REFLECTOR: Recovery from Deep Stalls

Fri Feb 1 21:55:16 CST 2008

I think you are confusing the leading edge cuffs with elevator cuffs.  The 
leading edge cuffs were a fix for the deep stall problems with early wings. 
I'm not sure vortex generators would help.

Scott Durham

----- Original Message ----- 
From: <doug.holub at tx.rr.com>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Cc: "Scott Baker" <sbakr at comcast.net>
Sent: Friday, February 01, 2008 5:28 PM
Subject: Re: REFLECTOR: Recovery from Deep Stalls

> Thanks for the good info, Scott. I've got a pre-1990 wing and I've decided 
> not to put the leading edge cuffs on yet, so I'm pretty interested in this 
> subject. The consensus is that vortex generators should do as much good or 
> more than the leading edge cuffs did. Here's hoping!
>
> Doug Holub
> ---- Scott Baker <sbakr at comcast.net> wrote:
>> 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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