Wide Open Throttle??

[Shadrach]

23 hours ago, varlajo said:

 

Wait, what? 
This violates (almost) everything I've held sacred! At 2500 ft, my SOP would have me fly at 24"/2400 rpm (KN=48), ram air closed, mixture leaned to 6.9 gph, and observing an IAS of 118 kts. Going to try your way tomorrow, but you owe me an engine if it goes boom 

I've been doing it this way for nearly two decades.  It was born out of a regularly scheduled 48NM trip over the river (and the woods) to Grandma's (RIP) house.  My IO360 runs really well LOP at high MP.  At DAs of 3000' or less, I see speeds just over 150kts. There is little to doubt when seeing over 150 across the ground when westbound into a known, light headwind.

[Larry]

I second the suggestion to read John Deakin's articles.  They're informative and entertaining.  

Larry

[N201MKTurbo]

Ya know, if you practice the best advice from this thread and optimize everything to the max it will probably get you to your destination a minute earlier.

[Echo]

Ya know, sometimes if you don't give a crap about a thread it is better to not say anything at all if you can't say something nice.

Have a nice day.   

[jetdriven]

1 hour ago, N201MKTurbo said:

Ya know, if you practice the best advice from this thread and optimize everything to the max it will probably get you to your destination a minute earlier.

Sometimes five minutes earlier, and with the same fuel at destination, so something happened there.

[Shadrach]

13 hours ago, N201MKTurbo said:

Ya know, if you practice the best advice from this thread and optimize everything to the max it will probably get you to your destination a minute earlier.

It’s mostly about reducing workload. Once rpm is set, there is one knob to contend with.  The airport I departed from is fairly busy and is less than 2 mins from the DC SFRA, the expanded area of P40 (Camp David) and lots of Bravo airspace.  The procedure is to level, set rpm and pull mixture until slight speed loss then continue the business of navigating and communicating. Check CHTs once things are settled. If they’re too cool, add a little gas, if they’re warmer than desired, take a little away. 

Less to do than screwing around with “Key numbers” or setting the power at “24 squared” and then leaning.  

It’s simple, marginally faster,  and burns less gas.  

That being said, I don’t begrudge anyone their desire to make setting power more complicated or to simply leave the throttle and mixture in and puke 15gph through it per the POH.

[N201MKTurbo]

4 hours ago, Shadrach said:

It’s mostly about reducing workload. Once rpm is set, there is one knob to contend with.  The airport I departed from is fairly busy and is less than 2 mins from the DC SFRA, the expanded area of P40 (Camp David) and lots of Bravo airspace.  The procedure is to level, set rpm and pull until slight speed loss then continue the business of navigating and communicating. Check CHTs once things are settled. If they’re too cold, add a little gas, if they’re warmer than desired, take a little away. 

Less to do than screwing around with “Key numbers” or setting the power at “24 squared” and then leaning.  

It’s simple, marginally faster,  and burns less gas.  

That being said, I don’t begrudge anyone their desire to make setting power more complicated or to simply leave the throttle and mixture in and puke 15gph through it per the POH.

I do pretty much the same thing. Once I get to altitude, I reduce MP and RPM  to 25, 2400, then pull the mixture till the power falls off, set the MP to 28 and then mixture to 1500 TIT. Then don’t touch the mixture and prop till I park the plane. Unless I need to go around, then I push the throttle up, retrim and put the gear up, then advance the mixture and prop then open the cowl flaps.

 

[Pinecone]

I do a similar thing, accelerate to cruise speed, MP to 29.5, RPM to 2300, Fuel Flow to 10.1 GPH, cowl flaps closed.

That is 63%% power and about 25 degrees LOP.  I can fine tune when I have time.

[Stephan Kablitz]

I regularly take cruise readings from all engine related parameters and put them in a spreadsheet when I have time on a rainy night. When I plot NM/gal vs. Density Altitude I can see running at 2400rpm ist ever so slightly more efficient than running at 2500rpm (NA IO360 in our J). It's not much, but after some smoothing of the slightly erratic raw data shown in the thin lines (I can not always lean exactly to the same ° LOP and the especially the TAS is always fluctuating a little and there is of course some error in all the readings) it still is measurable and it s not the other way around.

