# Bird strike

#### v_pino

I was wondering how bird strike works... I'm thinking that it's something to do with Newton's Laws which cause bird strikes to do so much damage.

Can someone please guide me into some further research? thank you

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#### DaveC426913

Gold Member
What's bird strike? Is that some sort of incendiary?

#### mgb_phys

Homework Helper
You are flying along at a few hundred mph and you hit a stationary (from your point of view) few kg of bird, the bird is going to accelerate faily quickly which is going to involve a certain amount of force being transferred to your plane. That isn't normally serious unless it hits somethign delicate like a radar dome or flap.

Or it goes into an engine!
Turbine blades are in a very stressful situation, they don't have a lot of spare strength to resist accelerating a bird to 200mph. When they break off they tend to go backward into the rest of the compressor - which is usually messy.
That engines don't explode into a million pieces when this happens is a real tribute to the engineering in them.

#### DaveC426913

Gold Member
From the wiki article:
"The energy of the impact increases with the square of the speed difference. Hence a low-speed impact of a small bird on a car windshield causes relatively little damage."

#### v_pino

But how come a bird strike has enough force to break the windshield of an airplane?

#### russ_watters

Mentor
Was there something about mgb_phys's post you didn't understand?

#### mgb_phys

Homework Helper
But how come a bird strike has enough force to break the windshield of an airplane?
Working out the force is a little tricky because you have to work out how long the bird is in contact with the plane for, which means modelling all the deformations. But the energy is simple.

Most bird strikes are near to the ground, so the plane is either taking off or landing and going relatively slowly.
Eg 0.5kg bird hitting a plane doing 200knots e = 1/2 * 0.5 * 100^2 = 2500 J
Worst case would be a fighter at mach2 hitting a Canada goose, E = 4,500,000 J
Comparison, a typical handgun bullet is around 500 J ( although concentrated in a smaller area)

Remember a plane hitting a stationary bird at high speed is equaivalent to firing the bird at that speed into a stationary plane. If I shot at chicken at you at 1000mph, do you believe it would do some damage?

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#### DaveC426913

Gold Member
Worst case would be a fighter at mach2 hitting a Canada goose...
I would bet that an event of this nature has never been reported.

Now, I didn't say it's never happened... I just said it's never been reported.

#### mgb_phys

Homework Helper
Fighters tend not to do Mach2 routinely in peace time, it's expensive on engines.
They do hit birds fairly regularly, fighters tend to spend a lot of time at low level and the noise scares birds. The nasty thing about geese is that they weight > 5kg and can fly at upto 30,000ft!
The only good thing is that there is a lot of volume of sky compared to the finite volume of geese and planes.
Utube has a few HUD videos of fighters being destroyed by bird strike http://youtube.com/watch?v=zN_Zl64OQEw

#### GT1

Working out the force is a littl etricky because you have to work out how long the bird is in contact with the palce for, which means modelling all the deformations. But the energy is simple.
What is the best indication to how much damage can be caused by the bird - energy or momentum, and why ?
If I take 2 birds- one wights 2m with speed V , and the second one wights m with speed 2V - both of them have the same momentum (2mV) but their kinetic energy is different (mV^2 vs. 2mV^2).
I guess the bird with the more energy will cause more damage, but why momentum is not good indication when you analyze the problem ?

#### esalihm

its all about inertia, the bird wants to stay where it is, doesn't make any difference if you fly a plane into it, it just stays there :lol:

#### Id10t

Remember a plane hitting a stationary bird at high speed is equaivalent to firing the bird at that speed into a stationary plane. If I shot at chicken at you at 1000mph, do you believe it would do some damage?
Well said but further consider that a projectile bird shot at a stationary plane does not have the same physics involved which would otherwise factor into a flying plane impacting with a nearly stationary bird (if only due to air pressure / flow considerations).

In the case of a plane being the object in motion, it’s aerodynamic design can have a can have very significant impacts on those factors (depending on the point of impact), no?

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