Too Lean?

[alextstone]

10 hours ago, Austintatious said:

thanks.... I have a deal in the works for a Rocket, but if it falls through there is a nice Bravo I have been looking at.  The cruise numbers are vastly different on those 2.

Those figures are running LOP...ROP, add 10-15kts. 

 

[Austintatious]

59 minutes ago, Shadrach said:

Are they really “vastly” different other than maybe in climb?

Ok, perhaps "vastly" is a bit strong of a word.  The trouble is that I cant find any good data for LOP op in the rocket.  The manual doesn't recommend it.  I know people are doing it but the data is hard to find other than bits here and there.

That being said, It appears the rocket will cruise around 208-210 at FL180 on 16 GPH ROP.  that is 30 knots faster than the above Bravo for 1.7 more gph. Add in the climb difference and it simply looks like the rocket is the more efficient bird.   Going LOP should make it even more so as LOP is even more efficient WRT BSFC.

 

[Shadrach]

3 hours ago, Austintatious said:

Ok, perhaps "vastly" is a bit strong of a word.  The trouble is that I cant find any good data for LOP op in the rocket.  The manual doesn't recommend it.  I know people are doing it but the data is hard to find other than bits here and there.

That being said, It appears the rocket will cruise around 208-210 at FL180 on 16 GPH ROP.  that is 30 knots faster than the above Bravo for 1.7 more gph. Add in the climb difference and it simply looks like the rocket is the more efficient bird.   Going LOP should make it even more so as LOP is even more efficient WRT BSFC.

 

Sorry, that math doesn't work for almost identical airframes. The extra 5" of the long body vs mid body adds little drag.  There is NFW a Rocket is going 30kts faster with an additional 1.7GPH of fuel when both are ROP (or LOP) even if at a much lighter weight.  The laws of physics still apply...

Edited April 1, 2019 by Shadrach

[bonal]

You have to use the new math

 

[Shadrach]

9 minutes ago, bonal said:

You have to use the new math

 

no doubt...the kind of math that gains you 2-4kts of cruise speed for every additional 1 HP. 

[Shadrach]

On 3/31/2019 at 11:25 AM, midlifeflyer said:

I know the guys who do the big courses on this, but for my money ($0 :D) , the best simple explanation is Martin Pauly's video on YouTube

 

This presentation offers a lot of info and is a good intro to procedure.  My critique is that he often refers to internal cylinder pressure without touching on the very important concepts of peak internal cylinder pressure and mean internal cylinder pressure.   I wish someone would do a video with a turbo engine showing same power settings both Lean and Rich.  I think it would offer a greater insight into how power is made. You can exert the same energy on an object with both a hammer blow (ROP) and a consistent well directed push (LOP)  The two biggest differences between LOP and ROP are 1) the high mean effective pressure when LOP (vs high peak pressure when ROP) and 2) that when LOP,  theoretically all of the fuel entering the cylinder is being used to make power. Side bonus is the lack of CO in the exhaust when LOP.

Edited April 1, 2019 by Shadrach

[alextstone]

Thanks, All, for the responses!  

[gsxrpilot]

20 minutes ago, Shadrach said:

This presentation offers a lot of info and is a good intro to procedure.  My critique is that he often refers to internal cylinder pressure without touching on the very important concepts of peak internal cylinder pressure and mean internal cylinder pressure.   I wish someone would do a video with a turbo engine showing same power settings both Lean and Rich.  I think it would offer a greater insight into how power is made. You can exact the same energy on an object with both a hammer blow (ROP) and a consistent well directed push (LOP)  The two biggest differences between LOP and ROP are 1) the high mean effective pressure when LOP (vs high peak pressure when ROP) and 2) that  when LOP,  theoretically all of the fuel entering the cylinder is being used to make power. Side bonus is the lack of CO in the exhaust when LOP.

Hmmm... I've got the turbo, full color easy to read engine monitor, plenty of cameras, come on Ross, let's do it.

[Shadrach]

1 minute ago, gsxrpilot said:

Hmmm... I've got the turbo, full color easy to read engine monitor, plenty of cameras, come on Ross, let's do it.

You don't need me! You've the tech, the plane, the knowledge and the time.  I'll be applauding from the cheap seats!  It would be good to see fuel flow and CHT readings at the same IAS both ROP and LOP. Can you do 70% in your bird at 125ROP and whatever needed to stay below TIT limit LOP?

