REFLECTOR: Recovery from Deep Stalls
Scott Baker
sbakr at comcast.net
Fri Feb 1 15:55:17 CST 2008
Regarding deep stalls -
I am not familiar with the stall characteristics of canard aircraft other
than the Velocity.
I believe there might be a general lack of knowledge and perhaps some
misconceptions regarding deep stalls amongst Reflectorites.
The flight test articles (see links below) focus on the deep stall
phenomenon in Velocity aircraft shipped prior to 1992.
It is important to note the difference between "deep stalls" and "sustained
(unrecoverable) deep stalls". Through flight testing and analysis of
accident reports from several deep-stall Velocity accidents prior to 1992 -
Danny Maher learned the aircraft could enter an unrecoverable sustained deep
stall, given extreme rearward CG conditions. For those who have not read
the articles, please do. They offer fascinating information.
As a result of these studies, Danny changed the shape of the main wing at
its outboard location to provide more lift at slow airspeeds; reduced the
size of the fuel header tank (which was behind the flight CG envelope); and
changed the orientation of the rear fuel containment bulkhead (inside the
strakes) so that they projected in a forward angle - thereby moving the
center of the fuel mass forward.(contributing to moving the aircraft center
of mass forward). Following these changes, one is still able to bring the
aircraft to a deep stall - but what's most important, the aircraft is
recoverable from a deep stall. I spoke to Danny about this - and he attests
that the aircraft is not only recoverable from a deep stall - it will do so
on its own and without stall recovery inputs by the pilot. Having never
attempted to put the aircraft into a deep stall, I defer to Danny's
knowledge and testimony on this subject!
As a former Velocity demonstrator pilot - and also in my experiences as a
CFI giving Velocity Flight Transition Training, I have performed literally
hundreds of stalls in various Velocity models. These include power off
stalls during straight and level; and during turns with bank angles in
excess of 45-degrees; power on stalls with a climb angle of 45-degrees pitch
up attitude; and accelerated stalls at bank angles of 60-degrees and
greater. I have purposefully put the aircraft in prolonged pitch-buck
situations when following slower traffic on final approach. The point I
wish to make is this - a Velocity will not enter a _deep_ stall during
normal maneuvering - nor any of the exaggerated maneuvers that I have just
described - providing the aircraft is within its recommended CG envelope.
Is there a stall "Boogie Monster"? I've observed that while Lancair
publishes a Vs of 74-mph; pilots often fly using an approach speed closer to
110mph, well over the 1.3 x Vso approach speed rule-of-thumb. What gives?
Why do so many Lancair drivers fly approaches 30mph faster than the
published stall speed? I've asked Lancair pilots how their aircraft behaves
during stalls - and was very surprised that several have _never_ performed a
stall in a Lancair! Apparently the Lancair IV's response to an uncommanded
stall is so bad that many pilots simply "do not go there". Is there a stall
"Boogie Monster" that haunts Velocity aircraft? I've never seen him.
That being said - I've never taken the Velocity out in search of deep
stalls. One would need to work at it. Gathering air speed and going
vertical would do it (I'm not suggesting we all go out and do this, by the
way!). According to Danny, recovery should be as simple as letting go of
the controls. There is, however, a recommended recovery procedure follow a
deep stall. The steps are simple - apply full throttle; full RPM (if using
a variable or constant speed propeller); full forward elevator; and wait.
If the aircraft responds to rudder authority, attempt to put the aircraft
into a wing-over. The goal is to get the pitch attitude pointing down and
bring air speed to the flight controls. --> Note to those who have flight
tested their aircraft into a deep stall - please share your experiences!
Several other tidbits of info - there are enough differences in stall
characteristics between Velocity models that caution should be taken not to
accept statements about the stall behavior of one Velocity as being
identical to others. They are the same; but different ;-) Several recent
contributions to the Reflector talk about landing the aircraft from an
aircraft carrier like "flared" attitude. This might work for one Velocity,
but not the other. I can tell you that one of our Velocity XL demo
aircraft, fully loaded, produced small oscillations in pitch at 75 to 80
knots during approach - still well above stall speed. Not a good situation
to perpetuate down to landing. I just want to point out that this is in
contrast to the behavior of John D's and Al G's aircraft.
Best to all,
Scott B.
----- Original Message -----
From: <doug.holub at tx.rr.com>
To: "Brett Ferrell" <reflector at velocityxl.com>; "Velocity Aircraft Owners
and Builders list" <reflector at tvbf.org>
Sent: Friday, February 01, 2008 10:51 AM
Subject: Re: REFLECTOR: Velocity video
> Wow. Mr. Rutan encourages all EZ owners to test for deep stall above 8000
> feet while wearing a parachute. If the airplane does enter a deep stall,
> bye-bye airplane.
>
> Doug Holub
> ---- Brett Ferrell <reflector at velocityxl.com> wrote:
>> Dave,
>>
>> I don't think it generally is recoverable, that's the problem. Here are
>> a couple of old articles on Deep Stall, offered in the name of
>> education/safety (fair use) since they're on my website without
>> permission.
>>
>> http://www.velocityxl.com/Downloads/CP76/CP76-P2.htm - Canard Pusher 76
>> reprint "The Latest on Deep Stall"
>> http://www.velocityxl.com/Downloads/VelocityDeepStall.pdf - Deep Stall
>> Solution - July 1991 Sport Aviation
>>
>> Brett
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