What are the small tabs on the trailing edge of the rotor for?

[Vortex what...ouch!]

Nobody ever explained why they were there.

[MightyGem]

They are trim tabs. Used to slightly adjust the flight path of the blades so that they all fly the same path. Used in combination with adjustable pitch control rods.

[Vortex what...ouch!]

I talk from genuine ignorance - nobody explained it to me.

http://www.mide.com/images/smarttab_chopper.gif

[ShyTorque]

I thought they were there to prevent the tie-down chains sliding off.

[SASless]

They are the Rotary Wing equivalents of Mexican Pinatas that provide great sport for the Pilots to bang around with the long handled brushes when when washing the aircraft. It becomes a group sport when the Engineers get to figure out why the aircraft is out of track following the wash job!

[Senior Pilot]

More in this thread: Trim tabs (http://www.pprune.org/rotorheads/270703-trim-tabs.html) :ok:

[krypton_john]

They're post-it notes. The engineers put them on so they know which way round to put the blades when refitting them.

HTH!

[PlasticCabDriver]

They're an optional extra that you can add to make your helicopter sound right. This is so old boys can hear the sound, look wistfully to the skies and say "ah, the 105, I recognise that sound anywhere". Also available in "Chinook Thump", "Bell 47 for Filmmakers" and "Blade Tape in the Rain".

[Bellrider]

Sorry guys!
But i think the picture is showing the following:

Eurocopter highlights its innovation and bluecopter® technology at Heli-Expo 2010 - Eurocopter, an EADS company (http://www.eurocopter.com/site/en/press/Eurocopter-highlights-its-innovation-and-bluecopterA-technology-at-Heli-Expo-2010_661.html?iframe=true&width=700)

Normal Flaps are not connected with cables!
This are piezo Electric elements designed for noise reduduction!

[3D CAM]

Pilots to bang around with the long handled brushes when when washing the aircraft.

Now I know you're having a laugh!:rolleyes::D
3D

[Thomas coupling]

Vortex: they are STATIC trim tabs, which allow engineers to 'tweak' them by bending them to allow the blade to fly in harmony with the other blades in the horizontal plane. In the ends of each blade there is a tip cap. Inside this tip cap can be found mini weights (shot or lead blocks) these are DYNAMIC trims. They assist in flying the wing in the vertical plane. New generation helos can adjust some of these settings whilst in flight :eek: Something to do with voodoo magic :E

[oldbeefer]

I used to think that they acted like an elevator ie, if the tab was bent down, more lift would be generated and the blade would fly higher. Only when i started doing in-flight tracking with the gingerbeers that I found they have the opposite effect- bending a tab down causes the blade to twist slightly reducing pitch and causing it to fly lower.

[Fareastdriver]

IIRC. probably not, was there a helicopter in service that used servo tabs to control the rotors. I think this because it could be tracked in flight.

[ShyTorque]

Kaman used servo tab control, didn't they?

Servo Flap Controlled Rotor (http://www.helis.com/howflies/servo.php)


Quote: Pilots to bang around with the long handled brushes when when washing the aircraft.

Now I know you're having a laugh! 3D

It's a bit like doing the washing up at home. Break a few bits of the best crockery, never get asked again. ;)

[RotaryWingB2]

TC


Vortex: they are STATIC trim tabs, which allow engineers to 'tweak' them by bending them to allow the blade to fly in harmony with the other blades in the horizontal plane. In the ends of each blade there is a tip cap. Inside this tip cap can be found mini weights (shot or lead blocks) these are DYNAMIC trims. They assist in flying the wing in the vertical plane. New generation helos can adjust some of these settings whilst in flight http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/eek.gif Something to do with voodoo magic http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/evil.gif


Not quite. The trim tabs are to get all the blades flying in the correct plane (tracking), which is carried out along with PCR adjustments, the weight chambers are to adjust the weight of each blade (balancing).

Most blades have static trim tabs and static weight chambers (which are set up at the factory, and none adjustable) and dynamic trim tabs, dynamic weight pots/washers which the engineer can adjust.

