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Are props good bird shredders or not?

W

wrongway john

Well Known Member
I made a comment on another thread which is closed, and besides this needed another thread to it anyway since it was off topic, but it had to do with me thinking that props should make good bird shedders and would probably make them mince meat before they hit our windshield.

To which another replied, that a propeller does nothing to protect us from birds. Particularly at high speed. In the 360 deg space covered by the propeller the blade cord only covers a very small portion of it. With the relatively slow RPM the propeller turns, a bird can easily get through without being hit.

I wanted to learn more about this, and if my simple calculations are accurate enough, it appears I?ve had a false sense of security about my prop being the ultimate bird shredder after all.

Here is what I?ve come up with. To make things simple, I allowed 180 mph for the plane, and 20 mph for a bird coming at you head on which would give us 200 mph to work with. That puts both the plane and bird at 293 feet traveled per second on a collision course.

With a prop turning, say, 2,400 RPM?s, that would be 40 RPS (revolutions per second). But since the prop generally is two-bladed, we can double that figure, which will give us 80 swipes of either blade of the prop hitting the bird in that one second of time. But the bird is going to go through the prop area in a small fraction of a second, so I used 8 propeller swipes in a one-tenth of a second time to hit the bird while the plane and bird traveled 29.3 feet or nearly 3 feet in one-hundredth of a second time. Not sure what figure to use here and won?t do anything further with it since it already seems the bird can get through quite easily. The length of the bird would only give slightly better odds of hitting the prop, but still everything seems remote. What do you think?

If this is pretty much accurate, the next question is, how well do the windshields hold up on bird strikes?

wj
 
wrongway john said:
...If this is pretty much accurate, the next question is, how well do the windshields hold up on bird strikes?

wj
Click to expand...
Not very well.

hawkstrike.jpg


For RVs, hawk size birds can come straight through the canopy. Can't think of an incident with a sparrow size bird.

This is what happened to Laird Owens.
 
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Every year a friend of mine has a balloon pop during his flyin, and in the RV the only way to get the balloon is to go slow. Many times I watched one of those danged balloons go thru the arc of the prop right over the canopy :mad:
 
I had a Black Bird hit my windshield on a climb out with my C-172.
No blood. Just a whack sound. Bounced off and up. Guess it was good we ducked!!!
 
Didn't they used to shoot guns right through the prop arc and simply hope for the best. I know they eventually sync'd em up, but I think I was told in a museum that they did without for quite a while.
 
szicree said:
Didn't they used to shoot guns right through the prop arc and simply hope for the best. I know they eventually sync'd em up, but I think I was told in a museum that they did without for quite a while.
Click to expand...

It is true...but they put steel deflector wedges on the back side of the blades aligned with the gun barrel(s) to deflect the occasional hit.
 
wrongway john said:
If this is pretty much accurate, the next question is, how well do the windshields hold up on bird strikes?

wj
Click to expand...

As you can see from the photo of Laird's airplane, they don't do very well. Actually general aviation aircraft in general don't do very well. I am aware of a C-172 that had most of the entire windshield taken out by a large bird. It caused so much drag that even with full power it could not maintain altitude.

The best thing we can do is avoid situations where we are more likely to encounter a bird, particularly when we are going fast. Such as flying low level down a coast line or river, or doing high speed low passes. A lot of bird species seem to be pretty good at avoiding airplanes if they can see you in time. In any environment that you are more at risk to encounter birds, use all your lights, make your self as visible as possible.
 
The T-37 suffered several bird strikes and windscreen damage. As a result an effort was made to protect the crew. The replacement windscreens were 1/2" thick polycarbonate.

The speeds we can fly in the RV do create a couple issues. The birds and pilots have less time to react and the energy of the impact becomes very significant almost hard to imagine as you go fast.
 
wrongway john said:
I wanted to learn more about this, and if my simple calculations are accurate enough, it appears I’ve had a false sense of security about my prop being the ultimate bird shredder after all.
(snip)
What do you think?

