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  #1  
Old 04-05-2021, 01:33 PM
Saville's Avatar
Saville Saville is offline
 
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Location: KBVY Massachusetts
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Default RV-8 V Speeds and Van's "Blue Line"

Sorry for the elementary primary School 101 question, but I want to be sure I understand. This is also a lesson I learned in taking things for granted.:

Over the weekend I updated my EFIS so that it showed airspeed in knots rather than MPH (was set to MPH when I bought the plane).

So then I flew some tests and noted indicated speeds - now in knots - of Power Off (clean/Landing Config) stalls, power on stalls etc. with the view of updating the POH.

I also decided to compare the existent settings on the EFIS and POH with the hard values specified in the builder's document. Things like Vfe, Vne etc just to be sure they are correct.

I saw the table shown in the the Thumbnail. I eliminated the values for the other RV's and kept only those for the RV-8, and also kept the MPH values and added my values in Knots.

We can ignore Vso and Vs1 as those values in knots are ones I obtained in last weekend's test flights and are not conversions from Van's MPH values.

Vfe - I was aghast to see that the top of the white arc on the plane was
not the stated 100mph, but 120mph. So that was changed to 87kts
(or 100mph)

I confess to being confused by the "Blue Line" and the Yellow Arc values.

1) I only know of "Blue Line" in multi-engine ops - Vyse.
- Besides which I don't have a blue line marking on my airspeed indicator.

2) I'm trying to differentiate between the "Yellow Arc" in this table and the
"Blue Line". I'm figuring that "Blue Line" means Va (142mph) and the
Yellow Arc runs from Vno to Vne (193mph to 230mph).

Is that the correct interpretation?

If so then I need to placard 123kts (142mph)for Va (no full control deflection),
and set the EFIS yellow arc for 168-200kts (193-230 mph).

Presently my yellow arc starts at 180mph. I have no idea where that number came from. It's conservative from the standpoint of Vno so it's value doesn't scare me like the Vfe value did.

So I learned a lesson in taking settings for granted.

Or maybe I'm misinterpreting these values in which case correction is appreciated.
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Last edited by Saville : 04-05-2021 at 01:47 PM.
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  #2  
Old 04-05-2021, 01:38 PM
Taltruda Taltruda is offline
 
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Blue line in twins is not Vmc.. Blue line is Vyse, best rate airspeed single engine. My guess is that the previous owner had marked a Vy speed? I think most light twins label Vmc by a little red line, don’t they?

Va (maneuvering speed) isn’t marked on any airspeed indicator that I know of..
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Last edited by Taltruda : 04-05-2021 at 01:40 PM.
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  #3  
Old 04-05-2021, 01:49 PM
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Saville Saville is offline
 
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Quote:
Originally Posted by Taltruda View Post
Blue line in twins is not Vmc.. Blue line is Vyse, best rate airspeed single engine. My guess is that the previous owner had marked a Vy speed? I think most light twins label Vmc by a little red line, donít they?

Va (maneuvering speed) isnít marked on any airspeed indicator that I know of..
My error on the blue line = Vmc - changed to Vyse. Thanks

Not sure what speed setting you are referring to when you say: "My guess is that the previous owner had marked a Vy speed?"

Va is placarded I do believe.
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Old 04-05-2021, 01:52 PM
Taltruda Taltruda is offline
 
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Quote:
Originally Posted by Saville View Post
My error on the blue line = Vmc - changed to Vyse. Thanks

Not sure what speed setting you are referring to when you say: "My guess is that the previous owner had marked a Vy speed?"

Va is placarded I do believe.
I misread your post.. I thought the previous owner had marked a ďblue lineĒ on your indicator.
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  #5  
Old 04-05-2021, 03:08 PM
BobTurner BobTurner is offline
 
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Of course Va varies with weight, decreasing as weight goes down.
In a departure from the rules for normally certified aircraft, Vans has stated that their published Vne is meant to be true airspeed, not indicated. Which means the max allowed indicated airspeed goes down, as you climb. Some EFIS units will let you enter Vne as a true airspeed, then calculate where the red line goes on the IAS, based on altitude and temperature.
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Old 04-05-2021, 03:12 PM
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Saville Saville is offline
 
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Quote:
Originally Posted by BobTurner View Post
Of course Va varies with weight, decreasing as weight goes down.
In a departure from the rules for normally certified aircraft, Vans has stated that their published Vne is meant to be true airspeed, not indicated. Which means the max allowed indicated airspeed goes down, as you climb. Some EFIS units will let you enter Vne as a true airspeed, then calculate where the red line goes on the IAS, based on altitude and temperature.
Yes Va changes with weight (8083).

I'm asking about what Van means by the "blue line" and if that is meant to be Va.

Do you have any info on that?
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Old 04-05-2021, 03:16 PM
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https://www.vansaircraft.com/wp-cont.../02/speeds.pdf

Blue Line
(Maneuvering speed. Maximum speed at which full control can be applied. Speed at which full elevator control would impose loads exceeding limits)


As a practical matter, most think of it as the limit speed for max elevator travel, in order to preclude inadvertent disassembly. Recall early on, Van's lost a demonstrator to an apparent over-G.

It's marked on airspeed indicators purchased from Van's, 123 knots or 143 mph for the -8
.
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  #8  
Old 04-05-2021, 03:26 PM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by DanH View Post

It's marked on airspeed indicators purchased from Van's, 123 knots or 143 mph for the -8
.
Really? Iíd consider that a poor practice, as someone flying below gross weight might think itís okay to do abrupt control inputs just below that blue line, when in fact he may be over Va.
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Old 04-05-2021, 03:28 PM
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Saville Saville is offline
 
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Quote:
Originally Posted by DanH View Post
https://www.vansaircraft.com/wp-cont.../02/speeds.pdf

[i]Blue Line


It's marked on airspeed indicators purchased from Van's, 123 knots or 143 mph for the -8
.
Ahhh ok so Van calls it the "Blue Line" because on his ASI's he puts a blue line there. That helps to solve that mystery.

Thanks
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  #10  
Old 04-05-2021, 04:26 PM
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RV7A Flyer RV7A Flyer is offline
 
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And THAT'S what happens when you don't follow standards and conventions...Van's used a term that is well-known to a large number of pilots and gave it a new (their own) meaning, thus causing confusion. Even more so now that most Van's aircraft being built don't use the old (and apparently custom) Van's gauges anymore, but rather glass panels, and yet it's still there in their documentation. And it's not even correct..."maneuvering speed" is also a function of weight; it's not fixed.
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