for the Math minded types

[Devil 505]

This is why I need this solved.

We had a T-6 Texan go down about 30 miles north of our base. We are tasked with locating the two ejections seats but they are only willing to give us basic information.

ie GVW 6300 (full load), altitude of ejection 12k and a distance traveled from aircrew to impact (7 miles).

all help is appreciated.


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When do the pilots separate from the seats and does their chute open immediately?

And does the seat have a chute of it's own? If so, when does it open?

[CptTrips]

[edit]Sorry I was being flippant....

If you had to estimate the  average square plate surface for drag to be?  6^2ft?

[Ciaphas]

roughly 2.5 seconds for crew separation, the seat does have a drogue chute that stabilizes and allows the seat to allow crew seat separation. The seat without crew is roughly 200 pounds.

this all happens within 2.5 - 3 seconds after seat initiation.


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[CptTrips]

Sorry bud.  I've had a couple of beers, but "1714 ft per mile is the starting velocity"  doesn't make any sense to me.  Can you double check that?

[Devil 505]

roughly 2.5 seconds for crew separation, the seat does have a drogue chute that stabilizes and allows the seat to allow crew seat separation. The seat without crew is roughly 200 pounds.

this all happens within 2.5 - 3 seconds after seat initiation.


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but the seat freefalls after this?


Also, there still seems to be too many variables in play. Seems to me that the attitude of the Texan when the ejection occurred will play a huge factor in determining the probable search area. Even if we can figure out this "feet per mile" problem, I do not see there being enough info to go by.

Might be easier to figure out where the plane was when the crew ejected relative to the crash site and figure out the trajectory of the crew from that point and go with the assumption that the seats would go farther than the crew.

[Ciaphas]

but the seat freefalls after this?


Also, there still seems to be too many variables in play. Seems to me that the attitude of the Texan when the ejection occurred will play a huge factor in determining the probable search area. Even if we can figure out this "feet per mile" problem, I do not see there being enough info to go by.

Might be easier to figure out where the plane was when the crew ejected relative to the crash site and figure out the trajectory of the crew from that point and go with the assumption that the seats would go farther than the crew.

I agree with you, I've been on many crash scenes and the ejection seats are typically easy to find. The weather is the factor here, the aircrew were no doubt tossed around in their chutes by the wind, disorientation is going to play a negative roll in this one. Unfortunately the seats do not interface with the FDR or any other system in the cockpit other than 1 electrical connector for the seat actuator.

I'm hoping that after the aircrew debrief, we will know more. All attempts to reach the crash site by recovery personnel were called off due to weather. We will have to try again in the morning. I just pray that if someone stumbles across them, that they have enough sense to leave well enough alone and contact the authorities.


Thanks for the help guys

 

[Easyscor]

Seems like you’re sincere in your question and have more details then you’ve presented.

If any part of the numbers you posted are accurate, I think someone’s messing with you.
Go down to the machine shop and bring me a left handed monkey wrench and be quick. And don’t come back without it!

Either that, or someone wants to teach the value of research. Hopefully that’s the case but I doubt it. In the sprit of having some fun with it, …

According to Wikipedia, the listed gross weight of your T-6 Texan II is 6,300 lbs. Well that’s helpful, it matches one of your numbers. As least you might know which T-6 that clown was using. The top speed, not even the cruise speed, for that plane is 364 mph, or ~533 ft/sec. if it were a legitimate exercise. You can find the model of ejection seat be googling the plane and then google the seat to see if a terminal V or other details are given for the seat.

V in your post is velocity: V is distance traveled over unit time, usually seconds in this kind of problem, but can be hours, minutes or seconds. Thus 1714 ft per mile is meaningless as given. The seat falls from 2.3 miles alt and it might travel 1714 ft (third of a mile) horizontally?

It can become a simple spreadsheet exercise targeting a range of distances depending on a cruse of 320 or max at 364 mph, unless you know the actual speed. Plug in the numbers for acceleration of gravity Ag, and terminal velocity. And you just added another vector for wind drift. 

[Ciaphas]

Seems like you’re sincere in your question and have more details then you’ve presented.

If any part of the numbers you posted are accurate, I think someone’s messing with you.
Go down to the machine shop and bring me a left handed monkey wrench and be quick. And don’t come back without it!

