My plane *is* slow! Please help.

[Slick Nick]

On 9/11/2024 at 9:01 AM, AndreiC 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.

It’s the prop that’s killing your speed though. You’re pretty much getting what you should be with that prop out front. They make a huge difference in cruise speed, depending on the profile, which is why they aren’t that popular on the 4 cylinder Mooneys to begin with. Never mind the whole “3 blade prop on a 4 cylinder engine” harmonics argument, that’s another story. 

[Echo]

Going rich of peak up high is a pretty cheap speed mod.  Without mods THAT s what you should do if you want more speed.  See what you get.  Your plane is NOT slow.  It IS a Mooney after all.  Enjoy.

[Kelpro999]

Throw a large bag of dog food in luggage area , that’ll wake up that pup.

[AJ88V]

On 9/11/2024 at 11:01 AM, AndreiC 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.

This is a wise and mature attitude.  All Mooney owners want more speed and in the practical sense, it's ultimately about bragging rights.  What you have is a lovely plane that delivers more knots per horsepower and more nm per gallon than just about anything else in the air, and you're doing it at a bargain price to boot!  Enjoy!

[Ragsf15e]

On 9/11/2024 at 10:19 AM, AndreiC said:

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.

Your ff of 11-11.5 to be ~100rop at 8500’ would match mine.  Heck, it might be 11.5-12 there if he’s at isa.

Running at peak is fine if you’re running low enough power, but if you’re trying to maximize speed, you’re going to have to be rop to get maximum power.

[Shadrach]

53 minutes ago, Ragsf15e said:

Your ff of 11-11.5 to be ~100rop at 8500’ would match mine.  Heck, it might be 11.5-12 there if he’s at isa.

Running at peak is fine if you’re running low enough power, but if you’re trying to maximize speed, you’re going to have to be rop to get maximum power.

I would submit that running at peak is OK at most cruise MP and RPM settings, provided you use the richest cylinder. The approximately 5% delta in power between peak and ROP just is not that large. 

Assuming the WOTRAO and 2500, 11.5 seems high at the 10.5K DA  @AndreiC describes. According to book power charts. At 2500, 2600rpm is no setting 100ROP setting at ISA 10,000' that consumes 11gph much less 11.5gph.  At 2700rpm and 100ROP, fuel flow would be around 11GPH...interpolated from the POH.

[Ragsf15e]

1 hour ago, Shadrach said:

I would submit that running at peak is OK at most cruise MP and RPM settings, provided you use the richest cylinder. The approximately 5% delta in power between peak and ROP just is not that large. 

Assuming the WOTRAO and 2500, 11.5 seems high at the 10.5K DA  @AndreiC describes. According to book power charts. At 2500, 2600rpm is no setting 100ROP setting at ISA 10,000' that consumes 11gph much less 11.5gph.  At 2700rpm and 100ROP, fuel flow would be around 11GPH...interpolated from the POH.

Yes, but @AndreiC and I were replying to @0TreeLemur saying that 10.3gph was around 70rop at 8500.  In my experience, my ff is higher than that there.  Maybe if it’s very hot?

[AndreiC]

1 hour ago, Shadrach said:

I would submit that running at peak is OK at most cruise MP and RPM settings, provided you use the richest cylinder. The approximately 5% delta in power between peak and ROP just is not that large. 

Assuming the WOTRAO and 2500, 11.5 seems high at the 10.5K DA  @AndreiC describes. According to book power charts. At 2500, 2600rpm is no setting 100ROP setting at ISA 10,000' that consumes 11gph much less 11.5gph.  At 2700rpm and 100ROP, fuel flow would be around 11GPH...interpolated from the POH.

This is what has been puzzling me too. Maybe the key words here are "provided you use the richest cylinder". I have been leaning using my EDM 700, stopping when the first EGT peaks. This (I guess) means that I am using the *leanest* not the richest cylinder. I hope operating this way has not damaged something in my engine (I always run well below 75%, closer to 70% or 65%). But next time I go I will try to use the richest cylinder for leaning to peak. 

Question: when going for 100 ROP, do you use the richest or leanest cylinder for reference?

[201er]

28 minutes ago, AndreiC said:

Question: when going for 100 ROP, do you use the richest or leanest cylinder for reference?

Depends on what your purpose is! If you're trying to go as fast as possible, gonna want to be around 80-100 ROP on the median cylinders (like 70, 90, 100, 120). That will probably give you the best possible power. But, it will also get quite hot. If you're trying to conserve cylinders, you'll probably want to be at least 100ROP on the leanest cylinder and richer on the others. You may not even be able to accept 100 ROP and need to go even richer (on leanest) to keep the CHTs below 380.

