Loop da loop in a jetliner?

Factual Questions
1

I have a clear memory of the following but have been unable to find it online, which makes me think I have at least one major detail wrong (perhaps all of them). Maybe someone here remembers?

Here’s how I recall it:
In 1979 or so, a Hughes Airwest pilot kinda lost it and tried to do a loop in a 727. He didn’t quite make it, wound up doing an Immelmann instead. Lots of press, terrified pax, etc. And of course he was cashiered. I remember a cartoon in BAM (hey, it’s still sorta alive online: https://bammagazine.com/) with a drugged-out looking pilot going “Loop da loop!” And an article quoting someone from Boeing who said the engineers were actually pretty pleased because they thought the wings would have come off.

Does this ring any inklings? I really don’t think I hallucinated it!

The fact that nobody mentioned it in Loop-da-loop does not encourage me, however.

2

I recall reading a similar story and I’m wondering if maybe our two memories have mixed the two things together: there was a Boeing 707 pilot who did a barrel roll on a test flight, infuriating company management. He said he was doing it to show the 707 was capable of it.

3

The Master Speaks

4

That’s what I thought first when I saw the OP. On 7 Aug. 1955, Boeing’s chief test pilot Tex Johnston, took it upon himself to do a barrel roll during a demo flight of the Boeing 367-80 (the prototype for what would become the 707 / 720 airliner and the 717 / 739 (C-135) tanker / transporter. It consternated the management, but earned Boeing its much-needed military purchases of the planned aircraft - and thereby funds to continue developing planes and outcompeting rival Douglas.

The story is here.

5

It doesn’t match every detail, but maybe TWA Flight 841 (1979)? The jet rolled twice during a steep dive, which was unintentional, before the pilots regained control and landed safely. The NTSB controversially blamed pilot error.

6

Guinness World Records credits the largest airplane to complete an aerobatic loop (aka “loop the loop”) as a Lockheed-Martin LM100J, a civilian derivative of the C-130J Hercules. So a midsized cargo plane, not an airliner. And this was in 2020.

I can’t link it because the Guinness World Records website won’t open for me.

7

I did find all those stories; the TWA one was the right year, too. But the “loop da loop” cartoon is VERY clear in my mind, and doesn’t fit either of those other incidents.

And while this was my last year of high school and this was California, I was NOT smoking dope or drinking at that point, so I can’t blame that!!!

8

You may be remembering TWA 841 from 1979. A 727 went into a spiral dive (described as a “barrel roll”) and dropped 30,000 ft. before the pilots regained control.

The incident was ruled caused by the pilots performing an unapproved shortcut to increase the plane’s lift. The crew denied they had acted improperly, citing other less-serious control problems with 727s.

ETA: Ninja’d by bibliophage

9

I should point out that the KC-135 (military version of the 707) is the aircraft we use to perform Zero-G testing. No loops are done but the aircraft goes into a very steep climb and allowed to “fling” over the top and descend in a free fall. Then it pulls up in a high G turn and resumes climbing for another go. It does this over and over on each flight. It’s one tough aircraft.

10

I saw an interview with Tex Johnston about doing that and he said that the structural loads on the plane when doing that were basically normal. It didn’t stress the airframe any more than normal flight.

I thought that was interesting.

11

Yep. zero g for 25 seconds, followed by 1.8 g for about 28 seconds, averages out to 1 g over time:

A private company does the same thing with a 727. If you’ve got a few thousand bucks burning a hole in your pocket, you can book a ride:

Wikipedia points out that a barrel roll applies a positive g load to the airframe, typically 2-3 g, but can be as little as 0.5 g. a 727 loaded out for a demonstration flight (few passengers, no luggage, and little fuel) would have no problem with this.

12

You can get away with pretty much anything you want on an airplane, if you’re willing to sacrifice lift for it, and you can sacrifice lift as much as you want, if you start with enough altitude to spend.

13

It’s not an airliner, but the space shuttle could do it. My brother is a former USAF test pilot. After getting out he worked for Boeing at the NASA JSC, on the space shuttle reentry scenarios. Over in the thread about the Columbia shuttle disaster, in the OP I wrote this:

That is in one shuttle reentry. I was in the sim when he did it. He had done it many times before. Of course nobody ever did it in the real space shuttle, but this is the real simulator for it so I’m confident the shuttle can do it.

About the jetliners, I’m a fan of watching those air disaster TV shows. I’ve watched nearly every episode of Air Disasters on the Smithsonian Channel. Jetliners have been in some terrible orientations due to mechanical failures or extreme weather. That must be frightful for passengers and crew. From what I’ve seen, given enough altitude I’m confident that jetliners can do a loop and a barrel roll. Keep in mind, IANAP.

14

Unlike a barrel roll a loop does require more of a load on the plane than regular flight. Usually 3.5-4.5g. Don’t pull hard enough and you lose all your speed before you make it over the top. Then you need to not go too fast (or hit the ground) pulling out of the dive at the bottom.

The design load factor for an airliner is only 2.5g. That is at gross weight, empty weight is usually about half maximum, so the wing would be strong enough if light, but not if fully loaded. But things like the engines might break off.

My first thought was this incident: https://www.youtube.com/watch?v=_IYaPWyokIA where an airline employee stole a plane and did some aerobatics before crashing. That is described as a loop, but looks to me like he did a roll and let the nose get low during the inverted portion then just barely recovered from the dive.