Either that, or someone wants to teach the value of research. Hopefully that’s the case but I doubt it. In the sprit of having some fun with it, …

According to Wikipedia, the listed gross weight of your T-6 Texan II is 6,300 lbs. Well that’s helpful, it matches one of your numbers. As least you might know which T-6 that clown was using. The top speed, not even the cruise speed, for that plane is 364 mph, or ~533 ft/sec. if it were a legitimate exercise. You can find the model of ejection seat be googling the plane and then google the seat to see if a terminal V or other details are given for the seat.

I work on the ejection seat for this aircraft and the ESUP MK16 for the T-38 (2011 - present) and previously the ACES II Ejection seat (1998-2011)

V in your post is velocity: V is distance traveled over unit time, usually seconds in this kind of problem, but can be hours, minutes or seconds. Thus 1714 ft per mile is meaningless as given. The seat falls from 2.3 miles alt and it might travel 1714 ft (third of a mile) horizontally?

I know that for an aircraft in a steady rate of decent from 12,000 ft (actual: 11,049) covering 7 miles to impact (impact site = roughly 951 ft, rounded down to 0 to make it a bit for the sake of simplicity) would require a decent of 1714 ft per mile (actual 11578.42 ft per mile)

It can become a simple spreadsheet exercise targeting a range of distances depending on a cruse of 320 or max at 364 mph, unless you know the actual speed. Plug in the numbers for acceleration of gravity Ag, and terminal velocity. And you just added another vector for wind drift. 

Since the speed nor time from punching out until impact are known at this time, I am trying to figure out an educated guess as to the speed the aircraft was traveling when the sortie went south. This will allow me to figure a time taken for the aircraft to impact the ground from punching. This will also allow me to figure out wind sheer and drag forced on the seats upon exiting the cockpit due to blunt wind shear and wind speed affecting the drogue chute and help me better map out probable impact sites for the seats, of course not exact but within a reasonable area.

[Easyscor]

Too much I don't know about the problem but that helps. If you have a spreadsheet program, Excel, you can plug in these numbers and formula as a starting point.

This can give the initial velocity V. It calculates the distance D in feet traveled in one hour at any given speed and converts it to feet per second.

320   mph (cruise speed)
5,280   ft/mile   
1,689,600   D ft/hour (320 x 5280)   
3,600   second/hr (60sec x 60 min)   
469.3333333   Vsec(ft) (feet per second) (D distance in feet per hour / second in an hour)

Further, more useful then the 1714 number is the time to impact for the aircraft. However, that is independent of the ejection seat. It's expected the plane accelerate as it descended. But using the initial Vsec(ft) and a straight line decent as you suggested, (unlikely?) we can estimate the time to impact thus.

7   miles
5,280   ft/mile
36,960   horizontal feet traveled
469.3333333   Vsec(ft) (from above)
78.75   seconds to impact (36,960 ft / Vsec(ft) )

Comparing the 79 seconds to the actual time can help define the curve for the plane.

 

[Vraciu]

terminal velocity?

semp

Eventually but not initially.    Depends on which way they ejected as they would travel in some sort of arc before reaching TV.

[Ciaphas]

Right, once the seat has been exposed to wind sheer and the effects of this wind sheer have been felt by the drogue chute, the seat will fall like a stone with some degree of horizontal velocity, also gaining speed within its own arc. I'm going out on a limb but I presume that the seat will be found roughly 6.75 - 7.25 miles from the impact site with about a 500 yard margin for error. I should know when I get to work tonight.


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[Ciaphas]

one of the unique aspect of this ejection is the effects of the weather. Most ejections are caused through mechanical/electrical fault and the aircrew is seldom affected by the weather in the manner that these two pilots were.

Typically pilots will locate the seats if they can and it becomes a non issue but high winds and parachutes = no bueno. We also have three terrain types to search: fields, heavily wooded areas and a lake.

like I said before, this is a very non-typical situation. It would be nice to have an ELT on the seat but MartinBaker decided that we didn't need one.

Thanks for all of the help!


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[Vraciu]

I wondered if you had a seat locator beacon.   Guess not. 

[Vulcan]

What did the pilots have for breakfast?

[Zimme83]

You dont have enough information to solve the problem.