reasonable M20J speeds

[dominikos]

@carusoam, how would you factor in reported density attitude at the local airport in KTAS calculations?

I realize that my reports were lacking precision - part of the learning curve for me. I also pointed out that there was a month between dropping plane for service and picking it up and the weather in south TX changed quite a lot. I also only had plane for 9 months, so I don’t have full appreciation for the impact of the summer weather on the plane performance. 

The key decision, do I go back to A&P and ask him to help tracking down the problem, or I actually don’t have issue. I’m leaning towards ‘I don’t have issue’ answer. As noted, I cannot fully test it due to weather (been raining on and off in TX since April) and I still don’t have IFR.

[carusoam]

The key thing is to separate out the real life issues from the crummy data issues…

It is quite possible that the weather has gotten so hot… 

Your power production is down…

Your plane’s ability to produce lift has been reduced…

 

The method I use to know if my plane is producing power…

1) MP, RPM, and FF usually tell the story, with the FF telling if the other two are telling the truth…

2) Using a WAAS source, and an app called CloudAhoy… measuring the actual T/O distance…

3) Comparing climb rate also works, but that is the old analog gauge and averaging over time debacle that we are discussing here…

 

So… the point of knowing DA and how it changes… and why it is important…. When you know this detail… it directly affects the other details  from the first post to the last…

 

Check your POH power charts to see what it has for notes regarding temp and rh… As Skip pointed out, both affect power output… your charts probably mention it briefly… in a note or a sentence….

Before going back to the mechanic… check your plane’s performance…  compare to the performance charts…

Do this often to get to know your plane… take notes on flights… 

Your data, in your plane, supported by the POH… is the best way to go…   Unless your data is completely unusable…  then work on getting better data…  

 

Our friend Patrick was not aware enough about the affects of Temp on his M20J’s performance…  on his last flight, he had two friends from school… all went to an aviation college…  after taking on fuel, they didn’t back taxi all the way to the beginning of the runway…

Patrick serves as our reminder to be more aware of the affects of temperature on our plane’s performance…  it makes a significant difference…

Best regards,

-a-

[PT20J]

28 minutes ago, dominikos said:

@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.

Water vapor is actually less dense than air. That’s why humidity increases density altitude. I believe compressibility effects are generally less than a knot for airspeeds < 200 KTAS.

[ArtVandelay]

I read a paper that summarized that humidity can reduce engine power as much as 10%.

[Gagarin]

My M20J average cruise speed heading to KAGC.

[A64Pilot]

14 hours ago, ArtVandelay said:

I read a paper that summarized that humidity can reduce engine power as much as 10%.

Yes, high humidity as far as engine power is concerned is under appreciated.

‘When the air is cold, I mean real cold not Fl cold, it can hold only a very small amount of water, so an engine gets a big power increase from cold, dense and dry air.

We did cold weather testing in Wisconsin in Feb 03, it was surprising to see what real cold did for aircraft performance, and what it did to aircraft systems.

[carusoam]

Congrats p_g…

Consider getting the instrument face re-screened…

exchange hate for happiness for a few dollars…

Got a good instrument shop?

Best regards,

-a-

[ArtVandelay]

Picked up a new to us j today.
I thought 171mph was a little slow. Rop didn't really matter, speed wise. I hate that it's in mph

A J should be marked in dual units, the POH is also in both.

[Shadrach]

On 7/1/2021 at 12:29 AM, Gagarin said:

My M20J average cruise speed heading to KAGC.

GS is not really helpful to a TAS discussion.  203kts isn’t bad for bragging rights but it’s not extraordinary either.

Edited July 4, 2021 by Shadrach

[201Mooniac]

The G500 can be switched to KTs but I think you need the dealer unlock card to do it.  Should only take a few minutes though if you have a dealer shop near by.

[jaylw314]

11 hours ago, philip_g said:

Picked up a new to us j today. At 6500 I got it down to 9gph 20f lop with chts all 300-350 and egt 1400-1450, 23" and 2500 rpm. I have not owned a NA Mooney before this one. Our cowl flaps trail about 3/4 inch and the chts really stay low.

I thought 171mph was a little slow. Rop didn't really matter, speed wise. I hate that it's in mph

That's got to be the most nochalant "I just got a Mooney!" post I've ever seen!  Congratulations!

