The Great Ongoing Aviation Thread (general and other)

Miscellaneous and Personal Stuff I Must Share
1501

Short version: It’s not small or large that matters. It’s straight versus swept wings.

Medium version:
Swept wings are very inefficient at low speeds. Despite very fancy, complicated and heavy flaps and other so-called high lift devices, it takes a lot more angle of attack to generate enough lift at low speeds. Everybody flies a geometric path that’s about a 3 degree descent towards the runway. What differs is a smidgen of how the wing is aligned versus the fuselage, and mostly how nose-up the airplane needs to be to have the AOA needed to generate the lift required at a speed they can stand to land at.

If you hunt up some YouTube vids of straight winged large planes such as WWII or 1950s bombers, transports, and airliners landing you’ll see they make the same relatively nose-low approaches as do modern Pipers & Cessnas. If you look at vids of straight wing jets like the early models of Cessna Citations you’ll see an intermediate case.

An interesting special case that illustrates the issue is the F-8 Crusader. Instead of wing flaps they chose to adjust the angle of the entire wing versus the fuselage for takeoff & landing. By tilting the wing up they avoided the need to fly with the fuselage tilted up so much.

Vids of delta-winged airplanes like Saab Drakens, F-102s, F-106s, Concorde, XB-70, will show the effect the opposite way. Delta wings are even worse at low speed lift than are swept wings. So they fly their approaches even more nose up to deliver even more AOA to generate the needed lift.

The latest fighters are not good examples because of things like canards, vortex lift, and thrust vectoring that muddy the picture versus the older simpler machines.

There’s a lot more why behind each of these points, but this’ll do for today.

1502

That looks like an accelerated stall/spin. If you’ve ever practiced stalls into spins that’s how vast the wing snaps over. The only way to keep the wings level is to use the rudder. If you use ailerons to keep it level it accelerate the wing dropping.

1503

Here’s one example of that vid showing the actual crash:

I’m not thinking accelerated stall because I don’t think he was turning. From the generic aftermath vids we know that street is neatly aligned with the runway centerline. In the vid I linked to the airplane appears from behind the white hangar in the foreground in the first half-second or so. Starting at 13 seconds they show the same sequence zoomed in which gives us a much better look.

At the moment the plane appears from behind the hangar it’s approximately wings level but with a slight left bank, is traveling parallel to the road, and is extremely nose-high. And at about 20-30 feet above the ground. A couple seconds later it violently wingovers to the left and impacts mostly nose first.

As @Magiver suggests, that’s probably a stall leading to the beginnings of a spin before the ground promptly arrives. But there is another possibility.

In the aftermath vid Johnny linked to at about 45 seconds we see there was a line of wooden power poles along the right side of the road and there was a power line running transversely across the road right above the crash site. And a power pole on the right side of the road right there.

From the crash sequence vid watch very carefully about mid-span along the left wing. You’ll see a momentary bright flash, then you’ll see the power pole with the attached street light stanchion deflect several feet to the left and then spring back into position as the airplane begins to cartwheel past it.

Putting all this together, I think he struck the pole or the attached wires with the left wing and was rapidly whipped around to the left. Which would of course instantly stall the left wing and add lift on the right, triggering the wing-over / spin maneuver.

Did he stall and fall against / through the pole & wire, or did he hit the pole / wire, get whipped around, and stall? I suspect the latter, but either way it ended badly. Note that Johnny’s aftermath article has witnesses saying the airplane hung up briefly in the overhead wires before ending up on the ground. The fire developed real quickly. Which would sure be helped along if a live power line was wrapped up in the mess.

Switching to piloting, not the crunch sequence. …

Another observation: He had half-flaps deployed. That mistake probably killed him. Presumably the flaps were already out when the engine failed. Had he promptly sucked them up he’d have had a longer total glide.

The extreme nose-up attitude just before things went haywire also shows he’d slowed well below L/D max. “Stretching a glide” never works. Perhaps he was wisely attempting to thread between the other power lines he could see that we can’t but couldn’t quite pull it off. Or perhaps he just wasn’t mentally ready to accept that this was going to be an off-airport landing and he just kept pulling back and pulling back to delay the moment of reckoning. Which resulted in him running out of airspeed and ideas before he’d run out of altitude. I hate it when that happens.

Regardless of what triggered the out-of-control situation one thing is very clear here. This accident demonstrates yet again that from even 20-30 feet of altitude, an uncontrolled fall to the ground is usually unsurvivable. Whereas a controlled touchdown, even one that then careens into ground obstacles, is much more survivable.

RIP my friend, whoever you were.