(snip)
wj
Click to expand...

I just did a quick "back of the napkin" at 190mph and 2400 RPM.

190 mph is 16,720 feet per minute.

Assuming a two-bladed prop at 2400 RPM, one of the blades will cross any given point in the prop disc about every 3.5 feet.

The dense part of a big mallard duck is about 10 inches long (I think we can reasonably ignore the neck and wings).

If we assume a stationary duck lined up in the direction of travel
9worst case) there is about a 24% chance that the blade will contact the duck's torso.

If the blade does contact the duck, it will contact it more or less on edge (remember that the prop blade is an airfoil). I don't know what a typical cruise AOA is for a prop blade, but I'd guess maybe 5 degrees (it's certainly less then 15 degrees).

Assuming a duck strike at mid chord (20 inches from the hub), 2400 RPM and 190 miles per hour, the prop blade will be moving roughly 350 miles per hour relative to the duck, and on edge. My guess is that it will slice the duck in two cleanly without altering it's trajectory enough to matter.

A mallard duck weighs 2-3 pounds. At 190 mph, our canopies aren't going to make any difference at all. I'm too lazy right now to try and calculate the force required to accelerate the duck to 190 mph during the time it would take the airplane to travel 10 inches, but i'd guess that it's orders of magnitude more than the windshield could exert.

Don't hit ducks :)
 
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I know what I did wrong!

Scott you just solved a mystery for me. Probably 20 years ago I built a Decathalon RC model. I spent a lot of effort to make it look great and on the first flight the windshield came loose and flew off. No way could I keep the plane flying. It finally stalled and spun in. The parts were scattered in a 20 ft circle. I just could not believe there was enough drag induced to cause the stall. Wrong!
 
flyeyes said:
...A mallard duck weighs 2-3 pounds. At 190 mph, our canopies aren't going to make any difference at all...
Click to expand...
I don't worry about Mallards much, although we have them. I have never seen a Mallard high enough to matter. I do live in fear of our Turkey Vultures, that are abundant in the warm months. I just looked up Turkey Vultures and found that they, also, are about 3 pounds. Surprising in light of the fact that the 6 foot wingspan is nearly the same as a Golden or Bald Eagle.

I know of several cases where a Turkey Vulture has come through the windshield of a car after flying up from feeding on roadkill. When I fly the Guadalupe Mountains canyons I keep a very restless eye out.
 
Not sure it is good even if the bird hits the prop

Just for info,... had the local Navy boys out running the pattern the other day in their Texan.

Seems an eagle decided to takeoff from active, just as they were setting down,.... prop caught it,.. ok did take the wings off it,.. and ripped out some guts,.. they still collected 6-8 lbs of bird.. a good bit of a trash can.

so how did that big ol prop with the turbine fair???? apparently drove it off line enough that the spinner contacted the cowling,. as it peeled up some of the spinner on the back side, and they felt enough vibration afterwards to pull it in and park it... (as one of the earlier posts said,.. lots of work to accelerate a bird to plane/prop speeds)

I think it is best we avoid the birds,...
 
No RV experience here, but what must have been a smallish bird managed to get sliced and diced enough in a Cherokee prop to prevent it from making it to the windshield as I was climbing out after takeoff at Vy (which, in a Cherokee is only 85 mph). In another incident, on a short cross country in the same plane, I felt and heard a small thump on what I thought was the left wing at about 9,500' (3,000' agl) and about 135 TAS. After landing I looked just under the leading edge and found remains of oily feathers and skin.

From what has been pointed out above, I've been pretty lucky, I guess. Less danger, I suppose, at my lower airspeeds.
 
Had a turkey vulture strike on base-to-final several years ago in a Citabria. Came right through the prop, but no damage to the prop or blood/debris on it. Made an awful stinking mess when it hit the front of the cowl though. :eek:
 
CraigH@KRPH said:
Had a turkey vulture strike on base-to-final several years ago in a Citabria. Came right through the prop, but no damage to the prop or blood/debris on it. Made an awful stinking mess when it hit the front of the cowl though. :eek:
Click to expand...

