RV-9 whistle
 

Has anyone figured out what is causing the whistle that seems to be in most if not all RV-9's? My son heard me from 9 miles out and he thought it was a turbine coming in to land. He heard the whistle before he ever heard the engine and prop. I asked him if it was annoying and he said not at all. It just sounded like a jet coming in. Does this mean I will have to be careful that a lineboy doesn't fill my tanks with JetA? :D

My -9 had the whistle and that's exactly what people would tell me - sounds like a turbine in the pattern. I do not want my beautiful, prop driven RV to sound like that. :(
So..I took a look at the tail surfaces and figured that it might be coming from the hinge openings at the elevators and rudder. Much like producing sound from a flute - air passing over an opening. I took some of that UHMV tape and covered the openings. Problem solved, and you can still see through the tape to check hinge bolts during preflight.
I recently repainted the airplane and removed the tape. Sure enough, when the plane was back in the air someone said it was whistling. I covered the rudder hings openings only this time and no one has said anything so I guess the rudder hinge openings are the culprit.

RV 9 whistle
 

My RV 9 has a noticeable whistle even for non aviation friends. There's no mistake about it coming by. Haven't tried to find out why . Anyone experimented with tape on various places to see if it can be located. Not sure I want to fix it. It's just part of its character. For those needing to fix it , I have a sliding canopy, Prince P tip prop and 0320 160HP. I however think it might be in the tail section faring or other tail config.

Hey, a Corsair has a very prominent whistle when it flies past, too. Not always a bad thing.

Hinge openings, huh? Maybe I should look into enlarging mine to get Smokey to whistle. Sounds pretty cool ... :D

Agree with Bruce
 

Cover HS/elevator hinge openings and you can go stealth.
http://www.vansairforce.com/communit...whistle&page=2

free bird repellent???
 

I'll just leave mine..... and consider it an eco-friendly way to ward off other flying objects! :)

Interesting....
 

If it's caused by the rudder hinge openings, why doesn't the RV-7 whistle? It uses the same vertical and rudder as the -9.

I always knew when Ted Chang was coming in. It is nice to have a unique sound. My wife commented the other day on how our -10 sounds compared to the rental 172.

Great question Mel. I don't know the answer but my first guess would be the differences in the wing airfoils changes airflow around the part that's whistling. My experience, albeit limited and not scientific, is on at least some flutes, it doesn't take much difference in the angle of the wind blowing over the hole to change a loud tone to a near silent woosh.

If I ever finish my 9A, and if it whistles, I'll be curious to see if I can isolate which hole or holes cause it. The it would be interesting to tuft test the area around that/those hole(s) and compare the results to a 7A, if the whistling parts are the same.

Whistling airplanes
 

May not really be germane, but back when I was employed by Noise Engineering at Boeing, a lot of flight testing revealed that a very loud whistle heard on 737s approaching to land was caused by an uncapped tube in the landing gear. Boeing capped the tube for a measurable noise decrease on landing. The uncapped tube produced the same effect you get blowing over the open neck of a Coke bottle. The effect even has a name: a Helmholtz resonator. Being unfamiliar with RV-9 elevator hinges I cannot say for sure that the same effect is involved here, but the "takeaway" is that any uncovered opening to an enclosed volume can potentially produce a tone in flight. Whether its loud enough to be heard or even be a problem, like on the 737, is dependent upon the geometry, airspeed and density.