A321 A320 A319 lower one wing while flying straight?

[jrbt]

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]

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

[FlightDetent]

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.org-vbulletin/1156x807/snippet_geometry_19d38114e80a02fb86b170d153ef93c86e6c7d01.pn g
https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/572x372/snippet_sharklet_3803c9d66f9165e830a112afab8eb2609e09b1cb.pn g




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.org-vbulletin/371x297/snippet_viewangles_fd8505b568603f1d51f1b7e6c1bbcc3398209285. png


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

[Check Airman]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

Touché hehehehehehe….:}

[atakacs]

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]

Baloon is the way to go.

[wiggy]

Question for the OP - Is this the June 10th annular eclipse and (looking at your address) are you planning on this flight taking place over North America - where the eclipse is visible at sunrise?

If that's the case if side slipping/lowering the into sun wing is there a possibility you can ask the operator of the flight if it's possible to displace the planned track further to the north east than the one you have planned at the moment in order to get the extra solar elevation you need?

[pattern_is_full]

I see a significant aerodynamic problem not yet mentioned specifically (but KingAir1978 nudges up close against it.)

DRAG in a slip (where the relative wind is hitting the side-area of the fuselage, not just on the nose).

And thus rapidly-decaying airspeed, if one is also trying to hold altitude. Especially so close to the operational limits of the aircraft (A321 ceiling - 39800 feet).

Slips are a really good way of killing off airspeed (and/or altitude) - see, e.g., the final approach of the Gimli Glider.

Might be on the order of losing 15 kts IAS per minute, even at full thrust. Maybe more, if there is pitch added to hold altitude as the airspeed decays. And depending on all-up weight.

Just how long is this slip ("observation window") expected to last?

"Punctuated slipping" might be a solution - slipping for 15 seconds - return to coordinated flight for 60 seconds to regain speed - slip another 15 seconds (rinse and repeat).

Assuming any other problems can be addressed.

[iggy]

atakacs

I used to fly BAE146 and it was not RVSM ceritified, so highest was FL280. And anyway, it really struggled to reach it,even not fully loaded. 300ft/min rate aboveFL250...

[zzuf]

Transport category aircraft, it is certificated for full rudder sideslips at speeds up to Vmo/Mmo. Either pilot rudder force limited or maximum rudder angle that the flight control system will reach.
I doubt that this aircraft would be thrust limited at the proposed altitude with the small sideslip angle required. If so, get a block of altitude and lose a bit of height during the observation - wouldn't be much.
Will need to select airspace which gives some operational flexibility
So, the proposal is within the certification envelope of the aircraft, the flight control system allows for flight with sideslip, may require flying without autopilot, should have the performance but may need to drift down a bit.
Use airspace that allows operational flexibility.
Most important, talk to the Ops manager/ chief pilot about the project.

[Roj approved]

You might hear "STOP RUDDER INPUT" if you push too hard.

[washoutt]

If the approved flight manual has no procedure for this manoeuvre, and if you perform it anyway, I believe you then act illegally and may be susceptible to judicial action. Better wait for an eclipse higher up above the horizon.

[DuncanDoenitz]

What you need, my friend, is a Tupolev Tu-154; no winglets, wings well set-back on the fuselage, and anhedral to boot.

Good luck with that.

[zzuf]

washoutt

Don't understand this comment. What manoeuvre should the OP look for in the AFM? Steady heading sideslip? Won't be there. But for example, the steady heading sideslip component of a maximum crosswind takeoff or landing would be far more demanding than what the OP is proposing. Perhaps a complete engine failure at maximum altitude and maximum continuous power? That will result in a far more demanding situation than that proposed but it is a manoeuvre for which the aircraft is certificated. There is no procedure in any AFM concerning, say, using full control deflection - if it is required, the pilot does it - staying within the aircraft certification limits. Probably the most important in this case would be Va restrictions but it could be something like a buffet boundary, which won't be a AFM approved procedure.

[FlightDetent]

zzuf, like your inputs and I am ready to believe what you say about the certification.

EO at max alt and max L/D speed yields about 3 degrees of bank. As a matter of fact, no more than 5 is allowed by those certification standards. The original poster may have been asking for 10. In that perspective, even full rudder may not have enough authority to achieve what's asked.