 

 

 

Edited October 17, 2024 by Stephan Kablitz

[KSMooniac]

Stephan, what prop do you have?  Since you're in Germany I wonder if you might have an MT (like I do) and might confirm my hunch that MT optimized their props for lower RPM due to noise concerns over there.  

[KSMooniac]

6 hours ago, N201MKTurbo said:

I do pretty much the same thing. Once I get to altitude, I reduce MP and RPM  to 25, 2400, then pull the mixture till the power falls off, set the MP to 28 and then mixture to 1500 TIT. Then don’t touch the mixture and prop till I park the plane. Unless I need to go around, then I push the throttle up, retrim and put the gear up, then advance the mixture and prop then open the cowl flaps.

Rich, can you cruise at 30" MP/WOT with your setup, but perhaps at a lower RPM?  Or does that bump TIT too high?  Nirvana would be turbo and WOT for max efficiency IMO.

[Stephan Kablitz]

Dear Scott, we have the original McCauley 2-blade prop. 

And it seems that in the battle between running at optimum prop rpm and optimum engine rpm, 2400rpm has a very very slight edge.

But then again, to really prove this, one would have to take a ton more measurements, preferably always in the same flights one 2500rpm data point and directly after that a 2400rpm data point to exclude other effects as far as possible. Some of the data points in my list are twin points - and not in every case the 2400rpm point has the higher NM/gal value. And in other cases the gross weight might have been different etc. 

Brgds, Stephan

[A64Pilot]

On 10/15/2024 at 8:18 PM, philiplane said:

camshafts are ground to deliver specific power at a desired rpm. No different than street, RV, or race cams for auto engines. The Lycoming cams are designed to get peak torque at 2450.

Torque is hugely misunderstood, it’s nothing more than the twisting force applied to a crankshaft in this case, but an applied force does no work because there is no movement, that’s where RPM comes in. Power is pretty much Torque x RPM, so therefore very often pretty much always max power isn’t max torque, if in fact the torque peak is 2450, I have no idea but a dyno chart, does anyone have one? A quick google didn’t come up with one and I’d suspect they are common? Problem is in theory max torque may be close to efficiency peak combustion wise, but it doesn’t take into account friction losses or prop efficiency, or airframe drag for that matter, drag is friction of course and reducing friction in all its forms if you have to extend range due to crossing water and running into unforcasted winds for example or just because your a CB and not in a hurry is how to increase range for a piston engine.

2450 may or may not be the engine efficiency peak, but there are other factors in play that overwhelm it.

Long story short years ago I tried reducing prop RPM etc on both turbines and piston engine aircraft adding or reducing throttle to keep airspeed identical and it honestly was in the weeds pretty much no difference in fuel burn, It’s easy go try it yourself, just remember you have to keep airspeed identical for a reasonable comparison. On paper you can easily prove it, but in the airplane it just didn’t make much difference, even LOP didn’t make a big difference, not if I kept the airspeed the same, problem was I flew between 9,000 and 11,000 ft wide open throttle as the airplane was fastest there, in my piston at the RPM that was in the middle of the green band, so yes LOP did save quite a bit of fuel, but it slowed me down quite a bit, if I slowed down to the identical airspeed 50 ROP it worked out to about .2 GPH on my IO-540, now it usually wouldn’t go LOP more than -15 degrees or so so maybe that was part of it, another part is Lycomings recommended 50 ROP isn’t real rich either. That IO-540 for some reason just didn’t like LOP, but my IO-360 seems to thrive on it. The IO-520 in my C-210 liked LOP, but it too slowed down quite a lot too, as I usually wasn’t buying the fuel I ran it full throttle and about 100-150 ROP as it seemed fastest there, I have no idea where it’s best power is

[KSMooniac]

41 minutes ago, Stephan Kablitz said:

Dear Scott, we have the original McCauley 2-blade prop. 

And it seems that in the battle between running at optimum prop rpm and optimum engine rpm, 2400rpm has a very very slight edge.

