Saturday, May 14, 2011

Wednesday, May 11, 2011

Botched Maneuvers - How Bad Can I Screw Up?

Acro Camp Sneak Peek 01 - The Hammer-Spin from Steve Tupper on Vimeo.
Jim discovered that the Pitts will make a nice inverted spin entry if the stick is held too far forward during a pivot on a hammerhead.  The Super D Jim flew previously has a metal prop and needed some forward stick on the pivot to overcome gyroscopic tendencies for the nose to pitch up, but the Pitts has the MT prop and little in the way of gyroscopic force - the same forward stick shoved it right into the inverted spin.  The problem was that Jim didn't see it for what it was at first and held it in the spin instead of letting it go - hey, if there's ground in the window I should push to break the stall, right?  Well, not in an inverted spin!

Time for a short summary of just how badly one might screw up a maneuver.  This is the unknown, the terror factor, the pucker, the thing that scares many out of trying aerobatics...we could bend the plane or worse!  What if we can't get out of it, whatever IT might be?  Well, we have a saying in acro - don't run out of altitude, airspeed and ideas simultaneously - and since we keep that altitude buffer healthy we have lots of time for airspeed and ideas.

Good news.  Botched maneuvers come in three flavors only.  That's it.  And the plane can be safely flown out of every one of these situations.  It just takes training.

Flavor 1.  Unintentional Spins
Flavor 2.  High speed excursions
Flavor 3.  Unintentional tailslides.

There's a place that a new aerobatics pilot reaches somewhere around the mastery of Sportsman maneuvers and botched maneuver recovery training where it dawns on them that they don't really care where they end up anymore.  I don't mean that they aren't trying to fly well.  I mean that if the maneuver doesn't work out they aren't worried about it at all.  They'll just laugh it off and try again, because they really know that whatever happens (pick your flavor above) they can fly out of it just fine.

My first really good I-can't-tell-what-is-happening botched maneuver was an unintentional outside snap (just an inverted spin really) from an outside half-loop, starting inverted and pushing to level upright.  At about 30 degrees nose up on the top side, looking out at the horizon to my left because there wasn't anything over the nose yet, I pushed too hard and got an inverted snap roll.  Being how I was looking left and not forward at the break I just remember an illogical sequence of Galveston Bay, sky and the Texas City coastline off to one side flashing momentarily into view and disappearing, all the while listening to my instructor laughing in the back seat and saying "ha, you really botched that one!"  And I was quite pleased to discover that I wasn't scared.  Close the throttle; let go, watch over the nose and try to pick off the yaw...before I could even get on a rudder pedal the plane fell out of the snap and I pulled it back level...and we tried it again with a successful outcome to the half loop on the second try.  But it had happened - a spin that I had not intentionally set up and to this day I don't know which way it was going around.

So here's the short version of botched maneuver recovery:

Unintentional spins.  Good news - while you might be getting dizzy, the aircraft could care less.  It isn't going very fast as the spin is preventing much in the way of any increase in speed.  You won't bend anything while you are spinning as long as you avoid hitting the ground before recovery.

Biggs-Muller to the rescue.  See this Dick Bevington article for more.  Close the throttle, let go of the stick and apply opposite rudder.  P.S. If it isn't clear which rudder to press (can't tell the yaw from the roll - they are opposite in an inverted spin) then press one rudder pedal all the way to the floor.  If the plane doesn't stop rotating nearly immediately then press the other rudder pedal!  The correct pedal to push will be the harder one to push.  The spin will stop nearly immediately; grab the stick and recover to level.   Works for any type of spin in the Pitts and most others. For Decathlons - when you let go watch out for the stick to float into a corner and stay there, especially for inverted spins...push the stick back a little toward neutral with an OPEN hand (don't grab it, just nudge it toward zero aileron and nearly neutral elevator) and the stick will suddenly take on a life of its own, pop into a neutral position and the spin will stop.  See the POH for comments on that one - I've seen it happen and used the technique a number of times.