If at all possible, never fly under a turkey vulture. They fold their wings up and drop. Don't ask me how I know.......:eek:
 
Seagull Hit

I hit a large seagull in my Archer II on slow "looking for a hole" downwind on my daily commute to work at El Monte several years ago. It was hit by the prop debris was spread mostly to the right of the airplane's center. A high mass part which I assume was the head hit the upper right cowling deflected it in temporarily and it bent down the front of the upper fuselage skin permanently in front of the passenger's seat. I was probably under 60 kts and looking back and down for the airport just befor this happened. When I looked back to the front the seagull was spread out in full span trying to avoid the impact. I always like seagulls so this was a doubly bad experience.

Bob Axsom
 
J4 bird miss

I was flying in a J-4 climbing out at about 100ft and a small sparrow sized bird clearly zigged when it should have zagged and went right through the prop and hit the windscreen without making contact with the prop. The tweety bounced off the window I wondered if it made it or not, I doubt it but then again it was a J-4 I wasnt really going all that fast. :)
 
This thread has made is clear to me that I NEED to avoid birds, but has left me very curious about any good research on how to actually accomplish this. I know to avoid flying low over wetlands and such, but I wonder what additional info the the ornithologists of the world could give us regarding these bird brains.
 
I have seen two seagulls come through the propeller arc while flying a Fairchild PT-19. I don't think a propeller blade hit either one of them. Both birds were in the same gaggle. The engine was running a cruise power.

Years later, I had a bird strike in my RV-6. That bird came diving through the propeller arc and struck the leading edge of the wing, intact. The dent in the wing was between the number two and number three ribs in the left fuel tank.

To answer the question, from my expereince, I think the chances of hitting a bird with the propeller are slim at best.
 
Osprey Strike

I had the misfortune of striking an Osprey (Large Raptor, sometimes referred to as "Fish Eagle") while climbing out from a touch and go in my 8A.

I was in a fairly max performance climb passing through approximately 400' AGL when I briefly saw him folding his wings just above and in front of me. He dove through the prop arc without touching the prop and impacted the windscreen at the top edge near the roll bar. The impact shook the airframe like it had been hit by a giant sledge hammer. This whole experience happened in 1 or 2 seconds -- there was no time to take any evasive action.

After performing controllability checks I landed to inspect for damage.

There were Osprey feathers impaled between the plexiglass and the fiberglass at the top of the windscreen. It looked like the airplane was wearing an Indian war bonnet. There was one crack approximately 3" long in the windscreen and lots of blood and guts.

I consider myself extremely fortunate. I have no doubt the windscreen would have shattered if the impact would have been any lower.
 
The discussion about the spinner painted 1/3 with contrasting colors caused me to do some research. Birds it turns out have up to 5 times the visual ability of humans. They see colors better and see more colors and can see UV. But what about seeing a strobe effect of a painted spinner. It turns out they see at a higher flicker rate than we do also! So a 40Hz flicker (2400rpm)on a spinner is no problem for a bird to discern. I found this in wikapedia "Birds can resolve rapid movements better than humans, for whom flickering at a rate greater than 50 Hz appears as continuous movement. Humans cannot therefore distinguish individual flashes of a fluorescent light bulb oscillating at 60Hz, but Budgerigars and chickens have flicker thresholds of more than 100 Hz. A Cooper's Hawk can pursue agile prey through woodland and avoid branches and other objects at high speed; to humans such a chase would appear as a blur."
So, it is reasonable to conclude birds could easily see a strobe effect on a spinner of our airplanes. What we don't know is if they see it will they stay away? I don't know but I would rather they see me coming than not :)
 
We hit a seagull on approach in our first few hours.. and the thump felt enough to cause damage :( Fortunately, on climbing out, I saw blood and guts on the prop, and meant we just had to clean the aircraft, not repair it :)

Allowing 1' for the bulk of a seagull, and 1800RPM/80KIAS I reckon it it's about 50% chance of the prop getting it - less of course since it maybe outside the prop arc.

