My plane *is* slow! Please help.

[AndreiC]

I have done lots of tests, and I decided my 1970 M20E is slower than it should be, and I need to do something about it. 

Please let me know what things you have done that got you back some of the lost speed. Things like rigging (what did you do?), remove antennas, etc. I don’t want to think about installing speed mods now; what I want is for my plane to do as well as it can with what it has. 

Specs: pretty much stock, except for the 3 blade McCaulay prop (non-scimitar) and the LASAR guppy mouth closure which helps with cooling but not with speed. Plane has been waxed and cleaned and as shiny

Why have I decided it’s slow? Today I did the following test run in smooth air: 8500 ft altitude, 30.13” altimeter, ISA+15, WOT+RAO (22.5” MP), 2500 rpm. Mixture leaned to peak, 9.4 gph, 70.5% power. Using the 3-way GPS measurements it turns out I was cruising at 143 knots (or 164 mph).  Plane was light, close to 2200 lbs  or even lighter.

My POH says that at 10000 feet DA (which with ISA+15 this is a good approximation), at 70.1% engine power, I should have been cruising at 156 kts (179 mph).

This is not a small difference, it’s 13 knots! People spend a lot of money for mods that would give then that… I want what’s mine for free

Thanks all. 

[redbaron1982]

I think your numbers are not bad at all. 

Getting the same numbers as in the POH means a perfectly rigged airplane, an engine that is producing full rated power, new/smooth paint, etc. 

Also, my understanding is that 3 blades are quieter and have better climb performance, but slower cruise. 

Finally, being light doesn't mean faster. Most likely your CG was closer to the fwd limit which means the elevator needs to generate more lift to keep the nose up, which means more drag. 

 

[AndreiC]

Just now, redbaron1982 said:

I think your numbers are not bad at all. 

Getting the same numbers as in the POH means a perfectly rigged airplane, an engine that is producing full rated power, new/smooth paint, etc. 

Also, my understanding is that 3 blades are quieter and have better climb performance, but slower cruise. 

Finally, being light doesn't mean faster. Most likely your CG was closer to the fwd limit which means the elevator needs to generate more lift to keep the nose up, which means more drag. 

 

Yes, but 13 knots? That’s almost a 10% loss!

[201er]

40 minutes ago, AndreiC said:

People spend a lot of money for mods that would give then that… I want what’s mine for free

Wash and wax religiously. Lose some weight. First on the plane. Anything you don’t need. Then on yourself. If you don’t want speed mods or to be spending a lot of money, that’s where it’s at.

[KSMooniac]

CG location has a lot to do with Mooney cruise performance, and I expect that HEAVY prop is hurting you with the extra drag of the 3rd blade, and especially the weight.  You might try to duplicate your test point as close as you can in terms of total weight, but put a few gallons of water in the back of the baggage area and offset the weight with less fuel.  (All of the metal 3-blade STC props for vintage Mooneys are the same diameter as the stock 2-blade ones, so they are not quieter, just heavier and slower.)

Other things to check while on jacks are the rigging of all of the gear doors, cabin door, and baggage door.  Make sure they close tight and leave no gaps.  If you have access to the rigging boards, you can check your flap positions and make sure they're not droopy, or asymmetric.  Does your plane fly hands-off with the ball centered?  

I doubt you'll ever find a bone-stock E that cruises at 156 KTAS, so don't set that as your goal. 

[AndreiC]

How would losing weight have helped here? I calculated now, and I was 450 lbs under MGW!

[Ragsf15e]

You might have some slight issues but they aren’t gross.  My F would have done the same speed there with the same Mcauley prop.  I would check the flap rigging and gear rigging but don’t expect all 13kts back.  Weight and cg and ~7k DA AT 100 ROP will get you a higher TAS.

[AJ88V]

Well, you know the brake rotation is only $200 and it's worth at least 5 knots.

[Hank]

32 minutes ago, AJ88V said:

Well, you know the brake rotation is only $200 

It's an STC, plus labor. Is it available from LASAR since they moved?

[PeteMc]

1 hour ago, AndreiC said:

My POH says that at 10000 feet DA (which with ISA+15 this is a good approximation), at 70.1% engine power, I should have been cruising at 156 kts (179 mph).

Are you sure your engine is putting out what it should.  You said you were WOT, so the MP gauge isn't the issue.  but what about your Tach?  Were you really at the required RPMs to get that 70.1% power you thought you were flying at? 

And I'm sure the engine folks here have other checks (compression, etc.) to confirm if  you're really operating at the Power you think you are.

