Is my Mooney slow?

[AndreiC]

I have been curious if my 1970 E-model is on the slow side, or if I am seeing pretty much the speed to be expected (whatever it is, I don’t think mine is particularly fast). So I am asking you guys to take a guess what kind of TAS I should expect for a long upcoming flight (around 16 hours round trip).

My plane has a couple of things running against it — three blade prop, and the less clean wings (fewer flush rivets) than the earlier models. On the plus side the engine is relatively new (about 600 SMOH and 300 since new cylinders), and it has the LASAR guppy mouth closure (but not the more modern J-style). Pretty much no other speed mods to speak of.

I plan to fly it at 8500’, WOT, LOP 65% (8.6 gph), 2400 or 2500 RPM. Will you please take a guess what TAS I should see in these conditions at the two RPM settings above?

[N201MKTurbo]

When I had an M20F, it went about 145 KTS in cruise. After I had it for quite a while, I added a cowl closure and adjusted the rigging and It would do 152 KTS. I never ran it LOP.

[AndreiC]

4 minutes ago, N201MKTurbo said:

When I had an M20F, it went about 145 KTS in cruise. After I had it for quite a while, I added a cowl closure and adjusted the rigging and It would do 152 KTS. I never ran it LOP.

At what kind of fuel burn did you see these speeds? I can see 145 KTS at around 9.4gph (just at peak), but to get to 152 KTS I need to add a lot more fuel, closer to 12 gph (ROP).

[N201MKTurbo]

I always planned for 10 GPH. and it was pretty close. I didn't have a FF in that airplane. I usually flew at 8500/9500 WOT and either 2500 or 2400.

[Hank]

50 minutes ago, AndreiC said:

I plan to fly it at 8500’, WOT, LOP 65% (8.6 gph), 2400 or 2500 RPM. Will you please take a guess what TAS I should see in these conditions at the two RPM settings above?

My C is the same as your E, less fuel injection and 20hp.

At 9500 msl, WOT- & 2500, I generally get 145-148 ktas, but I fly ROP.

Let us know how you do!

[McMooney]

1974 E WITH Top Prop,  i get between 140 to 145ktas  8000@ 23in/2300rpm.  if i hvae something to give me a more rear-ward cg, she'll approach 150

this is LOP something like 8.9 gph

 

Edited August 16 by McMooney

[A64Pilot]

Assuming you can get 8.6GPH at 8500 and be LOP, then you will be at 65% power. I don’t think I can, but then I likely am at a higher temp so 8500 MSL is likely a higher DA than where you are.

However if everything is equal, you will burn slightly more fuel and therefore develop slightly more power and therefore go slightly faster at 2500 RPM than 2400 RPM.

However if you lean more at higher RPM to keep the fuel burn the same, then you will go slightly slower due to power being the same, but increased friction of both the engine and prop. Higher RPM only increases speed due to higher power output, but higher RPM is slightly less efficient due to greater frictional losses, again small numbers, not much difference.

WOT is slightly more efficient than partial throttle due to lower pumping losses, no vacuum.

We aren’t talking big numbers here, a kt or two.

If I were to guess I’d guess your airplane is lighter than a newer aircraft as most often newer aircraft weigh more than earlier ones and that lower weight will offset any additional drag you may have from more button head rivets etc.

Loading any heavy baggage in the rear etc to push the CG back as long as your well within acceptable range seems to do as much to increase speed as many of the speed mods.

LOP really hurts speed, but of course does increase MPG, a significant amount of that better MPG comes from lower speed, but whatever, LOP does increase MPG.

 

[wombat]

9 minutes ago, A64Pilot said:

LOP really hurts speed

 

LOP only hurts speed compared to a higher power setting.  At the same amount of produced power, you will get the same speed.

If you consider MP the measure of power you'll get lower speeds running LOP because you need a higher MP (and/or RPM) in order to achieve the same power output when running LOP.

Some people cruise ROP at power settings that they cannot achieve LOP at, so you'd have to choose a lower power setting to fly LOP, and in that case you'd fly slower.

