From: jlw@world.std.com (James L Walker)
Subject: Re: trigear type vs bigear type
Organization: The World Public Access UNIX, Brookline, MA
Distribution: rec
Date: Thu, 3 Sep 1992 22:14:54 GMT

In article <1992Sep2.232523.12078@rtsg.mot.com> svoboda@rtsg.mot.com (David Svoboda) writes:
>In article <Btp515.I1B@world.std.com> jlw@world.std.com (James L Walker) writes:
>|
>|Trikes will land easier "hot" (ie. fast ground speed) than a
>|taildragger.  
>
>No, I don't think so.
>
>|When a taildragger rests on the ground the wing's angle
>|of attack is high because it's tail is resting on the ground.  When
>|the plane is comming in fast, the angle of attack is low so the mains
>|touch the ground first and the tail settles in later.  If the tail
>|settles in too quickly, the increased angle of attack will generate
>|enough lift to get the plane airborne again.  This accounts for the
>|"bounce" when you land a taildragger to hard.  
>
>Well, except for the fact that the landing gear is very close to the
>CG of the airplane, so it takes quite a hard landing to bounce the
>airplane back into the air.
>

In a taildragger the mains are forward of the CG, in a trike they are
behind the CG.  They are no closer for one type than another, it just
depends on how you build the plane.  Since the mains are forward of
the CG the tail in a taildragger will "settle" to the ground, the
harder the landing, the more pronounced the change in AOA.  The more
pronounced the change in AOA, the quicker and more dangerous will be
the ballooning effect on the landing aircraft.  The same goes for your
airspeed, if you are moving fast the change in AOA will cause a
serious ballooning effect.  That is why a taildragger is harder to
land hot.  Because the mains are behind the CG in a trike the nose will
tend to settle to the ground, thus lowering the AOA.  The plane will tend
to stick to the ground once it gets there.

>A taildragger will more gracefully handle a "pancaked" landing, in
>which the model is flared to a stall while still above the ground, and
>the airplane sort of drops nearly horizontally.  This is the most common
>sort of botched landing by a beginner.  The likely event in that case 
>in a nose-over and a broken prop.
>

What's gracefull about a pancaked landing?  No plane is graceful if
you stall it above the ground.  I would trust a trike alot more than a
taildragger in such a "landing."  The trike will pitch forward onto
its sturdy nose gear while a taildragger will take a hard knock to
what is usually a relatively weaker tailgear.  It is the tail that
takes the force in such a landing.  I think a broken prop is
preferable to a cracked tail.

>|If you are really good
>|you can land a taildragger really fast by putting the mains gently on
>|the ground and then using down elevator to throw the tail up.  The
>|force of the air over the tail will keep the plane from nosing over
>|until you are going slow enough to drop the tail.  
>
>You don't have to be really good to do this.  Simply freeze the elevator
>at the position it was when you touched down (don't continue to flare)
>and most models will stay on the mains.  The important thing is to
>have a small rate of descent when you touch down.  This minimizes the

     ie. put the mains gently on the ground, not an easy trick

>positive pitching force due to the tail moment.  But that pitching
>force is nearly independent of landing speed (except if you fly from

Pitching force isn't the only force acting on the tailplane.  The
faster you go, the more pressure the air will cause on your tailplane.
If the tail pitches up, the air will push it back down.  The reason
you have to be good is to judge when the pitching force overcomes the
force of the air as you are slowing down.  The reason you have to use
the elevator to push the tail up is to lower your AOA and keep from 
ballooning.

>grass, where the drag on the wheels can cause a nose-over if you land
>too fast).
>
>|The easy way to
>|land a taildragger is to make a "three point" landing where the plane
>|is going slow enough that the tailwheel will touch the ground at the
>|same time as the mains.  
>
>This is only easy if you are good enough to bring all the elements of
>landing together perfectly.  Most beginners (and most sport fliers) can't
>do this so well.
>
>|Of course in a trike the plane rests on the
>|ground with a nice low angle of attach so you can grease it in very
>|fast with very little bounce.
>
>No.  A tricycle model is VERY easy to bounce, esp if the wing, at rest
>on the ground, is at any kind of positive AoA.  See, if you bring in a
>trike too fast, the flare angle is less than the rest angle, so the nose
>gear touches first.  Since the nose gear is so far from the CG, it easily
>lifts the nose, which increases the AoA and produces more lift, which lofts 
>you back up into the air.  Then the speed lowers a bit, the nose drops (you 
>are a bit slower by now, and do not give enough elevator to keep it up), 
>the nose- wheel touches, and, here we go again.  And again.  And again.

Wait a minute... isn't that what I said about a taildragger?  The
advantage of a trike is that you can shorten the nose gear and get rid
of the positive AOA when the plane is at rest.  Unless you want to put
a rediculous tail gear on a taildragger, you don't get this advantage.
In general trikes have a much lower AOA on the wing when it is at
rest.  Why make things difficult for yourself?  At least you have the nose
wheel to bounce off of in a trike.  In a taildragger that type of landing
will cause serious ballooning as well as a probably broken prop.
Bouncing off the nose gear lands a trike on the mains which are behind
the CG.  Sure the plane will bounce back and forth between the mains and
the nose, maybe twice before it bleeds off enough airspeed.  Meanwhile
a taildragger would either have its nose buried in the ground or be
out of airspeed at about 5 ft AGL.

-- Les Walker
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