 

[LANCECASPER]

1 hour ago, AndreiC said:

Specs: pretty much stock, except for the 3 blade McCaulay prop (non-scimitar) and the LASAR guppy mouth closure which helps with cooling but not with speed. Plane has been waxed and cleaned and as shiny

My POH says that at 10000 feet DA (which with ISA+15 this is a good approximation), at 70.1% engine power, I should have been cruising at 156 kts (179 mph).

This is not a small difference, it’s 13 knots! People spend a lot of money for mods that would give then that… I want what’s mine for free

First thing I would do is take it to someone who really knows whether your Mooney is in rig and flying straight.

After that I would blame some cruise speed loss on your three blade prop - 3 to 5 knots. Then figure out if you want to give up the looks and the climb performance of the 3 blade prop for a better cruise 2 blade prop.

Finally it's your expectation - when your airplane was being built there was a lot of competition in General Aviation: Cessna, Piper, Beechcraft, Grumman, etc, etc. were all competing for sales. Very few airplanes that ever left any of these factories did what the POH said they would do. Expecting POH numbers for airplanes built in the 60's-80's leads to some disappointment. (Example: How many 201's did 201mph? Same goes for the 231 and 252? It was kind of understood that those were marketing numbers not what you were going to actually see.)

[Hank]

12 minutes ago, LANCECASPER said:

First thing I would do is take it to someone who really knows whether your Mooney is in rig and flying straight.

After that I would blame some cruise speed loss on your three blade prop - 3 to 5 knots. Then figure out if you want to give up the looks and the climb performance of the 3 blade prop for a better cruise 2 blade prop.

Finally it's your expectation - when your airplane was being built there was a lot of competition in General Aviation: Cessna, Piper, Beechcraft, Grumman, etc, etc. were all competing for sales. Very few airplanes that ever left any of these factories did what the POH said they would do. Expecting POH numbers for airplanes built in the 60's-80's leads to some disappointment. (Example: How many 201's did 201mph? Same goes for the 231 and 252? It was kind of understood that those were marketing numbers not what you were going to actually see.)

My 1970 C, same age as the OP's E, makes book speed (165 mph) at 1000 msl on a fall morning, with a Hartzell 3-blade prop.

[varlajo]

Between 5500-11500 ft, WOT and 2400 rpm, my 71E makes approx. 95% of POH TAS 100 ROP and approx. 85% POH TAS 50 LOP (where I run it).

100% stock.

Edited September 11, 2024 by varlajo

[Bart Chilcott]

Your three blade is responsible for a portion, if not all of your slow issues.  My M20E consistently shows 154 KTS TAS above 8500’.    IO 360 A1A, two bladed Hartzel scimitar. No speed mods. 

Edited September 11, 2024 by Bart Chilcott

[201er]

@jetdriven tried everything possible with his ‘77 201 and documented the speed differences. Blade antennas, composite gear doors, cowl strengthening, rigging, engine overhaul, body filler, paint, and lots of smaller stuff. Might do you some good to ask him what repairs, mods, and improvements were the best bang for the buck. All in, he got it back to book value and can actually make 201mph.

If you’re in the northeast, you could pay him a visit and have him do it for you.

I used to cruise my ‘78 201 140-145ktas on 8-9gph. Now I do 150-155 on same fuel and can push 160-170 plowing hard. That’s after all speed mods, engine, paint, repair, and improvements.

[gacoon]

Have tach and manifold gage calibrated, old plane, old instruments.

[Shadrach]

2 hours ago, AndreiC said:

How would losing weight have helped here? I calculated now, and I was 450 lbs under MGW!

Right. So likely forward CG. Forward CG require nose up elevator trim. Nose up elevator trim = additional induced drag.

[AJ88V]

2 hours ago, Hank said:

It's an STC, plus labor. Is it available from LASAR since they moved?

We’ll, I was just joking, but, since you asked, $52 plus labor

https://lasar.com/stc-kits/laskit103

[AndreiC]

To answer some of the comments. I did a careful W&B calculation, and my CG was smack in the middle of the acceptable envelope. (2133 lbs, 96.19 moment.) So, no, the CG was not far forward. I will try next time to add about 30 lbs of water jugs in the back of the plane, and we'll see how that goes, but it is a bit artificial.

I have a digital tachometer, and the MP gauge was repaired and calibrated less than a year ago. I trust them.

Other suggestions of what to try? Engine is 600 SMOH, with new cylinders about 250 hours ago, runs like a top. 