[jaylw314]

32 minutes ago, Shadrach said:

You don't need me! You've the tech, the plane, the knowledge and the time.  I'll be applauding from the cheap seats!  It would be good to see fuel flow and CHT readings at the same IAS both ROP and LOP. Can you do 70% in your bird at 125ROP and whatever needed to stay below TIT limit LOP?

It's not exactly what you're looking for, but Mike Busch had a photo of his engine monitor in his Cessna 310 that was pretty cool.  He had one motor set up for LOP and the other for ROP to compare the temps and fuel flow.  Obviously, they were producing the same power, but the lower fuel flow and temps to compare were a nice visual demonstration

[Shadrach]

10 minutes ago, jaylw314 said:

It's not exactly what you're looking for, but Mike Busch had a photo of his engine monitor in his Cessna 310 that was pretty cool.  He had one motor set up for LOP and the other for ROP to compare the temps and fuel flow.  Obviously, they were producing the same power, but the lower fuel flow and temps to compare were a nice visual demonstration

I’ve never seen Mike’s but GAMI has this one on their site.  This is an Aerostar running the same power on each engine. Left is ROP, right is LOP. Ball centered and same trim as when both were ROP. Notice the MP for the LOP engine.

 

[gsxrpilot]

1 hour ago, Shadrach said:

You don't need me! You've the tech, the plane, the knowledge and the time.  I'll be applauding from the cheap seats!  It would be good to see fuel flow and CHT readings at the same IAS both ROP and LOP. Can you do 70% in your bird at 125ROP and whatever needed to stay below TIT limit LOP?

Yeah, I'm pretty sure I can do that. I'll go try it out.

[jaylw314]

25 minutes ago, Shadrach said:

I’ve never seen Mike’s but GAMI has this one on their site.  This is an Aerostar running the same power on each engine. Left is ROP, right is LOP. Ball centered and same trim as when both were ROP. Notice the MP for the LOP engine.

 

Oh, I think that's the one I was thinking of.  I think I was conflating info from a couple different places.

[Austintatious]

4 hours ago, Shadrach said:

Sorry, that math doesn't work for almost identical airframes. The extra 5" of the long body vs mid body adds little drag.  There is NFW a Rocket is going 30kts faster with an additional 1.7GPH of fuel when both are ROP (or LOP) even if at a much lighter weight.  The laws of physics still apply...

well, you can disagree... I have photos of the cockpit in the rocket I am buying at 17.5 doing 208 at 16 GPH...

Here is a video of a rocket at 180 doing 210 on 16 gph... 

 

Furthermore, the performance chart I have seems to be pretty well right in line with this video and the in flight photos I have of the specific rocket I am buying.  ROP data.... i cant find good LOP numbers, but one would think they would be more economical.

Edited April 1, 2019 by Austintatious

[ArtVandelay]

well, you can disagree... I have photos of the cockpit in the rocket I am buying at 17.5 doing 208 at 16 GPH... Here is a video of a rocket at 180 doing 210 on 16 gph... 

 

 

Actually it’s 196 or less, you have the TAS adjustment set to +15°C, should be -15C, and you have baro set to 29.92 instead of actual, and you are no where to close to max gross.

 

 

Tom

 

[Shadrach]

41 minutes ago, Austintatious said:

well, you can disagree... I have photos of the cockpit in the rocket I am buying at 17.5 doing 208 at 16 GPH...

Here is a video of a rocket at 180 doing 210 on 16 gph... 

 

Furthermore, the performance chart I have seems to be pretty well right in line with this video and the in flight photos I have of the specific rocket I am buying.  ROP data.... i cant find good LOP numbers, but one would think they would be more economical.

I can't speak to your data on either airplane.  Only the physical impossibility that one is 30kts faster on 1.7gph more fuel.  They both burn the same type of fuel and have the same compression ratio (7.5:1).  One (the Cont) just has the ability to be run much harder  (38" and 2700 RPM vs 34.5 and 2500?).  At normal cruise settings (say 30" and 2500 RPM), there is not a lot of horsepower daylight between these two engines.  In terms of flat plate area and Cd there is almost no daylight between the airframes. So yes, I will continue to believe that the idea that a Rocket (all other things being equal) cruises 30kts faster than a Bravo burning just an 1.7gph additional is a total fairytale.  I would caution you against believing otherwise. You have one data point on one day. I don't know what happened that day but I know that meager addition to fuel energy won't do what you're claiming. 

