Tethering things in case of bird strike 3

[dshaffer1001]

Has anybody heard of this being done ?

I am involved in a project in which we are installing a number of antennas and external sensors on an aircraft. I have one particular installation where our customer wants us to take bird strikes into account. The installation is a combined sensor/antenna mount. It consists of an aluminum base assembly that houses two small IR sensors. At the top, it is attached to the underside fuselage. At the bottom, a VHF blade antenna is attached. The whole thing is located on the bottom of the aircraft up near the nose. Our aero people tell me that it's possible, under the right flight conditions, for any broken-off pieces in this area to go into the engine inlets.

It's been suggested that we use a tether, such that if our mount breaks loose, it will remain attached to the airframe by a cable or something similar. That way, at least it won't be sucked into any inlets.

I have never heard of such a tether being employed this way, I have had no luck finding any examples of such installations.

Can anyone help ?

 

[rb1957]

i'm with you ... never heard of such ... think what damage would happen to the fuselage with a VHF antenna wacking against it at some high speed.

other thoughts ...
1) what if you mounted the installation on very stiff springs so that the bird impact would be taken in elastic deformation ... at a minimum i think you'd get a really neat bird strike test !

2) what about ice ? being shed off the antenna into the engines ?

3) if the VHF antenna is the problem, relocate it !

Quando Omni Flunkus Moritati

 

[MintJulep]

A tether will only serve to allow the broken off thing repeatedly smash against the fuselage until ultimately either the tether or its attachments fail, and the thing gets sucked into the engine anyway.

 

[rerig]

IMHO the right flight conditions for a belly mounted antenna to be "sucked" into an intake would be INVERTED!

 

[IRstuff]

Based on math, however, for a 150-kt aircraft, the intake would need to be set back by 19-m to avoid ingesting an antenna, assuming a 1-ft tall intake.

TTFN
faq731-376

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[WKTaylor]

IF the blade antenna is located such that a bird strike could release debris into an enginge inlet, then the same could be said for the bird carcass.

Many times these antenna blades have a thin plastic skin, foam core and the antenna wire running-up the core, IE: not much that could seriously harm a large engine. Suggest contacting the antenna/blade manufacturer to discuss bird impact and debris release patterns for the blade.

Another idea if a small-enough blade: install a rigid-mounted bird-splitter [bird cutter] forward of the antenna installation. The bird splitter will divert the carcass [in pieces] from striking the vulnerable base of the antenna, preventing release of antenaa fragents that could harm the engine. Bird splitter sould be mounted securely to one-or-more frames, directly forward of the antenna install. The Splitter should have a 0.3--0.5-blade-height delta profile with a wedge cross-section [pointy edge forward!] made of hard-anodized aluminum [2024-T8, 7075-T73, etc].

Regards, Wil Taylor

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