Aeros in Sims?

[martine]

So to settle a 'discussion' can anyone with experience of serious flight sims (not PC based) tell me if they will reproduce accurate aeros. I know there have been cases of airliners being barel-rolled and surviving. Does the sim respond as it should - aerodynamically?

[Denti]

I think there are wery few pilots who have experienced a barrel roll in the real airplane, so how can we say if it does the roll right? Yes, you can roll the plane in the simulator (some of the unusual attitude require completing a roll) but you can't simulate more than one g (at least for more than a few microseconds). So how do you know if you overstress the plane? Okay, the simulator says "crash" if you do, but it's not the real thing.

[sudden Winds]

Most airplanes will perform aerobatic maneuvers. During certification they do many things to them. I was once told the Citation 10 was flew at Mach 1.0 for example. During a demostration, they barrel rolled a 707.

Most sims will let you do the aerobatic maneuver, but if you are rough, you can exceed the sim limits. When the sim reaches certain extreme positions, or when it generates a big impact due to a hard (enough) landing, some safety switches will be activated and the thing will erect and motion will be stopped until reset.

good luck to ya all.

[jtr]

Yes you can attempt aeros in a sim with the motion on, and the visuals will illustrate it. The motion can only cope so far, so for the majority of a move such as a roll, you will get moved around in no apparent representation of the true feeling of the move.
Done it in a A330 sim with the flight control computers turned off.

[paulo]

Here's a previous thread about looping a 747. You'll find a link in one of the posts where a 747 captain describes doing it in a Sim. Great story.
http://www.pprune.org/cgibin/ultimat...&f=57&t=001885

[fokker]

Call me Mr. Picky but, although no simulator can mimic more than 1G for more than an instant, a properly flown barrel-roll is a 1G manoeuvre anyway.

The A320/321 sim. will certainly fly one quite happily - in direct law, of course.

[Shaggy Sheep Driver]

The 737 in FS2000 does very nice loops and barrell rolls ;~) In 'real' sims, it will depend on the sim's accuracy of modelling outside 'normal operatons' envelope. Probaly not very accurate - why should they waste money modelling such flight phases?

In reality, any aeroplane can be barrel rolled IF DONE ACCURATELY - otherwise excessive speed and 'G' as the nose goes low in the second half. Loops depend on allowable 'G' (again, not too bad if flown accurately) but entry and exit speeds may be beyond VNE in large aeroplanes, especially in the 3rd quarter of the loop.

However, RAF Victors and Vulcans used to do a half loop with roll off the top in the 50s during 'lob' bomb practice. I've got it on vidoe at home from a Farnborough show of the time. Very impressive.

In the airline world, as well as the well documented 707 and Concorde barrel rolls, there was the 727 that performed extreme unauthorised aerobatics when the crew accidentally extended LE slats while experimenting with 1st stage of flap in the cruise. One slat was ripped off and the aeroplane 'departed controlled flight'. It was recovered by an aerobatically-experienced captain using 'parts of the attitude indicator not seen in normal flight'.

SSD

[martine]

Thanks guys for your replies but some of you missed the point. I know you can do some aeros in real planes not originally designed for them. I know the motion in a sim can only go so far. I know you can't experience more than a sustained 1g in a sim.

My question was does the sim accurately reproduce the aerodynamics/newton/gravity hell...physics laws well enough to be realistic. In other words...if you could fly it in a sim, could you be reasonably confident of doing it for real (subjective g force aside).

Don't worry, this is purely an academic question to understand how well big-boys sims model the world.

[martine]

Shaggy Sheep: I've heard about the 707 roll but Concorde? Tell me more!

Fokker: whats 'direct law' mode?

[fokker]

It's really too much this time of night, but the airbus family has all sorts of protections to pitch rate, roll rate, angle of bank etc. 'Direct law' is a reversionary mode (requiring multiple failures and,therefore, pretty much unachievable outside a simulator) where normal protections are lost and the aeroplane responds directly to side stick inputs. You may find the thought wierd, but how many times, on a civil air transport, do you need more than 67 degrees bank angle anyway?

BTW, it also has a lovely table (space between legs vacated by side stick) for eating one's lunch from. These Froggies; think of everything!

[fantom]

fokker! back to school for you.if the barrel roll was a 1g thing you could never get out of s+l. think about it. what you meant to point out is that the barrel roll is a vertical manoeuvre. the subjection of more than 1g in the sim, and sustained,is a different matter entirely.can not be done, of course. at entryspeeds of, say 400kts,the barrel will require about 3g - depending how you want to fly it.and another thing....
hope you are not current on the airbus. d law
practically unachievable??? back to the fcoms for you matey!

