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  #1  
Old 08-12-2017, 06:05 PM
Dorfie Dorfie is offline
 
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Default Vx, Vy, Vg

How exactly did you determine these numbers?
I would appreciate some of the numbers that were determined for the RV10.
Thanks.
Johan
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  #2  
Old 08-12-2017, 06:10 PM
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bkervaski bkervaski is offline
 
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I'm curious of this as well .. since there are a lot of differences between builds .. I'm assuming you just go figure it out by testing various speeds?
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  #3  
Old 08-12-2017, 06:41 PM
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snopercod snopercod is offline
 
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Quote:
Originally Posted by bkervaski View Post
I'm assuming you just go figure it out by testing various speeds?
Exactly. It's a PITA, but it should really be done for each aircraft. Props, especially, make a big difference. Here's how I found the "best glide" on my plane, and the Vy and Vx are done the same way, only climbing. This is just the 80 KIAS run, and I also did them at 90, 100, and 110. My Garmin Virb allowed me to dictate the numbers into the Intercom and also see the numbers on the panel.

I did this particular test where there were mountains in the area, which was a bad thing; You never know if you are in an updraft or downdraft. Later, I reperformed the tests in a flat area on a windless day.

https://www.dropbox.com/s/dz98ah3d5x...80Kts.mp4?dl=0

P.S. The "landing gear" warning was going off because I was below 90 Kts with my gear up. The "stall" warning was going off because I didn't have it set quite right (yet).
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  #4  
Old 08-12-2017, 07:00 PM
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Ironflight Ironflight is offline
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The first thing I'd suggest is that you find a local EAA Flight Advisor to chat with - he or she can help coach you through a real flight test program, provide good sources of information on precise flight testing methods and techniques, and probably help you to develop test cards. Box and Vy are numbers you legally must determine for YOUR particular airplane in order to sign it out of Phase 1, and it might take you a number of flights to refine them accurately - it all depends on teh conditions and your ability to fly accurately.

There are a number of good books on flight testing light aircraft - unfortunately, I'm not near my bookshelf at the moment to dig out titles. Check teh EAA store online. there are also FAA Advisory Circulars that will help.

But start with a Flight Advisor - if you're new to this (and it sounds like you are), they can give you a good start in a robust flight test program.

Paul
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  #5  
Old 08-12-2017, 07:13 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Ironflight View Post
there are also FAA Advisory Circulars that will help.
Yup

Get your self a copy of Amateur Built Aircraft Flight Testing Handbook AC 90-89B HERE

It is not as in depth as some other references are but it is a good start towards getting familiar what is involved in a general flight test plan.
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  #6  
Old 08-12-2017, 09:03 PM
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ChiefPilot ChiefPilot is offline
 
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Quote:
Originally Posted by Dorfie View Post
How exactly did you determine these numbers?
I would appreciate some of the numbers that were determined for the RV10.
Thanks.
Johan
Bootstrap to get close, then some additional testing at different weights and CGs to get closer, then development of mathematical models to account for different conditions (weight, density altitude, etc), then additional flight testing to validate the models.

The references listed previously are good starts.
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  #7  
Old 08-12-2017, 09:24 PM
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RV6_flyer RV6_flyer is offline
 
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Quote:
Originally Posted by Dorfie View Post
How exactly did you determine these numbers?
I would appreciate some of the numbers that were determined for the RV10.
Thanks.
Johan
I got my license 35-years ago. Your subject line has Vg in it.

What is Vg? I am familiar with V speeds but not Vg.

Are you trying to determine a maximum gust speed? That would come from the designer
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  #8  
Old 08-12-2017, 10:42 PM
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RV8JD RV8JD is offline
 
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Default Vg = Best Glide Speed?

Quote:
Originally Posted by RV6_flyer View Post
I got my license 35-years ago. Your subject line has Vg in it.

What is Vg? I am familiar with V speeds but not Vg.

Are you trying to determine a maximum gust speed? That would come from the designer
My guess is the OP meant Best Glide Speed.

(And I got my license more than 35 years ago also. That just means we're getting older! )
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  #9  
Old 08-13-2017, 06:09 AM
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Auburntsts Auburntsts is online now
 
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EAA has a Hints for Homebuilders video on finding Vy and Vx: http://bcove.me/8ch18ik8

Finding best glide is similar to finding Vy except you are recording distance covered for a specific amount of altitude loss (say 1000 ft) at a specific airspeed instead of the amount of time it takes to gain a specific amount of altitude (again say 1000 ft) at a specific airspeed.

This is one of those flight tests where the additional pilot program or an autopilot that has an IAS function comes in real handy.
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  #10  
Old 08-13-2017, 09:26 AM
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ChiefPilot ChiefPilot is offline
 
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Quote:
Originally Posted by Auburntsts View Post
EAA has a Hints for Homebuilders video on finding Vy and Vx: http://bcove.me/8ch18ik8This is one of those flight tests where the additional pilot program or an autopilot that has an IAS function comes in real handy.
It's not hard to hold an indicated airspeed to within one knot for 90 seconds of climb or descent given an electronic airspeed indicator and reasonable conditions. I doubt autopilots in our birds could do any better.
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