From: nlapposNOSPAM@miami.gdi.net (Nick Lappos)
Subject: Re: Helicopter Loops
Date: 27 Nov 1999
Newsgroups: rec.aviation.rotorcraft

In article <19991127003317.04422.00000806@ng-fv1.aol.com>, micbloo@aol.com (Micbloo) wrote:
>
>>Look - we can't keep calling for "Nick" every time we have a technical
>>question
>>here. Besides, he's busy test flying the Comanche.
>
>Cant be THAT busy. He's posted about 5 times on this thread alone!!
>LOL!!
>NIIIIIIIIIIICK!!!!!!
>
>Gerard


Yea, Thanksgiving weekend gives us all too much time ;-)  Guys, I don't want
to wear out my welcome here, let me know when to stop.

Regarding aerobatics in non-aerobatic machines:

1) Don't do them unless you have the skill and a special dispensation from the
Pope.

2) Fear airspeed build up while pointed at the farm.  Mcbloo is dead on,
airspeed buildup is a real problem.  With your nose 90 deg down, you will
build speed like a Mosler safe, so plan the maneuver to get 90 nose down while
real slow and get the nose back up fast.  Load factor is caused by pitch
attitude rate and airspeed, so the penalty of waiting a few seconds before
pulling out is that the pitch rate to get the nose level causes a lot more
g.  Since the load factor of the rotor reaches a max at about 80% of Vne, if
your speed builds too fast, you're sunk, cause you will stall the rotor trying
to raise the nose.  This is kind of what happened to Egyptair, where he got so
fast it was actually unrecoverable (mach effects in his case).

3) Avoid wasting load factor while pulling out. Keep the wings close to level,
so all your rotor's poop is working to get you back to level flight.

4) When you ask too much from the rotor, it mushes through, and you get an
attitude change but your flight path is still unchanged. This means you'll
still hit, but you'll be looking at sky while doing it.  Stall will limit the
load factor,  and may cause high vibes and sloppy roll control.  In older
machines (50's vintage) you may accidentally perform the classic pitch up and
roll left retreating blade stall maneuver, accompanied by control feedback).
In this hairy flare, you might actually autorotate the rotor, and will need to
pull collective to keep the rotor speed somewhere on the gage.

5) Most helos have lots of static structural strength (static structure is the
non-spinning kind, everything from the tranny down), with that stuff designed
to take what the rotor can dish out.  The weak link is usually the rotor, and
the controls.  When you get control feedback, you are actually back driving
the servos, which means they are putting out max force, and the rotor is
pushing them backwards, making your controls pulsate.  Imagine that you park
your machine up against a concrete wall, and cast the rotor blade into the
wall with extra concrete.  Then you put hydraulic power to the servos and
start playing with the control sticks, making the blade, horns, push rods,
swash plate, and servos take the beating because the rotor blade is stuck in
the wall.  Ouch!  That's what happens to a helicopter when you push it around
too much.  All this assumes you have a certified helicopter, where someone,
Military or FAA, has setsome standards as to the strength and servicibility of
these systems.  For experimental kit builts, there really are no standards,
and therefore no real assurance of anything.  Let the buyer beware, with a
parachute.

6) The loop is the worst maneuver to try since the critical place is when you
run out of airspeed at the top, where there is little you can do if you
misjudge except try to roll off the maneuver. If you start falling through,
the cyclic will be less effective, or maybe ineffective, and you'll become a
passenger.  The next bad place is when you are staring at houses over the top
of your glare shield, and your airspeed is going rapidly beyond Vne.

7) The worst rotors for aerobatics are teetering ones, since they rely on
positive load factor to stay together and to provide cyclic control power. The
literally give you no out if something goes wrong. Recall that mast bumping
can occur, especially when you put big cyclic denands in when the load factor
is low.  Most articulated rotors hold good roll and pitch control power down
to zero g or even lower, and rigid rotors are even more forgiving, but
teetering rotors will not only lose control, they may help you sever the mast
at the wrong time.   BTW, all tilt rotors have teetering rotors, so they can't
be too sporty as helos.


Some specific comments on the excellent thoughts presented by others:

>Ron (Sikorsky fan) said:
"The guy that accidentally put the Jet Ranger into a loop probably didn't
>have to complete the loop, just roll (or pull if you're vertical) to the
>nearest horizon....."
Good escape technique, as long as there is positive G to work on.  Pull
collective and keep back stick in to keep the load factor positive, while
rolling back rightside up.

Matthew said: "you have the option of rolling upright and pulling out if your
speed looks like it would be too great.....(regarding engine failure) .I'd
guess that with sufficient airspeed, aft cyclic would keep your rotor spinning
for some time.  Use the collective to control your Nr."

Sounds right to me.  The worst luck on earth is to lose your only engine right
there at the top of a loop.  Maybe it just isn't your day.....

Bob Barbanes said:  "Guys, guys, guys...ANY helicopter can be looped, provided
that positive-G was maintained throughout the maneuver."

