From: billphil@ix.netcom.com (Badwater Bill)
Newsgroups: rec.aviation.homebuilt
Subject: Re: [Q] Spoilers vs. ailerons for roll control? Also V tail as well.
Date: Fri, 03 Jul 1998 19:07:39 GMT

Lots of good questions and some misunderstandings.

>Hello:
>
>Spoilers vs. ailerons for roll control, what are the
>advantages and disadvantages?

Depends on the airplane and the mission.  Spoilers produce no adverse
yaw.  In fact one of the reasons birds don't have rudders is because
they can change the shape and area of their wings to counteract yaw.
We human pilots are stuck with a fixed configuration although some
jets have swingwings the wing is still pretty much in a fixed position
for turning.

If you want to turn right, you lift the right spoiler.  It reduces
lift on that wing and it also produces drag over there so you don't
need to feed in any rudder.  This works fine until you get banked up
to about 90 degrees, then you yaw right (down) and dive.

So, if you want to fly inverted or even past about 70 degrees,
ailerons are the answer.

The spoilers on gliders are not for roll control.  They are more speed
brakes and lift reducers than anything else.  You use them to get the
glider down to the runway in an approach just like you use a throttle.
The spoilers are usually attached to a big knob on your left that
slides backward to deploy them and forward to stow them.  You use it
just like you do a throttle on final approach.  If you're low, push
forward and the glider perks up with some speed and extended glide.

>Most gilders use spoilers only, am I right (I could be wrong)?
>They are pretty efficient so why not most powered planes?
>
>If a plane has spoilers only,does that mean to make a turn
>one spoiler go up and to loose lift both go up? (I am assuming
>gilders don't have flaps, again, I could be wrong). How about
>when you need to make a turn and loose lift at the same time?

Most gliders do have flaps but they are more for reducing the stall
speed so you can turn slower and tighter in a thermal to stay in the
lift.



>Last, V tail. Never flown in one. How does it work? How does it
>do the job of both the rudder and elevator?

You need to draw it on paper and see how it works for yourself.  If
both control surfaces are deflected up or down, there is a net
resultant force that causes the tail to go up or down.  If one goes up
and the other goes down by the same amount, the Up-Down force is
cancelled but there will be a net force to the right or left depending
upon which way you deflected them.

Now, what happens is that you really have control in both those ways
and when you MIX them you still have good control in both the yaw axis
and the pitch axis.

BWB

>Thanks
>
>Stephen
>(a bit confused)

From: billphil@ix.netcom.com (Badwater Bill)
Newsgroups: rec.aviation.homebuilt
Subject: Re: [Q] Spoilers vs. ailerons for roll control? Also V tail as well.
Date: Sat, 04 Jul 1998 21:52:51 GMT

>>The spoilers on gliders are not for roll control.  They are more speed
>>brakes and lift reducers than anything else.
>
>1. Spoilers are NOT speed brakes at all. As proof, some gliders have
>speed brakes to go with spoilers.

Yes they are speed brakes.  I've used them for years as speed brakes.
You punch the nose down and throw out the boards to keep you from
picking up a ton of speed.  That's exactly what they are used for.  On
my Jantar 15 meter ship the spoilers elevated vertically out of the
center of the wing  They spoiled lift and reduced speed.  I'm missing
some fine point you are trying to make here Bob.  In a glider you
shoot your approach high so you ALWAYS have the runway made.  You use
spoilers to get the thing down.  You can also use flaps but flaps are
more for decreasing the stall speed so you can stay in core of the
thermal better.

If I didn't throw out the boards in most of the gliders I've flown in
my life, I would just sail right on down the runway and never land.
You need the boards so you can point the nose down, keep the speed
down and get the thing to quit flying.


>>Most gliders do have flaps but they are more for reducing the stall
>>speed so you can turn slower and tighter in a thermal to stay in the
>>lift.
>
>Maybe most NEW/late model gliders have flaps. Not sure.
>MOST other gliders do NOT have flaps and those that do -- the primary
>use is for landing. Somewhat tighter turns may be achieved with very
>moderate use of flaps, if ya gottem'. It also means more drag that can
>hinder your climb in the thermal.

I disagree again.  What you want to maximize in a thermal is climb.
That happens at the  minimum SINK RATE, not the best glide-angle (lift
to drag ratio).  Dropping 15 degrees of flap on a Lark LS-2  reduces
sink rate from about 190 feet/min to about 170 feet/min if I recall
correctly (been 15 years since I owned a Lark).  What this means is
pure and simple.  If the air around you is rising at 200 ft/min and
your sink rate is 190 ft/min, then you only climb 10 ft/min.  If you
can reduce the sink rate to 170, you climb at 30 ft/min.