[jaylw314]

On 6/30/2021 at 7:41 PM, 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?

Those sound pretty darn close to what I get, maybe just a couple knots slower.  There's also always the question of how accurate your MAP and RPM gauges are.  If you fly at peak or LOP, fuel flow is a better measure of power since it's only one variable instead of two, and it's rare to see FF be inaccurate once set correctly.

100% humidity and 35C give or take 5C????   You are made of sterner stuff than me! 

Edited July 4, 2021 by jaylw314

[EricJ]

17 hours ago, philip_g said:

Picked up a new to us j today. At 6500 I got it down to 9gph 20f lop with chts all 300-350 and egt 1400-1450, 23" and 2500 rpm. I have not owned a NA Mooney before this one. Our cowl flaps trail about 3/4 inch and the chts really stay low.

I thought 171mph was a little slow. Rop didn't really matter, speed wise. I hate that it's in mph

That's about right.   Mine makes a pretty reliable 150 kts at 9-10 gph.

[EricJ]

57 minutes ago, philip_g said:

Ugh. It's no rocket that's for sure.

 

The mixture is really fiddly too. You set it and it wanders a bunch 

That's not normal unless you're changing altitude or the ambient pressure is changing a lot.    Do you have a good fuel pressure gauge?   See whether that is wandering around.    If not, you may have an intake leak somewhere.

[Danb]

I had two J models 1977 201, in say mid 1986 for a couple years and a new 1988. Same plane different performance. I also had the ‘77 rigged. I would get approximately 150-155  at 8000. The 1988 new was around 160+, when I sold the ‘88 in 2005 I planned on 158-160. As our guys age they must be kept in rig, the engine gets a little tired etc. The book numbers are as new in perfect conditions. My 2005 Bravo even though I try to keep it as new and s about 5 knots slower than fresh from factory, weighing in the factors of age you most likely won’t get what’s in the POH

 

[ArtVandelay]

Don’t forget book numbers are for the basic plane. After adding all the antennas the average plane has ( 2 VOR, 2 COM, GPS, ELT, stormscope, marker beacon, 2 transponder, ADF, plus temperature probe) you can expect the cumulative drag to lower your speed.

[A64Pilot]

45 minutes ago, ArtVandelay said:

Don’t forget book numbers are for the basic plane. After adding all the antennas the average plane has ( 2 VOR, 2 COM, GPS, ELT, stormscope, marker beacon, 2 transponder, ADF, plus temperature probe) you can expect the cumulative drag to lower your speed.

Why two transponder? I have what looks to be two transponder antennas, and I don’t have a diversity transponder.

I was assuming one may have been a DME antenna, with the DME long removed and the antenna and co-ax left behind?

 

On edit, can I take my multimeter and measure resistance and determine if anything is connected to the co-ax? I think one is an abandoned DME antenna and on my Maule I had to install a transponder antenna on the belly for my GDL-39 to receive ADSB ground stations above 10,000 ft or so, I was thinking I may have to do that on the Mooney as well and I’d rather not have three antennas down there.

Edited July 5, 2021 by A64Pilot

[ArtVandelay]

Why two transponder? I have what looks to be two transponder antennas, and I don’t have a diversity transponder.
I was assuming one may have been a DME antenna, with the DME long removed and the antenna and co-ax left behind?

ADSB in/out and normal transponder….I forgot about DME.

[PT20J]

2 minutes ago, philip_g said:

We're a solid 5kts off of that. Our map gauge is also an inch off which isn't helping. The longest leg I can fly here is about 188nm. 5kts isn't anything over that length I guess. The climb performance is super disappointing too. Took forever to get to 6500.  Thats barely over the traffic pattern altitude where I used to live.

I assume that you mean that the manifold pressure gauge reads an inch high. If so just set power an inch higher until you get it fixed. Are you climbing at full power? Most of us do that in a normally aspirated Mooney as there is no good reason to reduce power in the climb. Climb performance is also heavily dependent on weight and density altitude. High humidity makes it worse. Another possibility is that the engine is not putting out rated power. Do you get 2700 rpm on a full power run up? A tired engine is usually first evident in increased takeoff distance and reduced climb rate since these regimes depend heavily on excess horsepower. A worn camshaft is sometimes the culprit if cylinders are good and everything else is running well.

