OT maybe" guessing/calculating an aircrafts hieght

[Daveroo]

the other night i was watching the california highway patrols cessna 206, call sign "H21",my dad came outside and said...whoa..hes waaaaaay to low..i said i didnt think so..he seemed to be atleast 500+..but if he was "working" he could be lower, i dont know if thats true or not...

but..im a huge CSI fan....and they take photos and work out wierd calculations ect...so if we knew the distance between the lights on the wingtips of the 206,and the lights were two inches apart in the sky..my eyes are at 6'4" inches from the ground....ect...could you calculate the hieght of the plane?.....make sence?..if they are 40 feet apart at ground level then they would be X inches apart at Y foot elevation??

 

[AckAck]

How would you measure the 2" distance? Did you hold a ruler above your head/arms length from you eyes? or span it with your fingers, then measure the gap in your fingers?

regardless, the precision probably isn't going to be enough, but you can do it with simple proportions.

I'm assuming 2 feet from your eye to your fingers (or ruler) when holding them (it) above your head. At that distance, 2 feet of height shows as 2" span. Which means that for every foot of height, the width would be 1", or each 1" in width corresponds to 1 foot in height. The Cessna wingspan is 36 feet, or 432", so proportionally the height would be 432 feet. Add the 6 foot height from the ground to your eyes, and the Cessna was 438 feet high.

As I mentioned, I would bet that the precision of the 2" and my guessing about 2 feet would probably throw the calculations off, perhaps significantly. But in theory, it can be done quite easily.

Brian

 

[Jagdflieger]

Daveroo,

An interesting question. Here's a couple of other formulas that might help.

Distance:

The mil radian formula won't help unles the plane is directly overhead. It works by changing your perception of the size of the object to an angular measurement, in this case mils. By knowing your target's size and then how may mils it appears, you can accurately determine its distance or alitude if above you.

It is: Size divided by mil(s) X 1000 equals distance or range or directly above, altitude

Examples:

A wing width of 40' / 20 mils = 2 X 1000 = 2,000' distance to the plane

If the plane was closer and took up say 40 mils it would look like this:

A wing width of 40' / 40 mils = 1 X 1000 = 1,000' distance to the plane

To properly use this formula, you will need binoculars or a scope with a milradian scale as well as know the size (height or width) of your target. If you remember the old submarine movies you will recognize this techique from the periscope view and the vertical and horizontal scales marked in 10s in the scope's reticle. Ships of various classes had known heights and lengths and by using the mil scale and formula, the skipper could determine the distance to the enemy ship. Of course ship angle and curvature of the earth would complicate the procedure. While a nautical description, you can see how it applies here.

Altitude:

To find altitude when the plane is at an angle from you, you can use trigonometry. you need to use the tangent of the angle of the aircraft above the ground and we also need to know the horizontal distance to our plane. What we are doing here is determining the ratio between two known sides of a triangle to determine the altiude of the third leg, in this case the aircraft's elevation or altitude.

Example:

Angle to aircraft of 20 degrees. Horizontal distance 5000'. height: Unknown

Tangent of 20 = 0.364 X 5000' = 1820' altitude

This will work well if you know the distance to the road or land feature that the plane is flying over. You can make a simple angle measuring device at home from carboard and a weighted string to determine angles. Some compasses have an angle scale built into them, but you don't see too many of them. Brunton used to make a compass that would measure angles and I just recently saw a Chinese military compass with the same feature.

Back in the days of anti-aircraft artillery, gunners often estimated altitude by firing shells until they detonated just below the clouds over their cannons. This would give the gunners a fairly good estimate of an attacking plane's altitude if it was near the cloud and a good guestimate or SWAG (scientific-wild-ass guess) if the plane was any distance below or above the cloud stratum. They could then set their fuzes accordingly.

 

[TARPSBird]

The two big variables here are slant range (if the aircraft wasn't directly overhead), and aspect angle of the aircraft (which would affect using the wing lights for measurement). AckAck's calculation is what photo interpreters call "local control", using the image dimensions of a known object to figure scale proportion of a photo image. Works pretty well for visual observation too. And I agree with AckAck, assuming the CHP plane was darn near directly overhead he was probably a bit under 500'.

 

[Bone]

Interesting. Not only can cops drive as fast as they want to with virtual impunity, they can fly as low as they want over congested areas. Lol.

 

[Daveroo]

Interesting. Not only can cops drive as fast as they want to with virtual impunity, they can fly as low as they want over congested areas. Lol.

that last part was just aguess on my part...ive seen the cessna below my house in the ravine,so it would have been 250'agl atleast..and the helos hover at 50 or so feet in that area often...lots of car dumps and the occasional body found...