My plane *is* slow! Please help.

[Ragsf15e]

2 hours ago, AndreiC said:

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.

Talk to your IA before tackling the governor.  Maybe it’s the governor, but there’s a low pitch stop as well that’s not on the governor.  I agree you should see much closer to 2700 for takeoff and climb. 
I might also recommend leaning to ~100 rop depending on your chts to get to max speed.  You’ll be closer to max power. Just keep an eye on cht and go a little richer if required to keep them below about 380ish.

[MikeOH]

@AndreiC

Probably doesn’t matter if wind was light but how did you calculate the 3-way GPS? Just taking the average, or even root sum of squares are incorrect methods and will result in error.

[AndreiC]

22 minutes ago, MikeOH said:

@AndreiC

Probably doesn’t matter if wind was light but how did you calculate the 3-way GPS? Just taking the average, or even root sum of squares are incorrect methods and will result in error.

Yes, this was a 3-way run. I even did it twice to double-check.

[MikeOH]

4 minutes ago, AndreiC said:

Yes, this was a 3-way run. I even did it twice to double-check.

I was asking how you made the calculation from the three GPS speeds. You can’t just average them.

[AndreiC]

1 hour ago, MikeOH said:

I was asking how you made the calculation from the three GPS speeds. You can’t just average them.

I used this calculator:

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

It fits a circle through three points (the three vectors of your three perpendicular speeds); the radius is your TAS, and the vector of the center of the circle is the wind.

[MikeOH]

6 minutes ago, AndreiC said:

I used this calculator:

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

It fits a circle through three points (the three vectors of your three perpendicular speeds); the radius is your TAS, and the vector of the center of the circle is the wind.

Very cool!

Much easier than the spreadsheet I created.

[M20F-1968]

On 9/10/2024 at 6:51 PM, AndreiC said:

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. 

I doubt your or any E is 156 kt airplane at 10,000 ft.  A J with it cowling and windshield change is 160 kts.

I suspect some manufacturer marketing tactics.

John Breda

[MB65E]

Mine is.  KTAS.

-Matt

Edited October 2 by MB65E

[Echo]

O.K. Matt.  oooooooook.

[MB65E]

It was a bold statement…

Flat out yes, do I flight plan that no.        
201 windshield, most airframe mods.

Baffling/cooling drag lets no light in with a flashlight shined from behind.              
Oil cooler baffling.                                    
Flaps and ailerons are rigged at the lowest drag settings.                                                

2 blade prop

Lighter than any J.

BY plugs, 25°+ timing

Flown at the aft CG limit.    

I would like to put aileron gap seals on.

And an annoying leaking right fuel tank. 

Yours should be pretty quick with the J cowl. 

I’ll see if I can get additional data points,

-Matt

Edited October 3 by MB65E