly, such as 360, 090, 180, and 270. 

According to Doug Grays, Published academic paper on the matter. This method has been published in many circulars.

 

Using the triangle method, 120 degrees (1/3 of 360) is the max difference you should use between tracks, in order to equal the uncertainty level of the GPS unit itself.

[FlyingMonkey]

On 3/20/2019 at 1:06 PM, Roger Lee said:

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

 

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

Sure, but mine was severely over-propped and nowhere near a normal, much less optimal range.  And I'm not faulting your methods, they work well, but like everything with a fixed pitch prop, they are a compromise.  My only point was that I don't think you can really get higher speed *and* lower RPM at that speed by flattening pitch.  Flatter usually means less speed and higher engine rpm, so something is not quite right there.  Rotax engines are a little different from other aircraft engines, but they're not magic devices that  alter physics.

[FlyingMonkey]

19 hours ago, Roger Lee said:

First the 5500 continuous is just a liability rpm. It makes sure you will never have an issue worldwide. The truth is far above that. The 5800 max is also a liability safe rpm. So if you liked 5600 it could do that all its life to. I ne don't.ver had to fly at 5500 rpm because I don't live and fly at your altitude. Just like the other 95%.

If that is true and I lived at Ed's altitude, I'd be tempted to run at higher than approved RPM.  Of course, even pitched for 5650rpm WOT you are going to see nowhere near that in a climb, but a higher WOT rpm in the climb (say 5100rpm vs 5000rpm) will equite to better climb rate.  I'd be hesitant to run much hotter in cruise because at higher altitudes you should be using TAS for airframe limits, and I would not want to cruise much past Ed's 127KTAS number above 12,000ft anyway.

I do think Ed should consider a different prop, the Warp is inexpensive and easy to fix, but heavy and not as efficient as some others.

[FlyingMonkey]

19 hours ago, Roger Lee said:

Andy,

Chime in on what you did to your prop.

 

 

Yeah, mine was grossly coarse.  IIRC I took about about 1.5° of pitch total.  I went from a top speed of 108kt indicated to 125kt at 2000ft solo.  I didn't seem to lose any climb.  I definitely think any CT owner should follow the 5600-5650rpm at cruise altitude rule of thumb.  But with Ed's situation it's harder to tell if that would make him better, since he's at the extreme of operating conditions.  

[FlyingMonkey]

4 hours ago, Skunkworks85 said:

According to Doug Grays, Published academic paper on the matter. This method has been published in many circulars.

 

Using the triangle method, 120 degrees (1/3 of 360) is the max difference you should use between tracks, in order to equal the uncertainty level of the GPS unit itself.

This thread makes me want to organize a CT race.  Maybe at Page...?  

[Roger Lee]

Andy,

Is your plane faster than others with lower rpm WOT settings? Does your plane climb better than others with lower WOT rpm? I already know the answer. Most are forgetting to figure in all the other factors. 

With your pitch setting and if Ed set his pitch to still only get 5500 at your altitude or yours at his altitude you would out climb him, get better fuel economy, have lower engine temps and have a higher top end speed. Ed is the only one of us that fly's at 5500 all the time and that's because he has to to get any performance at his altitude and with his prop. Your 5500 speed may be like his, but he will absolutely use more fuel and he will have less climb performance at take off. Your top speed will always be higher than his. This has proved out over and over again  in real time testing since I started CT testing in 2006. 

 

[Roger Lee]

21 minutes ago, FlyingMonkey said:

If that is true and I lived at Ed's altitude, I'd be tempted to run at higher than approved RPM.  Of course, even pitched for 5650rpm WOT you are going to see nowhere near that in a climb, but a higher WOT rpm in the climb (say 5100rpm vs 5000rpm) will equite to better climb rate.  I'd be hesitant to run much hotter in cruise because at higher altitudes you should be using TAS for airframe limits, and I would not want to cruise much past Ed's 127KTAS number above 12,000ft anyway.

I do think Ed should consider a different prop, the Warp is inexpensive and easy to fix, but heavy and not as efficient as some others.

You won't see that 5600 in climb, but you will out perform him in climb.

 

Don't forget we are picking the BEST BALANCED rpm at WOT in level Flight at your average altitude. There is no way for us to have the best performance for the engine and prop with only a ground adjustable. Some of you are hung up on just one aspect. Balance is the key for ALL AROUND best performance and trying not to give too much away on either end.

I won't give the public any numbers, but yes you could fly over 5500 continuous. 

Here is a situation that you would do exactly that. Your WOT rpm is let's say 5700 rpm WOT (like Andy's) and you break a throttle cable a long way from an airport. You either land right away because you are afraid of being over the 5500 rpm, but you're over hostile terrain like in ED's pictures. Your other option is to go WOT so both carbs are now wide open and you're at 5700 and fly to the nearest airport which may be a long time past the 5 min. max published. Option one is a fools decision. Option two fly's you to an airport where you get on a long  final and shut the engine down on approach and land. Don't fear what you don't know about the published rpm limits. They are safe limits to make sure you last for a few thousand hours. 

