Does Vno change with weight?

[Mark James Boyd]

I know that stall speed, and min sink and best L/D and\
Va, all change with weight. But what about Vno?
I have never heard of Vno changing with weight.
I know it is predicated on a vertical gust of
some amount (anywhere from 20-45 ft/sec depending
on certifying rules). For now let's assume
it's just 45ft/sec.

How is Vno determined? Does it vary at all with weight?
It seems strange that it would not, but I must say I don't
really know how it is determined.

Part of a question on my checkride yesterday was how
does ballast affect Vspeeds. I didn't know this answer,
but passed anyway (the FAA inspector only required
a 70% level of knowledge to pass).

By the way, many thanks and gratitude to all the
folks who participated (sometimes very strongly :)
in threads over the past few months. It really helped
me to understand a LOT of the more challenging
aspects of soaring. It takes many eggs to make an
omlette! I really appreciate the folks that really
took time to contribute, and even the folks that
got very excited taking a different side sometimes
added a lot to the group for me. The Lennie's and Bill's
and Al's of the group may sometimes seem a little
grumpy, but I'm also grateful for them, because they
represent those colorful folks we also meet right
there at the local gliderport who give a frank and
bald opinion sometimes (when maybe some of the rest of
us would let it drop :)

In the end, thanks for ALL of your input and various
experience levels. It has been VERY enlightening!

Merry Christmas!

Mark

[Ivan Kahn]

"Mark James Boyd" > wrote in message
news:3fe48d7d@darkstar...

>
> I know that stall speed, and min sink and best L/D and\
> Va, all change with weight. But what about Vno?
> I have never heard of Vno changing with weight.
> I know it is predicated on a vertical gust of
> some amount (anywhere from 20-45 ft/sec depending
> on certifying rules). For now let's assume
> it's just 45ft/sec.
>
> How is Vno determined? Does it vary at all with weight?
> It seems strange that it would not, but I must say I don't
> really know how it is determined.
>
> Part of a question on my checkride yesterday was how
> does ballast affect Vspeeds. I didn't know this answer,
> but passed anyway (the FAA inspector only required
> a 70% level of knowledge to pass).
>
> By the way, many thanks and gratitude to all the
> folks who participated (sometimes very strongly :)
> in threads over the past few months. It really helped
> me to understand a LOT of the more challenging
> aspects of soaring. It takes many eggs to make an
> omlette! I really appreciate the folks that really
> took time to contribute, and even the folks that
> got very excited taking a different side sometimes
> added a lot to the group for me. The Lennie's and Bill's
> and Al's of the group may sometimes seem a little
> grumpy, but I'm also grateful for them, because they
> represent those colorful folks we also meet right
> there at the local gliderport who give a frank and
> bald opinion sometimes (when maybe some of the rest of
> us would let it drop :)
>
> In the end, thanks for ALL of your input and various
> experience levels. It has been VERY enlightening!
>
> Merry Christmas!
>
> Mark
>

Vno is not effected by weight, I think this is the applicable regulation:

§23.1505 Airspeed limitations.

(b) The maximum structural cruising speed VNO must be established so that it
is --

(1) Not less than the minimum value of VC allowed under §23.335; and

(2) Not more than the lesser of --

(i) VC established under §23.335; or

(ii) 0.89 VNE established under paragraph (a) of this section.



Ivan

[Mark James Boyd]

In article <BE1Fb.164924$_M.749040@attbi_s54>,
Ivan Kahn > wrote:
>"Mark James Boyd" > wrote in message
>news:3fe48d7d@darkstar...
>
>>
>> I know that stall speed, and min sink and best L/D and\
>> Va, all change with weight. But what about Vno?
>> I have never heard of Vno changing with weight.
>
>Vno is not effected by weight, I think this is the applicable regulation:
>
>§23.1505 Airspeed limitations.
>
>(b) The maximum structural cruising speed VNO must be established so that it
>is --
>
>(1) Not less than the minimum value of VC allowed under §23.335; and
>
>(2) Not more than the lesser of --
>
>(i) VC established under §23.335; or
>
>(ii) 0.89 VNE established under paragraph (a) of this section.
>
>Ivan
>

You mention Vc (Design cruising speed).
JAR 23.335
(a) Design cruising speed, VC. For VC the following apply:
(1) VC (in knots) may not be less than -
(i) 33 x sqrt(W/S) (for normal, utility and commuter category
aeroplanes); and
(ii) 36 x sqrt(W/S) (for aerobatic category aeroplanes).
where W/S = wing loading at design maximum takeoff weight lb/ft2.
(2) For values of W/S more than 20, the multiplying factors may
be decreased linearly with W/S to a value of 28.6 where W/S = 100.


You will notice that Vc is marked on the ASI and in the POH,
and doesn't change. But it was determined by the manufacturer
based on the max takeoff weight (which is fairly arbitrary).
For instance, Vc = Vno for the PW-5. At max weight the wing
loading is 6.06 lb/ft2, and Vc is calculated for the utitlity
category. 33 x sqrt (6.06) = 81 knots. This matches the
PW-5 POH.

So Vno (which is often equal to Vc) is really a
limiting airspeed for max weight. And if the max weight was
increased by the manufacturer, a new series of tests would be
needed to verify a vertical gust would not overstress the
glider at this new calculated Vno.

So Vno does not vary by weight, but is calculated and verified
based on the max gross takeoff weight and wing loading of
the aeroplane. Weights less than this are fine, but exceeding
max gross means flights at Vno may exceed design stress limits.

So heavy weight is good for aerobatics (allows full deflection
of the elevator at a fairly high Va, since the wing will stall
before exceeding the max g loads) but bad for turbulent air
(since it's like going fast in a heavy car over a
speed bump). This is consistent with why pilots avoid ballast
when flying Vno in wave/rotor (which may have stronger vertical
gusts than the certification requires).

Thanks for the 23.335 reference!

Mark