reasonable M20J speeds

[jaylw314]

4 hours ago, dominikos said:

Unfortunately with the wet weather in TX, I was only able to run a 3-way speed test at 2,000 ft.

Here is what I got - 2000ft, 92F - corrected POH numbers for temperature. All my gauges are original, analog gauges.
cowl flaps open:
- 24/2400 - 139 kts - POH: 153 kts (adjusted for temp: ~ 150kts) - 11 kts difference
- 22/2200 - 127 kts - POH: 142 kts  (adjusted for temp: ~ 138kts) -  11 kts difference

cowl flaps closed:
- 22/2200 - 131 kts - POH: 142 kts  (adjusted for temp: ~ 138kts) -  7 kts difference

Do those speeds look right? 

Thanks, Dominik

Hey, what was the reason you had your cowl flaps open?  with cruise you should be able to cruise with the cowl flaps closed.

AFAIK, leaving them full open in cruise can put undue force on them.  If you need to open them at cruise speeds, leave them in trail (1/2 open).

At 35C, your MAP should be corrected down about 0.6", so it's more like 21/2200 instead of 22/2200.  That's somewhere between 45% and 55%.  On the POH speed chart, halfway between 45% and 55% is something like 137 KTAS, so you're not horribly far off there

Hey wait a minute, you did correct your KIAS to KTAS, right?

[jaylw314]

9 minutes ago, dominikos said:

my peak is around 875 C, quite consistently, hence, I always aim for 725C when leaning. as Shadrach pointed, with current instrumentation, I don’t have granular view - my temps reads are within 10-15C 

Ooof!  I hope there's a typo in there?  You're leaning for 150C rich of peak?  Best power is at about 75C ROP

[Shadrach]

4 minutes ago, dominikos said:

my peak is around 875 C, quite consistently, hence, I always aim for 725C when leaning. as Shadrach pointed, with current instrumentation, I don’t have granular view - my temps reads are within 10-15C 

That's over 1600F and is hotter than I would expect from a naturally aspirated engine.  

[dominikos]

13 minutes ago, jaylw314 said:

Hey, what was the reason you had your cowl flaps open?  with cruise you should be able to cruise with the cowl flaps closed.

AFAIK, leaving them full open in cruise can put undue force on them.  If you need to open them at cruise speeds, leave them in trail (1/2 open).

At 35C, your MAP should be corrected down about 0.6", so it's more like 21/2200 instead of 22/2200.  That's somewhere between 45% and 55%.  On the POH speed chart, halfway between 45% and 55% is something like 137 KTAS, so you're not horribly far off there

Hey wait a minute, you did correct your KIAS to KTAS, right?

I keep them open to help with cooling. Otherwise, the cyl temp is creeping up over time. On the third test, I realized that I could close them, the temp was comfortably in the middle of green arch.

The speeds reported were TAS speeds from GPS test. I did approximation from POH to allow for non-standard air temperature.

[dominikos]

22 minutes ago, jaylw314 said:

Ooof!  I hope there's a typo in there?  You're leaning for 150C rich of peak?  Best power is at about 75C ROP

Apologies, typo. I meant, peak at 775C and leaned to 725C. I fixed typo in the original post.

[jaylw314]

24 minutes ago, dominikos said:

I keep them open to help with cooling. Otherwise, the cyl temp is creeping up over time. On the third test, I realized that I could close them, the temp was comfortably in the middle of green arch.

The speeds reported were TAS speeds from GPS test. I did approximation from POH to allow for non-standard air temperature.

Ah, ok, watch out for TAS from the GPS.  That requires all the same info you need for your E6B, like mag heading, IAS, altitude, altimeter setting, temp, etc. so if any one of them are inaccurate, you're getting an inaccurate result.  TAS from your IAS requires only altimeter and OAT (even the temp adjustment is small enough to be usually irrelevant) to be working and accurate.

Edited June 30, 2021 by jaylw314

[dominikos]

5 minutes ago, jaylw314 said:

Ah, ok, watch out for TAS from the GPS.  That requires all the same info you need for your E6B, like mag heading, IAS, altitude, altimeter setting, temp, etc. so if any one of them are inaccurate, you're getting an inaccurate result.  

I used this method, http://www.csgnetwork.com/tasgpscalc.html. In my understanding it gives you quite accurate KTAS.

[jaylw314]

Just now, dominikos said:

I used this method, http://www.csgnetwork.com/tasgpscalc.html. In my understanding it gives you quite accurate KTAS.