[zzuf]

Flight Detent, don't get carried away with engine out - it is not required in this case, just use a bit of rudder to induce sideslip and set a bank angle for zero yaw rate.Take just a minute or two to sort out what sideslip angle v's bank angle the particular aircraft type gives you. This is a standard flight test method when assessing lateral/directional stability and control.
Don't forget the Vmcg and Vmca are really just performance speeds to get you safely, considering particular handling characteristics, from brakes release to a V2 climb having had a critical engine failure at Vef. The limits are arbitrary - a higher or lower rudder force could be prescribed or different bank angle limits. It is a grave mistake to think that Vmca, for example, can be applied safely in flight conditions other than those specified in the airworthiness standards. Depending on the aircraft it may be possible to safely use, say, 10 degrees of bank towards the live engine and fly at a speed lower than scheduled Vmca - of course, this speed is not Vmca as the bank angle is not compliant. Scheduled Vmca has no meaning in normal engine out handling - power setting is probably wrong, bank angle probably wrong, rudder force applied probably wrong, sideslip angles probably not what was experienced during Vmca testing
Also don't forget that a manufacture may use Vmca determined at 5 degrees of bank (lowest compliant Vmca} but use around 3 degrees of bank for the engine out climb performance (zero sideslip minimum drag).

[FlightDetent]

Lost in translation, not sure what the Vmca connection is. My reaction was to yourcomplete engine failure at maximum altitude and maximum continuous power? That will result in a far more demanding situationWhich I find to be the other way around. By his own description, the OPs required manoeuvre is about 3x more aerodynamically displaced than an EO situation at max alt & MCT.

I still take your word for it that as part of the certifying flight tests, full rudder sideslips had been tested all the way up there. Not sure what the limiter provides at M 0,8. Thank you for confirming my 3-degree hunch.

[wiggy]

washoutt

If the OP is catering for a specific observing group embarking at a particular airport he/she may have a very long wait for a repeat performance.

As I mentioned in post #21 one possible way of increasing the sun's elevation for this eclipse may be to shift the planned ground track - depending on where in the world this is being planned it might not need to be much of a shift, but doing that may bring in other complications (e.g. change timings, which can lead to other subtle and sometimes not so subtle changes) .. It'll be interesting to see if the OP thinks shifting the track is an option or not.

[muppetdodger]

Surely you could just sell 5 less tickets for 24-28. Or as someone else said, move around. What do you do if you are on the other side?

[compressor stall]

Muppet - when I did one of these, they sold the "window" so no moving about and they pulled the seats out on the viewing side.

@JRBT - a minute of internet sleuthing and a mail search on my computer reveals our paths crossed in Tahiti 11 years ago....

My considered opinion is that for this one flying one wing low is not advisable / practical nor feasible. Whilst I have not looked at Fred's predictions for this one, but I assume you are FL390 to get the sun's disk as high as possible. This altitude is fast approaching the limit of the flight envelops for the type (although likely you will be lightish). You don't want to be doing anything that upsets the ability of the aircraft to fly (like create more drag by flying slightly sideways). Furthermore, you can't just switch the Autopilot off and fly one wing low without ATC RVSM issues.

The best approach is to ask the charter company to contact Airbus directly via their Technical Pilot through the Airbus Tech Request channel. Airbus flight test pilots and engineers will review and advise. You don't want your charter company trying anything odd up there with you and your pax on. 2 weeks should be enough time.

Final thought - if you are going to not sell the shadowed windows, you will need the crew to fly the aircraft in heading, not track. A crosswind on a fixed track will alter the heading of the aircraft and in turn change the wingtip shadow location on the fuselage.

Good luck antumbra chasing!

[washoutt]

Thanks for all your interesting observations. If a non-normal flight condition arises, then good airmanship dictates that all necessary actions be taken to ensure a safe flight and landing. If a 10 degree bank is considered a normal flight by the manufacturer and certificated by the aviation authority, then it's ok. If not, then not. Of course, you can always ask the manufacturer if a certain flight attitude e.g.condition is within limits and approved.

[Sailvi767]

Airmann

At 39,000 feet I think this would produce a very bad result.

[FlightDetent]

https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/700x95/audio_dont_slip_b40a6aa0dd55492b184ac5c49b0d930274e3889d.png
10 characters.

[jimjim1]

At the latitude of New York (which someone mentioned) one degree at a constant latitude is about 55 statute miles.

So you could achieve the 5 degree elevation change by moving your observation point approx 275 miles to the East or West.