[Parker_Woodruff]

Ditch the 3-blade prop for a 2-blade Hartzell Top Prop.  You'll probably also lose some vibration.

Clean the plane - clean leading edges are worth a couple knots (seriously).

Check rigging of all control surfaces using the Mooney rigging tools.

Check gear as @KSMooniac said

 

[KSMooniac]

23 minutes ago, AndreiC said:

To answer some of the comments. I did a careful W&B calculation, and my CG was smack in the middle of the acceptable envelope. (2133 lbs, 96.19 moment.) So, no, the CG was not far forward. I will try next time to add about 30 lbs of water jugs in the back of the plane, and we'll see how that goes, but it is a bit artificial.

I have a digital tachometer, and the MP gauge was repaired and calibrated less than a year ago. I trust them.

Other suggestions of what to try? Engine is 600 SMOH, with new cylinders about 250 hours ago, runs like a top. 

Why were the cylinders replaced?  Was the camshaft inspected at that time?  Has it sat since then?  If you suspect a power issue, you could be losing a lobe on the cam and not opening your valves fully.  You can measure this at the rockers with the covers off and a dial indicator and appropriate fixturing.  I had that suspicion in 2013 and found that my #1 & #2 intake cam lobe was measurably worn so I had to overhaul at that point.  But that engine had 22 years and 2150 SMOH at that point too.  The engine was running very smoothly at that point too.

[AndreiC]

27 minutes ago, KSMooniac said:

Why were the cylinders replaced?  Was the camshaft inspected at that time?  Has it sat since then?  If you suspect a power issue, you could be losing a lobe on the cam and not opening your valves fully.  You can measure this at the rockers with the covers off and a dial indicator and appropriate fixturing.  I had that suspicion in 2013 and found that my #1 & #2 intake cam lobe was measurably worn so I had to overhaul at that point.  But that engine had 22 years and 2150 SMOH at that point too.  The engine was running very smoothly at that point too.

The plane has flown regularly > 50 hours per year (last year I flew it 120 hours) for the past 7-8 years, since the engine was OH'ed by Penn Yan with new cam. The cylinders were replaced by the previous owner with new Lycoming cylinders due to a diagnosis of "rough running". My mechanic, when seeing this logbook entry, suspected that they may have had sticking valves and he was surprised that they did not try to hone the guides and instead elected to replace all 4 cylinders. But I guess if money was no object at that time... I have no reason to suspect a power issue, the plane climbs very well and performs excellent in all respects, short of the cruise speed.

[AndreiC]

45 minutes ago, Parker_Woodruff said:

Ditch the 3-blade prop for a 2-blade Hartzell Top Prop.  You'll probably also lose some vibration.

Clean the plane - clean leading edges are worth a couple knots (seriously).

Check rigging of all control surfaces using the Mooney rigging tools.

Check gear as @KSMooniac said

 

As I said earlier, I am hoping to get as much as can from what I have now. I don't have the money to replace a perfectly good prop for a couple of knots. If at the end of all investigations it turns out the prop is costing me all this speed loss, so be it. 

The plane was perfectly clean, with smooth leading edges.

I will see if my mechanic can borrow the Mooney rigging tools, to check the controls, at the annual. I'll also get the gear checked.

[0TreeLemur]

At 8500 ft and 70F ROP my m20j cruises at 155 burning 10.3 gph.  If I lean to 10F LOP it burns 8.3gph and cruises at 145.   LOP ops cost me 10 knots WTH 20% fuel burn savings.   Others have reported similar performance hits running LOP.  You will only approach Poh numbers ROP.   You gotta produce something close to max power.

 

[AndreiC]

1 hour ago, 0TreeLemur said:

At 8500 ft and 70F ROP my m20j cruises at 155 burning 10.3 gph.  If I lean to 10F LOP it burns 8.3gph and cruises at 145.   LOP ops cost me 10 knots WTH 20% fuel burn savings.   Others have reported similar performance hits running LOP.  You will only approach Poh numbers ROP.   You gotta produce something close to max power.

 

For these numbers, how close to standard atmosphere (ISA) were you? (I see you're in AL, so you may be much hotter than ISA.)

I am puzzled by the fact that with basically the same engine (IO360-A1A) I am nowhere near 70F ROP with 10.3 gph. I know my fuel calibration is accurate, because when I fill up the tanks it is within less than one gallon. Yesterday I was at 8500 ft but ISA+15 (so closer to 10500 DA), and at peak I was at 9.4 gph. To get to 70F ROP I probably would have needed at least 11-11.5gph.