Edited April 1, 2019 by Shadrach

[Austintatious]

7 minutes ago, ArtVandelay said:

Actually it’s 196, you have the TAS adjustment set to +15°C, should be -15C, and you have baro set to 29.92 instead of actual, and you are no where to close to max gross.

 

 

Tom

That is not me or the aircraft I am buying.  Just a video I found... I think I can make out how he has it set and i will concede it is set wrong.  However even at 196, that is still 16 knots faster than what was stated for the Bravo.  As to the altimeter being 29.92, it sort of has to be if he is flying at FL180.

 

let not forget that the Bravo in Question has TKS.

 

[Shadrach]

1 minute ago, Austintatious said:

That is not me or the aircraft I am buying.  Just a video I found... I think I can make out how he has it set and i will concede it is set wrong.  However even at 196, that is still 16 knots faster than what was stated for the Bravo.  As to the altimeter being 29.92, it sort of has to be if he is flying at FL180.

 

let not forget that the Bravo in Question has TKS.

 

All other things being equal.  That means we don't compare FIKI birds to non FIKI birds.

[alextstone]

Just now, Austintatious said:

That is not me or the aircraft I am buying.  Just a video I found... I think I can make out how he has it set and i will concede it is set wrong.  However even at 196, that is still 16 knots faster than what was stated for the Bravo.  As to the altimeter being 29.92, it sort of has to be if he is flying at FL180.

 

let not forget that the Bravo in Question has TKS.

 

My Dad used to tell me often: "Son, you're in a lot of trouble when you start believing your own bullshit."  There are so many parameters here that I do not think you can make such a comparison nor does it really matter.  Each to his or her own though.

 

[Austintatious]

1 minute ago, alextstone said:

My Dad used to tell me often: "Son, you're in a lot of trouble when you start believing your own bullshit."  There are so many parameters here that I do not think you can make such a comparison nor does it really matter.  Each to his or her own though.

 

cute way of telling me I am full of shit....  I guess the rocket published numbers are full of shit as well.

[Shadrach]

8 minutes ago, Austintatious said:

cute way of telling me I am full of shit....  I guess the rocket published numbers are full of shit as well.

Indeed most manufacturer’s published numbers are very optimistic. They are in most cases, best case scenarios burnished with a bit of optimism.  I laid out the physics above.  You might be able to find 8 to 12kt difference between the two aircraft based on subtle aerodynamic tweaks and  differences in prop efficiency.

[ArtVandelay]

27 minutes ago, Austintatious said:

cute way of telling me I am full of shit....  I guess the rocket published numbers are full of shit as well.

All published numbers are anywhere from best case to marketing dreams.

They test the planes with no antennas, perfectly adjusted controls and engine settings, ideal weight distribution, and very clean if not waxed. Possibly missing stall strips since they are an afterthought to get plane to stall straight ahead after variances in the manufacturing process. Not to mention the CAS is about 3-4 knots less than IAS.

I believe we have somebody who races their J, and it took some effort to get to book numbers.

 

 

Tom

[alextstone]

23 minutes ago, Austintatious said:

cute way of telling me I am full of shit....  I guess the rocket published numbers are full of shit as well.

My apology if you took offense.  I was actually trying to lighten the mood a bit. I'm not known for my social tact.  I understand you are certain you are right.

[alextstone]

13 minutes ago, Shadrach said:

  You might be able to find 8 to 12kt difference between the two aircraft based on subtle aerodynamic tweaks and  differences in prop efficiency.

Hmm, that's important.  My aircraft was re painted before I purchased it and I suspect it was not re rigged perfectly.  I'm also dragging TKS around and I have yet to tune my GAMI injectors so I may be losing more airspeed than I should LOP. I used to worry about all of this a lot more until I realized that there is a beautiful view out of the glarescreen to be had at any speed.

[EricJ]

On 3/31/2019 at 8:14 AM, N231BN said:

To correct #1 above...You can go not lean enough, if you stop in the red box you are too rich.

The key to understanding LOP ops lies in the original question. You cannot hurt your engine by running it too lean. You CAN hurt your engine by not running it lean enough.

I think that's a bit deceptive, since it's a matter of perspective or reference.   If you're on the rich side of the red box or red fin and start leaning, you can certainly hurt things by going leaner, which would be too lean compared to where it was.   That's pretty much what carusoam said, if you stop in the box while leaning you're too lean compare to the richer side of the box.   Can you fix it by going outside of the box on the lean side?   Sure, and that point was made in carusoam's #2.    So you're right, but #1 was correct as stated.