A question for you jet engine experts

[Holedigger]

I seem to recall that the A-37 Dragonfly (Tweet) had retractable screens for it's engines since they were SO close to the ground. Once airborne and up to speed, they retracted, granted, probably not beefy enough to stop a bigger bird at speed!

[dhfan]

And lets not forget volcanic ash, there was a pretty new KLM 747 that had all four choked out by Mt. Redoubt burping several years ago in Alaska, they were lucky to get a couple restarted and made ANC with badly frosted windshields and ribbons for a radome from the abrasive ash plume.

That happened 7 years earlier to a NZ bound British Airways 747 too.

http://en.wikipedia.org/wiki/British_Airways_Flight_9

[Jack Frost]

Just a couple of observations after reading this very interesting thread:

The window screen on a house window reduces window airflow by 25%.

In 35 years of airline flying, much of it at the low altitudes I only had one serious bird strike. I was flying a Convair 580 betweer Columbus and Grand Island NE at night and took 2 Canadian Snow Geese into the air inlet on the right engine. Banging, popping, surging and an off-scale EGT. A quick prop feather solved the problem. The engine was changed at GRI. How did we know it was 2 geese? The mechs found 3 geese feet inside the engine.

During the migratory fowl season, we always turned on the weather radar at low alititudes. Not to spot the birds but for whatever reason, nobody got a serious bird strike with the radar on. That incident made a believer out of me since I had the radar off that night.

[warbird1]

I seem to recall that the A-37 Dragonfly (Tweet) had retractable screens for it's engines since they were SO close to the ground. Once airborne and up to speed, they retracted, granted, probably not beefy enough to stop a bigger bird at speed!

The Mig-29 has an alternate engine intake where the main ones are closed off during the takeoff roll to prevent the ingestion of FOD, and louvers on top of the engine are opened for the alternate air source. A former Mig-29 pilot had this to say:

"In response to Warpboost's original question about the MiG-29's air intake doors-
The doors operate automatically. On the ground, the doors close at 35% RPM during engine start for each engine. The upper intake louvers are spring-loaded and open due to low pressure created in the intakes by the running engines. The doors automatically open during takeoff roll at
200 kmh. During flight, the ramps are used to control the speed of the air entering the face of the engines. By moving the ramps up and down, shock wave are formed. Supersonic air is decelerated to subsonic (up to a point) after it passes through the shock wave. You don't want supersonic air entering the engines. Even the SR-71 had subsonic air entering the engines. The doors again close during landing roll as the aircraft decelerateds through 200 kmh. If the doors get stuck closed, it is possible to manually open the doors with a switch in the cockpit. In this case, the doors won't schedule to control the intake shock waves. There is a flight manual limit of 0.8 Mach in this case to avoid supersonic flow at the face of the engine."

http://www.abovetopsecret.com/forum/thread150606/pg1

Here is a picture showing the louvers on top of the wing strake, slightly behind and on either side of the cockpit:

[warbird1]

In 35 years of airline flying, much of it at the low altitudes I only had one serious bird strike. I was flying a Convair 580 betweer Columbus and Grand Island NE at night and took 2 Canadian Snow Geese into the air inlet on the right engine. Banging, popping, surging and an off-scale EGT. A quick prop feather solved the problem. The engine was changed at GRI. How did we know it was 2 geese? The mechs found 3 geese feet inside the engine.

I've had about 6 or 7 in my airline career so far, with about 20 over my whole aviation experience, though none have been serious, and none caused any engine damage.

During the migratory fowl season, we always turned on the weather radar at low alititudes. Not to spot the birds but for whatever reason, nobody got a serious bird strike with the radar on. That incident made a believer out of me since I had the radar off that night.

Wow, I didn't know that "technique" had been around that long. I've often heard that birds can "sense" the radar and will avoid it. I've always chalked that up to being an old "wives-tale" and legend that was probably not true. Every once in a while, I'll fly with a pilot who insists that we always have the radar on at low altitude, regardless of the actual weather for this very reason. I still don't know whether to believe this or not. I would love to see some actual statistical analysis to prove this. On one of the airplanes I fly, the radar is always on and can't be turned off with the engines running, because that's what gives input into the Predictive Wind Shear system. Those airplanes still get bird strikes, and I've had them, so I don't know what to think.

[The Inspector]

One early attempt used to try and scare birds away from big inlet engines was the spiral painted on the inlet fan spinner. The thinking was it would look like the 'evil eye' to a bird and make them fly away, didn't work on birds and almost doesn't work on ramp bound humans, they leave it on for humans and hope some birds are dumb enough to be frightened.

[warbird1]

One early attempt used to try and scare birds away from big inlet engines was the spiral painted on the inlet fan spinner. The thinking was it would look like the 'evil eye' to a bird and make them fly away, didn't work on birds and almost doesn't work on ramp bound humans, they leave it on for humans and hope some birds are dumb enough to be frightened.

Yes, I've seen that painted on before and heard the same exact thing. The problem with it, is that it only barely works at idle power when the inlet fan spinner is spinning at a slow enough speed for the eye to discern the spirals, hence movement, and attract attention. Once you apply power to the engines, the spiral blends in with the background, and it all looks like one solid color and you can't tell that it is moving. It's basically worthless at anything other than idle and/or low power, IMO.

[Airplanejunkie]

Had plenty, don't know how to prevent them but.....

Flying into Newark one evening...SPLAT...my windscreen was totally obscured. After an appropriate pause the copilot deadpanned, "I guess he won't have the guts to try that again...."

[The Inspector]

.....and your first thought was 'darn, a coach meal'

[Jack Frost]

I also had a small bird strike on the left windshield in a B-737 cruising at 15000' between OKC and Tul. No damage but the F/O had to land the airplane at TUL because my glass was covered with blood & guts. My guess was that the bird got up that morning and decided to see how high he could fly and then BAMMM, he found out! It was a severe clear summer morning so I didn't have the radar on.

The airline also had an incident north of DEN in a CV-580 cruising at 15000" @ 250 IAS on a clear winter day. The Captain was bent over adjusting something on the panel and the F/O said that first bird (Duck?) cracked the windshield and a second one right behind it came through the weakened glass. When the Captain sat up again he discovered a chunk of glass impaled in the bulkhead behind him right where his head would have been. They said the worst part was that they nearly froze to death in their shirtsleeves until they could get it on the ground at DEN and they and the cockpit were covered with remains. Radar off.

[Second Air Force]

My employer had a 767 climbing through 12,000 feet out of Orly that took multiple bird strikes. One punctured the fuselage and got into the cockpit on the captain's side just above the floor level and another went into the forward equipment bay under the floor beams. Inboard slats, fixed leading edges, radome etc. also got some major damage. That was one smelly mess during the repair process.

Jack Frost, I've had a few encounters with migratory fowl in Nebraska also. We were in a 172 going into Lincoln one bright day and a Canadian popped up, just missing the prop arc and passing between the wing, fuselage, and lift strut without hitting a thing. My wife looked at me with that "did this just happen" look. After we landed I actually gave some thought to what would have happened if that monster had gotten into the cockpit.

On the subject of screens in inlets, an incident occurred some time ago where a test cell was damaged when the inlet screens iced so severely that the negative pressure of a BIG turbine caused damage to the walls of the cell.

S