Avoiding birds - apart from the obvious avoiding of the times of day and areas they fly:
  1. Lights are highly effective. Of note we did not have the Landing Lights on when we had that Birdstrike - we now always have them on.
  2. If you are going to "avoid" a bird, they will tend to break down, so aim to go above them...
  3. Give the things a chance - they are likely to come off second best :eek: Often you can fly right through a flock and at the last second or 2 they will avoid. An abrubt yank on the stick can present more surface area to the bird without actually changing your flight path by much...
  4. A birdstrike will rarely "seriously" damage you / your aircraft. A stall just after takeoff/before landing, or a yank on the stick above Va might just do so :(
Andy & Ellie Hill
RV-8 G-HILZ
 
I was landing in my Kitfox one evening and happened to see a bird sitting right in the middle of the runway just past the threshold. All the coaxing I did idin't work...."Ok, little fella, don't move and everything will work out OK. Just stay put and I'll go right over top of you." You get the idea. He/she was looking right at me, I swear. Of course it happened faster than I can tell it. But, sure enough, as the last minute he/she took flight and went right through the prop. No damage to airplane or prop, but the airplane stunk for a month of Sundays!
Two summers ago I was at 3000' underneath the Class B in Altanta, and I saw a black dot ahead of me. I didn't understand why it wasn't showing on the TIS, when (again, much faster than I can tell it) a big vulture went right down the left side propeller arc without a nick and right down past me. It was almost comical watching the bird try to put it's "brakes" on to no avail. I about jumped into the passenger seat. I know that would have hurt, but both of us were very lucky that day.
Earlier this Fall I posted on this board a flight at 9000' on top of a solid overcast where I narrowly missed a flock of Sandhill Cranes. They weren't squawking either. :)

Vic
 
I saw a TV program once on the old Discovery Wings channel on an attempt to come up with a bird proof windshield for airlines. The testing involved shooting dead birds out of an air cannon in test windshields.

The bottom line -- it failed miserable. Small mass, large converging velocities, equal LARGE force of impact--basic physics.

The best way to keep a bird from penetrating a windshield in ANY aircraft is to keep the birds away from the aircraft and the windshield.
 
Guess I was just (un)lucky when looking at the numbers and probabilities of striking the prop, but when I was taking my initial training in a 172, on a solo flight doing practice landings I took a sparrow in the prop on takeoff, just after rotation. Prop strike, spread him all over about 1/2 of the windshield, made an awful mess. I made the pattern, landed, taxied in, and my instructor was waiting for me, laughing so hard he could hardly stand up.
 
In that interesting thread that asav8tor posted (http://www.vansairforce.com/communit...ad.php?t=24147) there is a discussion of painting your spinner two colors to ward off birds as the Germans supposedly did in WWII. They did 1/3 black 2/3 white. Questions were raised as to how visible this is and is the ratio important? So I did an experiment with LEDS. For a 62 year old guy (me) at 2400 rpm I can not detect flicker in an LED with an on/off ratio of 1 on to 2 off (33% duty cycle like the German spinners). The LED (prop) would have to slow to 2160 rpm for me to begin to see a flicker, at 1500 rpm the flicker is obvious. Using a 50% duty cycle (spinner painted half white half blcak) I could not see flicker in the LED until it was slowed 1860 rpm. So old human eyes are not to good at flicker detection. But as I said in my earlier post birds detect flicker much better than humans, so much better that they should be able to see ficker at a full 2400 rpm and the duty cycle should not make a diference. Sorry I don't know how to verify that in a bird. So if you want to paint your spinner contrasting colors to help avoid birds a 1/3 to 1/2 ratio should be fine. To make your airplane more visible to old guys use 1/3 contrasted color. Just for fun I think I will try this.
 
