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What is the best way to determine speed improvements?

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ronlee(at)pcisys.net
Guest

Posted: Tue May 02, 2006 4:45 pm Post subject: What is the best way to determine speed improvements?

I have used 3-way GPS runs in the past.



I have started using 4 way GPS runs.



I tried using the Excel program on Kevin Horton's site and did not

do very well.   Both runs (yesterday and today) had a Standard Deviation

of around 3.



Point 2 below is the data in knots and today's is Point 3 (in MPH).  The 

final TAS

was identical in both cases which seems oddly coincidental.



I use a GPS to average the speed for each directional run which I had hoped

would smooth out piloting errors.  Apparently it did not.



I am curious how well others do on this and whether I should just go up

and record the IAS under set conditions then redo it after making a change

that may improve airspeed (such as Pressure recovery wheelpants).



Ron Lee

Point 2 Vwind Wind dir Vtrue

Vg Track (kts) (deg) (kts)

148 352 14.7 336 161.8

160 252 12.1 308 166.8

176 166 19.2 307 161.7

175  84 20.8 326 166.6

ave    16.7 319.4 164.2

std dev 2.9



All these values are MPH



Point 3 Vwind Wind dir Vtrue

Vg Track (kts) (deg) (kts)

190 352 21.7 265 192.5

171 256 17.5 286 186.4

194 168 10.3 271 191.9

202  80 15.8 247 186.6

ave     16.3 267.5 189.3

std dev 3.3

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khorton01(at)rogers.com
Guest

Posted: Tue May 02, 2006 5:43 pm Post subject: What is the best way to determine speed improvements?

On 2-May-06, at 7:37 PM, Ron Lee wrote:



 	  Quote: 	
		   



 I have used 3-way GPS runs in the past.



 I have started using 4 way GPS runs.



 I tried using the Excel program on Kevin Horton's site and did not

 do very well.   Both runs (yesterday and today) had a Standard  

 Deviation

 of around 3.



 Point 2 below is the data in knots and today's is Point 3 (in  

 MPH).  The

 final TAS

 was identical in both cases which seems oddly coincidental.



 I use a GPS to average the speed for each directional run which I  

 had hoped

 would smooth out piloting errors.  Apparently it did not.



 I am curious how well others do on this and whether I should just  

 go up

 and record the IAS under set conditions then redo it after making a  

 change

 that may improve airspeed (such as Pressure recovery wheelpants).



 Ron Lee

 Point 2 Vwind Wind dir Vtrue

 Vg Track (kts) (deg) (kts)

 148 352 14.7 336 161.8

 160 252 12.1 308 166.8

 176 166 19.2 307 161.7

 175  84 20.8 326 166.6

 ave    16.7 319.4 164.2

 std dev 2.9



 All these values are MPH



 Point 3 Vwind Wind dir Vtrue

 Vg Track (kts) (deg) (kts)

 190 352 21.7 265 192.5

 171 256 17.5 286 186.4

 194 168 10.3 271 191.9

 202  80 15.8 247 186.6

 ave     16.3 267.5 189.3

 std dev 3.3




	


Ron,



There are several possible explanations for the poor quality data:



1. The weather conditions may not have been good enough.  You need  

really smooth air, and the wind direction and speed at the test  

altitude must be steady.



2. You made a mistake when copying down one or more of the numbers.   

This is easy to do.



3. You didn't fly as accurately as necessary.  If you want good  

quality data, the flying must be very accurate.  The altitude and IAS  

for each run must be exactly the same.  You need to fly a constant  

heading long enough for the GPS to filter out any variations and  

provide a steady track and GS.



The key to success - I find it extremely difficult to get good data  

unless I have someone with me to record the data.  That lets me  

concentrate on flying the aircraft.  If I have someone to record the  

data, I can normally get a std deviation of less than one knot, but  

I've been doing this sort of stuff for many years.



Don't get discouraged.  Practice makes perfect.  Accurate performance  

testing takes a lot of work.



As far as simply recording IAS.  That can work, if you have developed  

a test procedure that gives a repeatable result.  If you get the same  

IAS on several different flights, then you have an idea of what the  

performance is.  Don't simply take IAS readings on one flight, and  

believe that they are guaranteed to be accurate.



Good luck,

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gcomfo(at)tc3net.com
Guest

Posted: Wed May 03, 2006 4:49 am Post subject: What is the best way to determine speed improvements?