Skip

[y2kiah]

As a point of comparison, I recently did a square pattern to measure TAS in my ‘78 J at 25” 2500 rpm, 2000 ft indicated, about 4K DA (28C oat). I was giving it 11.2 gph to keep cylinder #3 under 400.

according to the book, I should have been getting roughly 158ktas with those numbers, my real world TAS was ..... wait for it..... 140.

take it for what it’s worth, but I think you should be happy with the performance you are getting.

Btw I plan at 140 because it is unrealistic for me to expect more from my plane without burning up the cylinders.

 

[PT20J]

1 hour ago, y2kiah said:

As a point of comparison, I recently did a square pattern to measure TAS in my ‘78 J at 25” 2500 rpm, 2000 ft indicated, about 4K DA (28C oat). I was giving it 11.2 gph to keep cylinder #3 under 400.

according to the book, I should have been getting roughly 158ktas with those numbers, my real world TAS was ..... wait for it..... 140.

take it for what it’s worth, but I think you should be happy with the performance you are getting.

Btw I plan at 140 because it is unrealistic for me to expect more from my plane without burning up the cylinders.

 

Several things might lead to higher #3 CHTS. 

1. If you are using a spark plug gasket probe, it will read high. I measured mine at 40F higher than the bayonet probe by putting it temporarily on CYL 1 to compare readings. JPI confirmed that this is typical. 
2. The early Js had a flat left cowl flap whereas later ones had a left flap with similar shape as the right. You might try adjusting the left flap to have a bigger gap when closed. Bob Kromer claims this actually improves speed. 
3. Check the baffle seals for leaks. 

You should get better speed than you are getting and the lower speed at high power might be making the temps high due to reduced cooling air flow. It might be worth checking the rigging. 

Skip

[y2kiah]

Thanks Skip,

I'll check #3 for the JPI probe, it always reads hotter LOP, but ROP the other cylinders catch up and can actually overtake it. This makes me think that #3 is running richer than the others.

I am pretty sure rigging has a lot to do with it. My left flap, when up, rests in a reflexed position with respect to the top wing surface, while the right flap is on a correct plane for the chord of the wing. This leads to a need for constant left rudder pressure to keep the ball centered at cruise and especially descent airspeeds. I also have a badly heat-cracked cowling that must be adding some drag. Rigging is on my short list of things to fix next.

[Bartman]

I occasionally do a 4-way GPS run and have done this at various RPM, temps and density altitude. I always get 155 or better and the best I have seen is 159Kts.  I don’t cruise like that and realistically I plan for 145Kts 

[N205S]

1987 M20J 205: Yesterday at 8500' MSL, 12degree Celsius at altitude, WOT, and 2500 RPM I saw 161kts TAS. I typically see between 158-162kts TAS in cruise and I have seen 164kts on 1-2 occasions. Seems fast to what most report but it's a solid plane. This is with a 500hr engine and 3-blade Hartzell top prop.

Edited July 18, 2021 by N205S
spelling

[Shadrach]

On 7/16/2021 at 8:26 AM, y2kiah said:

Thanks Skip,

I'll check #3 for the JPI probe, it always reads hotter LOP, but ROP the other cylinders catch up and can actually overtake it. This makes me think that #3 is running richer than the others.

I am pretty sure rigging has a lot to do with it. My left flap, when up, rests in a reflexed position with respect to the top wing surface, while the right flap is on a correct plane for the chord of the wing. This leads to a need for constant left rudder pressure to keep the ball centered at cruise and especially descent airspeeds. I also have a badly heat-cracked cowling that must be adding some drag. Rigging is on my short list of things to fix next.

#3 is typically the hot cylinder for IO360s. The fins on the back of the cylinder stop at the barrel and will not allow airflow around the cylinder. Mooney solved this by dishing out the baffle behind number #3. If the baffle is poorly oriented, there is little to no airflow around the back of cylinder #3. Go out to your hanger at night sometime and put a light in the lower cowl under cylinders 1 and 3. Looking down from the top of the engine youu will note that you can see light and therefore a path for airflow, everywhere but behind cylinder 3. Make sure the dish out on the baffle is oriented in such a way as to allow air to flow behind the cylinder.

Edited July 18, 2021 by Shadrach