If you consider fuel burn to be your power setting, you will fly faster LOP than ROP, since LOP has a higher BSFC.  Of course you can pick LOP and ROP settings where this isn't true, like extreme LOP is actually less efficient than barely ROP, but in general, LOP is going to be more efficient, and therefore you'll be faster LOP than if you are burning the same amount of fuel ROP.

[A64Pilot]

31 minutes ago, wombat said:

LOP only hurts speed compared to a higher power setting.  At the same amount of produced power, you will get the same speed.

If you consider MP the measure of power you'll get lower speeds running LOP because you need a higher MP (and/or RPM) in order to achieve the same power output when running LOP.

Some people cruise ROP at power settings that they cannot achieve LOP at, so you'd have to choose a lower power setting to fly LOP, and in that case you'd fly slower.

If you consider fuel burn to be your power setting, you will fly faster LOP than ROP, since LOP has a higher BSFC.  Of course you can pick LOP and ROP settings where this isn't true, like extreme LOP is actually less efficient than barely ROP, but in general, LOP is going to be more efficient, and therefore you'll be faster LOP than if you are burning the same amount of fuel ROP.

Your mixing analogies, picking cases to support you assertion that LOP is “better”

Let’s use the case the OP posted about to start this thread.

”I’ll be flying WOT at 8500 LOP”

He will be flying slower than if he was ROP, yes he will be getting better MPG, I stated that, but at a slower speed, IF speed was more important than MPG, then you go ROP, burn the fuel and go faster. He was asking about what A/S he will get so speed is at least an interest.

Most of us cruise at higher altitudes when flying significant distances, most of us do so WOT, because even WOT we are most likely below 75% power, so if speed is most important, then ROP is the way to go, if efficiency is sought, then LOP, AND slow down will get you there with the least fuel burned. So most of us cannot fly at the same power setting LOP that we can ROP

Sometimes depending on length of the leg being flown, slowing down and LOP can get you there faster, because if ROP you would have to stop for fuel, while LOP and slower you won’t. It’s not common but worth flight planning to see.

There is no one “best” mixture to fly, I have nothing against LOP, probably 90% or better of my flying is LOP, because I’m Retired and not usually in a hurry, but if I am I know to screw the mixture knob in until I’m 100F ROP, the increase in speed is significant, but of course so is the fuel burn.

It’s a pretty safe statement to make that LOP makes less power than ROP.

[Echo]

Data Point

 

[Echo]

What a guy on youtube logged:

[Echo]

I have a J cowl.  No ram air.  Interesting I can achieve same MP as he achieved without ram air.  Efficiency of J intake (that eliminates benefit of ram air and the dreaded accordian rubber baffle).   The half gallon an hour saved is not important to me.  I would rather fly faster.  

Edited August 16 by Echo

[Echo]

I fly at 2500RPM vs. his 2400.  Cylinders are all fine for temps.

[Echo]

At 8500 on return

 

[A64Pilot]

Some numbers I see on the internet I’ve come to think that IAS must mean Internet Airspeed, because my J can’t get there.

[Echo]

2 minutes ago, A64Pilot said:

Some numbers I see on the internet I’ve come to think that IAS must mean Internet Airspeed, because my J can’t get there.

He had a video.  Shot a photo of airspeed, Temp etc.  Maybe your plane is slow?

[A64Pilot]

7 minutes ago, Echo said:

He had a video.  Shot a photo of airspeed, Temp etc.  Maybe your plane is slow?

21.6 MPG at 150 kts?

No I can’t even come close to that,  For me to get 20 NMPG I have to be around 120 indicated and of course LOP and RPM pulled way back. Been awhile but I think I was 21 squared.

Or said another way I can’t true out at 150 Kts at 8 GPH, can you?

Even if he was using Statue Miles it’s tough to get his numbers.

I can give you a video of 196 kts indicated at 23 squared, doesn’t mean I can cruise that.

[Echo]

3 minutes ago, A64Pilot said:

21.6 MPG at 150 kts?

No I can’t even come close to that,  For me to get 20 NMPG I have to be around 120 indicated and of course LOP and RPM pulled way back. Been awhile but I think I was 21 squared.

Or said another way I can’t true out at 150 Kts at 8 GPH, can you?

Even if he was using Statue Miles it’s tough to get his numbers.

I can give you a video of 196 kts indicated at 23 squared, doesn’t mean I can cruise that.

