Don't Snap Roll A Hawker

[inigo88]

However, some aircraft may not have been tested in various regimes with x amount of variables and combination factors so however the engineering would be validated without the specific maneuver accomplished is realistically anyone's guess. As far as light aircraft goes, many manufactures would rather not assume extra liability, so they're perfectly happy to keep the normal or utility category.

I'd agree that from a structural point of view, the airplane doesn't care which way it's pointed. The structural design engineers care about the sizing their parts to certain load cases which encompass the necessary points on the V-g diagram and gust envelope necessary for certification (based on Part 23, 25, etc), and throwing on those 1.5 ultimate and 1.1 yield safety factors to give the pilot a little bit of leeway.

But that doesn't necessarily guarantee to the pilot that the airplane won't do something "weird" during the roll from an aerodynamics or stability and control perspective. The aero engineers do CFD and wind tunnel test the airplane at certain expected attitudes, and you can then derive a bunch of stability derivatives and design your flight controls based on the forces and moments you got. Is the airplane still statically or dynamically stable while rolling thru inverted, or does it diverge? Is there some weird aerodynamic interaction between parts (ex T-tail deep stall) that maybe only happens in that flight attitude? It's not on the engineers to find out if the airplane was never certified to be in that position in the first place.

The few second hand test pilot stories I've heard about rolls gone wrong are never that being upsidedown overstressed the airplane, but rather that something scary and unexpected happened half way through - which could easily lead to a botched recovery and exceeded G limits if not properly responded to.

 

[Joshwa]

One of my work colleagues rolled the Lear to 85°. To be fair to him, he had just hit an A380's wake!

 

[knot4u]

One of my work colleagues rolled the Lear to 85°. To be fair to him, he had just hit an A380's wake!

Was he wearing a parachute?

 

[fholbert]

Was he wearing a parachute?

Chino Airshow, every year.

 

[BobDDuck]

If you're keeping a constant 1G load on the airframe, how would the fuel and engine lubrication systems 'know' they're inverted?

This is what I get for editing on my phone. Should have read, "even if you are keeping a 1G load on the airframe to get there".

 

[BobDDuck]

All of this braggadocio about rolling airplanes solidifies my nagging paranoia about renting airplanes.

I worry about this even on the airplanes at work some times. A while back there was a memo about a massive overspeed event that was never written up by the crew. The plane flew for a few days before the FOQA dump occurred and the issue was caught. And then of course there is the classic Mesa at Roanoke story.

 

[knot4u]

Chino Airshow, every year.

I helped put the smoke system on that airplane.

 

[Baronpilot244]

This thread brings to mind a crash that I've linked to below. This happened about 20 miles from my house, it was a horrific event (I won't call it an accident because by all accounts it was intentional).


http://www.aopa.org/News-and-Video/All-News/2007/July/1/What-was-he-thinking

Bp244

 

[fholbert]

http://www.aopa.org/News-and-Video/All-News/2007/July/1/What-was-he-thinking
Bp244

Another friend heard the accident pilot say, "I think I can roll this airplane."

@Inverted if you ever even damage an airplane the entire forum will be pointing at this thread; "See he tried to snap roll it!"

 

[Deleted member 27505]

The fact that the airplane didn't come apart is a freakin' testament to the stout construction of the Hawker, I guess! When I saw them putting the wings on a new Citation at the factory in Kansas I was blown away by how skookum the jigs were and I can only imagine that the Hawker is just as strong.

Skookum!!! Liking post for that word alone. God, I miss the North.

 

[Deleted member 27505]

http://www.plus7minus5.co.uk/FlickedBizJet/FlickedBizJet.htm

Story sounds all kinds o' fishy to me. A snap roll involves an accelerated stall and lots o' rudder. A snap roll occurs largely in a stalled condition. If initiated and then an attempt to reverse is made while inverted, it's unlikely there would be much aileron effectiveness at all. Certainly not enough to cause structural damage. What would probably happen is the airplane would fall inverted. During the "righting process" from that, who knows what kinds of stresses might be imparted. But, if that IS what happened, there is no way any sane person would try that again.

 

[Deleted member 27505]

We had 2 instructors that rolled training aircraft when I was a student at ERAU.

1 rolled a 172 with 2 students onboard. He ended up cracking the spar. The scary thing was, they didn't find it until they tore it down for the 100-hour check. They eventually traced it back. Ended up having to send it to Kansas on a flatbed.

The other rolled a Piper Seminole with 2 students on board. He went on to be a Captain at Pinnacle. He flew a ferry flight one night. We all know how that story ends.

Like the "roll cartoon" pointed out, there are lots of different kinds of rolls. I'm soundly of the opinion (based on all kinds of aerodynamic facts) that any certified airplane (regardless of loading Cat) can be rolled without hurting the aircraft. But... there is only one kind of roll that works (NOT shown in the roll cartoon). To wit, the ballistic aileron roll. This is the roll in which 1 positive G may be maintained throughout the roll (as others have pointed out). It MUST be done correctly, but it if is done correctly, the airplane won't even know it happened. When in the air, airplanes don't care where the earth is. All they care about is where the relative wind is.
The secret to doing a proper (though still illegal and generally speaking, stupid) ballistic aileron roll in a Normal category airplane is first to practice doing them a whole bunch and make your inevitable lots of mistakes in an Aerobatic category airplane.

