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"straked Tail Booms"


Mark Dip
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I believe that this was a hot topic a long time ago on this board but have any of you out there had the opportunity to fly one of the modded tail booms with the strake on the left (?) side in order to improve tail rotor authority and cyclic authority especially in right sidewards flight or with a right hand crosswind. I think that the mod was aimed at BH205s, but the Canadian Military uses one on their S-61s, was the mod successful and if so have many companies implemented it on thier machines?

 

Thanks.

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i flew one for a month last year but it wasn't long enough to be able to really notice a HUGE difference. it would have been nice to fly one without then one with. i know our training captain at the time swore by them. i was out splashing water on flame in the flats at the time. i think one would notice it more up high.

 

412

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We've been flying our 212's with strakes on them for about 4 years now, we estimate about 400 lbs increase in useful load. It would appear from most of the Bell mediums that I have seen in the past couple of years that just about everyone in Canada has jumped on the band wagon. The bonus to the strake is it seems to be saving us a few pesos on tail rotor parts.

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The patent is held by NASA, but licensed to a manufacturer.

http://www.larc.nasa.gov/news_and_events/i...c98/98-097.html

 

The manufacturer of the strakes is Boundary Layer Research. They build all sorts of stuff for fixed-wings, and strakes for many different helicopter types.

http://www.blrvgs.com/

 

Whatever makes it work, the idea is popular. Whether the additional lift is worth the cost is often debated, but most pilots agree that they do allow the aircraft to lift more, especially in a vertical lift, such as pulling a drill or bucket out of a hole.

 

Some additional thoughts......

I may be wrong (an all-too-regular occurence) but I believe it involves some form of the "Coanda Effect", which is an aerodynamic effect relating to pressure-changes caused by air moving past a round-shaped object. This pressure then moves the object in a required direction.

Sometimes pressure is increased on one side of an object to "push" it away from it's present position, or a vacuum could be created to "pull" an object, using the same basic ideas of flow.

 

The Coanda effect has already been used in helicopters, such as MD Notars. They tried strakes or "fences" and ended up using slots in the tailboom.

http://home.wanadoo.nl/helicopter/development.htm

 

Henri Coanda was a Romanian aircraft designer. He designed the world's first jet airplane in 1910, but discovered the flow of exhaust along the airframe acted in some interesting ways. His research of these flows led to the effect being utilised, and named after him. (He dropped the jet-plane idea and other people such as Heinkle and Whittle were credited with inventing it 30 years later).

 

Most physicists think this is how pitchers can make a baseball do weird things on its way to the batsman, and why golfballs are dimpled.

Many physicists still argue about why a wing creates lift. However, they all seem to agree that it is not just caused by Bernoulli's theory, but also by some amount of Coanda effect, and other factors.

 

It has also been used to power ships. The Coanda "mast" area produces alot more power than a conventional sail, per square foot. The masts are spun around on a vertical axis, and a normal diesel engine and propellor starts the ship moving forward. The spinning masts are now moving forward through the surrounding air and create a vacuum in front of themselves (due to the Coanda effect). Once the ship starts sucking itself forward the diesel engine is shut down.

http://www.cousteausociety.org/vessels/vessels.htm

 

I hope this helps and is somewhat accurate.

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Guest Bullet Remington

F.A.

 

We were doing that Strake Mod when I was stationed there. I believe we included that in the OmniBus Mod. Was not aware how much effect the mod actually had on the Sea Pig performance!

 

Thanks for the tidbit of info!

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Flown a 205 with a strake for a few years now. There is a difference, especially in the hover. I saw the biggest difference when jumping from our 2x4 (no strake) to a 205 (with a strake). During re-current training, we noticed a 2 1/2 psi difference in hover power required for the same weight, with the power on the one with the strake being lower (205 vs. 205).

 

Cheers

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