It has nothing to do with drag.  You don't give a damn how draggy you
are in a thermal.   You just want to go up at the fastest rate you
can. I know guys who thermal parachutes.  They are about as draggy as
you can get but will leave a high performance sailplane in the dust
for time-to-climb races.   Drag never enters your mind in a race while
thermalling.  When you finally get the altitude you want, then sure,
button up the wing and rig for clean running between thermals, i.e.,
no flaps, no spoilers, infact I could raise the flaps up 5 degrees on
the Lark to camber the wing for speed.

More on flaps.  If you look at the polar curves for a sailplane,
minimum sink occurs about 2 to 3 knots above stall where best L/D
happens at about 1.5 Vs.  In turbulent air  w(hich you live in most of
the time in a thermal)  you may stall 2 or 3 times during each circle
on your way around the thermal.  So each 360 turn means many stalls.
When you stall, you screw the pooch because your sink rate goes way
up.   If you are thermaling correctly, you just hang it on the edge,
right above Vs.  If you lower some flap, Vs moves down and you can fly
slower, turn sharper and stay in the core better with fewer stalls.

Badwater

From: billphil@ix.netcom.com (Badwater Bill)
Newsgroups: rec.aviation.homebuilt
Subject: Re: [Q] Spoilers vs. ailerons for roll control? Also V tail as well.
Date: Sun, 05 Jul 1998 01:18:29 GMT

Peter.  Did the F-14 have ailerons too?  I've seen complete rolls with
spoilers deployed along with ailerons but the spoilers had a dual
function and the second function was to reduce advers yaw, pulling the
wing into the direction of the roll to compensate for the aileron's
negative yaw moment.  Have you seen a fighter roll completely without
the use of ailerons too?

In other words have you seen a fighter make a complete roll using
spoilers only?

You know, when you watch the wing of an airliner in turbulence there's
alot of spoiler play to keep that big wing level.  I can see this in
normal 1 g flight very easily.  I just can't see how it might work
inverted or even doing a roll without ailerons.

What do you think?

BWB



>3.)	In regard to BWB's earlier posting suggsting that spoilers only work
>when you're banked less than 90 degrees (in fact, he suggested less than
>70): 'tain't necessarily so.  The F-14, for example, uses differential
>angles of its slab tails ("tailerons") for roll control at high speed
>(as do many other modern fighters), but also has extremely effective
>spoilers which come into play when the wings are unswept.  I've seen the
>airplane rolled at remarkably low airspeeds (including from the inside
>while riding with then-Grumman test pilot Kurt Schroeder some 23 years
>ago!), and the spoilers remained remarkably effective.  Admittedly, this
>was with the airplane at zero G, rather than actually flying upside down
>(-1 G)...but the spoilers still produced enough difference between the
>lift of the two wings to roll the airplane very smartly.

From: nauga@Glue.umd.edu (David Hyde)
Newsgroups: rec.aviation.homebuilt
Subject: Re: [Q] Spoilers vs. ailerons for roll control? Also V tail as well.
Date: 5 Jul 1998 10:48:25 GMT

BWB writes:

>Did the F-14 have ailerons too?

No.

>Have you seen a fighter roll completely without
>the use of ailerons too?

Yes.  While -14's use spoiler and diff tail, A-6's use(d) spoilers
only for roll control.  Worked just fine, too, even at negative g.

>In other words have you seen a fighter make a complete roll using
>spoilers only?

Calling the Intruder a 'fighter' is a stretch (well, they could
carry 'winders), but yes, see above.

>I just can't see how it might work
>inverted or even doing a roll without ailerons.

Spoiler don't just 'destroy lift', they increase the pressure on
the upper surface of the wing.  At negative AOA, deploying (for
example) the left spoiler is still going to make the airplane
roll left.

Dave 'rotten' Hyde
nauga@glue.umd.edu

From: billphil@ix.netcom.com (Badwater Bill)
Newsgroups: rec.aviation.homebuilt
Subject: Re: [Q] Spoilers vs. ailerons for roll control? Also V tail as well.
Date: Sun, 05 Jul 1998 16:47:18 GMT

Thanks Dave.  I obviously had a misconception on that one.  I didn't
know there were any high performance airplanes that used spoilers
only.  I can see how the differential stablator would help in roll
though.  If one goes up and the other down along with a deployed
spoiler adding to the roll moment I can see that.

Since I've never flown anything like that I'm unaware of many of the
new concepts.  Thanks for taking the time to inform me(us).

BWB


>Spoiler don't just 'destroy lift', they increase the pressure on
>the upper surface of the wing.  At negative AOA, deploying (for
>example) the left spoiler is still going to make the airplane
>roll left.
>
>Dave 'rotten' Hyde
>nauga@glue.umd.edu