Loop in a B747 :-)
 

OK, blame a colleague of mine for this one...

...late night bar conversation leads to a debate; Is it possible to complete a loop in a 747. The debate is unresolved, and the participants soon after fly the seperate ways, both on 747s. Independently they do cockpit visits, and ask the question.

One crew say no, the other say "theoretically" although the stress point would be the engine mounts so you might lose a few in the process. They also say that "it's been done once" but don't say whether any structural damage occurred.

B747 Loop - possible? been done?
We have to know... :-)

I'm no expert, but I would say no. Unless it is going to be a very big loop, and you are going to use flap over the top as the speed decays, you will need something like 4g to kick off with. Barrel Roll, almost certainly, although I don't know of one. Come on experts, and if there is film of it then it must be required viewing.

Well there was Tex Johnston's famous 707 barrel roll...

http://www2.prestel.co.uk/crawford/p...07inverted.jpg

http://www.pfdteam.com/log18.htm

and now for something completely different:

http://www.aviationpics.de/t/rollit.gif

The light aerobatic aircraft I've flown used about 3g to get around a loop. Even 2.5g if you didn't care about it being very round.

It's a +3g limit on transport category from memory so it might well be possible with a slight dive & full thrust to build up enough energy to get around the loop.

I wouldn't like to try it though.

You need a 4g pullup for a loop: the 747 g limit is 2.5g. So no.

It certainly wasn't 4g for a loop when I was taught aeros.

In Oz I thought a B747 is certified as a 'normal category' a/c, in which case the usual 'g' limits are +3 / -1.xx (can't remember exactly).

Different in different countries? Or certified under an exception to the rule?

Still might be possible since many a/c are constructed to withstand 50% above their certified load limits.

China Airlines sort of managed it in a B747SP in Feb 1985. the offical investigation reported that the aircraft nose had pitched down 67degrees and rolled onto its back at a bank angle of 176degrees. This had subjected the wings and frame to a +5g, which at the time Boeing maintained was impossible, and it was not until they saw the flight and data recorders that they belived it happened. It turned out the commander regained control just 40seconds from impact with the sea. He continued to fly for a further hour to San fransico. It appears the cause was incorrect actions by him when he had an engine failure at 41,000 ft and all flight deck were caught unawares , they disengaged the autopilot and thats when all hell broke loose. The effects of falling 15,000ft per min and the 5g locked the undercarriage into place, and it seems this is what helped to slow them down in order to regain control and the report did praise the crew for regaining control of a situation even boeing said could not happen.

Hope this answers your question.

I think they did more of a 'dive then roll inverted then pull through' sort of manouvre.

Generally a bit of a no-no for unusual attitude recovery. :D

What a great thread! They should spend billions of pounds investigating this!
I dont really know anything about it though but I did hear about someone doing a roll in one but that may have been a 767 or something that sounds similar because I was small when I was told and could have it wrong.

Tiger_Moth - you've heard of a Boeing barrel roll more recent than the 707 one shown in the photo?

It was done in the original B720 test a/c. When Boeing dragged it out for a celebratory flight a couple of years ago - 50yrs of jet flight or something - they did the barrel roll again.

On the news tonight they showed the Wallabies taking a tour of the Qantas Jet Base at Mascot.

One very obliging captain (with 1st officer Steven Larkham in the R/H seat) demonstrated a barrel roll in the 747 sim. It certainly looked quite impressive.

LUCIFER : Just because an aircraft has a G limit of 2.5 or 3, doesn't mean to say it couldn't actually do a 4G loop. Might pop a rivet or two & need a relight here & there but hey!!!

China airlines had to retire that particular airframe after the spin outside of San Francisco. So my guess is that you could possibly do it once.

Lucifer

You don't have to have 4g for a loop. The initial pull of g determines the size of the loop. For example a light pull will result in massive loop and the aircraft may run out of thrust (and therefore airspeed) half way up if the engines are not sufficient. For example a 2g pull in a bulldog would result (most probably) in a stall in some sort of vertical attitude. An F18 or something similar could probably loop with about 2g although the manoeuvre may take about 20000ft! The more g you retain makes the manoeuvre smaller, tighter and retains airspeed therefore keeping the aircraft flyable.

Same priciple for fighters or heavies but as the thrust/weight varies considerably I would say you'd need a massive pull from very high speed on a 747 that would probably exceed the g limits. Similarly the pull out would be more critical than the way up as speed is building and gravity is working against you. Therefore I think you might lose an engine or two on the recovery! :p

In the sim, start at 300000ft, shallow dive max power to mmo/vmo and you'll make it. Needs about 250000ft of altitude.

250,000ft :eek:

Surely then the issue is not G-loading but burning up on re-entry :D

Dave,

The issue may be not going out of the back end of your sim slot trying to lose the 250000 feet !

I guess you could position the sim at that height (maybe), what happens to the numbers on the PFD/ND?


;)

I also agree that you don't need to pull 4G for a loop. For a nice loop in a small plane, between 3 and 3.5 is enough.

Now for commercial jets...
I knew the barrel roll during the first flight of the 707, but I've also heard Concorde pilots saying that they did the same during line training (no pax o/b unfortunately). The instructor would do one to the left and the trainee would then do one to the right. That was quite a long time ago, I don't know if they still do it...huh... if they used to do it until last year.
;)