OK, yes, that method does, I thought you meant you were using the TAS off the GPS directly

 

[A64Pilot]

33 minutes ago, Shadrach said:

That's over 1600F and is hotter than I would expect from a naturally aspirated engine.  

Back in the day, EGT gauges didn’t have numbers on them, and that’s the way it should be. The number is completely irrelevant, all you need to know is how much less than peak you are, so yes you need to know the graduations but not the number associated with them.

Since adding temp numbers to the gauges, people have become concerned with total temp, and for a NA airplane it’s completely irrelevant, as there is no max allowable EGT.

If memory is correct lower compression engines will peak well over 1600F, first time I saw that I thought something was wrong and became concerned with running the engine so hot.

Edited June 30, 2021 by A64Pilot

[jaylw314]

32 minutes ago, Shadrach said:

That's over 1600F and is hotter than I would expect from a naturally aspirated engine.  

I'll hit 1600F above 65% power or so at low altitude, too, so there does seem to be enough variation between different installations

[A64Pilot]

IF you notice your running higher EGT’s than usual, especially if the airplane just came out of maintenance, check timing, incorrect timing can raise EGT’s, and if it’s just one cylinder, suspect a stuck valve or anything that could reduce compression, broken rings or whatever.

To see how timing can effect EGT, do a mag check and watch egt when you do, it will increase significantly, retarded timing will usually increase EGT 

Edited June 30, 2021 by A64Pilot

[Shadrach]

21 minutes ago, A64Pilot said:

Back in the day, EGT gauges didn’t have numbers on them, and that’s the way it should be. The number is completely irrelevant, all you need to know is how much less than peak you are, so yes you need to know the graduations but not the number associated with them.

Since adding temp numbers to the gauges, people have become concerned with total temp, and for a NA airplane it’s completely irrelevant, as there is no max allowable EGT.

If memory is correct lower compression engines will peak well over 1600F, first time I saw that I thought something was wrong and became concerned with running the engine so hot.

It's not completely irrelevant if you know the upper and lower limits of what a healthy system should display.  If I were departing from sea level in any NA recip and saw EGTs on take off of 1475 ,I would likely abort because of likely hood of inadequate fuel flow.   If I saw EGTs in the high 1600-1700 or more, I would suspect that I was looking a partial ignition failure.   Slight differences in EGT (30-60) from cylinder to cylinder are irrelevant but that does not mean that the numbers don't operate within a spectrum of acceptable readings for a given operation.  I suppose they are irrelevant to those that don't understand their relevance.  

[A64Pilot]

Read this

https://resources.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2010-10_egt-myths-debunked.pdf

[Urs_Wildermuth]

There is nothing but a true TAS indicator, such as present in the Aspen PFD or similar to really know where you are at in speed. Ok, there are the old style analogue ASI's which have a TAS scale of sorts, those also work out sort of. Doing calcs and trying to work out tables in flight usually does not really work.

Yes, there is the GPS method, 3 or 4 way and average, which also works out well. But having TAS on a display is simply a lot easier. I learnt a lot about my C-Model's performance after we got the Aspen installed.

[Vance Harral]

35 minutes ago, Shadrach said:

It's not completely irrelevant if you know the upper and lower limits of what a healthy system should display.

There is no way for you to know the "healthy" upper and lower limits of someone else's airplane.

The biggest reason for this is that the temperature sensed by an EGT probe varies dramatically with the placement of the probe in the exhaust pipe.  There is no universal standard for this, and probe placement differences of less than an inch can result in indicated temperature differences of over 100 degrees Fahrenheit.

My own airplane is a good example of this.  Most modern engine monitor installations place the EGT probes 2-3" from the cylinder flange.  Ours is about 4" out, simply because there were pre-existing holes in that location from an older, analog, 4-cylinder EGT rig, that we chose to reuse.  The result is that our EGTs indicate cooler than most numbers I typically see posted on aviation forums.  But as several of us are saying here, the absolute numbers don't matter.  In particular, an indicated EGT of 1600 is not necessarily "too hot".  Engines with probe placements near the short end of the recommended range will commonly show this.

[Ragsf15e]

We can definitely debate his engine management and egts all day long, we might even be able to teach him something, but to answer his initial questions, 135ish knots at anywhere near full power and 2,000’ seems awful slow.  I’d like to see a 6500’ run done at wot, 2500 rpm and 100rop(f) to know for sure, but yeah, it seems slow.