 

[Deleted member 27505]

A pissed of fed is like a pissed off cop. They can usually find something to ding you with if they look hard enough, and long enough.

91.3, 91.13, and 91.103 come to mind real quick like... The FAA's equivalents of a cop's "resisting arrest" catch all.

 

[Deleted member 27505]

I think I would simply observe that the notion that one need be a "certified test pilot" in order to safely roll an aircraft is preposterous. WW1 pilots flew things held together by baling wire and chewing gum which had the aerodynamic characteristics of a paper mache snake while getting shot at and rolling RATHER A LOT, and even a lot of them managed not to crash, in spite of the fact that they were not CERTIFIED TEST PILOTS.

Now that's obviously leaving aside the question of how wise it is to advertise such things.

With that said, @CK and I have talked about it and he has no problem with me snap-rolling the Hawker, which is a good thing because I do it all the time!

Just don't be rolling that Brit box in ice. Your heirs and assignees might have to face uncomfortable questions from stiff-lipped investigators regarding whether you were shaken or stirred.

 

[Deleted member 27505]

Who here has never broken a FAR?

If by FAR you mean Freaking Adrenaline Rush, then it seems most of us.

 

[Deleted member 27505]

This whole discussion comes down to the difference between "can" and "should." Can a pilot execute a roll in a non-aerobatic airplane? Sure. Should a pilot execute a roll in a non-aerobatic airplane? Well...

I recall learning a long time ago that a hallmark of a "professional" is somebody who does the right thing even when nobody is looking.

Nah. You're thinking about a person with a conscience. The professionals are the ones who do the right thing when people ARE looking and put money in their purses the rest of the time.

 

[Deleted member 27505]

Where it may come into play is that many fuel systems and engine lubrication systems won't work inverted, even if you are keeping a constant 1 G load on the airframe.

Wait, what? Why? If the airplane is at +1G, it is NOT inverted.

 

[Pilot Fighter]

Wait, what? Why? If the airplane is at +1G, it is NOT inverted.

You can pull positive G's, upright or inverted. Inverted flight doesn't mean negative G's. That said, being at 1G inverted has consequences with regards to fluids.

 

[Deleted member 27505]

I'd agree that from a structural point of view, the airplane doesn't care which way it's pointed. The structural design engineers care about the sizing their parts to certain load cases which encompass the necessary points on the V-g diagram and gust envelope necessary for certification (based on Part 23, 25, etc), and throwing on those 1.5 ultimate and 1.1 yield safety factors to give the pilot a little bit of leeway.

But that doesn't necessarily guarantee to the pilot that the airplane won't do something "weird" during the roll from an aerodynamics or stability and control perspective. The aero engineers do CFD and wind tunnel test the airplane at certain expected attitudes, and you can then derive a bunch of stability derivatives and design your flight controls based on the forces and moments you got. Is the airplane still statically or dynamically stable while rolling thru inverted, or does it diverge? Is there some weird aerodynamic interaction between parts (ex T-tail deep stall) that maybe only happens in that flight attitude? It's not on the engineers to find out if the airplane was never certified to be in that position in the first place.

The few second hand test pilot stories I've heard about rolls gone wrong are never that being upsidedown overstressed the airplane, but rather that something scary and unexpected happened half way through - which could easily lead to a botched recovery and exceeded G limits if not properly responded to.

I get where you are going, and I certainly agree that the best reason NOT to do aerobatics (of any kind) in a non aerobat airplane is that PILOTs screw up.
But lets be real clear here and go back to basic aerodynamics 101. An airplane in controlled flight DOES NOT CARE where the earth is. All the airplane cares about is where the relative wind is. To an airplane, rolling out of a +1G turn to the left is exactly the same as entering a +1G turn to the right. To an airplane, being "inverted" at +1G is exactly the same as being "upright" at +1G. At +1G there IS NO INVERTED to an airplane (in the air)... only to a pilot. Control surfaces, interference drag, stability... NONE of those change to the airplane if you are actually flying "upside down" at +1G. Again, the airplane doesn't know it. "Upside down" is a human perception, not an airplane's. A wing is just a machine that does work based on airflow over it. We control the work it does by controlling that airflow. The airflow, and consequent work, in a positive G flight regime is NOT related to its position relative to the earth.

 

[Deleted member 27505]

You can pull positive G's, upright or inverted. Inverted flight doesn't mean negative G's. That said, being at 1G inverted has consequences with regards to fluids.

How? I can keep water (or hydraulic fluid, or fuel, or oil) in an upside down bucket. Particles are particles and respond to physical forces. If those forces don't change, the particles don't sense change.