Blades revisited. Dangerous shortcomings.

[Sesame]

The only Torsions I ever owned developed what looked like chip marks all along the leading edge, enough so I stopped using them, and I dont fly anywhere near the level of Barney.

This is all quite worrying

[Sqwidge]

Rotor blade manufacturers are just pumping them out by the thousands to make a profit so they won't be perfect, if each one was hand made then the likely hood of it being faulty would be reduced.
You also have to remember that rotors are designed for hovering to sports flying only as this was their intentional use, I personally don't think that blades were ever designed for the use of 3d, yes they made the blades stronger to cope with 3d but not actually ever designed for this purpose.
I recently was given from a shop a pair of '3d' blades and they were paper thin (they are actually advertised as Align 3d), the second I got my heli up they failed and I deemed them sh*t forever.
What we need is someone that can 3d and knows about blades ie Barney and a blade manufacturer to get together and discuss the actual happenings of a blade whilst in 3d flight.
Cant say they would be cheap but provided you don't crash through pilot error they are sure to last if designed properly.
As a final thought: You all use expensive blades and have found faults with them, I use proper carbon blades but they are imported from Hong Kong and I have never had a problem with them, I'm not a 3d master but I do like to throw my heli about a little and they take it and they are only £7 a set! They may be cheap and cheerful but they do a job that obviously the more expensive ones can't.

[trillian]

As a final thought: You all use expensive blades and have found faults with them, I use proper carbon blades but they are imported from Hong Kong and I have never had a problem with them, I'm not a 3d master but I do like to throw my heli about a little and they take it and they are only £7 a set! They may be cheap and cheerful but they do a job that obviously the more expensive ones can't.

You must be talking about small blades, like 315 / 325mm.

It is much easier to get a small blade that can cope with the stresses because the thing about scaling up or down is that tensile strength remains the same for the same material, so the bigger you make something out of the same material the weaker it becomes, relatively speaking, without increasingly clever design mods.

So the geatest challenge is for the 90 size blades to cope with everything thrown at them.

[Edders]

I can comment on the Torsions. I too have had teh same issue and ive been in discussion with petr and the crack you see is just the gel coat and not the carbon. I too wasnt sure about flying with them, but after speak with petr he too has a set with fine cracks on his machine to quote
" You can not be afriaid to use all of them it is only on the surface and inside the material is ok. I had that problem once on my T rex 700 and I use that blades till this time whitout any problems."

Hope this helps

Edders

[Ashley Davis]

I have the same issue with Torsion 710s of the chips all along the leading edge of the blade...... I need to get the changed, I'm not sure if this particular issue has now been resolved.

[Tom Burgess]

I have the same issue with Torsion 710s of the chips all along the leading edge of the blade...... I need to get the changed, I'm not sure if this particular issue has now been resolved.

I had a set of 690's that developed holes on the leading edge. They whistled as I spooled up Got them changed but they only lasted 6 flights before I crashed. However, the holes on the originalss developed after 3 flights, the replaced set had no holes other than crash damage.

[BobJ]

Hi

The vast majority of blades are still hand laid up using resin and dry cloth as aposed to using Pre-preg materials.

Using pre-preg gives much better control of the make up of each blade and with this system there is no possibility of any of the blade not getting fully "wetted out"
Obvously human error can still creap in but it's certainly the way to go, NHP are one of the few who use this process and have from day one.

Cheers
Bob

[Smoothound]

There is another thing to bear in mind I guess.

Although a lot of these blades do seem to be suffering from manufacturing defects rather than general wear and tear. No one has suggested any sort of MTBF value. How many flights of hard 3D should a blade be expected to withstand? Is it fair to expect them to take that sort of abuse for week after week after week? Maybe you hooligans and even the sport fliers should start thinking about the blades as a consumable generally not just after a crash

[barney]

Ok here some others I've chopped so you can see the internals. NHP Razor Pro 680. This is the original with carbon Tow layup with a foam core. The NHP FAI 680's look to be extremely similiar. (note the brass bush is removed) There is no retention wire for the tip weights. The Light Grey area is a Foam core so the root is essentially Hollow relying on the Skins/Bush for strength.



Next is a MAH 690. This has a solid root that contains a retaining wire again the bush was removed. Not sure If its just a fill of Resin/Glass Bubbles between the skins. It has a wooden (spar (looks to be Balsa) that tie upper/lower skins together that buts into the Root area leaving the blade hollow.



