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lcottrell

Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or

Posted: Tue Oct 16, 2007 5:08 pm Post subject: VX

How does one figure VX in a firestar. I need it for the sheet  that I will turn in when I have completed my 40 hour test flights. WAG  do?

 Larry C

    [quote][b]

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d-m-hague(at)comcast.net
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Posted: Tue Oct 16, 2007 5:45 pm Post subject: VX

At 09:08 PM 10/16/2007, Larry Cottrell wrote:

  	  Quote: 	
		  How does one figure VX in a firestar. I need it for the sheet that I will turn in when I have completed my 40 hour test flights. WAG do? 	


 One way would be to fly with your GPS, doing climbs at different speeds, then download the tracklog onto your computer and run it into a flight analysis program... I've been using GPLIGC, which is free softward intended for analyzing soaring flights.  It can give you all kinds of useful performance information.



                                 -Dana

 --

 --

 But do you trust the _government_ with semi-automatic assault rifles?    [quote][b]

lcottrell

Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or

Posted: Tue Oct 16, 2007 6:14 pm Post subject: VX

[quote]   



At 09:08 PM 10/16/2007, Larry Cottrell    wrote:

    	  Quote: 	
		  How does one figure      VX in a firestar. I need it for the sheet that I will turn in when I have      completed my 40 hour test flights. WAG do? 	


One way would be to fly with your GPS, doing climbs at different    speeds, then download the tracklog onto your computer and run it into a flight    analysis program... I've been using GPLIGC, which is free softward intended    for analyzing soaring flights.  It can give you all kinds of useful    performance    information.



                                -Dana

    

   Personally I would have nothing that would tell me what any    angle that I would fly anyway, even if I could figure out what VX is, the    information would be useless to any one flying my plane since I have    absolutely no instrument to measure it with. I use 50 MPH for my best speed    for climb. My inclination is to shine it. I was just wondering what some of    the rest of you EAB's used.

   Larry C

[b]

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lcottrell

Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or

Posted: Tue Oct 16, 2007 8:22 pm Post subject: VX

Personally I would have nothing that  would tell me what any angle that I would fly anyway, even if I could figure out  what VX is, the information would be useless to any one flying my plane since I  have absolutely no instrument to measure it with. I use 50 MPH for my best speed  for climb. My inclination is to shine it. I was just wondering what some of the  rest of you EAB's used.

 [quote]   Larry C

    

    

   Please excuse my ignorance, I just looked it up on Google,    and am a bit embarrassed by the revelation. 

   Larry C

[b]

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jindoguy(at)gmail.com
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Posted: Wed Oct 17, 2007 3:10 am Post subject: VX

Larry, Here's how I did it. All you need is an altimeter, an airspeed indicator, a stop watch, a pen and a pad to write on. A knee board is optional. 

VX = the speed that gives the most altitude gain in the shortest distance, also known as obstacle clearance speed.  

VY = the speed that gives the most altitude gain in the shortest time. For brevity, cruise climb speed.

Pick an altitude to start the test. I used 1000' above my field. I did 2 minute climbs at airspeeds from 3 mph above stall to my normal cruise speed in 5 mph increments. I started each climb at 800' so I could get stabilized and started the stop watch as I passed through 1000'. At 2 minutes I read the altimeter and recorded the altitude gain. VX, is the slowest speed that gives the best rate of climb with an adequate margin for stall recovery. You can also get VY if you want to do a bit of calculating. 

To get a chart of how these speeds are effected by density altitude, do the test on many days at a variety of barometric pressures and temperatures. 



Rick



On 10/16/07,  Larry Cottrell <lcottrell(at)fmtcblue.com (lcottrell(at)fmtcblue.com)> wrote:[quote]         

 Personally I would have nothing that  would tell me what any angle that I would fly anyway, even if I could figure out  what VX is, the information would be useless to any one flying my plane since I  have absolutely no instrument to measure it with. I use 50 MPH for my best speed  for climb. My inclination is to shine it. I was just wondering what some of the  rest of you EAB's used.

 [quote]   Larry C

    

    

   Please excuse my ignorance, I just looked it up on Google,    and am a bit embarrassed by the revelation. 

   Larry C

[b]  http://www.matronics.com/Navigator?Kolb-List http://forums.matronics.com  [quote][b]

jindoguy(at)gmail.com
Guest

Posted: Wed Oct 17, 2007 3:12 am Post subject: VX

Oops, forgot to add, to cancel out any convective activity, do the tests at sunrise.



Rick



On 10/17/07, Richard Girard < jindoguy(at)gmail.com (jindoguy(at)gmail.com)> wrote:[quote]Larry, Here's how I did it. All you need is an altimeter, an airspeed indicator, a stop watch, a pen and a pad to write on. A knee board is optional.  

VX = the speed that gives the most altitude gain in the shortest distance, also known as obstacle clearance speed.  

VY = the speed that gives the most altitude gain in the shortest time. For brevity, cruise climb speed.

