Best RPM for Mooney 20 F

[jetdriven]

On November 7, 2015 at 9:15:21 AM, Bob - S50 said:

this forum is nearly impossible to use on an iPhone now.  It keeps coming up with an old quote so I have to delete 2 pages of quoted words  

Here is the thread with the photo of the paper.  Use the bottom, the test attempted on the top 2/3rds of the page wouldn't work. The speed difference is real.  2209 rpm was 110 ROP to keep the fuel flow the same but there is no way it is going to be faster at peak EGT at 2200 rpm.  I've tried cruising below 2400 rpm and, short of a sightseeing flight, there's no economical reason to, it's simply a lot slower for the FF and the NMPG goes down as well.    This is a J with a C214 prop  others may vary  

http://mooneyspace.com/topic/14817-continental-motors-webinars-lop-operations/#comment-202838

[Shadrach]

4 hours ago, jetdriven said:

this forum is nearly impossible to use on an iPhone now.  It keeps coming up with an old quote so I have to delete 2 pages of quoted words  

I think it's all iOS devices. My iPad is the same. It sucks to have to delete old posts that just appear as though you are editing them, what's worse is that the cursor is not doing what it should. I will highlight to delete, but when I hit the delete key it takes me to the top of the page (without deleting what I wanted to delete).

[M20F]

19 hours ago, ChrisH said:

I've seen similar results, and LOP theory says FF ~ HP, so same FF should be same HP. But, it's hard to jive that much improvement in TAS with just RPM. 

Peak EGT is where you develop the most horsepower in the example Jetdriven gives he uses that as baseline, changes RPM, and  keeps fuel flow constant.  The thing changing here is % of power.  You don't run at peak EGT burning xxgph and then shift to 40LOP still burning xxgph and increase 7 knots without an increase in power, there is no free lunch. 

My point isn't to debate LOP/ROP just pointing out if you want to determine prop efficiency than everything else has to remain constant while only the prop changes to determine the ideal setting.  That setting could be (and probably is) different based on things like density altitude, % of power, etc.  

[jetdriven]

1 hour ago, M20F said:

Peak EGT is where you develop the most horsepower in the example Jetdriven gives he uses that as baseline, changes RPM, and  keeps fuel flow constant.  The thing changing here is % of power.  You don't run at peak EGT burning xxgph and then shift to 40LOP still burning xxgph and increase 7 knots without an increase in power, there is no free lunch. 

My point isn't to debate LOP/ROP just pointing out if you want to determine prop efficiency than everything else has to remain constant while only the prop changes to determine the ideal setting.  That setting could be (and probably is) different based on things like density altitude, % of power, etc.  

There is a steeply discounted lunch here. 80 ROP is best power, the 2200 RPM setting is richer than that, so subtract a half to even a full GPH for that, and 40 LOP is actually a bit leaner than best trip fuel for 2700 RPM, but its still 7 knots faster.  The % power changed because the RPM changed, btu not 7 kntos worth based on the POH.

[Bob - S50]

57 minutes ago, M20F said:

Peak EGT is where you develop the most horsepower in the example Jetdriven gives he uses that as baseline, changes RPM, and  keeps fuel flow constant.  The thing changing here is % of power.  You don't run at peak EGT burning xxgph and then shift to 40LOP still burning xxgph and increase 7 knots without an increase in power, there is no free lunch. 

My point isn't to debate LOP/ROP just pointing out if you want to determine prop efficiency than everything else has to remain constant while only the prop changes to determine the ideal setting.  That setting could be (and probably is) different based on things like density altitude, % of power, etc.  

At peak EGT you have the perfect mixture of oxygen and fuel.  Unfortunately you don't have a perfectly distributed mixture so some fuel and some oxygen go unused out the exhaust.

When ROP the limiting factor for producing power is oxygen.  Once you use up all the oxygen, no amount of extra fuel is going to produce any more power.  As a matter of fact you start to lose power because of less efficient burning.  By the time you get to somewhere around 50 to 100F ROP you are essentially using up all the oxygen.  Power is then determined by air density (MP) and volume (RPM).  That's why the MP + RPM for % power setting works.

When LOP the limiting factor is fuel.  However, similar to ROP there is some unused fuel.  However, by the time you get to somewhere around 30 to 75F LOP you are essentially using up all the fuel with plenty of oxygen left over.  Since the limiting factor is fuel when LOP, MP and RPM do not determine power.  Fuel flow does.

With all that said, since Jetdriven did use mixtures between 40 LOP and peak, there would be slightly more wasted fuel at peak EGT but I don't know if it is enough to make the difference in power to result in the stated performance.