But then again, to really prove this, one would have to take a ton more measurements, preferably always in the same flights one 2500rpm data point and directly after that a 2400rpm data point to exclude other effects as far as possible. Some of the data points in my list are twin points - and not in every case the 2400rpm point has the higher NM/gal value. And in other cases the gross weight might have been different etc. 

Brgds, Stephan

It's definitely hard to get very precise data but I like your habit of recording points as a normal course of action as eventually a trend will emerge.  I am an aerospace engineer by degree and even took a real flight test engineering course in college, but haven't worked directly in flight test since 1997 as I specialize in structural analysis primarily.  To get to "real" numbers you have to correct for all sorts of things, especially atmospheric, but also instrument errors, weight, and CG.  CG movement has a large influence in Mooney cruise performance, so it might be useful to record the easy things like fuel quantity and cabin load (pax & bags + locations) for CG estimates later when you're crunching your data. 

I think I want to start doing this as well just for fun.  I wish I had done so for years before I have been cleaning-up my '77 J aerodynamically to see if I can measure some real improvements with solid data.  And I'm about to resume flying soon after adding dual electronic ignition and I'm really curious to see if I can measure a performance improvement in LOP cruise.

[N201MKTurbo]

1 hour ago, KSMooniac said:

Rich, can you cruise at 30" MP/WOT with your setup, but perhaps at a lower RPM?  Or does that bump TIT too high?  Nirvana would be turbo and WOT for max efficiency IMO.

WOT is 32 inches. The MP red line is 30 inches. I have tried running it way over square. It started detonating at 29 in and 1900 RPM.

I reduce power with mixture.

[Shadrach]

50 minutes ago, N201MKTurbo said:

WOT is 32 inches. The MP red line is 30 inches. I have tried running it way over square. It started detonating at 29 in and 1900 RPM.

I reduce power with mixture.

Were you trying to test it?  I would expect it to detonate at that setting. 

I have always assumed that MP redlines were based on limiting output to rated horsepower.  It could, under some scenarios, be useful to have the option of running MP >30" while on the lean side of peak allowing for close to max rated power on less fuel. Do you think this would be feasible with your set up?

[wolfbyte]

As someone who doesn't have a fancy engine monitor (I have digital RPM and EGT read outs), what is a good recommendation for an E?

Currently I am aiming for 21" of MP and 2500 RPM around 1350 EGT. Desperately wanting to get a JPI or a 275 so that I can get some true engine monitoring for fuel flow, CHT and EGT combined.

[A64Pilot]

For what’s it’s worth I normally cruise 23 squared down low and leaned to 8 GPH, that is well lean of best BSFC but it gives me 135  kts true. Oddly for reasons that I don’t understand higher altitudes require more fuel flow even at the same MP that gives me 16.7 NMPG down low.

If I want to go slow I run I think it was 21 squared and 6 GPH that gives me 120 kts true that gives me 20 NMPG, Carson’s speed is I think slower but 120 is obnoxious it just feels like her Butt is dragging.

‘Running squared is just from being lazy, but 21 squared LOP has to be done it hot weather or cyl head temps drop out of the green, and I won’t run out of the green, not saying it would hurt if you , but I figure it has a bottom to it for a reason/

For a comparison a Legend Cub cruises I think about 85 MPH at 5 GPH, convert to kts it’s 74 and at 74 kts it’s getting 14.7 NMPG.

‘I know they say they are faster but my C-140 cruises at 100 MPH and it runs away from them. I’m pretty sure though that the 0-200 burns more than 5 GPH too, just used that number because my C-85 burns that, but an O-200 is 15 more HP so I’m sure it burns more.

A C-140 is about the most efficient of the little old airplanes, but it still only gets 17 NMPG, it’s interesting that a four seat Mooney traveling 65 kts faster can get pretty much the same milage as the 140 and better than the Cub

Edited October 17, 2024 by A64Pilot

[A64Pilot]

3 minutes ago, wolfbyte said:

As someone who doesn't have a fancy engine monitor (I have digital RPM and EGT read outs), what is a good recommendation for an E?

Currently I am aiming for 21" of MP and 2500 RPM around 1350 EGT. Desperately wanting to get a JPI or a 275 so that I can get some true engine monitoring for fuel flow, CHT and EGT combined.

