REFLECTOR: CG Determination (was Stall Characteristics)

Sat, 15 Nov 2003 11:18:05 -0800

Tom,

The design Center of Gravity range is set by the aerodynamics (wing shape,
angles of attack, etc.) and should be very close for all aircraft completed
in accordance with the plans.  That's published in the manual.  However,
your actual CG location must be determined by careful weighing of the
completed aircraft (each wheel at effectively the same time) and calculating
the CG location.  Then the CG for each proposed loading can be determined
from the weight and location of people, cargo, etc. and a little simple
mathematics.  The measured/calculated CG location is then compared to the
design CG range to assure that you are going to be within the specified
range.

The "minimum control" (aka "stall") speeds are to be determined
experimentally at various points within the CG range during your test flying
period to check that the aerodynamics of your plane are actually the same
(or at least close) to the design aerodynamics.

By the way, did you sell that prop?

Keith

----- Original Message ----- 
From: "Tom Martino" <tmartino@troubleshooter.com>
To: <reflector@tvbf.org>
Sent: Saturday, November 15, 2003 8:11 AM
Subject: RE: REFLECTOR:Stall Characteristics

> Here is a very basic, yet important question.
>
> Does the original CG envelope hold true for all subsequent aircraft or
> will the envelope vary with modifications.
>
> For example, some of us may have heavier wings, different engines and
> props, variation in interiors, etc.
>
> I realize that with most aircraft with basic envelope holds true and you
> simply calculate the CG based on the loading and "station" of the
> loading.  Is that so with an experimental aircraft that could be
> different from one completion to another?
>
> Is there a way (a safe way) to calculate your CG range?  Or should we
> use the original factory envelope?  (By the way where is that envelope
> published?)
>
> Any info would be appreciated!
>
>
> -----Original Message-----
> From: Scott [mailto:scott@tnstaafl.net]
> Sent: Saturday, November 15, 2003 7:11 AM
> To: reflector@tvbf.org
> Subject: Re: REFLECTOR:Stall Characteristics
>
> Scott B,
>
> Thanks for that follow up.
>
> Glad you got a hold of "The Expert" for some horses mouth info.
> Danny's
> expert opinion is right in line with the pilots I have spoken to who
> have
> performed aerobatics( I know Dan, Puffer and Rutan said don't do it ),
> in
> canard aircraft.
>
> I think this would be good grist for the mill, for your next article in
> the
> next V.V.
>
> Scott D.
>
> At 05:08 PM 11/14/2003, you wrote:
> >John and fellow Reflectorites -
> >I read in John's post that he is concerned that stalls in the Velocity
> might
> >be something that is ready to bite the unsuspecting pilot.  I don't
> think
> >that is the situation at all.  I think the aircraft should be stall
> tested
> >throughout the published cg range during flight testing (there is a
> >recommended flight test procedure for this).  I am not worried about
> doing
> >stalls in the Velocity as long as the aircraft is within cg limits.
> >Velocity routinely demonstrates stalls during demonstration flights -
> from
> >normal pitch bucks to the "dreaded" cross-controlled base-to-final
> stall
> >scenario.  The stall behavior is so benign that it isn't - as least in
> my
> >opinion - anything to worry about ... it's pretty much a "non-event".
> In
> >that regard, I agree with you that there isn't a need to "practice"
> stalls,
> >since the technique for recovery is simply relaxing the stick.  But if
> you
> >want to demonstrate the stall behavior of the aircraft to friends and
> >neighbors ... why not?  In answer to your question -  No, under normal
> >circumstances, I think it is nearly impossible to unintentionally cause
> a
> >deep stall.   (Note: there is an instance where a Velocity entered the
> wake
> >turbulence of a commercial jet aircraft - and it is thought the
> aircraft
> >entered an inverted deep stall condition from which the pilot was
> unable to
> >recover.  Also - slips to landing are not recommended because it
> "upsets"
> >the lift relationship between the canard and the main wings - which
> could be
> >a cause for concern if the slip were aggressive, and the airspeed slow,
> and
> >the cg fully aft.).
> >My theorizing and concerns about deep stalls focused on what might
> happen if
> >the aircraft were stalled at near zero airspeed - like following an
> >aerobatic hammerhead type of maneuver.  I think many of us are
> interested
> >this - even though we never envision ourselves in this type of attitude
> or
> >situation.
> >I have read quite a few articles on the web, including an article
> authored
> >by the infamous test pilot who purposefully flew one of the earlier
> Velocity
> >models into a deep stall - was unable to recover - and elected to
> "ride" the
> >aircraft into the Atlantic Ocean (even though he was wearing a
> parachute).
> >The more I read, the more I am turning to agree with (the other)
> Scott's
> >opinion that the aircraft nose _will_ drop through the horizon
> following a
> >deep stall - meaning, today's Velocity will not enter a sustained deep
> stall
> >condition (providing it is loaded within the normal cg envelope).
> >I spoke today with Danny Maher, the designer of the Velocity, and asked
> his
> >opinion about all of this - knowing that he has done extensive study
> and
> >testing of deep stalls in the Velocity.  Danny had this to say:
> >(paraphrasing his responses)
> >1.    "People need to realize that the Velocity is a "normal" aircraft
> and
> >that it is not designed to do aerobatic maneuvers ... so don't do
> them."
> >2.    "We (Maher and company) did extensive flight testing of the
> aircraft
> >using a movable 200 pound weight on a pulley - where we tried to force
> the
> >aircraft into a deep stall at various cg locations.  It is difficult to
> get
> >the aircraft to enter into a deep stall.  We set the weight well behind
> >today's recommended aft cg station and had to 'work' at getting the
> aircraft
> >to deep stall.  Of course, back then we had gap seals on the elevators,
> >which make it more difficult to stall the canard.  We needed to 'pump'
> the
> >stick at slow airspeed to get the main wing to enter an accelerated
> stall,
> >which then resulted in a deep stall condition.  In every instance, when
> the
> >weight was in the normal cg range, the nose dropped through the horizon
> >during the recovery - and the aircraft would not sustain itself in a
> deep
> >stall.
> >3.    Danny also went out of his way to say this - "If you enter a deep
> >stall, you better have lots of altitude to recover".
> >In my mind I thought forward elevator - and thus forward motion - was
> needed
> >to keep the aircraft from entering a sustained deep stall.  Danny's
> findings
> >say that this is not the case - the nose will drop through the horizon
> and
> >the aircraft will not sustain itself in a deep stall, providing the
> aircraft
> >is loaded within it's recommended cg limits.  The nose drop happens
> slowly
> >(not like a dart) - and the aircraft will loose "a lot" of altitude
> during
> >the stall recovery.  An aircraft with a constant speed propeller will
> help
> >the aircraft accelerate out of a deep stall more quickly.
> >Interesting stuff, huh?
> >Best regards,
> >Scott B.
> >
> >
> >
> >
> >
> >----- Original Message -----
> >From: "John Dibble" <aminetech@dixie-net.com>
> >To: <reflector@tvbf.org>
> >Sent: Wednesday, November 12, 2003 12:58 PM
> >Subject: Re: REFLECTOR:Stall Characteristics
> >
> >
> > > It seems to me that stalls should not be practiced in a Velocity for
> the
> >following
> > > reasons:
> > > 1)    The remote possibility of a deep stall that can't be recovered
> from.
> > >
> > > 2)    Recovery from normal stalls is automatic so there is no need
> to
> >practice a
> > > recovery technique.
> > >
> > > I suppose it is good to experience one or two so you know what they
> feel
> >like and also
> > > to determine the power-off stall speed of the airplane.  Sometimes
> on
> >final with two
> > > people at 70 kn, I feel a gentile, slight, slow oscillation of the
> nose
> >which is easy
> > > to correct with down trim or power as needed.  Is it possible to
> >unintentionally cause
> > > a deep stall?
> > >
> > > John
> >
> >
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