[KSMooniac]

If flying ROP, you want to use your LEANEST cylinder as the reference point, so that all of your cylinders are richer than the first to peak when leaning from the rich side, then enrichening to whatever setting you're trying to use.  If you confuse this, you might think you're setting 100 ROP, but one or more jugs might end up at 60 ROP which is a bad setting if running more than 65 or 70% power.  use the leanest cylinder as a reference, and you might end up with 100, 110, 120, 130 on all of them... much better.

The converse is true... when running LOP, you want to reference the RICHEST cylinder so that all of the others are safely leaner than your reference cylinder.  The bad situation here if you mix it up is that you set a cylinder at 20 LOP, but you used the leanest cylinder and you'll end up operating one or more at 20 ROP, which is a horrible place to be if running more than 65% power.

For those with IO-360 engines, I'd encourage everyone to chase down all induction leaks and try to get the fuel:air ratios balanced across all 4 cylinders.  the Lycoming IO-360 can be very well balanced, even without GAMIjectors.  I figured out my richest and leanest cylinders and swapped injectors (after verifying no induction leaks) and got my GAMI spread down to 0.0.

[Will.iam]

If you do have a cylinder in the red zone and at 75% you will know it soon enough as that cylinder will be climbing up past 400cht. If you richen or lean enough to get all the cylinders below 400 (lycoming 380 continental) you will see a fuel flow will also be outside the red box area. In very cold temps in winter drop your limit another 20 degree to be safe. 

[AndreiC]

Even in climbs I do not see CHT’s over 370, so I hope my misadventures did not damage anything. But thanks for the advice, I will keep it in mind. (My concern was that as I now understand it, by running at peak but using the leanest cylinder as reference, ai may have been running with a few cylinders 20 ROP, which is bad.) I’ll adjust my leaning procedure. 

My EDM-700 reports a difference of about  50F between the highest and lowest EGT. Is this what the GAMI spread is?

[KSMooniac]

24 minutes ago, AndreiC said:

 

My EDM-700 reports a difference of about  50F between the highest and lowest EGT. Is this what the GAMI spread is?

No, it is the difference in fuel flow between the first and last to peak.  

I'd suggest taking the www.advancedpilot.com online seminar... it is not free but worth way more than the cost.  I took the live version 17 years ago and learned more in a weekend than in some of my college courses.

[Hank]

18 hours ago, Echo said:

Going rich of peak up high is a pretty cheap speed mod.  Without mods THAT s what you should do if you want more speed.  See what you get.  Your plane is NOT slow.  It IS a Mooney after all.  Enjoy.

Thus is quite a surprise to me, I thought the E would significantly outperform my little C. We're much more comparable than I imagined! At 7500 msl, 2500/21" the E is faster but the C goes farther . . .

The important thing is that they're both Mooneys!

[0TreeLemur]

4 hours ago, Ragsf15e said:

Your ff of 11-11.5 to be ~100rop at 8500’ would match mine.  Heck, it might be 11.5-12 there if he’s at isa.

Running at peak is fine if you’re running low enough power, but if you’re trying to maximize speed, you’re going to have to be rop to get maximum power.

Sorry for my delayed response.  I've been flying.  A lot.

That's recent performance between AL and MI, it has been warm.   T=11C at 8500'.  At least 14C above ISA.

[Ragsf15e]

5 hours ago, AndreiC said:

This is what has been puzzling me too. Maybe the key words here are "provided you use the richest cylinder". I have been leaning using my EDM 700, stopping when the first EGT peaks. This (I guess) means that I am using the *leanest* not the richest cylinder. I hope operating this way has not damaged something in my engine (I always run well below 75%, closer to 70% or 65%). But next time I go I will try to use the richest cylinder for leaning to peak. 

Question: when going for 100 ROP, do you use the richest or leanest cylinder for reference?

These guys got you straightened out. Don’t run peak on the leanest.  If you run peak on the richest, the others are by definition lean of peak and should be cooler.  The converse leaves 3 cylinders in a bad spot just rich of peak.

If you want raw speed, closest relatively safe power setting is around 100 rich of peak from the leanest.

In all cases, keep an eye on your chts as they should remain below 400ish (I keep mine below 380ish). If you’re at peak/lop, leaner is cooler.  If you’re rop, richer is cooler.

