Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site masscomp.UUCP
Path: utzoo!watmath!clyde!bonnie!masscomp!ahv
From: ahv@masscomp.UUCP (Tony Verhulst)
Newsgroups: net.aviation
Subject: Re: spoilers/airbrakes
Message-ID: <870@masscomp.UUCP>
Date: Fri, 24-Jan-86 14:12:24 EST
Article-I.D.: masscomp.870
Posted: Fri Jan 24 14:12:24 1986
Date-Received: Sat, 25-Jan-86 04:01:24 EST
References: <5@petrus.UUCP>
Reply-To: ahv@masscomp.UUCP (Tony Verhulst)
Distribution: net
Organization: Masscomp - Westford, MA
Lines: 79
Summary: 

In article <5@petrus.UUCP> daniel@petrus.UUCP (Daniel W. Nachbar) writes:
>An engineering question --
>Most gliders have spoilers. Most simple singles do not.
>Is there any good reason for the difference?
>Dan Nachbar
>BELLCORE -- Morristown, NJ
>bellcore!daniel

The FAA claims thet the primary purpose of flaps is to increase the rate
of descent without increasing airspeed.  Although this certainly
is true, most of use use flaps because using them on landing lowers the
nose (providing a better view of the runway) and because they lower the touch
touch down speed.

Spoilers increase the rate of descent.  Period.
Sail planes don't need flaps because final approach speed is considerably
higher than cruise speed (weird ain't it?) so the nose is already low
enough to provide good visibility of the runway.  Also, the landing speed
of most sailplanes is in the 40mph ball park so the lower touch down
speeed that flaps provide is not that crucial.

Note that Mooney is offering spoilers as an option on some of their
singles.  It seems that Mooneys are so clean (parasitic drag wise) that
their descent rate wasn't high enough to satisfy air traffic controllers.
Those poor Mooney pilots were going too fast to use flaps (enroute
descents) and couldn't throttle back any further without cooling their
engines too much and were still being requested to increase their rate of 
descent.  Now, with the spoilers, the Mooney pilot can throttle back and
fall out of the sky with the rest of us.

OK, so much for the background.   The reason that sailplanes have
spoilers and airplanes don't is because airplanes have throttles and
sailplanes don't. In an airplane, you control your descent on final with
the throttle.  If you are too low on the approach you add power, if you
are too high you decrease power.  This is tough to do in a sailplane.
What you do instead is to initiate the approach a little high and add
a some spoiler.  If you find yourself under shooting the approach, remove
some spoiler.  If too high on the approach, just increase the amount of
spoiler.  So, basically, on final approach the spoiler does for the sailplane
that the throttle does for the airplane.

Incidentally,  besides flying airplanes and sailplanes I also fly
hang gliders (11 years).  For several years I have been pushing for
spoilers on hang gliders.  Hang glider performance has increased 
tremendously over the years. Here in the northeast, a typical hang
gliding landing area is the parking lot of a ski resort surrounded
by 70 foot oak trees.  Naturally a parking lot in the woods on a sunny 
day is a great thermal generator and the turbulence .... well never mind,
it's too painful. 

It's easy to come over the parking lot at tree top level
and get a REAL good look at the trees on the other side before you land.
Some fancy low level turning occurs to stay within the boundaries of the
parking lot (a good glide angle has SOME disadvantages). Spoiler in this
situation could make the difference between an uneventful landing and
parking it in the top of a tree.  We claim that if a New England
hang glider pilot has never landed in a tree, he hasn't been flying 
long enough.  Iv'e been flying long enough to land in three trees.  

A tree landing is not a bad as it sounds.  Basically, once you know
that you can't reach an open clearing and commit to the tree landing,
you find a bushy tree (Lord spare me from the pointy dead pine trees)
and stall the glider (15-16mph) just ever so slightly above the tree.
The glider will settle in the tree (getting it out bill be discussed
in the next chapter) and you just climb out of the tree.  Out of the
dozens of tree landings I have heard about and seen, I know of only one
injury.  Al Mulazi (connecticut) broke his wrist while climbing out
of a tree he had landed in.


Wow, I started of by answering Dan's spoiler question and kind of
went off on a tangent.

				yours in good flying,

				Tony Verhulst
				treasurer; Windward Kite & Gliding Club
				Private pilot - ASEL 
				student - sailplane (35 flights)