 

p.s.

"I would not want to cruise much past Ed's 127KTAS number above 12,000ft anyway."

Why not the plane can handle it. I've cruised at 135 - 140 knts in the SW, but it wasn't for his extended periods.

[Skunkworks85]

Rodger,

Have you every set up a propeller for max climb tests? Say for instance, for a STOL competition?

If so, what kind of FPM could one expect to see?

[Roger Lee]

If you were using a Rotax I would use around the 5800 at take off. BUT,  You would then need to do a little testing and see what prop worked better and if hopping over that 5800 limit helped you or hurt you. Many props are close to the same performance, but you'd have to do a few test on prop types and prop length to get real life numbers if you wanted to be at your peak performance. Unfortunately it isn't a one size fits all.

This advise would hold true for our main discussion above because of several variables.  The discussion above is for a balanced performance and not peak on either side.

[Skunkworks85]

Any guesses at what max climb rate could be on lets say a standard day/altitude?

[JLang]

1 hour ago, Roger Lee said:

With your pitch setting and if Ed set his pitch to still only get 5500 at your altitude or yours at his altitude you would out climb him, get better fuel economy, have lower engine temps and have a higher top end speed.

I hesitate to jump into this debate, especially since it seems like you guys are not talking apples-to-apples regarding the measurable, but in the interest of confirming my understanding, I believe the following to be true, for a given altitude:

For best possible top speed (short duration), pitch for WOT at 5800rpm (conforming to official Rotax rpm guidelines).

For best possible cruise speed (long duration), pitch for WOT at 5500rpm.

For best possible rate of climb, pitch for WOT at 5500 rpm at Vy.

For best possible efficiency (miles per gallon or similar), pitch for WOT at 5200rpm (torque peak).

FWIW, my CT is set up for ~5650rpm at WOT at ~4500' (have never changed it), and I am happy with the performance balance at the low-to-medium altitudes I fly; pretty much book or slightly better numbers.  Incidentally, my Dynon is optimistic by about 8kts at cruise.

[Ed Cesnalis]

18 minutes ago, Skunkworks85 said:

Any guesses at what max climb rate could be on lets say a standard day/altitude?

So weight dependent.  My Ct weights 719lbs, I weight 157, minimum fuel weigs 18lbs.  At that weight I get 1,500fpm @ 8,000'

Other configurations I can't get 500

[Ed Cesnalis]

2 minutes ago, JLang said:

I hesitate to jump into this debate, especially since it seems like you guys are not talking apples-to-apples regarding the measurable, but in the interest of confirming my understanding, I believe the following to be true, for a given altitude:

For best possible top speed (short duration), pitch for WOT at 5800rpm (conforming to official Rotax rpm guidelines).

For best possible cruise speed (long duration), pitch for WOT at 5500rpm.

For best possible rate of climb, pitch for WOT at 5500 rpm at Vy.

For best possible efficiency (miles per gallon or similar), pitch for WOT at 5200rpm (torque peak).

FWIW, my CT is set up for ~5650rpm at WOT at ~4500' (have never changed it), and I am happy with the performance balance at the low-to-medium altitudes I fly; pretty much book or slightly better numbers.  Incidentally, my Dynon is optimistic by about 8kts at cruise.

I agree

[WmInce]

1 hour ago, Ed Cesnalis said:

So weight dependent.  My Ct weights 719lbs, I weight 157, minimum fuel weigs 18lbs.  At that weight I get 1,500fpm @ 8,000'

Other configurations I can't get 500

Ed,

What RPM are you turning, at rotation, when departing your home airport?

[Ed Cesnalis]

1 hour ago, WmInce said:

Ed,

What RPM are you turning, at rotation, when departing your home airport?

I think around 5,150

[FlyingMonkey]

17 hours ago, Roger Lee said:

 

"I would not want to cruise much past Ed's 127KTAS number above 12,000ft anyway."

Why not the plane can handle it. I've cruised at 135 - 140 knts in the SW, but it wasn't for his extended periods.

I would not want to fly too close to the 145kt Vne, and at higher altitudes TAS overtakes IAS for calculating load limits.  140kt doesn't leave much margin if you get a really strong gust or turbulence.  I'd do it in smooth air though.  I'm not at all agraid of the CT's wing, it's strong as hell.  But that stabilator...

[Roger Lee]

Do you know the real limit is higher and do you know why?

[FlyingMonkey]

32 minutes ago, Roger Lee said:

Do you know the real limit is higher and do you know why?

I know that some CTs in different legal jurisdictions have a Vne over 160kt.  I also know I personally experienced stabilator flutter at 122 knots in level flight.  Forgive me if I'm a little shy about pushing the limits...     

 

https://www.flyingmag.com/technique/proficiency/technicalities-are-you-feeling-lucky

[Jacques]

162Kts VNE on mine     but no chute installed

I stay FAR from there  specially since I saw this