Overweight takeoff / flight

G-forces are directly related to weight. Since the size of the
control surface is directly related to the forces exerted on it,
control surfaces are dependent on weight.

Sorry, you lost me. The forces exerted on the control surfaces are
going to depend on airspeed and angle of deflection.

The size of control surfaces is irrelevant in this discussion, since
they are fixed at design time.

"G.R. Patterson III" wrote in message
...
Seems to me that you have listed most of the effects correctly. One thing
you
should consider, however, is the fact that the balance envelope for most
(if
not all) planes gets narrower at the top.

A true generalization as far as I know, but I'm sure there are a number of
exceptions and in many cases, the shape of the W&B envelope has as much to
do with what test parameters the manufacturer chose to look at, as it does
any real structural or aerodynamic issues.

The main thing is to make sure one is paying attention to the W&B envelope.
When flying overweight (with FAA approval, of course) one can make an
educated guess by extrapolating the existing graph, but the bottom line is
you don't really know what the shape of the W&B envelope is over gross,
unless the manufacturer has been kind enough to publish it (and they usually
aren't).

In other words, the more weight you
put in an aircraft, the closer to the center of lift that weight has to
be.

Not really. In some aircraft, the envelope is sloped on the aft portion too
as weight goes up. For rearward CG configurations, additional weight needs
to be put farther from the center of lift, not closer. All you can say
without seeing the actual W&B envelope is that usually you have a narrower
range at higher weights. You can't say which direction that range trends,
and even that generalization has exceptions.

[...] At some point, all of the weight will have to be in the front seat.

Even if the previous statement were true, not all airplanes have their
center of lift aligned with the front seat.

I have read of cross-Atlantic ferry flights in which the aircraft was
loaded to
weigh about 1.6 times the normal MGW. In one account, a Bonanza loaded
that way
took over 6,000' to get airborne.

How much runway did Voyager take? I'll bet it was a LOT.

Pete

"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

"Greg Esres" wrote in message
...
BUT, there are 2 things (at least) which contribute to the setting
of Va in the first place.

Neither one of the things you mentioned is given in Part 23 as a
requirement for Va. Part 23 uses the speed solely to provide the
design requirements of the elevators, ailerons, and rudder.


Well, right conclusion even if you don't agree with my method.

Va might be used in the design of the control surfaces, but I
was eluding to how Va is established in the first place.

And certainly one of the limitation is ensuring that you can't
exceed 3.5G at Va by yanking the yoke back. Isn't that
what Va is all about?

Since the forces on these control surfaces will not vary with weight,
you certainly can't scale it up.

Now you've lost me. If that were the case, Va would be
the same at any aircraft weight, which it certainly isn't.

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

Alex,

You make the assumption that the center of gravity envelope edges
(fore and aft c.g. limits) are linear as one goes above published
gross weight. While they may be, it is still an assumption...and test
pilots usually get paid pretty well...and never seem to take
passengers along when doing those tests....

All the best,
Rick

(Koopas Ly) wrote in message . com...
Howdy again,

After reading NTSB reports that attribute the cause of the accident to
exceeding the airplane's maximum takeoff weight, I began wondering
about the effects of an overweight takeoff within C.G. limits.
Specifically, what would I have to do differently when flying an
airplane that's heavier than what the POH specifies. I am not
supporting the practice, of course, so let it be purely educational.

Corrections, additions, and comments welcome.

I would start by considering the increase in weight as comparable to
an increase in load factor. Hence, all your aoa-related speeds would
increase by the square root of the load factor. Vs, Vx, Vy, Vglide,
etc. would all increase. Va would also go up.

Now, by virtue of rotation speed being a function of stall speed, I
conjecture you'd have to liftoff at a faster airspeed which would
equate to a longer takeoff roll.

Then, after pitching for your faster Vy airspeed, you'd notice a
decrease in climb rate at full power due to the increased power
requirement. During cruise, you'd notice a reduced cruise speed and
an increase in stall speed. At approach to landing, should you bump
up your approach speed, you'll find yourself sinking faster when
chopping off the power even though your glideslope will remain the
same.

Since your stall speed is invariably higher, you'll eat up more runway
when landing.

So to sum up:

Takeoff: higher takeoff distance, higher rotation speed.

Climbout: lower climb rate at higher Vy speed, same angle of climb for
obstacle clearance at higher Vx speed. Should Vx not be flown faster,
a poorer angle of climb would result, making obstable clearance
doubtful. *I may be wrong here* I am not sure if the max. angle of
climb is constant regardless of weight...my calculations don't show
so...could someone clarify?

Cruise/Maneuvering: lower cruise speed, higher maneuvering speed,
higher clean stall speed.

Approach to maintain glideslope & descent profile: higher approach
speed, higher sink rate for a given power setting. Higher dirty stall
speed.

Landing: higher landing distance

Question (1 of 2): Seems to me that flying "overweight" is possible if
you're aware of the performance reductions. So why do you read so
many NTSB reports with probable causes listed as "overweight takeoff,
exceeded performance limitations"? As you slowly pull the yoke to
rotate, wouldn't a pilot *realize* through control forces, feel, gut
feeling that something is wrong?

Question (2 of 2): When considering accidents due to exceeding maximum
takeoff weight, do the majority occur during takeoff? If so, is it
typically due to not reaching proper liftoff airspeed for that
increased weight, stalling, and spinning to the ground? Would this
scenario be consistent with failure to set the flaps/slats to their
takeoff value?

Alex

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.

Isn't that what Va is all about?

Conventional wisdom says so, but there is no requirement in Part 23
that says this must be true. Part 23 only uses this speed in its
requirements for control surfaces.

In my view, the most correct definition of Va will be it's the speed
above which you cannot make full or abrupt control movements, due to
control surface integrity.

New airplanes are supposed to come with a new Vo speed, which DOES
require that the airplane stall before exceeding the load factor.

Here's a copy from a draft copy of an AC 23.something that I found.
The AC was intended to make this clear to test pilots, but I don't
think the draft was ever finished:

------------snip-----------------
VA should not be interpreted as a speed that would permit the pilot
unrestricted flight-control movement without exceeding airplane
structural limits nor should it be interpreted as a gust penetration
speed. Only if VA = Vs sqrt(n) , will the airplane stall in a nose-up
pitching maneuver at, or near, limit load factor. For maneuvers where
VAVS n , the pilot would have to check the maneuver; otherwise the
airplane would exceed the limit load factor.

Amendment 23-45 added the operating maneuvering speed, VO in §
23.1507. VO is established not greater than VS sqrt(n) , and is a
speed where the airplane will stall in a nose-up pitching maneuver
before exceeding the airplane structural limits.

------------snip-----------------


Va would be the same at any aircraft weight, which it certainly
isn't.

It is in some airplanes. My Piper arrow doesn't scale it with weight.

Moreover, Part 23 says that Va is *only* defined at max gross. Some
manufacturers do publish Va's at lower weight, but that appears to be
at their option. As written, it doesn't match Part 23 definition.

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
...
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

"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