Fairing design approach
Fairing design approach
(OP)
I need to design a fairing to deflect air flow and water/ice from an open area on the nose of an aircraft. We did a modification which required cutting a large hole (8.5x13.5) in the avionics bay nose door, and creating a type of a chute from inside the area. Concern has been shown towards this area when the aircraft is flying in icing conditions, the customer is concerned about this cutout acting as an ice scoop. The probability of there being an issue is low, but definitely there. They would like me to design some sort of air dam or fairing that would deflect the air flow and ice enough to keep ice from building up on the aft face of the chute. However, I've never approached a fairing design on the nose of an aircraft before, and I'm unsure where to start as far as effects on air flow, performance in those regards. To make matters more difficult, there is a vent just aft of the area in question which pulls air out of the A-bay through use of creating a lower pressure outside of the aircraft. The fairing must be large enough to deflect any ice buildup, yet be small enough to have minimal affect on the overall aircraft performance and on the vent performance. Any guidance would be greatly appreciated.
James Bennetts
Aerospace Engineer





RE: Fairing design approach
what about bird strike ?
RE: Fairing design approach
James Bennetts
Aerospace Engineer
RE: Fairing design approach
RE: Fairing design approach
James Bennetts
Aerospace Engineer
RE: Fairing design approach
The dam could open with the hinge on the leading edge, or push straight out like a brake. Accumulation of ice on the dam might impede retraction, in either case.
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A solution used in helicopters is a reverse-flow fairing, where the engine intake is completely covered. Engine air comes in through two ducts open to the aft, travels forward in the fairing, and then enters the normal engine duct.
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Steven Fahey, CET
RE: Fairing design approach
I know this is hard to visualize, I wish there was a way to attach a photo, but I don't think there is. Ah well, any thoughts you have are appreciated, including those already given.
James Bennetts
Aerospace Engineer
RE: Fairing design approach
Otherwise, you could place a 3" wide air dam straight down far enough to protect the hole and fair it as best you can.
I don't think either of these would effect your avionics cooling discharge if it solely works of differential pressure to discharge air.
RE: Fairing design approach
The 3 inch fairing/air dam is basically what they are looking for, but I'm a little concerned about the flight performance effects that would have, not to mention that would require another flight test which they are hoping to avoid. The reason I'm concerned with how that would effect the air flow out of the vent is because the lower pressure is generated by the air flow across the vent cut out (this vent is very similar to the reverse ram scoop you mentioned), and I'm not sure what kind of effect turbulent flow would have on that system. I have only a rudimentary knowledge of aerodynamic flow (two undergrad courses) and no wind/smoke tunnel to test it.
James Bennetts
Aerospace Engineer
RE: Fairing design approach
for obvious reasons i think you can't be too forthcoming about this installation. actually you can link web pix onto posts (but don't ask me how, but i've seen it on other posts) ... but then i think you very limited in what you could post without getting into trouble (nudge, nudge)
anyways, it sounds like there isn't a large demand for airflow (in or out) ... could you add a deflector, open at two ends (like a "top hat" channel) ? this would provide some airflow (but then i think your question is how much ?) but would also remove any ram effects that would be there with an open inlet, but maybe this isn't important ?
RE: Fairing design approach
Regardless, you all have offered up some good information and ideas, and I appreciate it greatly. I think I'm pretty much dead in the water unless I can get some simulation programs or some detailed airflow analysis to go by, and that's not likely in this case.
Thanks again for the ideas and by all means offer any others you have, it's greatly appreciated.
James Bennetts
Aerospace Engineer
RE: Fairing design approach
Like RB1957, I'm guessing this isn't the run-of-the-mill project, so have you checked that the aircraft isn't already in the restricted category?
Steven Fahey, CET
RE: Fairing design approach
James Bennetts
Aerospace Engineer
RE: Fairing design approach
RE: Fairing design approach
James Bennetts
Aerospace Engineer
RE: Fairing design approach
This would be a simple installation connecting it into the normal anti-ice systems. Pitot/static etc.
Karl
RE: Fairing design approach
Thanks much for the input.
James Bennetts
Aerospace Engineer