I was teasing.  Yes I agree that the MPG and airspeed seem not "doable".  That was a hell of a tailwind.  I could not do 196 knots in the Missile.  I got an extra 3 knots out of an extra 100 rpm.   I was ten degrees warmer. (vs his calculations).  Me with no ram air.

[A64Pilot]

1 minute ago, Echo said:

I was teasing.  Yes I agree that the MPG and airspeed seem not "doable".  That was a hell of a tailwind.  I could not do 196 knots in the Missile.  I got an extra 3 knots out of an extra 100 rpm.   I was ten degrees warmer. (vs his calculations).  Me with no ram air.

Push the nose down, I promise you will see 196 kts.

1989 I think it was I was getting my fixed wing Commercial / Instrument. I was just getting into their M20AT’s. The procedure in the other aircraft when in cruise was to leave throttle in, but to trim for a 500 FPM rate of descent at twice the number of minutes per thousand feet you had to lose, meaning if you had to lose 5,000 ft, start descent a little more than 10 min from destination. We always flew ROP as it was 1989 and that’s what the school wanted.

Anyway first time I was by myself and did this in the Mooney I noticed after a few minutes that I was creeping past VNE, which hadn’t been an issue in the Pipers or 152’s etc.

[MikeOH]

In my M20F I see 143 kts TAS at 8500 WOT 2500 rpm 9 gph (67% LOP)

[Echo]

8 minutes ago, MikeOH said:

In my M20F I see 143 kts TAS at 8500 WOT 2500 rpm 9 gph (67% LOP)

I think that is VERY respectable.  Worth $5.50 an hour for me to see ten additional knots.  I wonder what yours would do burning an extra gph?

Edited August 16 by Echo

[Echo]

My plane can NOT go much below 9gph WOT without running rough.

[MikeOH]

8 minutes ago, Echo said:

My plane can NOT go much below 9gph WOT without running rough.

Hmm, that doesn't seem right.  I can keep pulling the mixture until the engine pretty much quits making any power without any roughness.  Have you done the GAMI test to see how balanced your injectors are?

[MikeOH]

18 minutes ago, Echo said:

I think that is VERY respectable.  Worth $5.50 an hour for me to see ten additional knots.  I wonder what yours would do burning an extra gph?

I do have most of the 'speed mods': LASAR cowl closure, 201 windscreen, flap/aileron/elevator gap seals, dorsal fin mod...

It's been awhile so my memory isn't exact on this, but I ran 'balls to the wall' at around 2500 feet and saw around 150 kts; again, best that I recall.

[Ragsf15e]

5 hours ago, AndreiC said:

I have been curious if my 1970 E-model is on the slow side, or if I am seeing pretty much the speed to be expected (whatever it is, I don’t think mine is particularly fast). So I am asking you guys to take a guess what kind of TAS I should expect for a long upcoming flight (around 16 hours round trip).

My plane has a couple of things running against it — three blade prop, and the less clean wings (fewer flush rivets) than the earlier models. On the plus side the engine is relatively new (about 600 SMOH and 300 since new cylinders), and it has the LASAR guppy mouth closure (but not the more modern J-style). Pretty much no other speed mods to speak of.

I plan to fly it at 8500’, WOT, LOP 65% (8.6 gph), 2400 or 2500 RPM. Will you please take a guess what TAS I should see in these conditions at the two RPM settings above?

I run this same profile as you in my very similar’68F model a lot, so I think ill get close, but your CG and weight will matter a lot!  I commonly do a 4 hour xc with kids, wife, baggage, etc and we take off close to mgw.  Over 4 hours, we burn ~36 gallons (220lbs) of fuel and the airplane is noticeably faster (maybe 3 knots).  So let’s say I level off at mgw, LOP (for me, at 65%, that’s barely lop, maybe 5-10 degrees past peak).  8.6 ff seems a little low but will depend on temp too.  Id see about 139 knots tas.  By the end of the flight, I’d see 142.  Rop, id see 4 knots faster.  Same prop, lasar cowl, 201 windscreen, mid time engine, surefly mag (which did improve lop power).

Id bet your E should beat me by ~3 kts just based on its lower mgw.

Edited August 16 by Ragsf15e