Painting your blades

[Waag]

Hi everybody!
Just wanna hear your uppinion about spraypainting the blades of a Bell 412??
Is this ok, or do you think that this is a hazzard in future operation of the aircraft? I am thinking about the paint contra metal etc.
Best regards

[NickLappos]

How about painting all those steel gears in the transmission - aren't they just hideous?

[Salusa]

How about painting all those steel gears in the transmission - aren't they just hideous?

Surely a nice chrome job would be better, we could chrome plate the mast at the same time maybe?

[helimutt]

only use Hammerite paint. It gives that nice hammered enamel finish which reduces the risk of epileptic shocks on a sunny day.

I believe it reduces wear considerably too. An R22 I flew with these 'painted' blades, had been in use for over 16 years without any problems and the blades themselves had done about 4000hours. Hammerite.
Great!!:rolleyes:

[quichemech]

Waag,

Just in case this isn't some form of wind up, then NO, you can't paint your blades. Send them to a blade repair shop who will be able to refinish them to the correct specification.

If it's a wind up, then feel free to go forth..............

[Encyclo]

Good Question Waag:ok:

There was thread a few days ago saying how difficult the 412 rotor is to work. That can sometimes be the result of improper blade painting:eek:

Bell published Info Letter 412-83-2 for high vis painting. It gives you tips on how to avoid messing up your blades while sanding & painting them:8.

[Blackhawk9]

I've repainted about 6 sets of 412 blades in the high vis scheme in the Info Letter, do all your blades at once and do a complete track and balance and you should be right ,this is one set I did
http://i17.photobucket.com/albums/b56/Sydhuey/DSC00892.jpg

[170']

Nice work Black Hawk9... :ok:

If you consider the OAS/USFS requirement for high viz blades for years. I've probably flown with more painted blades than unpainted...

Waag...Follow Black Hawks advice and you can't go wrong...170'

[shak'n]

Sort of right BlackHawk 9 (Sid??).

You are correct if you intend to fly these blades as a fixed set for their intended service life. The potential problem you face is when you inevitably have to start to mix the blades due to removing one of these blades for repair and get a "loaner" or another out of stock to try and fly with the remaining 3 x blades in the mean time.

This is the big mistake all operators have been making since Igor and Bell began to swing blades.

Independant painting of blades results in span moment arm migration which in turn will ultimately produce "rogue" blades and prohibit - or at very least make extremely difficult, the interchangeability of blades within a fleet of same type of helicopters........you would have seen this in the UH1 fleet in the RAAF and Oz Army.....plus all other fleet operators. It also manifested itself in Oz BlackHawk fleet around 1995 after about their 2nd R3. It was caused because all the blades had been "touched up" or repainted every R3 without having their span monet arm checked and reset if required.

After the 2nd or 3rd R3, the accumulation of paint migtrated the span moment arm to such an extent, that if a new blade were attempted to be flown with 3 older, in service blades having had at least 1-2 repaints, it was more often than not impossible to get them all to fly together. It resulted in excessive laterals with insufficient dynamic balance authority to correct the lateral out-of-blance.

A common indicator of this problem is excessive flight hours required to successfully dynamically balance your blades eg anything in excess of 3-4 flights (assuming the operator/LAME knows what he is doing). The strongest indicator on your dynamic balance equipment (RADS, CH, ACES, Helitune, etc) is if the correction move line for the laterals begins to move tangential to the origin and indicating that the best (or minimum) level of lateral is still greater than what is acceptable eg greater than 0.1-0.15IPS.

The problem of migrating span moment arm can easily be solved.

For a far greater understanding of this commonly experienced phenomonia (ie "rogue" blades) of migrating span moment arm and how to fix or cure it, visit www.rwas.com.au......makes for some enlightening reading into balancing rotor blades and some common misconceptions held throughout the industry.

(Besides Sid, Golf Alpha Victor says you can't paint for Sh.t....so I am reliably informed)http://www.pprune.org/forums/images/smilies/badteeth.gif

[chuckolamofola]

shak'n said:
Independant painting of blades results in span moment arm migration which in turn will ultimately produce "rogue" blades and prohibit - or at very least make extremely difficult, the interchangeability of blades within a fleet of same type of helicopters.

