Plane down at Dayton Airshow

[🦈💜]

The pilot rolls to the left in both acts.

Without speculating, I have to say that from the looks of it that maneuver was going nowhere good from the start.

I have my own stupid question, and this isn't acro related:

In high-humidity, hot conditions, is it possible to get visible condensation from airflow separation at stall at relatively low airspeeds?

-Fox

 

[Skåning]

in high-humidity, hot conditions, is it possible to get visible condensation from airflow separation at stall at relatively low airspeeds?

-Fox

If you mean like a vapor trail I would say no. They occur when air is compressed and the water is effectively squeezed out of it, forming a cloud. With a stall you have flow separation, not an increase in pressure that would be greater than just prior to the stall.

 

[Bumblebee]

Hopefully that wasn't condescending, too simple, too complicated, too short or too long... but I'm sure it managed to be all of those. I'll have to work out a better explanation.

~Fox

this was awesome-thanks.

 

[PhilosopherPilot]

If you mean like a vapor trail I would say no. They occur when air is compressed and the water is effectively squeezed out of it, forming a cloud. With a stall you have flow separation, not an increase in pressure that would be greater than just prior to the stall.

The vapor comes from the drop in pressure, not increase in pressure. Drop in pressure = a drop in temperature. If it drops enough, it matches the few point and voila, vapor appears. The cooler air cannot hold the moisture, so it condenses into visible moisture.

That's why on humid days you can see vapor on top of a wing or trailing the flaps, especially transport category aircraft. The low pressure on top of the wing is decreasing the temperature of the air to match the dew point

The vapor you see from a pressure wave (like on a supersonic jet) is where the air is slowing behind the shock wave. Same cause. Same effect. The supersonic air becomes subsonic, and cools down.

At least, that's my understanding. Correct me if I'm wrong please.

 

[TwoTwoLeft]

Without speculating, I have to say that from the looks of it that maneuver was going nowhere good from the start.

I have my own stupid question, and this isn't acro related:

In high-humidity, hot conditions, is it possible to get visible condensation from airflow separation at stall at relatively low airspeeds?

-Fox

If it wasn't being produced by the prop. Then I'm pretty sure wouldn't see it on the wings.

Now the -only- confounding factor that we have on this planet that makes it different from that little experiment is gravity. If you're flying upright and you weigh 2240lbs, you need to be producing 2240lbs of lift to not descend.
Now, take the same airplane and flip it over. How much lift do you need to produce to stay aloft? at least 2240lbs. That's all gravity does for you that changes anything.

Don't forget to include the downforce of the horizontal stab.

 

[🦈💜]

If it wasn't being produced by the prop. Then I'm pretty sure wouldn't see it on the wings.

Don't forget to include the downforce of the horizontal stab.[/quote]

Yeah... I considered mentioning that but decided I was being way too wordy already. My rationale was that it alters the load on the wings, but it's not strictly a necessary component of aerodynamics from a "lift basics" point of view. (Hopefully I'm not shooting myself in the foot with that)

You can have an aircraft without a horizontal tail, but the horizontal tail doesn't materially change the behavior of the wing. It does increase (and decrease) the airload supported by the wing, of course, which can require a further increase/decrease in angle of attack to maintain level flight, but if we have an alternate method of controllability and stability we can do without it entirely.


At least, that's my understanding of the issue. As always, I welcome comments.

~Fox

 

[Skåning]

The vapor comes from the drop in pressure, not increase in pressure. Drop in pressure = a drop in temperature. If it drops enough, it matches the few point and voila, vapor appears. The cooler air cannot hold the moisture, so it condenses into visible moisture.

That's why on humid days you can see vapor on top of a wing or trailing the flaps, especially transport category aircraft. The low pressure on top of the wing is decreasing the temperature of the air to match the dew point

The vapor you see from a pressure wave (like on a supersonic jet) is where the air is slowing behind the shock wave. Same cause. Same effect. The supersonic air becomes subsonic, and cools down.

At least, that's my understanding. Correct me if I'm wrong please.

Ok you know more about pressure than I do! Your answer makes more sense

 

[stormchaser]

Flip the plane over, and what do you have to do to maintain level flight? You have to increase angle of attack... in a negative direction. By pushing forward on the stick.

Thanks for the *cough cough* simple explanation. ha!

No, but this sentence is really what I was curious about. In straight-and-level upright flight at a certain speed and weight, let's say you require 2 degrees of AoA. Thankfully, our engineers designed that into the angle of incidence of the wing. We fly level, no stick input.

Let's also say our critical AoA is 18 degrees. That means upright in the scenario mentioned above, I have 16 degrees of "buffer" before a stall.

Upside down at the exact same speed and weight, just by me having to put in that forward control on the stick, it's telling me that I am eating into that buffer. In other words, I need a higher angle of attack while upside down vs. right-side-up to maintain level flight with all other variables being the same. Let's say I need 9 degrees AoA while upside down while I only needed 2 while upright. In this scenario, my buffer before a stall is now down to 9 degrees (I've eaten up half of my critical angle just by flipping upside down).