High Speed Excursions.  This one usually won't get you dizzy because you are just diving something silly, upright or inverted, and we really can bend something if we don't do something about it properly.  Remember, getting rough with it way above maneuvering speed is an issue.  The trick is to load the airframe properly.  Pulling g's cranks up the induced drag and stops the speed excursion in its tracks.  So: 1) close the throttle, 2) roll blue side up (without pulling!) and 3) pull about 4 g's to level to stop the acceleration.  I see this most often early on in the half Cuban.  A student will take too long fishing around looking for the 45 downline, all the while accelerating at full power in the inverted dive.  It doesn't take long to get uncomfortably close to redline.  Pulling the throttle to idle slows the acceleration remarkably.  Rolling without pulling will avoid over-stressing the wing with the higher angle of attack in the roll.  Then a straight back 3 to 5 g pull will stop the acceleration completely.  Using this technique I can take a straight down vertical, 140 mph full power dive and have the plane level at 160 mph.  The mistake most make early on is pulling during the roll and/or not pulling hard enough after the roll upright is completed.

Unintentional Tailslides.  This is more of an issue in aircraft that aren't approved for tailslides (like the Decathlon) but we treat them the same in all aircraft.  If the nose is pointed way up and the speed is almost gone, it is much easier and cleaner to yaw out than pitch out.  The idea is to do something like a hammerhead - not a humpty.  I've seen unintentional tailslides in the Decathlon when a student pushed too hard on the roll in a half reverse Cuban, loosing sight of the horizon; I'm watching us push up to a vertical attitude out the side while the student is looking for the long-gone horizon high in the window and wondering what happened to it. If the situation isn't recognized until it is too late to avoid it 1) pick a rudder (hopefully toward the low wing if there is one) and stand on it; 2) hold the stick really tight and usually a little forward (to make the plane flop over on it's back if it doesn't yaw out first - that seems more comfortable for most pilots to handle) and 3) close the throttle if it doesn't yaw out right away, but do close it as the nose swings down.  Be prepared for the maneuver to continue into some sort of spin entry and do the usual recovery from that if it happens.  The Pitts will sort of stick in a nose up vertical slip...if the right wing is really low, full left rudder won't make it pivot and full power holds it there - it just slides down sideways.  Eventually it will flip over (with sufficient tailslide speed) but closing the throttle results in an immediate end-swap and recovery.  Hanging on tight to the stick will help prevent the controls from slamming to the stops in the tailslide - and believe me, they will try to get away from you.  I usually grab it with both hands if I think it might happen.

In summary, there's no situation which will result in bending the aircraft if the pilot recognizes it and properly recovers.  The key is getting enough training to not lose track of what is going on.  Then the worst of a botched maneuver is a bruised ego.

Contest Registration On-Line (Michigan Aerobatic Open)

Go here to register for the competition!  Game on!  We have sponsors, we have staff, we've got a waiver for the aerobatic box approved.  Airport is on board, as is ATC and the county safety folks.  Hotels arranged.  Gotta plan the Saturday evening banquet food - yum.  We have a speaker - Steve Tupper of Airspeed will speak about military rides, AcroCamp movie and AcroCamp II plans and other fun stuff and might have a few clips to show.  We are off to order shirts and trophies next week.  So far so good - and thank goodness the IAC gives us a big checklist so that we don't forget anything.  Potties.  Gotta order the potties.

Wednesday, May 4, 2011

Clear Prop Actually Means Something

That's either a really big prop or a really small Pitts.  Actually, it's both.  Hugh flies Unlimited in it (S1E).

We take safety more than seriously at IAC competitions and a student I had yesterday reminded me of a pet peeve - and for what are blogs if not pet peeves?

What good is yelling "CLEAR!" if the prop is turned before there's time for an answer from a surprised individual in front of the aircraft?  What good is saying it if not loud enough that someone in front of the plane would hear it?  Isn't that the point?  I sometimes say "hey, wait!" to a student right after they say "clear!" and guess what - most start the engine anyway because the key was turning even as they shouted out the window.

At IAC competitions we provide a "Starter" person who clears the area and signals the pilot before the plane is started.  If you don't have a Starter person, I strongly suggest waiting a few seconds to see if a surprised voice says anything from out under the cowl before turning the key.  If you don't think there's any possibility of that then stop looking stupid and yelling clear.  It obviously doesn't mean anything.