Is my Mooney slow?

[N201MKTurbo]

14 minutes ago, AndreiC said:

OK, I went up today and did 5 different 3-way runs to test things. The conditions were all ISA+25F (so DA was about 1500FT over PA), but unfortunately the air was not quite perfectly smooth at 7500 and 8500 -- there was some very light chop. I don't know how much this affects things. The plane was light, well under 2200 lbs.

In any case, as I had thought previously, I did not get anywhere close to the numbers predicted above; I think my plane has a penalty of about 8-10 knots over the book numbers. I would appreciate it if people could tell me what aspects of the rigging can be improved, so I can talk to my mechanic to look at these at annual.

Here are the various runs. All were done with Ram Air Open, WOT. This meant I got 23.2" MP at 7500, and 22.2" at 8500.

Run 1: 7500 FT, 100F ROP, 2420 RPM -- TAS 142.4 kts

Run 2: 7500 FT, 100F ROP, 2550 RPM -- TAS 146.4 kts

Run 3: 7500 FT, peak EGT (9.0 gph) 2400 RPM -- TAS 138 kts

Run 4: 8500 FT, 100F ROP, 2550 RPM -- TAS 144 kts

Run 5: 8500 FT, peak EGT (9.0 gph) 2400 RPM -- TAS 139 kts.

So it seems there is not much difference between 7500 and 8500. Running at peak and 2400 RPM saves about 2 gph (= 17.8 mpg) over 100F ROP 2550 RPM (= 15 mpg), but it means losing about 8 knots.

Main questions:

a) Can a light chop affect the TAS significantly?

b) Can a strong wind at altitude affect measurements? (The winds were about 24-29 kts.)

c) What aspects of the rigging can be checked relatively easily and improved upon?

Thanks, Andrei.

Sounds about right.

be glad you weren’t flying an Arrow!

[MikeOH]

20 minutes ago, AndreiC said:

Here are the various runs. All were done with Ram Air Open, WOT. This meant I got 23.2" MP at 7500, and 22.2" at 8500.

Run 1: 7500 FT, 100F ROP, 2420 RPM -- TAS 142.4 kts

Run 2: 7500 FT, 100F ROP, 2550 RPM -- TAS 146.4 kts

Run 3: 7500 FT, peak EGT (9.0 gph) 2400 RPM -- TAS 138 kts

Run 4: 8500 FT, 100F ROP, 2550 RPM -- TAS 144 kts

Run 5: 8500 FT, peak EGT (9.0 gph) 2400 RPM -- TAS 139 kts.

So it seems there is not much difference between 7500 and 8500. Running at peak and 2400 RPM saves about 2 gph (= 17.8 mpg) over 100F ROP 2550 RPM (= 15 mpg), but it means losing about 8 knots.

Main questions:

a) Can a light chop affect the TAS significantly?

b) Can a strong wind at altitude affect measurements? (The winds were about 24-29 kts.)

c) What aspects of the rigging can be checked relatively easily and improved upon?

Thanks, Andrei.

Hmm, I guess I'm missing something as I don't see a problem with those numbers!  Maybe my plane is slow, too

[Shadrach]

6 hours ago, AndreiC said:

OK, I went up today and did 5 different 3-way runs to test things. The conditions were all ISA+25F (so DA was about 1500FT over PA), but unfortunately the air was not quite perfectly smooth at 7500 and 8500 -- there was some very light chop. I don't know how much this affects things. The plane was light, well under 2200 lbs.

In any case, as I had thought previously, I did not get anywhere close to the numbers predicted above; I think my plane has a penalty of about 8-10 knots over the book numbers. I would appreciate it if people could tell me what aspects of the rigging can be improved, so I can talk to my mechanic to look at these at annual.

Here are the various runs. All were done with Ram Air Open, WOT. This meant I got 23.2" MP at 7500, and 22.2" at 8500.

Run 1: 7500 FT, 100F ROP, 2420 RPM -- TAS 142.4 kts

Run 2: 7500 FT, 100F ROP, 2550 RPM -- TAS 146.4 kts

Run 3: 7500 FT, peak EGT (9.0 gph) 2400 RPM -- TAS 138 kts

Run 4: 8500 FT, 100F ROP, 2550 RPM -- TAS 144 kts

Run 5: 8500 FT, peak EGT (9.0 gph) 2400 RPM -- TAS 139 kts.

So it seems there is not much difference between 7500 and 8500. Running at peak and 2400 RPM saves about 2 gph (= 17.8 mpg) over 100F ROP 2550 RPM (= 15 mpg), but it means losing about 8 knots.

Main questions:

a) Can a light chop affect the TAS significantly?

b) Can a strong wind at altitude affect measurements? (The winds were about 24-29 kts.)

c) What aspects of the rigging can be checked relatively easily and improved upon?

Thanks, Andrei.

Just to be clear, you were flying heading, not gps track?  Headings were 90° off and turns were  in the same direction?

[AndreiC]

4 hours ago, Shadrach said:

Just to be clear, you were flying heading, not gps track?  Headings were 90° off and turns were  in the same direction?

Yes: was flying compass headings 360, 90, 180, letting it stabilize, and recording GPS speed, then put it in the calculator.

[Fly Boomer]

16 hours ago, AndreiC said:

b) Can a strong wind at altitude affect measurements? (The winds were about 24-29 kts.)

I don't know about the others, but your airplane does not know if it is flying in a moving air mass.  If the air mass you are flying through is moving across the face of the planet at 100 knots, the airplane will behave exactly as it would in still air.  Now, if that air mass is variable between 90 and 110 knots, that will make a difference.