Egt values are pretty meaningless.  You just need to know what order the cylinders hit their peaks and how far you are on either side of peak for the richest (running lop) or leanest (running rop).  Your gami spread is the difference in ff from first peak to last.  The tighter that is, the easier it is to get all the cylinders near the same setting (peak, lop or rop) which helps it run smoothly.  Typically this is more important at peak or lop.  
 

Ask if you have more questions!

Edited September 13 by Ragsf15e

[AndreiC]

Alright, I have more data points. I just completed yesterday and the day before two flights of around 3 hours each. I tried different settings to see what changes.

The flights (KEFT-KJWN and back) were conducted at 9500 and 6500 feet, respectively. The overall point-to-point average was 143 knots, and this includes the climb/descent times. On the way out ForeFlight said I had a 7-8 knots tailwind, on the way back the winds were roughly calm.

Moving my seat back as far as it could go (basically flat against the rear bench) gave me another 2-3 knots. The trim indicator was close to (but not quite at) the nose down stop, so I guess I had a fairly far aft cg.

Running at 50F ROP (10.8 gph) gave me a lot of speed increase, about 8-9 extra knots over peak (9.3 gph). When leaning I used the strategy described above, where to lean to peak I was making sure all cylinders were lean of peak, while when running ROP I made sure all cylinders were over 50F above peak. I don't know why the difference in speed was this large, it is not justified by the calculated difference in power output. This would be interesting to try to hear opinions from others why it happens. All the cylinders stayed nice and cool, CHTs in the 335 range for three cylinders, and 355 range for the highest one (#2).

Also, it appears my airspeed indicator is showing somewhat on the high side. Doing everything above to get speed (seat back, max power) I managed to squeeze 146 knots out of the airframe, calculated with a 3 direction GPS measurements (at 90 degrees compass headings). The calculated indicated airspeed at 9500 feet, ISA+10, 10.8 gph was 152 knots. So probably my ASI shows 6-7 knots fast. All measurements were done at WOT/RAO/2550 RPM. I was probably 300 lbs under gross.

I am wondering if the numbers above strike everyone as expected, or some of you see them as wrong in any way (for example I was puzzled by the high fuel flow at peak).

[MikeOH]

As I have an F model so I'm not sure what value my numbers will have for you.  But, here goes:

1) Normal cruise for me is right around 140-143 kts at 65% (LOP) and 8.5-9.0 gph. (WOT, RAO, 2550 rpm) at 8,000 ft.

2) Just did a 'balls out' 3-way GPS run: 152 kts 100 ROP, WOT, RAO, 2600 rpm, DA=7400 ft., 14.5 gph

152 kts is pretty close to book numbers for an F model.  Which is somewhat disappointing as I have 201 windshield, cowl mod, dorsal fin mod, and all the gap seals.  Forgot to close the fresh air intake on the cabin roof...I'm sure that's the problem

[Ragsf15e]

10 hours ago, AndreiC said:

Alright, I have more data points. I just completed yesterday and the day before two flights of around 3 hours each. I tried different settings to see what changes.

The flights (KEFT-KJWN and back) were conducted at 9500 and 6500 feet, respectively. The overall point-to-point average was 143 knots, and this includes the climb/descent times. On the way out ForeFlight said I had a 7-8 knots tailwind, on the way back the winds were roughly calm.

Moving my seat back as far as it could go (basically flat against the rear bench) gave me another 2-3 knots. The trim indicator was close to (but not quite at) the nose down stop, so I guess I had a fairly far aft cg.

Running at 50F ROP (10.8 gph) gave me a lot of speed increase, about 8-9 extra knots over peak (9.3 gph). When leaning I used the strategy described above, where to lean to peak I was making sure all cylinders were lean of peak, while when running ROP I made sure all cylinders were over 50F above peak. I don't know why the difference in speed was this large, it is not justified by the calculated difference in power output. This would be interesting to try to hear opinions from others why it happens. All the cylinders stayed nice and cool, CHTs in the 335 range for three cylinders, and 355 range for the highest one (#2).

Also, it appears my airspeed indicator is showing somewhat on the high side. Doing everything above to get speed (seat back, max power) I managed to squeeze 146 knots out of the airframe, calculated with a 3 direction GPS measurements (at 90 degrees compass headings). The calculated indicated airspeed at 9500 feet, ISA+10, 10.8 gph was 152 knots. So probably my ASI shows 6-7 knots fast. All measurements were done at WOT/RAO/2550 RPM. I was probably 300 lbs under gross.

I am wondering if the numbers above strike everyone as expected, or some of you see them as wrong in any way (for example I was puzzled by the high fuel flow at peak).

