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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.
 
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
 
Doesnt the Agusta A109E and 119 have them on the boom as well.

Heli Ops
 
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.
 
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.
 
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!
 
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
 
We put them on our 204C's last year and I think all of the pilot comments on them have been positive. With a reasonable load, you hardly seem to use any left pedal on liftoff, and the T/R authority at high D/A is markedly improved. We'll be putting them on the 205 this winter, too. B)
 
You need to address the pilots flight step also, I'm getting tired of boosting mini Coop way up in to that 205 all the time.... 😀 😛
 
:lol: Have to agree with ya on that one 407 😛 . Downwash what about the blades on that old 205, don't they need to be changed first 😀 . I'll try not to injure LIL'Coop, drin... I mean skiing this weekend 😛 😀
 
Definitely more T/R authority on the 2x4 ,especially in the hover IGE or OGE.

But you gotta love those flight manual supplements, especially the performance sections.

How do you explain when a customer asks “What can you lift?â€

The book says that in my –13 I can only pull what a –11 could pull at a given altitude & OAT. I know I’ll have Tq, N1, and EGT to spare but according to the –13 supplement, I’m not allowed to use it. Then the boss goes and tells the customer “It’ll lift 3000 lbs.†which I know is true enough but means using that left-over Tq, N1, or EGT that I’m really not supposed to use.

Between the –13 and the strakes, I know I can pull more Tq & lift more weight higher up the hill than the book says and still be within all engine limits and the external GW, but have no charts to back it up.

Wah, wah, wah…I’ll be OK now!

Right…what were we talking about?…Oh yeah, …strakes…great mod!
 
Let's not forget the Astar B2 has a factory strake on the right side (blades spin the other way) but it was not included on the B3.
Each different model of Astar seems to have a different strake on one or other of its tail fins. I don't know what they are all supposed to do, or why they would keep changing.
 
Over talke, wat are u talking about you inglish pig dog, wat iz dis "strake" you speak of, hey Dedier fetch moi mes Gauloises.

We bild dis helicoptere and we poot dis strake wherever we want to, dis is France, I cannot drink my wine and work until le souper...silly english man....

Manon ma cherie, make a note to charge dose stupide inglish more money for our great helicopteres, they are too stupide to know why Free French men make dem de way we do...crazy Anglais!
 
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