--

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rv8(at)lazy8.net
Guest

Posted: Wed May 03, 2006 5:03 am Post subject: What is the best way to determine speed improvements?

Ron and Kevin

I am assuming the program on Kevin's website is similar to the one I use 

from the Nat'l Test Pilot School. Sounds the same.

I agree with Kevin, getting good data is not easy. I have run at least 

100 4-legged GPS runs in the last 3 years testing 4 different props and 

numerous speed mods on my RV8. If the standard deviation is more than 1, 

I throw away the run. This is an indication that either I did not fly it 

right, did not wait long enough for the speed to settle down after the 

last turn, or the air  1) has vertical movement, or 2) the winds aloft 

are varying in direction or speed.

Ron, as you know already, here in the mountains it is hard to find 

smooth steady winds. Especially on the front range where you are, the 

chance of having zero mountain wave in the spring is small. So, you 

really have to watch the winds aloft forecasts and choose your test 

days. Today, for example, I was going to test my latest cowl mod, but 

the winds are too strong, and showing variance in direction in my area 

(4-corners).

Also, I always use my autopilot with altitude hold to fly the patterns. 

This gives me time to take data and watch for traffic. I used to test 

without an autopilot, and it is very hard, and probably dangerous 

because you run out of time to watch for traffic.

It is also important to fly your tests at the same density altitude, 

rpm, fuel flow, weight, bug density on the wings, etc. to have data to 

compare. Even then, there will be some variations, so I always fly 3 

different days, and 3 or 4 patterns each day, and take an average to 

assess each mod.

Have fun...it is a lot of fun.

John

Kevin Horton wrote:

 	  Quote: 	

On 2-May-06, at 7:37 PM, Ron Lee wrote:

>

>

>I have used 3-way GPS runs in the past.

>

>I have started using 4 way GPS runs.

>

>I tried using the Excel program on Kevin Horton's site and did not

>do very well.   Both runs (yesterday and today) had a Standard  

>Deviation

>of around 3.

>

>Point 2 below is the data in knots and today's is Point 3 (in  

>MPH).  The

>final TAS

>was identical in both cases which seems oddly coincidental.

>

>I use a GPS to average the speed for each directional run which I  

>had hoped

>would smooth out piloting errors.  Apparently it did not.

>

>I am curious how well others do on this and whether I should just  

>go up

>and record the IAS under set conditions then redo it after making a  

>change

>that may improve airspeed (such as Pressure recovery wheelpants).

>

>Ron Lee

>Point 2 Vwind Wind dir Vtrue

>Vg Track (kts) (deg) (kts)

>148 352 14.7 336 161.8

>160 252 12.1 308 166.8

>176 166 19.2 307 161.7

>175  84 20.8 326 166.6

>ave    16.7 319.4 164.2

>std dev 2.9

>

>All these values are MPH

>

>Point 3 Vwind Wind dir Vtrue

>Vg Track (kts) (deg) (kts)

>190 352 21.7 265 192.5

>171 256 17.5 286 186.4

>194 168 10.3 271 191.9

>202  80 15.8 247 186.6

>ave     16.3 267.5 189.3

>std dev 3.3

>

>    

>

Ron,

There are several possible explanations for the poor quality data:

1. The weather conditions may not have been good enough.  You need  

really smooth air, and the wind direction and speed at the test  

altitude must be steady.

2. You made a mistake when copying down one or more of the numbers.   

This is easy to do.

3. You didn't fly as accurately as necessary.  If you want good  

quality data, the flying must be very accurate.  The altitude and IAS  

for each run must be exactly the same.  You need to fly a constant  

heading long enough for the GPS to filter out any variations and  

provide a steady track and GS.

The key to success - I find it extremely difficult to get good data  

unless I have someone with me to record the data.  That lets me  

concentrate on flying the aircraft.  If I have someone to record the  

data, I can normally get a std deviation of less than one knot, but  

I've been doing this sort of stuff for many years.

Don't get discouraged.  Practice makes perfect.  Accurate performance  

testing takes a lot of work.

As far as simply recording IAS.  That can work, if you have developed  

a test procedure that gives a repeatable result.  If you get the same  

IAS on several different flights, then you have an idea of what the  

performance is.  Don't simply take IAS readings on one flight, and  

believe that they are guaranteed to be accurate.

Good luck,

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