Overweight takeoff / flight

"Greg Esres" wrote in message
...
Since the forces on these control surfaces will not vary with weight,
you certainly can't scale it up.

Huh? You have to scale Va with weight. Even within legal configurations, a
specific Va is valid only at a specific weight, with lower weights resulting
in lower Va and higher weights resulting in higher Va.

Just because you went outside the design/certification envelope, that
doesn't change the nature of Va.

Pete

a specific Va is valid only at a specific weight, with

Show me a Part 23 requirement that says so.

Todd Pattist has lectured on this a couple of times, and he's right.

"Greg Esres" wrote in message
...
a specific Va is valid only at a specific weight, with

Show me a Part 23 requirement that says so.

Part 23 isn't what makes an airplane fly. Aerodynamics are. And those
aerodynamics clearly show that at a given weight, a slower airspeed is
required in order to limit acceleration to a given number.

Oddly enough, many aircraft manuals bear this out, providing lower Va speeds
for lower weights.

Todd Pattist has lectured on this a couple of times, and he's right.

I seriously doubt Todd has told you that Va remains the same regardless of
aircraft weight. You obviously misunderstood him.

Pete

The definition of Va in Part 23 is clear. It has nothing to do with
control surfaces and everything to do with stall speed and load
factor.

Then you haven't read Part 23.

Let me point out the sections to you:

-------------snip------------------
Horizontal Stabilizing and Balancing Surfaces

§ 23.423 Maneuvering loads.
Each horizontal surface...must be designed for the maneuvering loads
imposed by the following conditions:
(a) A sudden movement of the pitching control, at the speed VA...

(b) A sudden aft movement of the pitching control at speeds above
VA...

Vertical Surfaces
§ 23.441 Maneuvering loads.
(a) At speeds up to VA, the vertical surfaces must be designed to
withstand the following conditions....

Ailerons and Special Devices
§ 23.455 Ailerons.
(a) The ailerons must be designed for the loads to which they are
subjected -
....
(i) Sudden maximum displacement of the aileron control at VA. Suitable
allowance may be made for control system deflections.
-------------snip------------------

Now, the section that may be misleading you is this
---------snip-------------
§ 23.335 Design airspeeds.
(c) Design maneuvering speed VA. For VA, the following applies:
(1) VA may not be less than VS * sqrt(n) where -
---------snip-------------


Note that it says MAY NOT BE LESS THAN... In other words, it can be
more.


Oddly enough, many aircraft manuals bear this out, providing lower
Va speeds for lower weights.

Oddly, you didn't read what I wrote.

The point is that at Part 23 doesn't require this. And not all
aircraft publish such variations.

does not mean that the maximum speed at which you can fly
and be assured of not overstressing the airplane does not go down as
weight is reduced.

Again, you didn't read what I wrote. I said it doesn't scale UP.
Flying over max gross may increase maneuvering speed, but it doesn't
increase VA, because the increased weight won't protect control
surfaces from failure.


Even your control surface tangent isn't really relevant to this
particular thread

Tangent? It's the essence of what Va is.


I seriously doubt Todd has told you that Va remains the same
regardless of aircraft weight. You obviously misunderstood him.


Ok, you read what he wrote and tell me:

----------------snip----------------------
Note that this is a minimum Va ("no less than"). Thus the
designer can specify a higher Va and then protect the tail
surfaces by limiting stick throw, or by making the required
force at the stick to produce a damaging load on the
protected structure higher than a standard pilot could
exert. Note also that the regulatory definition of Va
*requires" that it be computed only at a stalling speed "at
the design weight" , i.e. max gross. Thus any lower speed,
or any lower weight cannot be Va as defined.
----------------snip----------------------

"Greg Esres" wrote in message
news
Then you haven't read Part 23.

Yes, I have.

Let me point out the sections to you:

Those sections stipulate, given an existing Va, how the control surfaces
must be designed. They do not in any way define Va.

The point is that at Part 23 doesn't require this. And not all
aircraft publish such variations.

You are still hung up thinking that Part 23 is what makes airplanes fly.

Again, you didn't read what I wrote. I said it doesn't scale UP.
Flying over max gross may increase maneuvering speed, but it doesn't
increase VA, because the increased weight won't protect control
surfaces from failure.

In this context "maneuvering speed" is synonymous with "Va". Yes, you're
right, there is only ONE Va. But in the world of piloting, we commonly
understand the shorthand "Va" to mean "maneuvering speed at a given aircraft
weight" where the weight is changeable.