Those numbers seem pretty good to me.  You didn’t say what the outside temp was, but a hot day (high density altitude) will be slower at those altitudes.  Your peak ff seems pretty normal to me for 6500’.  Try going just leannof peak, not far, but maybe 10-20 degrees.  Lose 4 knots and another.5gal of ff.

[Paul Thomas]

I'm confused by the calculated indicated airspeed. Indicated should be just that, indicated. If you are indicating 152, or even 146 at 9,500, you would have a fast airplane.

If your KTAS is 146, you KIAS should be in the 120 (exact speed depends on alt setting and temperature).

[AndreiC]

20 minutes ago, Paul Thomas said:

I'm confused by the calculated indicated airspeed. Indicated should be just that, indicated. If you are indicating 152, or even 146 at 9,500, you would have a fast airplane.

If your KTAS is 146, you KIAS should be in the 120 (exact speed depends on alt setting and temperature).

No, sorry, I realize now that what I wrote is confusing. My KIAS was about 130, if I recall correctly (I did not write this down).

The GNS 430W has a TAS calculator, where you plug in your altitude, altimeter setting, air temp, indicated air speed and it calculates for you the corresponding true air speed. The 152 kts was the calculated TAS from my indicated airspeed, after all the corrections. So it *should* have been my actual airspeed if my ASI was showing correctly. Compared to the TAS calculated from three GPS readings at 90 degrees each, and inserted in this calculator here

http://www.csgnetwork.com/tasgpscalc.html

the TAS computed from what the ASI shows was about 6 kts fast.

[Ragsf15e]

8 hours ago, AndreiC said:

No, sorry, I realize now that what I wrote is confusing. My KIAS was about 130, if I recall correctly (I did not write this down).

The GNS 430W has a TAS calculator, where you plug in your altitude, altimeter setting, air temp, indicated air speed and it calculates for you the corresponding true air speed. The 152 kts was the calculated TAS from my indicated airspeed, after all the corrections. So it *should* have been my actual airspeed if my ASI was showing correctly. Compared to the TAS calculated from three GPS readings at 90 degrees each, and inserted in this calculator here

http://www.csgnetwork.com/tasgpscalc.html

the TAS computed from what the ASI shows was about 6 kts fast.

My ~50 year old airspeed indicator also indicates a few knots fast at cruise speeds.  Maybe not 6, but ~3-4.  I found it the same way you did.

[AndreiC]

On 9/22/2024 at 2:22 PM, MikeOH said:

2) Just did a 'balls out' 3-way GPS run: 152 kts 100 ROP, WOT, RAO, 2600 rpm, DA=7400 ft., 14.5 gph

152 kts is pretty close to book numbers for an F model.  Which is somewhat disappointing as I have 201 windshield, cowl mod, dorsal fin mod, and all the gap seals.  Forgot to close the fresh air intake on the cabin roof...I'm sure that's the problem

I just tried yesterday the same kind of "balls out" run. My results (in an E, mind you, which should be faster than an F, but with no speed mods to speak of) are a bit disappointing.

149 kts, full rich, WOT, RAO, 2620 rpm, DA = 8400 feet, 16.2 gph.

My book numbers (which perhaps were produced by the same marketing manager that produced @Shadrach's before 1967, even though my plane is from 1970) say I should have been at around 158 kts. So I am about 9 kts slower than book.

One other thing to ask: I can never set RPM to 2700, in cruise or during take-off. When I first advance the throttle for take-off I see around 2680 for a second or two, but then in climb and in cruise, even with the prop control fully forward, I can only see around 2600-2620. Should I get my prop governor adjusted? I have a digital tach, so I think it should be accurate.

[MikeOH]

@AndreiC

That rpm seems low. I can get 2680 (digital tach) in level flight. If you have an accurate tach then I’d get the governor checked.

[philiplane]

On 9/10/2024 at 7:23 PM, AndreiC said:

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

Half of that loss is due to forward CG alone. The three blade prop has more drag than a two blade, but worse, it's heavier. And that extra weight is all the way upfront, causing more load on the tail. Figure out how to get your CG further back. Push your seat back in cruise, add weight to the baggage, etc. Mooney, like all other manufacturers, got the book speeds with the plane loaded to gross weight, but also with the most favorable CG. But most pilots fly at or near the forward limit, which adds a lot of drag, slowing the plane down.

Cooling drag is the next big item to tackle. If the engine baffles aren't perfect, a lot of air goes through the cowl, but in the wrong manner. You end up with higher CHT's, and can lose 2-4 knots depending on how bad the leaks are. 

External things like antennas and gear door rigging, and flight control rigging, are the smallest contributors to your problem.