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Birds flying through props unharmed?

Assume prop at 2,400 rpm and closing speed 125 kts, I’m still trying to work out how a bird could fly through a prop unharmed.

A guy I was flying with today did the calculation, but I’m still not convinced.

Any views?

Swanborough Farm (UK), Shoreham EGKA, Soysambu (Kenya), Kenya

Say the trailing edge of one prop blade and leading edge of the next are 170 degrees apart and the bird has an arc length of 10 degrees for simplicity. That leaves empty space of .44 rotations which at 2400 rpm would take 0.011 seconds. A 30 cm bird with a closing rate of 62 m/s will travel front to back through the prop arc in .005 seconds. So it looks like the bird has a reasonable chance to take out your windscreen instead!

Last Edited by zuutroy at 10 Sep 18:17
EIWT, Ireland

For the fun of it:

Assume a two-blade prop turning at 2400 RPM. This means that a blade is at any given position within the arc every 4800th of a minute. Therefore:

60 / 4800 = 0.0125 secs: this is the time the bird has to get through the spinning disk (I ignore the obvious variation between root and tip here)

At 125 kts, the airplane travels 759.514 ft / hr. This equates to 211ft/second (759.514 / 3600 = 211 rounded)

Multiplying this now by the above time of 0.0125 we arrive at a distance of 2.63 ft which the bird has to get through the arc.

Probable? Not. Possible ? I’d say, yes, especially near the prop tip.

Now go on and pluck this apart !

I remember a picture of a motorglider during take off. The prop tips made traces of condensing water. I was surprised about the distance of the tip traces for a 360 of the prop. Bottom line is that it is very probable NOT to catch the bird. With increasing speed and reduced rpm it is even more probable. And, of course, there are stories of birds flying directly into a canopy.

Even if the bird vs airplane are doing 300kts to pass clear in between blades, the assumption that it will fly straight along wing airflow instead of propeller airflow is a very big assumption? while this does work for canon bullets it may not work for birds unless they fold their wings….

Last Edited by Ibra at 10 Sep 19:14
ESSEX, United Kingdom

My first (of two in twelve years of power flying) involved a bird getting through the propeller disc and down the cabin air intake. In an infinite universe everything is possible (or at least very improbable as the great Douglas Adams put it).

More on topic, fighters from about 1916 to about 1936 managed to get machine gun rounds through the propeller disc. Actually later than that, the Bf109 and I think the Aircobra (P-39?) had machine guns on top of the engine.

strip near EGGW

Ibra wrote:

Even if the bird vs airplane are doing 300kts to pass clear in between blades, the assumption that it will fly straight along wing airflow instead of propeller airflow is a very big assumption?

If you are travelling at 300kts, the exact direction of bird travel will not make much of a difference, the relative motion of bird vs aircraft will be preeeeetty much head on.

However, once it made it through the prop, it will PROB25 then splat on your windscreen, which won’t be very pleasant, least of all for the bird.

Biggin Hill

Cobalt wrote:

If you are travelling at 300kts, the exact direction of bird travel will not make much of a difference, the relative motion of bird vs aircraft will be preeeeetty much head on.
However, once it made it through the prop, it will PROB25 then splat on your windscreen, which won’t be very pleasant, least of all for the bird.

When I worked on turbofan certification, I recall they were accurately modeled as “heavy fluid”
https://www.researchgate.net/publication/282966148_Impact_Simulation_With_an_Aircraft_Wing_Using_SPH_Bird_Model

On a slow SEP, I guess they “still fly” but get affected by propeller wash/stream so much that I doubt bullet calculations work
Tough I am PORB100 sure, the bird will not make it

Last Edited by Ibra at 11 Sep 18:05
ESSEX, United Kingdom

Some WW I era fighters actually had steel protectors on parts of the wooden propeller blades for the specific purpose of protecting from own gun bullets… Then they perfected gun-to-propeller synchronizers…

tmo
EPKP - Kraków, Poland

Then they perfected gun-to-propeller synchronizers…

My understanding is that the word “perfected” could never have been said to have happened. Going from “barely worked” to “generally worked except when they didn’t” might be more accurate.

EGKB Biggin Hill
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