[mike_elliott]

On ‎11‎/‎7‎/‎2015‎ ‎12‎:‎02‎:‎46‎, Culver LFA said:

I read the article and do respect his expertise and agree with his opinion - for most efficient operations.   Running wide open definitely has it's advantages but I would love the opportunity to learn from him discussing his statement of, "There is no reason on a normally aspirated engine to reduce the throttle for climbs. Why sacrifice climb performance for nothing?".  I'm quite certain that we would come to an agreement that there are such times that this could be appropriate.

 

You missed your opportunity to talk personally with Bob Kromer at last months' Mooney Summit III. Bob gave 2 excellent presentations on how to operate your Mooney based on his many hours as a test pilot for Mooney using real data to support his conclusions. We have invited Bob back to once again speak at the next Mooney Summit, Sept29-Oct 2, 2016, hopefully he can once again commit. We will post when Registration opens here on Mooney space, on mooneyevents.com, on www.mooneysummit.com, announce it on the Mooney Flyer,  AOPA, MAPA list and on aviating.com. Hopefully, this will give everyone sufficient heads up to plan and to get registered! I did hear from a few people that "we didn't know about it" last time, and *hopefully* this action will mitigate the problem. At this time, we will only be accepting 95 pilots and spouses for physical space limitations, but plan to have an "open house" for everyone on Friday once again at KECP.

[Culver LFA]

Just now, mike_elliott said:

You missed your opportunity to talk personally with Bob Kromer at last months' Mooney Summit III. Bob gave 2 excellent presentations on how to operate your Mooney based on his many hours as a test pilot for Mooney using real data to support his conclusions. We have invited Bob back to once again speak at the next Mooney Summit, Sept29-Oct 2, 2016, hopefully he can once again commit. We will post when Registration opens here on Mooney space, on mooneyevents.com, on www.mooneysummit.com, announce it on the Mooney Flyer,  AOPA, MAPA list and on aviating.com. Hopefully, this will give everyone sufficient heads up to plan and to get registered! I did hear from a few people that "we didn't know about it" last time, and *hopefully* this action will mitigate the problem. At this time, we will only be accepting 95 pilots and spouses for physical space limitations, but plan to have an "open house" for everyone on Friday once again at KECP.

I tried to register but capacity was full, I'll be quicker to do so next time!

Count me in!

[Yetti]

So a summation view is that people climb out based on what they were taught and sometimes add sound to that and pull back the prop RPMs.   What I was hoping to hear was.   a 74 inch prop at 2700 RPM is not at peak efficiency.   It really should be spinning at 2800 or 2850 depending on temperature to be at peak efficiency. Lycoming says the engine is good to 2900 (would not 2900 be a more accurate WOT)   It is only the Type data sheet that limits down to 2700. Even at 3200RPM the tips of the 74 inch prop are not supersonic.  So why does the type data sheet say 2700?

[mike_elliott]

2 minutes ago, Yetti said:

So a summation view is that people climb out based on what they were taught and sometimes add sound to that and pull back the prop RPMs.   What I was hoping to hear was.   a 74 inch prop at 2700 RPM is not at peak efficiency.   It really should be spinning at 2800 or 2850 depending on temperature to be at peak efficiency. Lycoming says the engine is good to 2900 (would not 2900 be a more accurate WOT)   It is only the Type data sheet that limits down to 2700. Even at 3200RPM the tips of the 74 inch prop are not supersonic.  So why does the type data sheet say 2700?

I asked that question to the Hartzell engineers when touring their plant in Piqua once for the prop on my F model and they gave me a deer in the headlight look, but eventually came back and said "your prop is most efficient at 2500 RPM'

[Yetti]

Which is probably what the engineer before him had told him....

 

This could get crazy fun discussion - http://www.avweb.com/news/airman/182418-1.html

 

Anyone have a Mac   http://www.seqair.com/benchmark/

 

 think I remember reading was the Wright Brothers propeller was at 60% efficiency and we have only moved it to say 75% efficient.

[Yetti]

What started this investigation was my transition pilot was concerned about over speed as when leveling out mine will go a little above 2700.  So we checked the Tach with a cheap RC optical tach.  And I have checked it with my phone app. So we agreed the mechanical tach was pretty accurate.  The transition pilot is very good mechanically and pilot wise.   Only when I started reading the documentation do I find out that we are not close to over speeding the Prop or engine.    The Type data sheet is the only thing that says 2700.   Does the TDS say 2700 because of earlier models and it would have required a bunch more flight testing and FAA paperwork to change it? Which is probably the best guess.

[ArtVandelay]

It would be interesting to see the airflow around the propellor. I would have thought faster RPM would be less efficient, ditto for 3 vs 2 blades because of the turbulence from preceding blade rotation, possibly improving with speed. Engine should have less friction losses at lower RPMs as well.