While this can and does affect the capability to balance the rotor after the painting process, the main reason 412 blades don't fly well after painting is that the paint finisher spends a nice long time on the blades with a d/a sander smoothing any defects out and feathering any abrupt edges in the paint and ends up reducing the thickness of the blade's trailing edge. Changes of the trailing edge significately changes the blade's flying characteristics. Improper paint prep has caused far more damage to the 412 fleet than applying paint. A paint only problem will manifest itself with the inability to hang enough weight on the m/r head to get the blade balanced. It is worth the cost to send the blade to a properly rated repair facililty so that they can finish it correctly. Over the long term it will cost you less.

If you have to paint your own blades, when prepping the blades be extra careful to scuff the blade just enough for paint adhesion and don't spend a lot of time trying to feather paint chips out. Hand sand only...

Chuck

[shak'n]

A paint only problem will manifest itself with the inability to hang enough weight on the m/r head to get the blade balanced.

Exactly Chucky,

That's called Span moment arm migration which results in insufficient mass adjustment on the head to counter significant lateral imbalance due to a change in mass distrubution across the blade. This is generally caused by either uneven paint distribution after successive paints or trapped water inside the blade. I am not suggesting that one paint job alone will make it very difficult to balance (unless it was a real amateur job). It is manifested after at least 2 or more paintings and then if not all the paint is removed and a nice even coat reapplied, this begins the process. Generally people will only sand the surface enough to allow the new paint to adhere (as you suggest in your recommendations). This is a problem in the making. Generally the leading edge and towards the tip have all the paint eroded off. Therefore we end up with an accumulation of paint (thus weight) on the inboard half of the blade. Over successive repaints this leads to a migration outboard of the blade's CofG (Span Moment arm). If all the blades on the same head are reapinted the same way, same time and retained as a set flying together, there will be no problem in dynamic balancing them, as their Span CogG will have been migrating together.

However, as soon as I replace one of those blades with a brand new blade, the head will become very difficult to dynamically balance or even impossible to. Because the span moment arm of the 3 remaining blades will have migrated quite markedly different from the OEM's original design specs.

The first thing maintainers will do is return the brand new blade as the other 3 flew perfectly well with the old blade. They will even return this brand new blade to the OEM or overhaul centre and even call it "too heavy" ......heard this before have we?? Sound familiar??? The OEM will simply compare this returned blade with his master blade, see no problem and return it back to service and bill you a fortune for the honour.

The real problem is with the 3 blades still on the head. Their Span Moment Arm has migrated (generally outboard) so much during operational use and maintenance that they now no longer become interchangeable fleetwide. We now are forced to fly our blades as "Sets" because certain blades appear impossible to dynamically balance together. Sound familiar also???

The secret is - in-service span moment arm migration. It happens to every rotor blade created but the industry has remained ignorant of its true effect on the dynamic balance solution.

This leaves only one other option - the static span weight adjustments generally located in the tip. Most helicopters have their tip weights relatively easily accessable. The 412 has their's cleverly disguised as lead shot in a bonded tip cap which are inserted via a little allen bolt in the upper surface. You can occassionallly hear them rattle if you jiggle the blade. The only way you can reduce the weight this package is by de-bonding the tip cap which really means it has to go back to overhaul. Alternatively their is scope to move by playing with the product weights. These are primarily designed to set the dynamic chord moment arm (changes tracking path of the blade tips as angle of attack is changed from flat pitch ground to hover picture) but if you look at the maintenance manual, you will see that Bell do give scope for max/mins for the individual pockets. The important thing is to maintain teh ratio of the mass between these two pockets as this determines the chord moment arm effect - afterall, that is what they are designed to affect. But if the mass of these pockets were equally reduced/increased to change the overall span moment arm, then you could counter the effect of a migrating span moment arm.

The trick is "how do I quantify my span moment arm for any one individual blade"? By this, I mean to actually provide a specificm inchlb or kgcm measurment to which I can then either reduce or increase my span weight package to bring the blade's ideal Span moment arm back into original design specs.

There is only one easy way - by using a digital static blade balancer. This is a tool that most OEMs and their approved overhaul centres still do not use although they are slowly being convinced.

