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-   -   A321 A320 A319 lower one wing while flying straight? (https://www.pprune.org/tech-log/640584-a321-a320-a319-lower-one-wing-while-flying-straight.html)

jrbt 21st May 2021 23:52

A321 A320 A319 lower one wing while flying straight?
 
Our group will be flying in a chartered A321 to observe, airborne at 39,000 feet, a solar eclipse which will occur on the astronomical horizon i.e. at solar elevation 0 degrees. (At 39,000 feet this will be 3.5° above the terrestrial horizon.) We'll fly a constant heading that makes the eclipsed sun exactly perpendicularly "straight out" the passenger windows. Normally, this will cause the full-size winglet to block the eclipse view for passengers in rows 24-28 (row 25 being an emergency exit with no window anyway). We'd like to be able to lower the passenger-side wing while flying straight so as to unblock the eclipse view from some or all of these rows. To do this, we'll fly a sideslip maneuver.

Question for PPRuNers: is this doable in an A321? Or is it doable in an A320 or A319, in which case surely it's also doable in an A321?

If it's doable, can we reliably achieve a wing-lowering of 1°? How about, preferably, 2° 3° 4° 5° or more?

We can't ask our charter airline to "test" this on any regular commercial flight which would be improper with passengers on board. Have any PPRuNe readers ever conducted such a maneuver on, say, a test flight?

We won't feel we can trust any indications derived from a simulator.

One concern is that our charter P.I.C. might tell us beforehand sure, it's no problemo, but then unexpectedly discover upon attempting to initiate the maneuver at 39,000 feet that the "software doesn't permit" the maneuver. Or maybe the P.I.C. will discover the software only permits the maneuver to, say, 1° or 2°, not 5° or more as we will prefer?

TURIN 22nd May 2021 01:33

I cannot answer the question but may I commend you on the way that you have asked.

FlightDetent 22nd May 2021 02:13

The software does permit the bank. Doing side-slips at 39k is foolish.

Not an answer either, but you need to speak to them directly anyway. For the PIC to help you, there would need to be a process within the company. Otherwise, he's actually paid to reject such suggestions.

The airline does have the means to ask Airbus directly, who are in general very helpful in assisting the customers. For your query though, the most likely answer is: We'd never tested anything like that and namely airflow stability at engine inlet is not researched for excessive angles of incidence (at Mach 0.79)

As you understand the impossibility to test that with other passengers beforehand, surely you do not want to be there either when the first attempt takes place.

On the practical side, 1-2° does not sound like something outside the normal wobbliness. Is that enough?
https://cimg4.ibsrv.net/gimg/pprune....c86e6c7d01.png
https://cimg6.ibsrv.net/gimg/pprune....609e09b1cb.png




N.b. for photo taking, the smoothness autopilot delivers might be preferable but that yields no sideslip. Over longer periods (3+ mins?) it's impossible to beat in manual flight.


https://cimg4.ibsrv.net/gimg/pprune....3398209285.png


Appears as if 10° is critical for your case on a sharklet-equipped one.

Check Airman 22nd May 2021 06:43

What you’re asking is doable, but an A320 is not a fantastic choice. A 737 or similar would probably be a better option.

That said, on the day in question, unless it’s ABSOLUTELY smooth, the bank angle will vary by about a degree or so in normal flight. If there’s any turbulence, you won’t be able to get the perfectly smooth conditions you require.

Best of luck!

DaveReidUK 22nd May 2021 07:33

You need to induce a Dutch roll. Give it long enough and passengers won't care whether or not they can see the eclipse ...

Webby737 22nd May 2021 11:30

Does the charter company not have some older A321s with the wing tip fences ?
These are a lot smaller than the sharklets fitted to the NEOs and would probably not block your view.

Airmann 22nd May 2021 11:41

Basically you want a side slip. I.e. go straight but maintain a bank.

Usually never done in any normal conditions on any Airbus except in engine out case, where up to 5 degrees bank in a side slip may be commanded.

So if they accept just need to simulate an engine failure. Reduce the thrust to idle on the engine on the opposite side to which you want to lower the wing on. Ask pilot to go to max engine out alt that way you'll get max power from engine producing thrust which will give the maximum bank.

use a 320 without sharklets.

Hahaha this is crazy.

zerograv 22nd May 2021 13:23


Doing side-slips at 39k is foolish.
+1

Reducing thrust on one engine at 39k feet will very likely generate the inhability of mainting that altitude, and the need to descend.

Fursty Ferret 22nd May 2021 13:26

I'd have thought that a FFS would replicate small sideslips at any level with good accuracy. That being said I think it's an utterly ridiculous idea and if anything happens this thread will be Exhibit A in the subsequent legal case.

Just ask the passengers to move around. You're worried about those in rows 24-28; well, what about everyone on the other side of the aircraft?

iggy 22nd May 2021 13:38

Keep the wing you want lower full of fuel, while the one you want higher totally empty, and... voila!!!

Obviously, keep the fuel x-feed open at all times.

zerograv 22nd May 2021 15:04

Don't know about the Airbus ... but normally there tends to be a "Max Fuel Unbalance" limitation which is normally less than an unbalance of 1 tank full - 1 tank empty.

Vessbot 22nd May 2021 15:42

I think he needed to add a healthy ":ok:" to his post. We're in a one-upmanship comedic contest of absurd alternatives to trimming the rudder.

FlightDetent 22nd May 2021 17:21

Can't trim the rudder on AB with the AP on.

In manual flight, she would slip nicely and FBW arrest any residual roll rate.

Unfortunately, on sharkletted A/C dispatch with one removed is not permissable.


vilas 22nd May 2021 18:09

Don't do it on Airbus. It's a software driven aircraft. FCOM doesn't tell you everything. Something may appear like 2+2 but it may come out with 7,8 or 9. You know the story of doing simple touch and go where trainer after touchdown tried prevented the trim from setting to zero? It ended in loss of control almost ended in a fatal.

KingAir1978 22nd May 2021 18:18

I think this is a very bad idea. Flying a swept wing jet close to its ceiling and putting in a significant amount of slip... I doubt that you'll be able to maintain altitude, with even a 'small' amount of sideslip. Other than that, I think there may be some untested aerodynamic effects.

B2N2 23rd May 2021 11:51

How long will this eclipse last?
How about setting the bank limiter to 5 degrees, time your flight so the eclipse starts at your 4’ o clock ( or 8) and make a shallow turn in its direction?
Its an Airbus, you can’t do pilot stuff in an Airbus. It’s been engineered out.
:suspect:

FlightDetent 23rd May 2021 13:57

Better engineered out than under-engineered. Any recent stories about B737 nacelles falling apart or rendering the A/C unstable, trim wheels too small to move THS and elevators lacking authority to overcome it?

Not relevant, I know. As long as the big stick is there inbetween legs and you can stroke it with both hands. :E

B2N2 23rd May 2021 16:21

Touché hehehehehehe….:}

atakacs 23rd May 2021 18:17

I obviously don't know the specifics of your planed flight but it would seem the 320 is not your best choice in this specific case.
What about chartering a different aircraft. BAE 146 (not sure it would offer a much better view, though) ?

FlightDetent 23rd May 2021 22:25

Baloon is the way to go.


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