Blade manufacturing story
 

Worth a read....

https://www.jetwhine.com/2018/06/ens...r-blade-maker/

Wooden blades. On the old Sycamore one would check the integrity of the wooden blades by grasping hold of the end, the blades drooped that far, and whipping the blade. As long as the wave went up to the root and back again smoothly the blade was OK>

Thanks,FED, I do that with my arms and legs every day.....

Maybe the Enstom folks could school the Robinson's on how to build MRB's.

Enstrom Blades
 

Compared to most, exceedingly good value, look after them and they will last a very long time.
I remember years ago we use to pop rivet the trailing edge if it debonded, Enstrom were not selling any blades so stopped that.:ok:

To believe that a given metal blade design is inherently more robust than a properly designed composite version is patently laughable to any rotors engineer who has any real experience from the last quarter century.

Sans,
Carbon fibre is not the utopia you think it is, when it let's go it really let's go and more worryingly with no warning. Have seen it on a very expensive carbon mountain bike. Yes I know it is not a blade but wow
!!!!!!!!

The Kmax has a Sitka Spruce spar in their rotor blades, although Kaman has recently initiated a program to replace them with a Composite design. https://www.kaman.com/news/kaman-lau...-blade-program

Never implied it was utopioan, but after 15 years of designing rotor blades, today I would never use metallic primary structure unless it was a design purely for cost (and not carrying humans).

Wood was the original composite material!

interesting subject - My dad, lets call him Barking,was a racing yacht builder when they built large free-standing carbon fibre masts they found that if all the fibres where aligned and strong the thing made a certain ring when tapped and if not all correct the tone changed. Kelly the designer apparently sold the technique to the yeovil mob - perhaps one of you learned types could confirm or deny this

Could you elaborate please.

Dagenham - I think the 'tap-test' is more about identifying any voids in the structure - areas where the fibres and resin are not homogenous and weakness could be present.

The Lynx Composite Main Rotor Blades (CMRBs) were checked regularly in the hangar using a 2 pence piece which was tapped along the blade whilst listening for any change in tone.

Didn't Robinson mandate a similar tap test to 44 blades some (12 ish) years ago? I remember watching a bloke do this so religiously that I expect those blades would probably look like golf balls now. Though they're robbo blades so would be fekked by now anyway. ;-D

I remember hearing that the a tap-test procedure for Sea King blades uses a halfcrown. Whilst in-service non-destructive testing for current platforms includes far more advanced techniques (such as ultrasonics), Westland inspectors will still carry a halfcrown in their kit for the Sea King...

Sans

Wish you would go talk to HTC about 500 blades then. They can't even produce them weighing the same, ha da recent set where the tip weights were 60 grams different !

1. Largely isotropic materials like classic metallics (even forged parts) are inherently less weight efficient for a given design than composites that take advantage of the orthotropic structural aspect of fibers within a matrix on a blade.
2. Metal blades, for an equivalent fatigue life, will always outweigh a properly designed composite part (see #1)
3. Metal fatigue failure is usually sudden and typically less predictable than a properly designed composite equivalent.

I have a question about composites, specifically I wonder about the state of the art in NDT? I remember the middle east 139 that lost the empennage ( on the ground ) due to a failed repair in the carbon fiber... Given the large amount of composites being used in modern airliners, I'm guessing testing composites must have advanced in recent years. What kind of testing exists today to detect internal manufacturing defects / operational damage in modern composite structures? How does state of the art compare to eddy current testing, x-ray, etc used in metallic structures?

I must admit to trusting older composites like fiberglass, but still regard carbon fiber composites with some distrust as a "new" material, despite the fact that they're not that new anymore, and are widely used.

First carbon-fibre compressor blades tested in service: 1968 (unsuccesfully).
First carbon-fibre floor panel installed in an airliner: 1970, flew in service for eight years with this panel.
First carbon-fibre brake pack installed on an airliner: 1972, test version for the Concorde brakes.
First carbon-fibre flight control certified for use: 1979, B727 elevator (five sets).

Not that new if you ask me.... ;)

In the late 1970s/early 1980s the RAF began replacing the old metal spar blades of the Puma HC1 with brand new, composite items. We were shown photos of these chopping down telegraph poles etc which really impressed us.

A couple of years later it was discovered that a faulty batch of carbon fibre had been used on some blades and guess who had bought them?

An NDT rig was sent out to Germany. It consisted of a jig with a hydraulic ram to deflect the centre of the blade. Sonic transducers were attached to the blade under test. The idea was that how much it "creaked" determined how good (or bad) the blade was. We were walking across the hangar to morning brief as the first "non destructive" test was being carried out. There was a loud "BANG" and the blade snapped!

We weren't impressed after that. :eek: