REFLECTOR: Gross weights

Rene Dugas dugasd at bellsouth.net
Mon Jun 26 18:07:37 CDT 2006


Chuck, I agree.  
I can frequently (3 of 5) set the mains down and ride the wheelie for
several hundred feet with just me and 3/4ths fuel.  The reason is - that
is how I fly most of the time and PRACTICE it.  Maintain concentration
on the balance of the plane until below 45 knt when I loose rudder
authority.  I always "plop" at Oshkosh with three on board and luggage
with half fuel load and slow.  I always "plop" with heavy passengers in
the front seat because I misjudge the weight and amount of needed tug on
the stick at touchdown.  (usually 1/4th inch to 1/2 inch at the top of
the stick - I was not looking but I asked my passenger to estimate.)  If
one expects and practices the tug on touchdown it is very satisfying to
hold the nose off.  I usually touch down at 75 kts - 7 kts above stall.
Usually 110 in the pattern and on final then 90 short final and 75 at
touch down.
Rene'

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Chuck Jensen
Sent: Sunday, June 25, 2006 7:10 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Gross weights

Here's my theory that explains the 'plop' landing characteristics
(notice, theory is used to describe every hair-brain, wild-eyed idea
that can't be tested, observed or support by real world experience!).  

Just before main gear touching, the canard/elevator is at a very fine
point of equilibrium as we tend to gradually increase lift on the
elevator to slow the rate of descent, even if we aren't flaring.  The
airspeed over the elevators is just barely adequate to provide the
needed lift, so there is not a lot of reserved lift available.

At touchdown, two thing happen simultaneously that loads up the elevator
when the mains touch; 1) weight shift: the center of gravity, well ahead
of the mains with passengers, causes a significant fraction of the
weight on the mains to be transferred to the canard, 2) deceleration:
since the axial center line of the plane's mass is well above the mains
(maybe 3.5'?), when the mains touch and instant drag created, the mains
want to stop but the forward momentum of the plane's mass is going to
transfer a significant amount of the weight forward onto the nose (much
like our upper bodies bob forward if someone slams on the brakes in a
car).

The sudden shift of weight to the nose upon touch down exceeds the lift
capacity of the elevator, or simply stalls out the canard.  Once touched
down with a plop, the nose can often be lifted off again as the weight
shift from main gear deceleration has been eliminated, so the elevator
only has to overcome the static weight on the nose wheel, which it does
on every take-off.  Or, that once-in-ten times you are right on speed
and can snatch the elevator at just the exact time, you may be able to
grease it.

For those that have a speed brake board deployed, the air cushion under
the front of the plane and perhaps some lift from the board itself mutes
the tendency of the nose to plop on touchdown.

So, unless a plane is loaded lightly in front, carries extra speed on
touchdown or the stars are lined up just right, we are probably destined
to do more plopping than greasing. 

Or not.............

Chuck Jensen

> -----Original Message-----
> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]
On
> Behalf Of Laurence Coen
> Sent: Saturday, June 24, 2006 1:55 PM
> To: Velocity Aircraft Owners and Builders list
> Subject: Re: REFLECTOR: Gross weights
> 
> When I took my transition training I was shown how to hold off the
nose
> gear
> on a landing.  One of these days I'm going to get it right.  The
problem
> is
> this.  When the mains touch, the weight shifts from being carried by
the
> wing to being carried by the gear.  This is like moving the center of
lift
> aft which wants to dump the nose.  The trick is to catch the nose with
a
> quick aft movement of the stick just as the mains touch.  The first
time I
> tried this I went flying again.  If your too late the nose plops and
> bounds
> back into the air.  That's the how you do it but it takes lots of
practice
> to make it work.  This is why I think transition training is worth the
> time
> and trouble.  It could save you from breaking something.
> 
> Larry Coen
> N136LC
> SE/RG Franklin/IVO
> 
> ----- Original Message -----
> From: "Chuck Jensen" <cjensen at dts9000.com>
> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> Sent: Saturday, June 24, 2006 11:13 AM
> Subject: Re: REFLECTOR: Gross weights
> 
> 
> > Landing technique:  Plop, plop, fizz, fizz, oh what a relief it is.
> >
> > My XLRG has always been a 'plopper'.  Some say those with a speed
brake
> > seems to create a cushion of air under the nose that reduces the
> > plopping.  Then again, some may have better technique than I...will,
> > actually most do.
> >
> > The odd thing is, though the nose always plops on, the couple times
I've
> > had nose wheel shimmy, I've actually been able to lift the nose off
> > again and hold it off for a go around or to lower it for a second
try.
> > It seems that the canard stalls/plops onto the runway, yet there is
> > enough elevator lift, when applied immediately, to raise the nose
again.
> > Strange.
> >
> > Chuck Jensen
> >
> >
> >> -----Original Message-----
> >> From: reflector-bounces at tvbf.org
[mailto:reflector-bounces at tvbf.org]
> > On
> >> Behalf Of Brian Michalk
> >
> >
> >> How good are some of  you guys greasing the landings?  Can you land
a
> > V
> >> without touching the nose gear on the ground?  Or is it a plop it
down
> >> manuever?
> >>
> >> What does the perfect landing look like?
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