Tangent? It's the essence of what Va is.

Not in this context it's not.

I seriously doubt Todd has told you that Va remains the same
regardless of aircraft weight. You obviously misunderstood him.

Ok, you read what he wrote and tell me:

If you think that he was explaining the aerodynamics of maneuvering speed,
you misunderstood him. If you don't think that he was explaining the
aerodynamics of maneuvering speed, then your comments based on that quote
are irrelevant to this thread.

Pete

we commonly understand the shorthand "Va" to mean "maneuvering speed
at a given aircraft weight" where the weight is changeable.

Then what is commonly understood is not correct, because that's not
how Va is *necessarily* determined.

Not in this context it's not.

PARTICULARLY in this context. The control surfaces were designed with
withstand full movements at PUBLISHED Va, not his new, derived, HIGHER
Va.

"Greg Esres" wrote in message
...
PARTICULARLY in this context. The control surfaces were designed with
withstand full movements at PUBLISHED Va, not his new, derived, HIGHER
Va.

There are any number of structural issues raised by overgross flight. It
was clear to me which one he was asking about, and the control surfaces
ain't it.

Pete:

Let me elaborate on my terse response (and see my response to Tony).
I agree that maneuvering speed, as defined in the aerodynamics books,
must be scaled with weight. However, Va, which is called DESIGN
maneuvering speed by the FAA, doesn't really match the definition of
plain ole "maneuvering speed". They really should have called it
something else, IMO.

However, it appears that most manufacturers are shooting for a
maneuvering speed, even though the regulations don't require it. If,
however, they chose to make the speed higher for some reason, it won't
protect you from overstressing the airplane, and neither will the
speed when you scale it for weight. GIGO. ;-)

Still, all this is of only academic interest. The one thing that IS
known is that the control surfaces must be protected at VA, and that
won't scale UP from published Va. Agreed?

"Greg Esres" wrote in message
...
Still, all this is of only academic interest. The one thing that IS
known is that the control surfaces must be protected at VA, and that
won't scale UP from published Va. Agreed?

No. Just because Part 23 doesn't stipulate that at a lower weight, a lower
airspeed must be used to ensure not overstressing the airplane in
turbulence, that does not mean that the maximum speed at which you can fly
and be assured of not overstressing the airplane does not go down as weight
is reduced.

Put another way: the minimum airspeed at which a given load factor can be
achieved before stalling the aircraft is positively correlated with weight
(i.e. it goes down as weight goes down, and goes up as weight goes up).
This is *known*. The fact that it's not stated in Part 23 does not make it
any less known.

Even your control surface tangent isn't really relevant to this particular
thread since you are intentionally limiting your comments to a single
weight. Again, just because Part 23 only requires a number to be defined at
a specific weight, that does not automatically mean that the number doesn't
exist at a different weight, nor does it necessarily mean that number is the
same at a different weight.

The definition of Va in Part 23 is clear. It has nothing to do with control
surfaces and everything to do with stall speed and load factor. Just
because Va is only used again within Part 23 for some other use, that does
not change the nature of the calculation. It is commonly understood that,
even though by definition Va exists only for a specific weight, that for the
purposes of flying, one needs to adjust the "operational Va" according to
weight if one expects to remain within the certificated load limits.

Pete

"Peter Duniho" wrote in message
...

The definition of Va in Part 23 is clear. It has nothing to do with
control
surfaces and everything to do with stall speed and load factor.

Actually, it seems to depend on both. I'm all turned around
on this having scratched my head for a while. Greg is
essentially correct.

23.335 says that Va must be = Vs.sqrt(load-factor)
If we take the equality, then this is the load-factor
relationship we get assuming "Lift prop. to AOA"
and "Lift prop. airspeed**2".

23.423 (and others I'd missed) say how the control
surfaces must behave at Va and above. Designers
can set anything they want for Va as long as it
passes the control surface tests.

But since they are likely to want to minimize
complexity & weight of the control surface
mechanism, they are likely to choose Va to be
the minimum allowed by 23.335. But they don't
have to.

Greg is right. They really ought to have invented
another term for it. Va isn't the maneuvering
speed at all, and should be renamed to something
completely different.

--
Dr. Tony Cox
Citrus Controls Inc.
e-mail:
http://CitrusControls.com/