Span moment Arm migtaion is your biggest problem - not trailing edge anomolies. This has been proven with data through the US Army and now an increasing number of other operators using this technology.

I suggest you read www.rwas.com.au for greater detail. I think it may enlighten.....

PS I am not suggesting that every Tom, Dick & Harry race out and start fooling around with their tipweights. I am suggesting that the industry start demanding of OEMs the ability to adjust these tip weights at operator level ........providing they have access to a digital Static Balance tool (NOT old technology Master Blades). It is the ONLY way of knowing exactly determining the magnitude and quantifying the exact changes required to reset blades back to OEM specs and return blades back to fleetwide interchangeability and easy RTB of no more than 3-4 flights.

cheers

[chuckolamofola]

Shaky said:
Span moment Arm migtaion is your biggest problem - not trailing edge anomolies. This has been proven with data through the US Army and now an increasing number of other operators using this technology.
I suggest you read www.rwas.com.au for greater detail. I think it may enlighten.....

Field span moment adjustment is not new, we were doing this back in the late 80's in the GOM on 412's using two digital scales from procedures supplied by Bell long before Avion started their program . Its definately a worthwile endeavor :D but to be honest with you applying paint and changing moment arm has only been a small part of the blade flying quallity issue on the 412. The Chinook, Apache nor the Blackhawk blades, can not easily be compared to a 412 as the airfoil, twist and blade makeup are quite different. Having tracked a significate amount of the 412 fleet and supported a host of others; the inability to dynamic balance the 412 is on the whole a smaller effect than what was done in the late 80's and early 90's by personnel trying to make the blades look pretty. Back then the 412 blade had a habit of peeling paint after flying through a rain storm and large areas of paint would peel. Operators thought it necessary to feather and repaint the blades so that they looked presentable. Not knowing at the time that they would not only affect the span moment but also the flying quality of the blade. There are shims put on by Bell along the trailing edge of the blade to effect the flying of the blade. If that thickness is reduced the blade will fly significately different. Caveat Emptor!

I am in total agreement that if you paint or work on the blade that the span moment be brought back into limit. However, it is not the end all answer to blade problems. Not knowing how to properly refinsh the blade will cause a lot of additional grief.

[Flapping to Equity]

I have noticed alot of people talking about the actual painting process, but IMHO, the preparation process is key to the whole thing coming off (no pun intended)!
Preperation: Last time I did it (R22), I didn't prep properly and all the paint flew off mid-flight....man, what a fright!!
Second time round, I spent considerable time preparing, stripping back the old paint with a mixture of Coke & Sellys Heavy Duty Strip All (c). The mix was roughly 50/50. Let the mix work for about 2 hours....good time for a beer or 2.
Application: I sprayed first time round, but used a hand roller the second time. (Little tip: be sure to let the top dry before flipping over to do the underside. Again, took me a few goes to get this right!).
Once she's all dry, bolt those bad boys back on and Bob's your Auntie!
You may get a few vibs for the first few hours of flight, but trust me, if you got it right, they should be all gone by 10 hours after the paitn job (this is a great check to ensure you got it right!!).
Good luck!!:ok:

[Colonal Mustard]

Its a lot cheaper if you go for these, its the new official bank indicator:E

http://www.bbc.co.uk/essex/content/images/2005/09/07/fluffy_dice_203_203x152.jpg

[Rotormotor]

I agree with Colonal Mustard; I can't work out if all that scientific moment stuff is a wind-up or not? :confused:

Will someone tell me whether I should laugh or learn? :)

[ShyTorque]

The old wooden blades were best; just a couple of coats of Cuprinol every year and some beeswax polish every week kept 'em vibrating nicely, just like the day they were made.

Best to inspect for woodworm on every pre-flight though. If they migrated spanwise it could be a real problem :suspect:

[Rotating Star]

I agree Shy Torque, you can't beat natural materials. However woodworm is an issue. It's important when dealing with the holes that you fill in the same number on each blade otherwise you can suffer some serious imbalance!

[500e]

Bet shaky will have an input regarding natural blades, have you seen termite damage in AUS

[Rotormotor]

OK it's wind up time, lesson learned. :)