I also noticed a slightly slow airplane after an annual, and some idiot pilot didn’t preflight it good enough… the nosegear door attachment bolts were not put back in.  Nosegear doors were swinging free.  Thank god they swung out and down without jamming the gear! But they did leave dimples in the doors where they hit the cowl flaps so i will never forget.

Edited June 30, 2021 by Ragsf15e

[Shadrach]

2 hours ago, A64Pilot said:

Read this

https://resources.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2010-10_egt-myths-debunked.pdf

 

2 hours ago, Vance Harral said:

There is no way for you to know the "healthy" upper and lower limits of someone else's airplane.

The biggest reason for this is that the temperature sensed by an EGT probe varies dramatically with the placement of the probe in the exhaust pipe.  There is no universal standard for this, and probe placement differences of less than an inch can result in indicated temperature differences of over 100 degrees Fahrenheit.

My own airplane is a good example of this.  Most modern engine monitor installations place the EGT probes 2-3" from the cylinder flange.  Ours is about 4" out, simply because there were pre-existing holes in that location from an older, analog, 4-cylinder EGT rig, that we chose to reuse.  The result is that our EGTs indicate cooler than most numbers I typically see posted on aviation forums.  But as several of us are saying here, the absolute numbers don't matter.  In particular, an indicated EGT of 1600 is not necessarily "too hot".  Engines with probe placements near the short end of the recommended range will commonly show this.

I will take this to a new thread. Dominik does not need this level of granularity in his thread.

 

Edited June 30, 2021 by Shadrach

[dominikos]

First, thank you all for very good pointers and feedback. Quite a lot to learn still ahead of me. And yes, engine monitor is next upgrade for the plane, once I finish IFR and can get on the installation calendar.

I managed to get to the airport today and run another GPS 3way test. Here are the results - let’s hope I can be much more clear and precise after all the feedback received 

Test done at 4,000 ft, used autopilot to fly courses, turns right. Trimmed plane and adjusted mixture to 725C EGT before taking measures.

Environment: humidity: 100%, OAT: approx 35C, give or take 5C

• 24/2400 - calculated KTAS: 147 - POH KTAS: 155 - difference 8kts - estimated power 70%
• 22/2200 - calculated KTAS: 142 - POH KTAS: 144 - difference 2kts - estimated power 56%

The results feel reasonably close. What do you guys think? Perhaps that’s acceptable in an older plane with semi-decent paint and slightly sagging engine? Does humidity play role - denser air? Why is the difference between calculated KTAS and POH getting smaller with less power?

[Ragsf15e]

15 minutes ago, dominikos said:

First, thank you all for very good pointers and feedback. Quite a lot to learn still ahead of me. And yes, engine monitor is next upgrade for the plane, once I finish IFR and can get on the installation calendar.

I managed to get to the airport today and run another GPS 3way test. Here are the results - let’s hope I can be much more clear and precise after all the feedback received 

Test done at 4,000 ft, used autopilot to fly courses, turns right. Trimmed plane and adjusted mixture to 725C EGT before taking measures.

Environment: humidity: 100%, OAT: approx 35C, give or take 5C

• 24/2400 - calculated KTAS: 147 - POH KTAS: 155 - difference 8kts - estimated power 70%
• 22/2200 - calculated KTAS: 142 - POH KTAS: 144 - difference 2kts - estimated power 56%

The results feel reasonably close. What do you guys think? Perhaps that’s acceptable in an older plane with semi-decent paint and slightly sagging engine? Does humidity play role - denser air? Why is the difference between calculated KTAS and POH getting smaller with less power?

The high temp and humidity dramatically raise the density altitude which will rob efficiency from the engine, prop and wings.  So yeah, that’s a factor, I can’t really comment on it being reasonable for a J, but I think my F is pretty darn close to that although I haven’t flown in that kind of heat too much.  If it was really 100f and 100% humidity, that might seem reasonable…

[A64Pilot]

Humidity plays a big part, it greatly decreases air density and therefore engine powerJust off the top of my head your density altitude at 2,000 was likely about 5,000 

https://www.faasafety.gov/files/gslac/library/documents/2011/Aug/56396/FAA P-8740-02 DensityAltitude[hi-res] branded.pdf

Your difference in book speed vs actual closes up at slower airspeeds as the power required is less

‘Any airplane that makes book speed is unusual, then we are pretty much left with the inescapable fact of what it is, is what it is, check timing sure it’s easy to do.