A combination of adjusting all three on the ground, some measurements at flight idle/hover/ differing speeds and then some more adjustments should hopefully have your helicopter flying smoother, help preserve wearing of components and keep your vision clear....:8

[Lonewolf_50]

Fareastdriver:

USN, Kaman SH-2F Sea Sprite (for that matter, A-E and G as well) had that feature which allowed for exceptionally fine tunning of the rotor disk. You could, using two switches in the overhead panel, adjust the cones, (A/C and B/D) as well as asjusting the track (using A and B) motors. I don't think any other helicopter I've ever flown could be tracked to such a fine degree, in terms of how smooth the ride is. (A well tracked CH-53E, with seven blades, produces nearly as smooth of a ride).

I flew SH-2F's back in the 80's. There are plusses and minuses to that design feature.

One plus is that you can fly the bird with zero hydraulics.

[MightyGem]

tracking
That was the word I wanted to say but couldn't think of. :( Old age. :{

[Soave_Pilot]

They are trim tabs. Used to slightly adjust the flight path of the blades so that they all fly the same path.

I thought they are NOT to supposed do fly the same path... Isn't true?

[SansAnhedral]

Your picture is from Mide, an engineering company that worked with Sikorsky on their AATD program offering nitnol-based active trim tabs. Sikorsky's actual AATD blade ended up being a S-434 blade with an electric linear motor and bellcrank, as the nitnol has a litany of issues.

There are a few AHS whitepapers out there with studies by DARPA using piezoelectric actuators for active trailing edge flaps, albeit with some inherent flutter and response issues at frequencies necessary to be actually useful (for vibration and acoustic attenuation).

Very large bandwidth trailing edge flap motion and sizing could be used for primiary flight control a la Kaman. Piezos are inherently unsuitable for these applications, regardless of that press releases you read from Eurocopter :E Even the MD900 blade with the force multiplying X-frame apparatus for piezos could not demonstrate full spectrum response and deflection.

Boeing, Sikorsky, and Bell have also been working with active blade flaps for some time. Nothing has been developed into a production application at this point.

[Gemini Twin]

If you want the helicopter to be free of vertical bounce, and who doesn't, you must adjust the track using the tabs, mentioned in the original post, to get the blades to "fly" in the same path.

In ancient times flag tracking was used when each blade had a differant colored marker applied to the tip and ground tracking was completed when, after individual tab adjustment, all the colors were transferred on to the flag in the same vertical position.

[Fareastdriver]

In ancient times flag tracking was used when each blade had a differant colored marker applied

........and in even more ancient times a oiled (used, dirty black oil) brush was slowly pushed up and then after shut down the lowest blade was ascertained and adjusted. Once the brush hit all of them together there was then a short airtest to see by how much the autorotative RPM had altered.

The Sycamore had bullet shaped mass balances on the end of the blades. A flag wouldn't have lasted a single revolution.

[Gemini Twin]

Lots of things didn't last long on the Sycamore :ok:

[Ascend Charlie]

Didn't the 214ST have one adjustable tab (from a wheel in the cockpit) to adjust the tracking in flight?

[imabell]

"nobody explained to me", are you kidding?, what kind of helicopter education did you get??
why did you never ask??
so that's what the JAR system turns out. pathetic.

[RVDT]

AC,

It was actually one of the pitch horns!

It adjusted the connection point of the P/L to the pitch horn on an eccentric on one blade.

http://oh1ninja.la.coocan.jp/details/Bell214/040522_Bell214_034_trim.jpg

The opposite blade had a counterweight in this position.

http://oh1ninja.la.coocan.jp/details/Bell214/040522_Bell214_098.jpg

[oldbeefer]

Soave pilot

They ARE supposed to have the same tip-path plane on conventional heads. For the Bell 412, where the pairs of blades are clamped one on top of the other, there will be that same split at the tips, but each pair of blades will have the same path.