On my PPL flight test the flight test examiner had radio'd the tower and asked them to tell me to go around on my next landing. Well as luck would have it, I had just flaired and the mains kissed the pavement when the tower told me to go around. Before the noswheel could touch the ground I had power on and was accellerating while reacing for the mic to acknowledge the controller's request. That's when disaster struck!

A seagull had been sitting right on the centreline. As I applied power it decided to get out of the way. Contact was made just to the right of the spinner, with a large proportion of the carcass ending up in every conceivable nook and cranny in the engine compartment. Some bits and pieces rounded the corner of the cowling and smeared down the side of the fuselage. Score Cessna 150 = 1, Gulls = 0

I aborted the takeoff, told the tower I was unable to go around and had a birdstrike and would be exiting at the first taxiway. The examiner was impressed with the go-nogo decision and the manner in which I kept the aircraft under control. As we left the runway she agreed that we should go back to the ramp. As I shut down she told me the flight test was complete, and was successful.

You have no idea how much mess and stink a seagull can make when spread all over a hot engine. After completing all the paperwork and a brief celebration in connection with becoming a newly minted pilot I got the lovely job of cleaning the airplane. YUCK!
 
I appreciate all the feedback from you guys. This has been a most interesting read. I knew many could relate to their or others experiences. You didn?t disappoint.

wj
 
A few years ago...

...there was an article in either Flight Journal, or the Smithsonian's Air & Space magazine, written by a WWII ETO pilot. He was in a P51 (or a P47, I don't recall) involved in some low level strafing.

He stated that his rotating prop was just inches off the field he was plowing, when a German soldier stood up right in front of him and his fast moving plane. There was no way to avoid the soldier, bullets were whizzing on either side of the guy, and the Mustang just flew right through the guy. Only, no mess, no bumps, no anything that would have confirmed the obvious. Looking over his shoulder in a pull-up, the soldier was still standing there...

It really bothered the pilot, and he spent the time (as the first poster has done) and calculated the prop RPM vs, AC speed, vs distance traveled...and came to the mathematical conclusion that, yes, it was possible that a prop blade arched through the air just in front of the soldiers chest, and the next blade passed just behind his back.
 
Empirical Evidence

I don't know about the calculations but I have had two bird strikes in light aircraft.

First was in a Mooney M20F with a three bladed prop. I was on an IFR approach, at night, into Albany,NY. I had just broken out of the clouds and was IIRC about 3000 or so. Heard this very loud noise that scared me to death. After checking everything on the panel all was in the green so proceeded to land normally.

Next day before departure line guy pointed out the trace evidence of a bird strike (feathers, blood, etc) right below the left cowl entrance. No other problems and the cowl was not cracked or anything.

Second case was in my RV-4. Flying along about 1500 AGl doing maybe 150 mph. Overcast day. Suddenly I see a flash and then WHAM! right in front of my face a bird hit the canopy. It was killed obviously and a few remains were left plastered on the canopy. It glanced upwards when it hit and again, save for some blood and guts on the canopy, not damage done to the airplane.

I probably could have replaced the underwear before normal TBO, however.

In both cases the prop didn't hit anything.
 
Don't hit ducks

I remember seeing a show, probably Wings, where they were testing F-16 canopies with bird strikes. At approximately 300 miles an hour the bird crushed the front of the canopy but did not penetrate it. The rest of the canopy was wobbling like warm jello. The canopy is 1 1/2 inches thick. Your math is right on. Don't hit ducks.

Dave
 
I have a 110" three-bladed Hartzell..

....on my Air Tractor that only turns 2000 RPM while I'm working (redline is 2200RPM) and part of my pre-flight checks is to look into the belly mounted air intake scoop for blackbirds, and also the side mounted oil cooler scoop...yep, whole birds in there occasionally.

Regards,
 
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