A GPS is phenomenally accurate in determining speed as a shed load of measurements are averaged out, it’s way more accurate than any true airspeed display can or will be, the fancy TAS indications on the glass displays are about as accurate as the % power readings on the fancy engine monitors are.

So far as flying at high power in hot weather with the cowl flaps closed, I can’t or won’t as I like my cyl head temps in the middle of the green, any higher than the middle I’ll open the flaps by whatever amount is required to keep the heads cool.

‘In hot weather I believe the maintenance manual says to adjust the flaps to where when fully closed, they are a half inch open or so, mine are a quarter inch as I will often cruise real LOP and way back on power and need them well closed fo keep the heads from being too cool.

But don’t be afraid of using the flaps to cool the engine, that’s what they are for, if it hurt to have them open the POH would say so.

[dominikos]

I have been using cowl flaps to keep cyl temps in green - must be the southern thing  all folks I fly with told me to keep them open most of the time to help the engine stay cool. I usually close them on descent but keep them half open during flight.

For the speed tests, I closed them. I thought that would give me comparable numbers to POH.

[carusoam]

Dominik,

I think one of the learning experiences in your thread….

Is all of the inaccuracies that arrive in each instrument…

When used, the small inaccuracies become gigantic in the next step…

Calculating TAS is one of those… holy cow, a small variation here and there, the calculation is dreadful…

 

As I was reading… and you said your Transition training had you flying and leaning to 50° ROP at 2k’.   That sounded like crummy advice

You mighty want to summarize where you have been…

With the change of °F vs °C….  Many things got lost…  throw on some edits, I got lost…

A64 gives interesting details about raw EGT data…. He is somewhat correct… it is hard to compare raw EGTs… unless the sensors are mounted with precision…

Somewhere along the way…Mooney was installing sensors with precision using a jig, probably at their exhaust vendor….

By the time Mooney built the M20R… the ship’s EGT gauge is an exact instrument measuring the temp in an exact location… and leaning is done with a scale using °F…

 

Without an engine monitor….  The old analog gauges are missing precision…. With unknown sensor locations… they are lacking accuracy…

You are heading the right direction… but trying to have a precise conversation with crummy data gets pretty challenging…

 

Briefly…

After maintenance you feel the plane is slower than before maintenance…

Time to collect data… with as much accuracy as you can…

 

See if you can pick up an engine monitor… 

I went a decade trying to do what you are doing without an engine monitor in my M20C…

It is super challenging to set expectations… without the instruments to assist…

Keep trying…

Keep collecting data…

Be real clear with your reports to not lose people… 

PP thoughts only…

Best regards,

-a-

 

 

 

[carusoam]

A good discussion on the affects of DA are in order…

What was the density altitude of the airport for your flight?

Even in NJ…. DA is a critical piece of information that affects your machine’s ability to make power and to make lift…

 

What was the DA in flights before maintenance…. What was the DA afterwards?

You may find a significant difference in this number is causing what you have reported…

 

NJ also has the ability in winter to generate negative DAs….  Which is like bolting on a supercharger that weighs nothing… 

With the temps rising…  everyone should be aware of DA prior to departure…  extra important when filling the cabin  or using shorter runways… (aka Patrick’s message)

PP thoughts only,

-a-

[dominikos]

@A64Pilot, out of curiosity. with high humidity, would it also cause KTAS reads to be more incorrect? I would imagine that denser air entering pitot tube would only magnify compressibility error.

[PT20J]

Humidity has a couple of effects. First, the engine is actually an air pump. It’s power is limited by how much air it can consume. Each piston stroke takes in a certain volume of air. The useful constituent of that air is oxygen - it’s what “burns” the gasoline. Water vapor displaces a certain amount of the oxygen in the air taken in, so this will necessarily reduce power.

Secondarily, the water vapor slows the combustion rate. The effect on power is similar to retarding the timing which also reduces power.

Here’s an article with some info on how to calculate the effect:
https://www.kitplanes.com/determining-engine-power/

When you did the GPS test did you use the NTPS method and data reduction spreadsheet? I have found variation in results if not done on a calm day because of variations in wind. The technique can only average out a constant wind velocity. Best to make the measurements quickly after each turn to minimize the distance travelled between measurements. Also, the NTPS spreadsheet will accept four headings which overdetermine the calculation increasing accuracy. 

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