Realistic TAS for Mooney Ovation

[THill182]

8 hours ago, jetdriven said:

the 4 heading method is somewhat accurate but as winds aloft increase it loses accuracy. The national test pilot school has a spreadsheet where it takes the root mean square of three different ground tracks and it’s accurate to one knot. Try that. 

That is why I love this forum: Always learn something new. Will try this....

[Mark89114]

Ok....maybe there is something I am not getting here on this test runs in 4 (or 100) different directions and their effect on TAS.  I always believed it wouldn't make any difference as the entire airplane is operating in the air mass and the plane doesn't know what the winds are doing aloft.  If we are changing our base premise on this it lends credibility to the "dangers" of the downwind turn.  GS, yes that is affected.  Just looking for a technical answer based on science.

[Jerry 5TJ]

14 hours ago, jetdriven said:

....The national test pilot school has a spreadsheet where it takes the root mean square of three different ground tracks and it’s accurate to one knot. Try that. 

Ok....I was eastbound at FL210 the day after Christmas. I took three GPS ground speed readings at ground tracks of 088, 090 and 092.  The square root of the average of the three ground speeds squared gives a true air speed of 306 knots.  

Winds per ForeFllight were 280 at 65, by the way.  

The air data computer alleged a mere 230 KTAS: Obviously fake news.  

(Just tugging on your leg with GDOP). 

[jetdriven]

Here’s a good description of how it works.  

Here’s the spreadsheet.   

https://www.ntps.edu/images/stories/documents/GPS_PEC.xlsx

[aviatoreb]

1 hour ago, jetdriven said:

Here’s a good description of how it works.  

Here’s the spreadsheet.   

https://www.ntps.edu/images/stories/documents/GPS_PEC.xlsx

I believe it was professor Rogers from usna who first published that method and calibrated it vs a test flight with navy test pilots with a trailing impeller for benchmark validation.

[Seth]

On 12/30/2017 at 4:38 PM, THill182 said:

First, how do you determine KTAS? While just flying around for fun or practicing I perform speed tests at regular intervals (fly N/E/S/W at specific power setting, then average speed); I have found that the KTAS measured that way is usually 3 to 5 Kts faster than using the simple "calculator" method on the air speed indicator (by selecting a specific altitude and OAT, and reading off the adjusted KTAS; I suppose that doesn't take humidity into account? Not sure).

I have done that before and after adding TKS, and before and after converting to 310 HP and 3-blade, and before and after an engine overhaul. Note that I also have air conditioning which shaves off presumably 2 kts or so

My basic results:

- Weight makes a big difference; fly light and add 3 kts easily; fly at gross weight and lose 3 kts easily

- The standard 2000 O2 with the two-blade would make pretty much book numbers -- so I could get to near / at 190 Kts at wide open and ROP, and at/around 8,000 ft

- TKS shaved off 8-10 Kts -- no question about that

- 310 conversion and 3-blade changed-my-world on take-off (in particular from high-density airports) and climb. Now I get at wide-open and ROP and at/around 8,000 ft about 192 KTas at mid-weight; but that is burning tons of fuel and I don't fly that way other than to test speeds...

- Finally, real-world x-country speed with a new motor, flying wide-open and LOP 13.1 Gph at/above 10,000 ft at 2550 RPM: 170-175 KTAS. I might be able to go maybe 3-5 Kts faster but the hottest cylinder (#3 CHT) prevents me from doing that except on very cold days (I keep temps below 370F CHT).

 

Anyway, that's the summary after 15 years of ownership and flying.... (and trying to "speed-her-up" with careful rigging etc.).

I have a manual dial for true airspeed - outside OAT and altitude slide - typical airspeed indicator and it gives you TAS.  However, for speed runs, as my airspeed calculator may be slightly off, I use GPS ground speed and fly the four cardinal directions.  Later I add them all and divide by 4.  I figure it removes the possibility of manual airspeed indicator error and the variance of the manual slide rule on the airspeed indicator for TAS.

I haven't used the three leg calculation yet.

-Seth

 

 

Edited January 1, 2018 by Seth

[jetdriven]

8 hours ago, aviatoreb said:

I believe it was professor Rogers from usna who first published that method and calibrated it vs a test flight with navy test pilots with a trailing impeller for benchmark validation.

Here’s Mr. Rogers 

http://www.nar-associates.com/technical-flying/horseshoe_heading/horseshoehead_screen.pdf

heres more info on why the 4-heading average is inaccurate.  These plane cost 100$ to go gather the TAS data, why not use the most accurate method? In fact the horseshoe heading technique takes less time since it’s only 3 legs not 4

http://vb.taylorcraft.org/attachment.php?attachmentid=12054&d=1492015397

Edited January 1, 2018 by jetdriven

[Hank]

I use thr back page on my 430W, entering OAT, IAS, etc., and it tells me KTAS.

Edited January 1, 2018 by Hank

[jetdriven]

In the Poh there’s a table where the CAS is ~2 mph less than IAS at cruise. Have to do that as well. But none of these methods are accurate to 1 kt. And they all base it on IAS which itself isn’t very accurate 

[Cruiser]

Back on track.............

I thought I would check. 310 HP and TKS

7000 MSL, 

MAP 23.6 RPM 2500 74% power, 15.3 gph, 150*F ROP, 12.2 mpg (all JPI data)

-8*F, 30.44 baro

~ 300 lbs under gross

KTAS = 183 per Aspen PFD

[M016576]

32 minutes ago, Cruiser said:

Back on track.............

I thought I would check. 310 HP and TKS

7000 MSL, 

MAP 23.6 RPM 2500 74% power, 15.3 gph, 12.2 mpg (all JPI data)

-8*F, 30.44 baro

~ 300 lbs under gross

KTAS = 183 per Aspen PFD

Sounds about right based on those conditions- your density altitude is only about 3500’... a pretty ideal day to be flying a NA airplane. Love the winter.

[kenyale]

177TAS, 8000’, 16.2 GPH, 50 ROP, 4 blade MT prop, TKS and A/C

[carusoam]

Great post #2, ken!

Got any pics of the MT on your O?

Best regards,

-a-

[mike_elliott]

8 hours ago, carusoam said:

Great post #2, ken!

Got any pics of the MT on your O?

Best regards,

-a-

Ken has a 2016 O3 absolutely beautiful plane. He is also the Sec/Treas. of the Mooney Summit, Inc.

[jackn]

not sure if you’ve seen this.