[RVDT]

They ARE supposed to have the same tip-path plane on conventional heads

But do not always if tracked for minimum vertical vibration as opposed to same track.

Evident on many different models.

[vfr440]

Yes, indeed, that's the theory, anyway - all in the same tip-path plane. That's what the aerodynamacists prescribe, but real life, on occasion, will define slightly differently :uhoh:

Two standards to bear in mind here, composite (modern) blade construction and traditional (old) design. The former are less 'individual' and, by and large, one can aim for constant tip path plane (TPP), achieve it, and probably the 1R vertical will be down to an acceptable level. :ooh: (OB is absolutely correct for the 412, you'd aim for two sets of TPP. BUT you would be using the RADS and if it recommended an adjustment that transgressed that generalisation, it might be a good idea to follow it's predictions/adjustments.:ok:). 'Modern' blades are mostly 'on condition' without a finite (Timex) retirement life. :oh:

The earlier standard is not quite so simple. Comprising metal construction with a spar, filler and Al skin, at design level the ethos is to have individually replaceable blades throughout the prescribed TIMEX life, i.e. the ageing process is predicted not to alter a blade's individual characteristics within that life, that cannot be compensated for with the adjustment of PCL and T'tab provided. :hmm:

BUT........ age can do all sorts of different things to the metal construction, particularly the spar. Some age-harden with the extreme flexing a blade must accommodate in normal service; others become more flexible over their lif-span, at the same time altering the amount of washout originally built-in to the blade at manufacture. :E

Now you begin to see the complexity of the task of getting all these blades to 'live' together. At the risk of being terribly policitically incorrect, I have described this aspect as an analogy to women. :mad: Difficult to get all of them to see eye to eye, and age adds a frisson of unpredictability to the equation. AND the more of them you have the more complex the problem can rapidly become, (Are you all still with me, or with the Woolwich?) :ugh:

A VERY senior engineer told me, before he disappeared to the great bar in the sky (where I'll bet he's racking up my bar bill like there's no tomorrow) that if the life discrepancy between the blades is more than 400 hrs, then you will have to accept a compromise on vibration levels somewhere between Hover and Vne. :( Fact of life as far as he was concerned, and as a maxim to guide you it has done me proud over the years. :ok:

So that's what I bring to the table. I'm not an expert, but been doing it for a few years (ask TRC!). Essentially we are looking for a vibration-free ride (utopia), and the actual TPP pf the blades is a secondary consideration. :cool:Can be a bitch of a rotor to work sometimes; think of your engineer with respect and affection, he doesn't want to be playing with it all day long, any more than you do. A beer would be a MUCH more worthwhile activity to pursue. :ok: :ok: :ok::D

Fly safe - VFR

[Gemini Twin]

Absolutely correct vfr440, the aim might be to track so that all blades fly in the same plane but in reality you track for vertical bounce free flight.
By using pitch rods for ground track and trim tabs for forward flight you can usually get it close but with a miss matched set of blades(altered blade characteristics) some times it's impossible and the only recoures was to try another blade to see if you can acheive a better match.
Oh yes and as fareastdriver mentioned always recheck auto rpm after track adjustments

[TRC]

... but been doing it for a few years (ask TRC) ...


Two or three decades more like. (Hello Chip).


...with a miss matched set of blades...

I had the pleasure of tracking a rental blade with a temporary partner of considerably different age/hours/temperament.
Ended up with max 'up' tab on one and max 'down' on the other - just got it acceptable up to about 110kts. Any faster would have meant a trip to the back doctor and the dentist. Lucky it was only while the original was being repaired - that was a bundle of fun when we got it back too.

[vfr440]

Hello Jack-not-bloody-Tom :D
Yes, I remember that one, and then Bell came out with TWO trim tabs/blade (and a convoluted chart to programme the Vibrex as well?)

And this is hard work for an expatriate Cornishman who's only just mastered joined-up writing. Chip Bath working overtime......:ugh: (Sorry, that's an in-joke from AMH, somewhat akin to 'Capt Average', you recall? ........:))

Keep the revs up - VFR