If you want to lean do so at well less than 75% power and go way lean. I don’t have a monitor either and run LOP pretty much exclusively, but then I stay at low power too and run real lean. I peak usually at 800 C and run it at least -25C lean, but often -50 C lean

[Will.iam]

2 hours ago, A64Pilot said:

as I usually wasn’t buying the fuel I ran it full throttle and about 100-150 ROP as it seemed fastest there, I have no idea where it’s best power is

You answered your own question best power is at exactly best speed. In your case 100-150ROP. 

[Andy95W]

42 minutes ago, wolfbyte said:

As someone who doesn't have a fancy engine monitor (I have digital RPM and EGT read outs), what is a good recommendation for an E?

Currently I am aiming for 21" of MP and 2500 RPM around 1350 EGT. Desperately wanting to get a JPI or a 275 so that I can get some true engine monitoring for fuel flow, CHT and EGT combined.

Most people like the JPI 730 (basic), 830 (w/rpm&MP), or 930 (everything and legal replacement for all instruments).

Another nice choice seems to be the Garmin 275 EIS, also legal replacement of all gauges.

[Will.iam]

42 minutes ago, wolfbyte said:

As someone who doesn't have a fancy engine monitor (I have digital RPM and EGT read outs), what is a good recommendation for an E?

Currently I am aiming for 21" of MP and 2500 RPM around 1350 EGT. Desperately wanting to get a JPI or a 275 so that I can get some true engine monitoring for fuel flow, CHT and EGT combined.

Egt doesn’t matter it all about CHT. Any setting that keeps all CHT at or below 380 degrees continental 400 degrees lycoming will last longer than engines ran with their CHT above these limits. And the further above these limits you go the more you are shorting the life of that cylinder. 

[Shadrach]

37 minutes ago, Andy95W said:

Most people like the JPI 730 (basic), 830 (w/rpm&MP), or 930 (everything and legal replacement for all instruments).

Another nice choice seems to be the Garmin 275 EIS, also legal replacement of all gauges.

I like everything about the 730/830 except the fuel totalizer functions, the UI sucks.

[KSMooniac]

1 hour ago, wolfbyte said:

As someone who doesn't have a fancy engine monitor (I have digital RPM and EGT read outs), what is a good recommendation for an E?

Currently I am aiming for 21" of MP and 2500 RPM around 1350 EGT. Desperately wanting to get a JPI or a 275 so that I can get some true engine monitoring for fuel flow, CHT and EGT combined.

9 years ago I installed the JPI EDM-900 to replace the -700 that came with my plane.  I would chose it again today, and plan to retain it whenever I install a big PFD someday as I feel it is the best on the market.  -930 is very nice, but too large to put on the pilot side of most Mooney panels, which is a strong requirement for me.  I removed all of the legacy engine instruments and don't regret it a bit.  The form factor is just the right size to integrate into legacy Mooney panels without too much pain and anguish.

Installation effort for any primary engine monitor is substantial, but it offers an opportunity for sweat equity if you're DIY-inclined.  Most of the labor is tedious work to route the harnesses, remove interior panels, etc. so you can save some money working it yourself if you're installer is willing to work with you.  If you pay a shop to do the whole thing and they know what they're doing, it should be in the ballpark of 40 hours of labor.  I likely spent 60 b/c I'm slow and inefficient. 

[A64Pilot]

59 minutes ago, Will.iam said:

You answered your own question best power is at exactly best speed. In your case 100-150ROP. 

Yes and no. Best power is of course just that, one exact number, any other number will be less power, but on the rich side there is very little reduction in power until way past best power. I think at 150 I was rich of it but speed didn’t suffer and oddly I had zero plug fouling issues too.

At lower altitudes I ran it at 25 squared. From memory it would turn 2850 RPM which made 300 HP out of a 520, 285 continuous but it had a 5 min time limit at 300  so I would roll it back to 2700 after wheels up climb at 2700, cruise at 2500, never touching the throttle until I got to where I was going. I rarely made short flights in it. Really easy airplane to manage