REFLECTOR:Re:Pure Jet Velocity XL

[reflector@tvbf.org]

At 10:14 AM 2/11/04 -0500, you wrote:
>In a message dated 2/11/2004 8:33:35 AM Eastern Standard Time, 
>robinream@earthlink.net writes:
>
> > even in a moderate dive it's not that hard to exceed
> > Vne in any type of aircraft.
>
>Exactly, it's hardly limited to canards. Clean high performance spam cans 
>like Cessna 210 and Beech Bo have significant in flight break up numbers 
>from exceeding VNE. Fly a slick airplane and put the nose down and bad 
>thing's can and do happen.

Generally speaking -

1) In a propeller driven airplane, you're probably not going to exceed Vne 
in level flight, or a climb. If you can, it's a poor combination of 
airframe design and engine - either the airframe should be stronger, or you 
don't need all that power.

2) With the power off, a wind milling prop creates a LOT of drag.  It's 
harder to exceed Vne with the power off, even in a descent - you have to 
stick the nose significantly down.

3) When you pull back the throttle on a jet there isn't a prop creating 
drag.  Instead, the engine continues to produce some residual thrust, no 
matter what speed you're at.  In fact, the faster you go, the more power it 
makes, regardless of throttle setting.  (The power doesn't increase at the 
same rate as speed, I'm not saying you're going to accelerate forever.  But 
the more air that the engine passes through, the more air it can 
accelerate, and the more power it's making.)

Pulling back on the throttle on a jet and putting the nose down will cause 
you to accelerate at a much faster rate than doing the same thing with a 
prop on the same airframe.

Yes, there are only two choices - a gentle descent or catastrophic 
destruction of the aircraft and occupants.  As long as you define "a gentle 
descent" as one below the aircraft's *real* Vne.  In a prop aircraft, 
"Gentle" can be pretty steep.  At the limit you have something like the 
Pilatus Turbo Porter that can throw the prop in beta and fly straight down.

Please note, Vne as I'm using it here isn't what's listed in a book.  On 
canard aircraft, those values tend to be conservative.  The Cozy is listed 
at a Vne of 230 MPH.  It's not going to disintegrate if you hit 250.  The 
Long EZ Vne is generally listed at 190 or 195 kts.  Mine cruised at 205 
kts.  As long as the ailerons and elevators are balanced, we don't seem to 
have a flutter problem (assuming you have strong rudder springs, but that's 
another post).

Because we list conservative values for Vne, we tend to think they're not 
that big an issue.  These airplanes don't break up in overspeed, like the 
early Bonanza's.  But there is a *real* Vne for these aircraft, above which 
they will have a catastrophic failure.  Even if it's not driven by flutter 
or structure, that speed is still real.  I've pointed out that critical 
mach could be a very serious problem, and nobody knows at what speed, 
exactly, it would occur.   We've had Berkuts at 300 mph indicated at low 
altitude, without a problem.  But somewhere above that speed is the Vdisaster.

A jet engine puts that speed within easy reach.  If you're flying prop 
speeds, there won't be a problem.  But it will be harder to fly those 
speeds than it would be with a prop.