The recovery from that dive would be pretty much the same load as a loop. Wings and engines did stay on, so that plane could have done a loop in the hands of a skilled pilot with enough altitude.

15

Isn’t it more difficult to look at high altitude because there is less for the control surfaces to “grab”?

16

I’ve been following aviation closely since the mid 1960s when I got old enough to have some understanding of the words alongside the pix. There’s never been a loop in an airliner that I heard about.

IMO/IME
You’re not going to succeed at performing a loop in an airliner. And definitely not in the hopelessly under-powered and high drag 727.

The problem is the comparatively low G-limits multiplied by the comparatively low engine power.

Even lightly loaded with no pax, low fuel load, etc. It doesn’t work. You can certainly build up speed in a shallow dive at full power to right up near or even a bit past redline maximum speed.

Then you start to pull the nose up. It’ takes 1G to offset gravity, and 2.5 is the limit, but for a one time experiment where you’re going to throw the airplane away afterwards you can probably push that to 3-ish. Which means you only have 2 G available for turning in teh vertical dimension. one of your 3 usable G’s is just fighting gravity. This concept is called “radial G”.

A net 2G pull means that at somewhere just before or just after getting vertical (= nose pointed straight up), you run out of airspeed and fall or stall out of the maneuver. ANd remember you can only sustain the full 3G pull wihle you’re fast. As soon as your speed starts decaying you need to start reducing G to avoid a high speed stall. You might start at 350 knots in a typical airliner, but by the time you’re down to ~200, you can’t pull much more than 1G without stalling.

With massively more power you could have thrusted your way all the way to the inverted top, then used gravity plus thrust to gain speed down the backside. With massively greater G available you could have turned more tightly = less time spent, and gotten at least well around to onto your back before the speed ran out and you sort of mushed your way over the top then once pointed downhill inverted you could wait a few seconds to regain enough speed to resume the pull.

If you did somehow succeed at the first half of a loop and now find yourself slow and inverted, but not stalled while pulling gently at low G. the good news is now gravity is pulling the same way you are and so now that 1G is adding to your turning, not subtracting from it. The bad news is that since you’re very, very slow, you may only be able to pull 1/2G without stalling. So you’re still only netting 1-1/2G turning force.

And now you get to the next problem. Avoiding getting supersonic and shedding parts on the way back downhill. Again it comes down to the hardest you can pull doesn’t get you past vertical straight down and into the dive recovery quickly enough to avoid having the airspeed get out of range. On the way up you ran out. On the way down, your cup most surely runneth over. That’s bad.

And all of that assumes you have a G-meter in your airliner so you can optimize your performance up until the airspeed exceedance low or high. Real airliners don’t have them. Guesswork on the pilots’ part can only detract from the theoretical optimum path with the best (but still hopeless) chance of success.

The effects of altitude on controlability are complicated, but by and large by flying based on indicated airspeed, many of those issues wash out.

There are two real problems with high altitude applicable to attempted loops

  1. Engine power declines precipitously with altitude. At high altitude cruise total thrust is maybe 10% of sea level thrust. Such that even getting unwitting slow in level flight can provoke a situation where ever full throttle won’t accelerate you even going dead horizontally. That situation rapidly deterioates and the only remedy is a descent (not quite a dive) to rebuild speed by trading altitude. Engines that can barely keep you at constant speed level are certainly not going to have the excess oomph to thrust you upwards and around in a loop.

  2. Mach. I said by flying based on indicated airspeed, controlability is about the same as at low altitude. E.g. seeing 250 knots on the airspeed indicator means the control surfaces are feeling the same poundage of air going by per second as they would at 250 actual knots at sea level. The gotcha is the air is actually going by at say, 450 knots, so you’re processing twice as much space of air per unit time, with each volume of air holding half as much molecules and pressure.

    And this is where Mach gets into it. Your maximum speed in a jet is twofold. If you exceed either the maximum indicated airspeed or the maximum Mach bad things happen. Excess airspeed leads to loss of fragile moving parts. Excess Mach leads to Mach tuck and loss of control. Down low indicated airspeed is the limiting factor. Up high it’s Mach.

    Trying to start a loop up high means your limiting airspeed, instead of being, say, the 350 it is down low, is now 250. Which leaves you even less headroom to slow down before you run out of indicated airspeed and stall.


More later. Gotta run.

17

Way back in Ye Olden Dayes we tried this stuff in the 727 sim. Rarely got past 45 degrees nose-up before the airspeed decayed to where you couldn’t move teh nose without stalling.

I bet you’d get a lot farther in a 787 or 777 with no pax & little fuel. Like maybe just past vertical nose-up. But you’re still not gonna succeed.

And if by miracle you did get to the top inverted at low speed in a 787 / 777 you would then have a much harder time not over-speeding and exceeding the Mach on the way back down.

Losing the situation on the way up just results in flailing and falling and recovery is not that hard if you start out with enough altitude below you. Losing the situation on the way back down is a much harder problem to recover from and tends to result in the airplane breaking apart into 2 or 3 large chunks.

Can. Not. Recommend.

18

On thinking about it some more, with sufficient initial altitude, I think you could always perform a maneuver where the aircraft rotates through the pitch axis by a full 360 degrees. But that wouldn’t necessarily be a loop, because with insufficient thrust and/or lift, the plane might not be moving in the right direction: You could end up with something that’s basically just tumbling while falling downwards.

And of course, in some cases, “sufficient initial altitude” might be greater than the height of the usable portion of the atmosphere.