1504

This is interesting (not sure where else to post it):

1505

Interesting. Here’s a paragraph from in there:

Only 11% of the world’s population took a flight in 2018 and 4% flew abroad. US air passengers have by far the biggest carbon footprint among rich countries. Its aviation emissions are bigger than the next 10 countries combined, including the UK, Japan, Germany and Australia, the study reports.

Said another way, ~90% of the world’s population simply doesn’t fly. So another way to write the headline is “10% of flyers cause 50% of emissions”. Which seems pretty consistent with the Pareto principle.

Of course the same is true about emissions from cars, from electrical production, meat consumption, cement consumption, etc. The only carbon the vast majority of the poor world emits is from their firewood. Which may be heavy in particulates but is a drop in the bucket measured in lbs of CO2. AGW is caused all-but-exclusively by the so-called First World. Even e.g. Amazonian deforestation is largely in pursuit of products to sell into the first world’s demand.

The planetary economy is vastly, vastly unequal. Yet we all share this rock and the air and water that sticks to its surface.

1506

A real life example: As I understand it back when John Travolta owned his own private 707, he had a private pilot’s license and a 707 type rating. Although from what I understand he had to sit in the right seat and essentially serve as first officer, while the other pilot, presumably with more hours than Travolta, was in command.

1507

Not exactly GA, so I won’t post the whole thing, but this post of mine and the few above it are about recent action on the ongoing saga of the 737 MAX’s return to service. Which is now imminent.

1508
1509

Want to own a little bit of actual Concorde?:
https://www.wright-bros.com/authentic-concorde-101-desktop-display.html

1510

Why did this nonsense take so long to fix? I can’t even begin to imagine how irate I would have become if someone brought an emotional support pig on a plane I was riding on.

1511

You’d be happy for it if the plane crashed in the Andes!

1512

I’d be happier if they let me bring aboard my emotional support jumbo pepperoni pizza.

1513

Well, this is supposed to be a thread about general aviation. In GA, if you own the plane you can even bring your pet snake Reggie.

1514

You eat one lousy foot, and they call you a cannibal.

1515

I know! As if we’re the only ones in this thread who have eaten human flesh!

1516

Yes but now we can go back to saying that’ll happen when pigs fly.

1517

For everyone going on about animals on airliners, here is the thread someone started yesterday for that specific topic:

1518

Why do turboprops have inertial separators? Or rather…why them and not other jets?

Is it just because they can?

What I am on about is a turboprop is a jet engine attached to a propeller.

I never hear of a regular jet having an inertial separator. Can’t imagine how they could. Yet turboprops seem to have this extra bit to help expel debris in the air (things like ice or little rocks and such) out of the engine. This spares the engine wear-and-tear. A good thing.

So, is this just they do it because they can thing or do regular jets have a similar system too? Or do regular jets just take their chances in this regard?

1519

Several separate 1-paragraph ideas not adding up to a coherent argument.

Turboshaft engines are designed by and for the helicopter mission. Mostly the military helicopter mission. That is to say, lots of dirt and dust and operations on unprepared fields. Particle separators are added to the engine at some cost in power / efficiency to buy acceptable engine reliability and time between overhauls.

Most turboprop engines are derivatives of turboshafts. Not all. The particle separator on such derivative engines was already built into the rest of the internal aerodynamics and it may not be worthwhile to build a significantly different model without it. Along the curve of product sophistication versus number produced for any given design, all airplane engines are still short-run items, not mass production items. So economy of design through reuse is important.

In a modern turbofan engine, about 90% of the air only passes through the fan and then goes around the outside of the hot & delicate engine core. The air and any entrained particles are given a mighty swirl by that fan. The fan is the particle separator.

Exposure to dust and salt declines more or less exponentially with altitude. An aircraft that spends the vast majority of its air time above 20,000 ft. will have a tiny fraction of the exposure of a machine that cruises at 8,000 or 800 or 80 ft. above the ground.

Exposure to debris larger than sand grains occurs substantially only when operating on / over a dirt surface. The exposure of an RAAF helo, a Twin Otter doing remote village resupply in the Aussie outback or a 737 in trans-Australian service have very different exposures to pebble-and-up sized debris despite operating over the same terrain.

A particle separator as incorporated into a turboshaft is a very un-aerodynamic beast. You really can’t ram high speed air into the front of one efficiently. Said another way, the efficiency hit on a low speed vehicle is far less than on a high speed vehicle. This is a variant on the theme that centrifugal compressors worked OK on low speed early jets but not well on later high speed jets. The axial flow compressor was the solution to that conundrum (among several other conundrums)

1520

I do not know about all turboprops but I know some can close the inertial separator and open it when needed. Best of both worlds.