Maybe so, but the need for enough speed to get you through the first 90
degrees of the pitch up might be hard to attain in some machines. Of course,
if you pitch up really fast, you don't need any speed.  I rode thru a partial
loop from a hover in a BO-105, as I described in a post above.  Bob, you
mention Ray Prouty's discussion of this stuff, which of his books is it in?

BTW, it would be great to draw Ray into this group.  One of his posts would be
 worth trashing thru a ton of flames to get to.

Nick Lappos

From: nlapposNOSPAM@miami.gdi.net (Nick Lappos)
Subject: Re: Helicopter Loops
Date: 26 Nov 1999
Newsgroups: rec.aviation.rotorcraft

 mandydog wrote:

1)    Is the Comanche considered fully Aerobatic ?

2) (about H-53 aerobatics)  Really incredible and shows the quality of the CH-53.
  I read the rotor and transmission were overhauled after
these tests.

BTW. Looks like the Germans will fly the CH-53 for another 20 years !!

Mandydog:

1) The Comanche is designed to be fully aerobatic, in the helicopter sense,
but has not yet done any of the traditional aerobatics.  Should be coming up
soon.  Can't claim it till ya do it, I think.

2) The H-53 aerobatics do nothing extraordinary to the machine, and require no
extra maintenance or overhauls.  Of course, that's because they were performed
by a test pilot who had the maneuvers down to a science.  It would be quite
possible for someone practicing these things to bend the machine or even take
it apart if something goes very wrong.

Aerobatic flight in helos is visually impressive, and stuns crowds, but has a
dark underside.  I had a military pilot create a really tough chore once a few
years back when he flipped an S-76 on its back at 120 knots and pulled max
collective pitch while I sat in the left seat feeling like I was encased in
molasses.  The fact that we were at about 450 feet AGL spiced up the situation
a bit.  Took some interesting stick work to arrange the green back to the
bottom and the blue to the top, and the stop the ground from getting closer.
It also took a side flare, some slotting between two pines and a collective
pitch pull that drooped the rotor to about 85% Nr.  It worked out, but a few
of the rotor parts were frazzled in the process. I very well know how an
articulated helo flies with no damper, since one damper lug was literally
ripped off the blade.  A very silent flight back to the ramp, punctuated by
the guy saying to me, "I bet you think I'm a real Asshole!"  Since I have
always tried to bring back my machine in the same shape I got it, this was not
one of my fonder memories.  Like the car ad says,  "Performed by professionals
on a closed course.  Do not attempt these with your car"

Nick Lappos

From: nlapposNOSPAM@miami.gdi.net (Nick Lappos)
Subject: Re: Helicopter Loops
Date: 25 Nov 1999
Newsgroups: rec.aviation.rotorcraft

In article <383D07C1.A6DA423F@nsw.bigpond.net.au>, Doug Marker
<dmarker@nsw.bigpond.net.au> wrote:
>I seem to recall that among production helicopters, it was a 'puma'?  or
>'lynx'?  that supposedly did the first controllable barrel rolls, but am
>sure that test pilots were playing with modified conventional craft long
>before.
>
>From memory the early helicopter loops were not so much a pure loop as a
>backward somersault. One craft that was supposed to have incredible
>manouvreability was the Lockheed Cheyenne, but too few of them got built
>& played with to ever really prove just what they could do. I had thought
>that the designer said they could almost roll, at speed, in their own
>rotor diameter (they had a pusher prop & 4 bladed rigid rotor) but on a
>recent discussion on this someone else as I recall, said they were never
>known to have performed rolls.
>
>Doug Marker

Doug,

I think the first recorded loop was a Sikorsky S-51 back in the early 50"s.  I
have seen the film.  Rolls were done at that time too, but not on film.

Most modern helos can do this stuff, with varying margins for error.

The best of the bunch are the rigid rotors of the BO family (now EC, I guess).
 They are simply unbelievable.  Udo Hausen of MBB took me out in a 105 and we
did it all.  great fun, and a complete eye opener.  At a hover, push over to
135 degrees nose down then recover back again in about 2 to 3 seconds.  Then
do that with a nose up pull.  Most impressive, and useful against those loud
and annoying airplanes that think they can maneuver....

Tigre and Apache have all done good demos of wild stuff, which doesn't involve
much if any negative G.

Comanche hasn't done upside down stuff yet, but will shortly....

In addition to having a main rotor like the BO family, Comanche does some real
yaw maneuvers that are similar to the supermaneuverability of the F-22.
Called a Snap Turn, the Comanche can point at speeds up to about 100 knots
without banking.  The Fantail is powerful enough to let the machine simply
pivot around and point in less than half the time of a balanced turn.  The
fuselage turn rate is 60 degrees per second while doing this.

Feels surprisingly natural, with low forces.  Sort of like the spooky feeling
when your car does a 180 on an icy bridge, almost too smooth.  Unlike the car,
all the control you need is at your disposal, however.  I flew the Fantail
demonstrator that perfected these Snap Turns, and had a ball.  90 degree turn
to stable pointing at 100 knots in 2.2 seconds!


Nick Lappos