[Shaggy Sheep Driver]

Martine - I've got a video of Concorde somewhere where a senior BA chappie (may have been that one who used to be chief Conc pilot but took early retirement after landing back at Heathrow with nowt but fumes in the tanks :~) was talking of his original checkout with one of the test pilots. "I've rolled it left", he said, "now you'd better unwind it".

SSD

[martine]

SSD - Blimey and blimey. So the Concorde roll story is probably accurate - anyone out there know the details?

Not heard about Concorde landing with not a lot of fuel - what's that one all about?

[Lucifer]

fantom: I think you are in fact more wrong than fokker. My experience of aeros is light aerobatic aircraft, and although for a barrel roll a 3-4g pullup was required, as was pointed out and I learnt when I said the same thing on looping a 747 thread, for the greater energy it whould require a lower initial g pullup. So although it will not be 1g throughout, it is a constant g manouevure, that at my best estimate would be under 1.5g. It is always said that you should be able to do it without the pax noticing as well (if they are all on the way to a blind convention).

In my experience, none yet have crashed on me doing aeros, though they certainly do nt like coping with extreme attitudes. The best we did was placing a 737 at the end of SondrestromFjord runway and txying it off the cliff at about 2-3 knots, then parking it in midair. The sim slowly relises you error, as you hang out of your straps facing down, but still a few hundred feet off the ground. 737(rediffusion) and Tristar(Thompson CSF) cope with the barrel roll and aileron roll OK, but have this funny jerky movement at about 270-360 degrees in the roll, as it gets back in position. Tornado GR and Harrier are fine any way you want, though of course the GR sim doesn't have a visual.

[ 04 December 2001: Message edited by: Lucifer ]

[Chimbu chuckles]

On my last sim check in a 146 sim, before leaving airline flying for corporate, I requested and recieved some play time from the checky.

The 146 sim does a very nice barrel roll and aileron roll, even at VERY low level down the runway

When I tried to loop it things went a bit pear shaped though. As I floated over the top the stick shaker activated, followed closely by stick push . They spin ok too Spin recover was normal with the + that the control column was already all the way forward Recovery was completed with both feet on the foot rests and a fair amount of effort on my part, G ? What G!!!

Stall turns resulted in the same stick shaker/push

Was a $hitload of fun though.

Chuckles.

[martine]

Chimbo Chuckles - so the 146 behaved itself as far as realistic aerodynamics/momentum etc?

Presumably you could have isolated the stick pusher?


How about a lomcevak followed by an inverted flat spin in a 777 anyone?

Sounds like fun.

[fantom]

lucifer.one can not be more wrong.either I am or I am not wrong.
in order to barrel at 1.5g you would need an
humungous amount of power (you mentioned the harrier - good, but would req outstanding pilot skills to perform). I mentioned 400kts
because that is, typically, what is rqd in
performance a/c. ok, me old and my last one was in the F4 but the principles still apply.
then there is the amount of sky reqd.......
get in the REAL a/c and see what happens.
sims re-posn in the manner you outline for
obvious reasons. it is only a machine!
by the way,the barrel reqs wing vertical at both horizons and wings horizontal at the top and bottom. easily forgotten. also should be symmetrical upper and lower of horizon.
and another thing....if fokker thinks 'very few pilots have flown it'...I do not know any of my mates who were not doing them within 10hrs of total flite time.

[Lucifer]

yes, that's what I had thought, but was informed otherwise on the previous thread (mentioned helfway down 1st page), which I did not make really clear, and certainly power available is a huge infuence. I too have flown it within about 15 hrs with the 3-4g pullup in a light a/c, but not in a transport aircraft. Perhaps the Dutch Herc display crew that specialised in the 'stall turn' fake might know?

Lower g would make for a larger and slower roll, thought we'd need to be aero engs to calculate to the lowest need to maintain enough energy.

It would be interesting to know what the 707/720 test guys had when they did it, though of course it was empty and had the power advantage.

[ 05 December 2001: Message edited by: Lucifer ]

[Alf Aworna]

You might want to check out this link to a video of Bob Hoover looping/barrel rolling a turbo commander light twin. Impressive. Bob Hoover web page
Believe there is also a cockpit video of him barrel rolling the a/c with the engines out with a glass of water on the coaming (!)but couldn't find it on the net.

[Tinstaafl]

I've seen the video of Bob Hoover doing the barrel roll with the glass of water.

It wasn't just a glass of water on the coaming. He was pouring the water from a jug into the glass as he did the barrel roll.

So that the camera wasn't blocked he had to pour the water while holding the jug handle 'palm up'. Bloody awkward grip to add to the task.