Pick an altitude to start the test. I used 1000' above my field. I did 2 minute climbs at airspeeds from 3 mph above stall to my normal cruise speed in 5 mph increments. I started each climb at 800' so I could get stabilized and started the stop watch as I passed through 1000'. At 2 minutes I read the altimeter and recorded the altitude gain. VX, is the slowest speed that gives the best rate of climb with an adequate margin for stall recovery. You can also get VY if you want to do a bit of calculating. 

To get a chart of how these speeds are effected by density altitude, do the test on many days at a variety of barometric pressures and temperatures. 



Rick



 On 10/16/07,  Larry Cottrell <lcottrell(at)fmtcblue.com (lcottrell(at)fmtcblue.com)> wrote:[quote]          

 Personally I would have nothing that  would tell me what any angle that I would fly anyway, even if I could figure out  what VX is, the information would be useless to any one flying my plane since I  have absolutely no instrument to measure it with. I use 50 MPH for my best speed  for climb. My inclination is to shine it. I was just wondering what some of the  rest of you EAB's used.

 [quote]   Larry C

    

    

   Please excuse my ignorance, I just looked it up on Google,    and am a bit embarrassed by the revelation. 

   Larry C

[b]   http://www.matronics.com/Navigator?Kolb-List  http://forums.matronics.com 

[b]

slyck(at)frontiernet.net
Guest

Posted: Wed Oct 17, 2007 4:09 am Post subject: VX

For EAB a logbook entry is all that is required.  Nothing to send in.

You can write anything you please for those V speeds.



BB do not archive

Dennis.Kirby(at)kirtland.
Guest

Posted: Wed Oct 17, 2007 9:52 am Post subject: VX

<< How does one figure VX in a firestar. I need it for the sheet that I

will turn in when I have completed my 40 hour test flights. WAG do?

Larry >>



Larry -



A few years ago, Richard Pike posted a very detailed, technically

thorough discussion on how to accurately find Vx and Vy for your (any)

airplane.



It involved creating a lift-over-drag curve and finding climb rates for

various airspeeds and power settings.  The "knee" in the curve

represented one V speed, while the point tangent to that curve that

intersects another point on the graph represented the other V speed.

(Obviously, this is a VERY generic and non-scientific description of the

process.  Check the archives for the nitty-gritty details.)



I did the flight tests, plotted the data points, and created the curve

on my graph.  Amazing!  I found the exact speeds for Vx and Vy for my

Mark-III.  (Thanks again, Richard!)  Turns out, the two speeds turned

out very close to each another for my plane - within five mph.



Dennis Kirby

Mark-III, 912ul, Powerfin-72

Cedar Crest, NM

lcottrell

Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or

Posted: Wed Oct 17, 2007 11:08 am Post subject: VX

---

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Oct 18, 2007 4:39 am Post subject: Re: VX

On April 5, 2007 I posted a spreadsheet showing the approximate relationship among the V-speeds on light aircraft. If you have spreadsheet software you can view it and use it. 



If you don't you can get a good estimate of the Vx speed for your airplane if you know the clean stall speed (Vs1) and max continuous cruise speed (Vh). Subtract the stall speed from the max. continuous stall speed and multiply that number by 14% and add it back to the stall speed.



Example:



Vh = 85 mph

Vs1 = 35 mph



Vh - Vs1 = 85 - 35 = 50



50 x 14% = 7



7 + 35 = 42



42 mph would be a good estimate for Vx for this airplane.

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Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Oct 18, 2007 5:25 am Post subject: Re: VX

While I'm at it I figure it wouldn't hurt to attach a jpg image of the approximate v-speed relationships to Vh and Vs1. See attached image and use following formula for approximate V-speed of interest.



R = Vh - Vs1



where 

R    = speed range

Vh  = max. continuous airspeed

Vs1 = stall speed without flaps



General formula or approximate V-speeds:



R x %(V speed of interest) + Vs1 = approximate V speed of interest

V-speed relationships.jpg

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Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
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planecrazzzy
Guest

Posted: Thu Oct 18, 2007 4:37 pm Post subject: Re: VX

Hi Bob,

            Isn't it all in the book 90-89A....



Seems to me that it's figured from the stall speed....

To get you in the "ballpark".....

Like you said....you write what you want...



                     Gotta Fly...

                                     Mike & "Jaz" in MN - Vx 40 , Vy 50 (FSII)



 	  slyck(at)frontiernet.net wrote: 	
		  For EAB a logbook entry is all that is required.  Nothing to send in.

You can write anything you please for those V speeds.



BB do not archive 	


.

.

.

.

  Here's what mine is....(See Attachment)



 it's NOT exact.....But it's what "I'm" comfortable with.

.

.

.

Best V speeds.bmp

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Fake miZer 005.jpg

Description:

You can see in this picture , That the computer "print out" was taped onto the panel....
(Til something is engraved)

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59.4 KB

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