The inner part of blades are always going to be less efficient since they don't generate much air flow. Maybe birds have it right and the next Mooney should have flapping wings.

 

[carusoam]

TopProp data for the 310hp STC indicates 2550rpm as an important spot for cruising...

2400rpm = Eagle1, 2 blade = 244 HP

2500rpm = O1, Mac 3 blade = 280 HP

2700rpm = O3, Hartzell TP = 310 HP

Sea level, rich, Max power, etc.....

In this case, more power, more speed, more fuel burned.  Based on more ignition cycles per minute.

Example using 10k'...

- Some pilots lean to a few °F LOP to maximize % of fuel burned, while converting the maximum fuel to speed.

- Others lean to 50°F LOP to maximize % of fuel burned. Efficient, but 10kts slower.

- Drag decreases exponentially with speed, efficiency measured by nmpg increases by going slower deep LOP. Time to complete the burn in each cycle is improved with lower rpm.

Thus proving the complexity of just USING a prop.

Efficiency of the prop itself has been challenging to collect data for, without specifically picking a FF and alter the rpm through the full range. I think that is what Byron did

Odd limitations to prop efficiency...

- too high rpm, tip speeds, sound and airflow distrurbences at the tips.

- too low rpm, high angle of attack for the prop.

- Deep LOP compresses a lot of air with no real value. In a similar way as a Jake brake/downshifting etc. (examples of drag produced by engines compressing air)

Marketing guys at work...?

- TopProp recommends cruise at 2550 rpm.

- O1s and a Eagles don't have 2550 available to them. Time for an efficiency upgrade!!!  

I think I burned a few hundred extra calories just trying to keep up with your discussion...

Best regards,

-a-

 

[Andy95W]

Unscientific experiment a few days ago:

2500' MSL, lightly loaded M20C, 57°F, level flight

25", 2500 rpm = 160 mph, 12.3 gal/hr 

25", 2700 rpm = 170 mph, 13.5 gal/hr

26.5", 2700 rpm = 177 mph, 14.4 gal/ hr.

Yellow arc starts at 151 mph, so I didn't leave it there very long.

My conclusions:

#1- 200 rpm = about 6% more horsepower and 1 gal/hr 

#2- Holy Crap!  Not bad for 180 HP!  

[carl]

On 11/12/2015, 1:07:05, Shadrach said:

2500rpm makes sense if you want/need to reduce noise. Pulling the throttle back makes no sense at all, though almost every pilot I know that learned to fly in the 50s, 60s and 70s does it. It is not kind to the engine, it is less efficient and gaurantees you spend more time in a place that is...not kind to the engine and less efficient.

My dad used to do this and it drove me insane.  

Ross,

I am thinking; pull the throttle back to 25 inches Manifold Pressure, then the prop back to 25 hundred RPM . 

If I just pull the prop back to 25 hundred rpm and leave the throttle full in  wouldn't the MP be greater then the RPM , a very bad thing, as I was taught.

RPM bigger than MP.

Carl

[Hank]

There's no problem flying over square. Read John Deakin and Mike Busch. I use 23"/2400 for intermediate level offs from 4000-6500 msl. Visit www.mooneypilots.com and read the sample articles written by Bob Kromer, a Mooney test pilot who rose to Engineering President and still works for other airplane manufacturers.

Reducing throttle in the climb only slows your airspeed, slows your climb rate and reduces cooling air to the engine, which leaves all engine temps more elevated for a longer time.

[carl]

HA !

you should study youtube

Flying the Grumman TBF "Avenger" Torpedo Bomber (1944)

HA HA Don't ,

Really , I am more confused each day, . I do feel now if I screw up and "over speed " (Square) than I'm OK at least a little. 

[Hank]

"Over Square" (MP > RPM) is fine. "Over speed" (too many RPMs) is bad.

[Shadrach]

3 hours ago, carl said:

Ross,

I am thinking; pull the throttle back to 25 inches Manifold Pressure, then the prop back to 25 hundred RPM . 

If I just pull the prop back to 25 hundred rpm and leave the throttle full in  wouldn't the MP be greater then the RPM , a very bad thing, as I was taught.

RPM bigger than MP.

Carl

The thing is Carl, you'll never get your plane "on the step" at 25 squared, you need that extra bit of power to achieve the ideal AOA for...I'm just pulling your leg.

The over square thing was taught for decades and probably a relic of the big super charged radials. Indeed if you could run 49" at  1800rpm, you might induce detonation in some engines. Remember though that when all these rules of thumb came out almost no one had a well instrumented engines. Old habits die hard and there are folks that still teach this method. Even the Mooney POH in 67 recommends 26" and 2600 as "climb power". There is no logical reason to do this. There's no logical reason to asphyxiate your engine unless you want less power from it. There are good reasons to reduce RPM, chief among them are noise, vibration and harshness. I don't get too hung up on the precise number as my tach is still on the far right. I ballpark it for 2500 in cruise. I am really looking for smoothness, not a number on the tach.

