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  #1  
Old 04-15-2021, 09:03 AM
Jeff1smith Jeff1smith is offline
 
Join Date: Mar 2020
Location: Port Angeles
Posts: 26
Default V FE

I have a RV8A that I purchased from an estate. There is no one to ask the obvious questions. I am trying to put together a more complete POH.
Iíve looked at several POH available with a internet search and noticed that some have the V FE at 85 kts and others have it as 100 kts.
Same plane, why the big discrepancy?
While I have your attention, also the Vx, Vy and best glide speed are also quite divergent between individual POHís.
I have a 200 hp with MT three blade cs prop
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  #2  
Old 04-15-2021, 09:19 AM
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Ironflight Ironflight is offline
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The discrepancy probably comes when people don’t specify units! The Vfe four the RV-8 is 100 mph, or 87 knots. Those are design numbers, so are the same for all examples of the airplanes.

Performance numbers (Vx, Vy, etc) are dependent on the specific airplane’s configuration (pro, engine, ASI calibration, etc), so you need to test them out for yourself if they are not already in the aircraft our book supplied by the builder. It’s a good idea to test them yourself anyway, to get more familiar with the airplane. You’re goign to find that Vy is obtained over a fairly wide range of speeds (it is a flat curve), and the difference between 96 knots and 110 knots is minimal - so it can be hard to pin down precisely. That also means you can climb at a speed for best cooling without giving up much.
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RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
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  #3  
Old 04-15-2021, 09:25 AM
Flying Canuck Flying Canuck is offline
 
Join Date: Jan 2015
Location: Red Deer, Alberta, Canada
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I fly a 9A so I can't help with the non documented reference speeds. The flap extension speed is provided in the construction manual and the one from my model's manual states that the RV-4/6/6A/7/7A/8/8A speeds are 110 mph for 20 degrees flaps and 100 mph for full 40 degrees.

Allow me to make 2 strong suggestions.

1. Buy the RV 8 plans on USB from Vans. It's very reasonably priced and contains a lot more than construction information. There is a lot of information about flying the plane included.

2. Plan out a test flight program, pick a decent weather day with light winds aloft and determine the Vx, Vy and best glide speeds for your airplane. This is a great way to get to know the plane. If you have an EFIS with logging, make use of the logs to help with figuring it all out. A more extensive test plan could get you other valuable performance numbers, like cruise speeds, that are unique to your plane.
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  #4  
Old 04-15-2021, 09:47 AM
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Mike S Mike S is online now
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Quote:
Originally Posted by Flying Canuck View Post
Plan out a test flight program, pick a decent weather day with light winds aloft and determine the Vx, Vy and best glide speeds for your airplane. This is a great way to get to know the plane. If you have an EFIS with logging, make use of the logs to help with figuring it all out. A more extensive test plan could get you other valuable performance numbers, like cruise speeds, that are unique to your plane.
This is a good suggestion, and this will help.

https://www.eaa.org/shop/product-det...926&pr=2695484
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Flying as of 12/4/2010

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  #5  
Old 04-15-2021, 02:04 PM
Norman CYYJ Norman CYYJ is offline
 
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Paul sometimes I think I am a bit dense. Can you please explain to me what a flat curve is.
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  #6  
Old 04-15-2021, 02:36 PM
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rv8ch rv8ch is online now
 
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Quote:
Originally Posted by Norman CYYJ View Post
Paul sometimes I think I am a bit dense. Can you please explain to me what a flat curve is.
Here's a good article talking about this from Paul's magazine:

https://www.kitplanes.com/using-leve...b-performance/

The curve does not change much in terms of Rate of Climb vs airspeed. Here's my data, for example:

Click image for larger version

Name:	Flat Curve - Vx Vy.png
Views:	64
Size:	1.50 MB
ID:	10419

Essentially if you fly at 80kts or 105kts it does not make huge difference in the performance.
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  #7  
Old 04-15-2021, 04:17 PM
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Quote:
Originally Posted by Norman CYYJ View Post
Paul sometimes I think I am a bit dense. Can you please explain to me what a flat curve is.
What Mickey said......
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RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
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Dayton Valley Airpark (A34)
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  #8  
Old 04-15-2021, 10:23 PM
Norman CYYJ Norman CYYJ is offline
 
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That to me looks like arc or a curve at the top of some straight lines. How is that curve called flat?
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  #9  
Old 04-15-2021, 10:59 PM
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Quote:
Originally Posted by Norman CYYJ View Post
That to me looks like arc or a curve at the top of some straight lines. How is that curve called flat?
Thatís not a typical RV. Ur e - I think Mickey just grabbed an example. The variation in climb rate for my RV-8 is about 50 rpm between 90 and 115 knots - thatís pretty flat compared to a lot of airplanes.
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Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
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Dayton Valley Airpark (A34)
http://Ironflight.com
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  #10  
Old 04-16-2021, 05:43 AM
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craig.roser craig.roser is offline
 
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What are the different curved lines? Different power prop or engine speed settings?
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2005 Cessna C182T G1000
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