REFLECTOR: Recovery from Deep Stalls

Fri Feb 1 21:28:23 CST 2008

Hi Doug, 

      Just curious... How did you arrive at the 'consensus' that VGs would be a better solution than the leading edge cuffs, and why are you settling for a "here's hoping" kind of solution ?  Are VGs the new factory recommendation for the original wings ?

  Regards,

  Jeff Barnes
  XL-RG Kit for Sale

doug.holub at tx.rr.com wrote:
  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 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: 
> To: "Brett Ferrell" ; "Velocity Aircraft Owners 
> and Builders list" 
> 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 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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