So I guess all other variables being the same, flying upside down gives you a much smaller envelope.

Oh, Wolfgang, how you've influenced me so.

 

[Itchy]

If you mean like a vapor trail I would say no. They occur when air is compressed and the water is effectively squeezed out of it, forming a cloud. With a stall you have flow separation, not an increase in pressure that would be greater than just prior to the stall.

Say WHAT? Don't think so......

 

[U_of_I_Tweak]

It is comments like this were no one learns, unnecessarily speculative and are cavalier (look at the bold part)...



Remember the Colgan 3407 on how EVERYONE outside of the investigation was speculating ice brought the plane down in a few hours after the accident? Looking at the conditions at the time of the accident people were assuming it was the ice on the airplane. They were completely wrong.

That's why speculating with broad statements as shown above is a dangerous and unnecessary.

Unnecessary? Perhaps. Dangerous? Hardly.

I recall that there was speculation about icing. Even though that turned out to not be the cause, it began a great discussion about icing and tailplane icing in particular. Links to articles and videos came to light because of that discussion. I learned about a subject to which I had previously had little exposure.

People were educated because of the conversation. Regardless of the final cause determination of this accident, there has been an interesting and insightful discussion of aerobatics, and low altitude, low energy maneuvering.

Finally, with all the hand wringing going g on about "speculation," keep in mind that the NTSB doesn't ever issue a cause of an accident. Isn't a probable cause a case of highly informed, expert speculation?

Sent from my DROID RAZR using Tapatalk 2

 

[Skåning]

Say WHAT? Don't think so......

Yea....I was just guessing!

 

[B200 Hawk]

Ban air shows

 

[🦈💜]

Thanks for the *cough cough* simple explanation. ha!

Yeah well... I tried. :> But...

No, but this sentence is really what I was curious about. In straight-and-level upright flight at a certain speed and weight, let's say you require 2 degrees of AoA. Thankfully, our engineers designed that into the angle of incidence of the wing. We fly level, no stick input.

TwoTwoLeft - You were right. ;>

Upside down at the exact same speed and weight, just by me having to put in that forward control on the stick, it's telling me that I am eating into that buffer.

You're probably eating into your buffer, but not because you're putting in forward stick. Now we're getting into the control of the aircraft. Angle of incidence is mostly important from a meat cargo and thrust alignment point of view, and from a 'rational aircraft' point of view. It has no bearing on AoA.

When you roll inverted and push, you're merely assuming a similar (symmetrical airfoil) or equivalent (asymmetrical airfoil) AoA for level flight. In an asymmetrical airfoil, you're losing efficiency inverted due to the camber, and thus you DO eat more into your AoA buffer to maintain lift.

This is where, as 22L had pointed out earlier, the horizontal stabilizer and elevator design becomes important in the practical aspects of realistic airplane design. But again, we're overcomplicating things a bit.

So, another thought experiment: A completely symmetrical flying wing. Fly it level. Fly it inverted. Does it care?

In other words, I need a higher angle of attack while upside down vs. right-side-up to maintain level flight with all other variables being the same.

Would you, given a completely symmetrical flying wing?

(You wouldn't, so what are the extra variables here?)

So I guess all other variables being the same, flying upside down gives you a much smaller envelope.

Again, not necessarily. For a symmetrical wing, AoA is AoA, and it really doesn't care. It may produce more drag at an equivalent AoA because the rest of the airplane is designed to fly upright, or you may run out of authority on some other control surface for the same reason. For an asymmetrical wing, you need a bit more negative AoA than positive AoA to offset the camber of the airfoil.

*Pant*

~Fox
IANAAS IANAA IANAP IANACG IANAL IANEAGF WTFDIK YMMV SRA NWEEOI

 

[stormchaser]

Makes sense to me.

 

[TwoTwoLeft]

If you really want to get crazy. Let's talk about what that dihedral does once you're inverted....

 

[MikeD]

Finally, with all the hand wringing going g on about "speculation," keep in mind that the NTSB doesn't ever issue a cause of an accident. Isn't a probable cause a case of highly informed, expert speculation?

It depends. Mainly on the evidence at hand, or not. But yes, statements of probable cause have run the gamut of a "best guess" (TWA800 and a few others) to some pretty darn good investigative work (UA232 and others).

 

[ScorpionStinger]

How do you figure that? I think the Bagram one was tougher because those guys were doing a job that did not purposely put themselves in a situation that exponentially raised the chances of something going wrong. In regards to this accident, people purposely put themselves near the limit and capabilities of their aircraft and therefore it was not as surprising when something went wrong.

Your thinking of it way differently than I am. Not comparing accident or job duties. Everyone has a pasion, some more dangerous than others. What I was saying is that seeing a human being (just waving on a wing of an aircraft) just go down like that while on the wing is tougher on the eye and mind.

No accident is better than, or worse than the other. The loss of life is the loss of life, especially in such tragic way (which most aircraft accidents are).

 

[n57flyguy]

If you really want to get crazy. Let's talk about what that dihedral does once you're inverted....

Do tell, I have never even thought of that!

And Acrofox great explanation of just how careless the wing is!