No 3 is a crashed Torsion 600 Glass blade that I've prised open further to reveal its Layup. As you can see the Carbon Tows are dry and not wetted through properly. Interestingly It uses Carbon in all the right places, has a retaining wire and a Root design without a sudden step. The root is also solid with a brass bush but only extends a small distance towards the tip, Balsa Spar as above. The joining appears to be very minimial (resin/bubbles mix). It's actually a very stiff blade which I enjoy flying but can be problematic to track if theres play in the model control system.

[BobJ]

Hi Barney

I do have some knowledge on the NHP construction and can say that the fact the root is hollow is not a factor, the root is made up of lots a layers of material lied out in a specific way and is very very strong, the only possible problems could be human error if some one forgot to build the blade up with some of this material (unlikely but possible) of there is a problem with the resin not fully curing though either not been heated for long enough of a mistake in mixing by the suppliers again both possible but unlikely.

The "check strap" of material at the root is also feathered so won't give a stress point where it ends.

Regarding the lead weight, I know they went away from a securing wire years ago as this has it's own issues, the lead weight is first roughend then squashed to shape, then fitted ina fider glass sleeve which is then wrapped in resin strips before been fitted in to the leading end of the blade duering construction, so they do go to some effort to secure it.
Ofcourse smash it into the ground or boom fast enough and the lead "might" come loose but not with out a fight.
Maybe flying style will start to dictate that the lead should have a check strap around the root again, not many blades have this at this time I think.

Cheers
Bob
Note I have no connection with NHP these days and don't fly there blades but I would never have a concern about there strength.

[barney]

I'm no engineer but it seems pretty obvious to me that It's both a design and construction issue combined with poor quality control .

You dont want any sudden tapering near the blade Roots..Torsion 690's GLX as all this does is point load the forces just outboard of the blade Root area where the bending forces are at there maximium. I also dont like using blade washers but somtimes you have no choice.

Ideally a Solid Root as blades are not only subjected to pull but also a lot of twisting forces at the Grip area and solid prevents crushing as the try to twist in the Grips. Any weakness here will cause the Bush (as its needed to tie top/bottom skins together) to work loose eventually with the posibility of it pulling through.

A Spar Ideally should be used to spread the load out along the the length of the blade especially the inboard 1/3rd. Or a varying stressed skin layup using a foam core for rigidity is another option. Not much point in a stiff blade if it flexes at the Root. Retaining wires certainly in larger blades should be mandatory.

I was told recently that the Trex 700 is particularly hard on blades and at least one Manufacturer has designed a specific blade for this model as it had experienced blade Root problems with its normal offerings..

Hope this has been informative and I strongly suggest you pop your blades Off and look very closely for any flaws for impending signs of failure. Using a Digi Camera in good light allows you to see things that are easily missed by the naked eye

[barney]

Hi Bob, have to agree, good quality control is essential and the skins of NHP's do indeed appear to be thicker than the Norm at the Roots and me chopping up old blades does not unfortunately show the quality aspect unless its very obvious.

I'm not keen on the hollow roots around the bolt hole as to me it leaves the possibility of a small amount of compression occuring as the blade twists both along its length and across its chord around the Bush which could result in problems further down the line.

Interestingly the Radix uses no bush and and has a solid root which tapers into the blade LE. This is the only one that has this taper to spread the load beyond the immediate grip area. Others rely on the Layup of the skins for this.

Brian

[Tim Procter]

Interesting thread.

Glad you brought this subject up Brian. Well worth knowing.

[Smoothound]

Like I said maybe we all assume too much.

Fit a set of blades and fly them till we wreck them in a crash.

Maybe we should all be treating them as a bit more of a consumable? 50 flights and then change for example? 100? 200?

[Sqwidge]

Well I stand corrected.....my cheap blades just caved on me and only after a handful of flights although in all fairness this is my first pair to do this and they are not carbon they are cheap foamie/plastic jobs that I bought by mistake ages ago, my carbon's were fitted after this happened literally ten mins ago.



Sorry its not clear it was taken on my phone which is more pc based than camera based. It looks as though the outer skin caved and started to slide, it did this whilst I was hovering about 4 feet off the ground, I managed to land ok but wasn't impressed.



And to think all I did was hit idle up and the rotor speed went to 100%!