You might want to read this: http://www.avweb.com/news/pelican/182179-1.html and the rest of the "Where should I run my engine" series. It will change how you view the engine controls and should add significantly to your confidence.

I never touch the throttle after firewalling it for take off unless I want to slow down or go down.

 

 

[Hank]

Ross, why do you reduce power to descend? That's your chance to make up for the slow climb to altitude. I reduce power to slow down for approaches, or when nearing my destination in visual conditions.

after listening to Bob Kromer at the Summit, I'm experimenting running my C with WOT, just can't do that down low on lunch runs.

[Shadrach]

2 hours ago, Hank said:

Ross, why do you reduce power to descend? That's your chance to make up for the slow climb to altitude. I reduce power to slow down for approaches, or when nearing my destination in visual conditions.

after listening to Bob Kromer at the Summit, I'm experimenting running my C with WOT, just can't do that down low on lunch runs.

I was speaking in a general. Cruise descent for me is 195MIAS in smooth air.  I will adjust the throttle if needed to maintain that speed depending on rate of decent.  I keep it under 160MIAS in the bumps.  At some point Hank, one has to reduce throttle if they're going land! 

[Guitarmaster]

http://www.avweb.com/news/airman/184483-1.html

Great article and it makes perfect sense.  I had to think about his comparison to car engines.

I do my own performance tuning on my car, and in doing so, I drastically reduce timing in the high load regions and aggressively advance timing in the low load areas.  While it is great to be able to do this with a car with an ECU, it is not possible with our engines.  We can't reduce the timing in the high load regions, so we compensate by increasing RPM. This has roughly the same effect as reducing timing due to flame propagation.  I think that time and engine monitors have proven many of the long-held beliefs are busted.  Just think about LOP operations.  Not ten years ago, it was a big NO-NO.  Now it has proven to be the best way to operate an engine.  IN fact, I remember when the Malibu came out and Piper told owners to operate it LOP.  Nobody would do it and the engines suffered.  

The automobile engine operates this way all the time (in cruise).  All that being said, I also have a '68 Cougar with a 351 that is tuned manually, and the timing curve, regardless of load, is linear (mechanical advance).  High-load or not, the timing remains the same for a given RPM and varying MAP.  I have yet to hear any detonation in that 400HP motor.

I think the biggest takeaway from the article is, there is little we can do through leaning or power combinations to hurt our very expensive engines if operated at and below 65% (low load).  With an ECU, the engine could be operated at 90% with low RPM. It's irrelevant though.

I too have fallen prey to the OS myth.  I am going OS next time I fly and listen closely to the airplane if it likes it or not.

 

[bonal]

I'm guessing thats a Cleavland not a Windsor 

[Shadrach]

1 hour ago, Guitarmaster said:

http://www.avweb.com/news/airman/184483-1.html

Great article and it makes perfect sense.  I had to think about his comparison to car engines.

I do my own performance tuning on my car, and in doing so, I drastically reduce timing in the high load regions and aggressively advance timing in the low load areas.  While it is great to be able to do this with a car with an ECU, it is not possible with our engines.  We can't reduce the timing in the high load regions, so we compensate by increasing RPM. This has roughly the same effect as reducing timing due to flame propagation.  I think that time and engine monitors have proven many of the long-held beliefs are busted.  Just think about LOP operations.  Not ten years ago, it was a big NO-NO.  Now it has proven to be the best way to operate an engine.  IN fact, I remember when the Malibu came out and Piper told owners to operate it LOP.  Nobody would do it and the engines suffered.  

The automobile engine operates this way all the time (in cruise).  All that being said, I also have a '68 Cougar with a 351 that is tuned manually, and the timing curve, regardless of load, is linear (mechanical advance).  High-load or not, the timing remains the same for a given RPM and varying MAP.  I have yet to hear any detonation in that 400HP motor.

I think the biggest takeaway from the article is, there is little we can do through leaning or power combinations to hurt our very expensive engines if operated at and below 65% (low load).  With an ECU, the engine could be operated at 90% with low RPM. It's irrelevant though.

I too have fallen prey to the OS myth.  I am going OS next time I fly and listen closely to the airplane if it likes it or not.

 

we can do a fair amount with mixture by controlling the speed of the flame front. My IO360 reacts to Low Altitude, High Power LOP quite well.

[Guitarmaster]

On November 14, 2015 at 6:54:39 PM, bonal said:

I'm guessing thats a Cleavland not a Windsor 

I wish... nope, it's a Windsor.