Rotor blade restrictions

[mdelzer]

While there isn't a snow balls chance in hell of getting a new Vario Allouette III anytime soon, it does bring up an interesting problem. If you live in the US and build one how do you deal with the rotor situation?

Vario recommends aluminum mains and tail because of the angle of the turbine wash but aluminum blades aren't allowed by AMA. Do you go with something composite and change them out from time to time and hope they don't delaminate? Or do you go with aluminum and not fly at an AMA field or event, which would take all he glory out of having such an amazing machine if you had to fly it by yourself?

At what point is there a provable difference between the kinetic energy of an aluminum blade vs. a composite blade? I can see aluminum having more potential to cause damage on a smaller machine then on a larger machine. I think the kinetic energy of either would be devastating enough from initial impact that the follow up would be negligible.

Considering that only the larger heavier turbine machines are about the only helis that would really benefit from the added safety of aluminum blades, I wonder if the AMA would allow for a special category like they do for the heavy turbine jets?

Or last but not least is there another solution I'm missing?

Mark

[cbergen]

You're right about the kinetic energybeing very similar, that's not the problem.

IMHO, the reason for not allowing aluminum blades has to do with metal fatigue.

Consider this, most, if not all, full scale birds now fly with composite rotor blades. WHY? Unlimited life span. The inspection criteria is very easy, it's a visual, with a tap test, in most cases.

Aluminum has a limited life span, they MUST be replaced at a given interval, must be destroyed at that time to prevent someone from trying to save a few bucks and selling them off or reusing them beyond their lifespan.

All the arguments for and against have been brought up before, these are only my opinions, and may not be the actual reasons, but they make sense to me after working in the full scale field and having to deal with both types of blades. Btw ISIS indicators suck....:)

Heat is definitely a problem in your application. I've heard of people using a rotor brake to hold the blades somewhere other than right over the exhaust untill after startup.

[mdelzer]

Thanks for the reply Chris. I never thought about the stress factor of it. Almost makes the whole idea of having ~$15,000+ wrapped up in a heli a bit stressful, no pun intended. I'm sure my first turbine will be pod and boom anyway.

Mark

[chopper jockey]

Where does the AMA get off from going against the Manufacturer's recommendations? Another example of "don't know, so let's ban it" I suppose.

[bcook01]

Doesn't make sense when you can magnaflux them, or time expire them based on mfgr recommendations.

Problem with composite is that you CANNOT determine fatigue or estimate failure until such time it fails..... :arggg: With NTSB it is a hair-puller that is going to create problems in the future.

Why argue with the AMA since they have a multitude of structural engineers on board to make the decisions........ that is...... they have the experitise to oversee the manufacturers. :thumbup:

or

Maybe they do not want to argue with an insurance underwriter (who thinks it is worth more money for a blanket insurance policy) to cover the "perceived additional risk"........ more like the truth.

Bob

[cbergen]

And you're typical hobbyist, who has to clear any expenditure's through the wife is going to pay for having them magnafluxed on a regular basis, and then throw away a "perfectly good" set of blades 'cuz their "out of time"??!!

Right.....Especially given the COST of the blades in the first place.

You guys are forgetting the fact that NOBODY is stopping you from buying and flying these blades. You're just NOT covered by AMA when you do. And you cannot fly them at an AMA sanctioned event or field.

If you're doing commercial work, then AMA does NOT apply ANYWAY!!

[AandP]

How do you magnaflux aluminum?!

[cbergen]

Giving the benefit of the doubt, I assumed he meant NDT of some sort....:)

Whether dye penetrant, which is very inexpensive to do (once you've purchased the chemicals)....Ultrasonic, eddy current, or radiological,(all of which can be very expensive), the point is can the individual hobbyist on a budget be expected to abide by these inspections and throw the blades away when it's time?

[AandP]

A waiver holder is expected to keep a log of flights on a turbine model or not to fly a turbine powered model at night. If one has that much time and money rapped up in a model $70 for a spot check kit would be a drop in the hat.

I would also think that these blades would be good for several hundred hours in service, more than most models fly in a life time. These blades have been flying in Europe for many years with no problems that I've heard of.

[AandP]

I bring all this up because I'm trying to get my waiver and figuring out what the AMA want and why has been a little confusing.

Some of the AMA's thinking does seem to be "behind the times" or the resson for a perticular rule not given, leading to assumtion.

[cbergen]

I understand the process may be a little confusing, BUT the only way changes are made is to bring the wanted changes to the board, the pros and cons are discussed, then any changes are enacted. Obviously this is a simplification of what MAY go on at AMA.

You as an A&P, I assume, are well aware of the requirements for tracking life limited parts. The question I STILL have to ask is WILL the HOBBYIST do what is needed, or is it "just too much work", "I'm only here to have fun, not keep logbooks...."

Even guys with the Jack to buy these birds sometimes can't "be bothered" to even keep up with normal R/C Heli maintenenance!!!

Here's a question, and only because I really don't know, does the manufacturer of these blades have a TBD? Have they come up with any necessary testing requirements? Have they been tested to failure?

Carbon or Composite blades do not require these types of inspections, have unlimited lifespans, and is EXACTLY why more and more full size heli's are using them!! Why do we want to go backwards???

[AandP]

I am an A&P and all too familiar with life limited parts.

I think most who would shell out over $1200 one set of rotor blades would do it, if for no other reason but to protect their investment. There are, of course, some who would ignore inspection intervals or time in service limits, but how would it be regulated or enforced. (short of the total ban of metal rotor blades all ready in place)

I have not been able to find any info on a TBD or what testing has been done by the manufacturer.

What I would like to know is the actual reason for the ban.

I'd be more worried about someones receiver battery thats been in a model a couple of years dropping a cell and loosing control than a set of metal blades coming apart. Mostly because the odds of seeing a set of these blades in flight will be rare. Lots of people have that battery pack that they'll "get around to changing someday".

[cbergen]

And that certainly happens.

Until the manufacturer goes through the process and convinces the AMA that their blades are safer/more reliable, better,etc, etc, then we're left with what we currently have which are extremely good quality carbon fiber blades with unlimited life spans and NO inspection criteria. What exactly is better about any Aluminum Blades?

Why would one spend $1200 for blades when the same or better performance can be had with Carbon at a much cheaper price?

[mdelzer]

My original intent for asking was due to the direction of the exhaust blast on 2 of the newer Varios, so they recommend to only use aluminum blades. If I knew it was safe to get away with carbon blades they'd be on their for sure. Here is another spin, maybe Vario has other reasons to recommend the aluminum blades. Maybe 1200 reasons :D I'm not trying to start a war, I'm just saying...

Mark

[chopper jockey]

most carbon fibre "prepregs" melt at 85 deg.C. Some will function up to 150 deg.C. At these temps the epoxy resin goes soft and the blades will fail. Obviously in this application, the metal blades would be the better and safer option. Perhaps the AMA can't work that one out ?

[mdelzer]

The problem is like Chris said, who is going to go lobby to the AMA for what would realistically effect 5-10 members EVER.

Mark

[Peter Wales]

I think the problem is much more basic than you guys are stating. These rules were written by airplane guys and adapted for helis. If an airplane had a metal propeller it would be a die casting and there would be bound to be someone who had a rough landing and bent it. He would then get a pair of pliers and straighten it out to within a thou. Maybe he would need a hammer as well, but he'd get it straight, sorta!

Then we have the stress fractures the AMA fears, our intrepid engineer fires up his engine and runs the prop at 15000 rpm and it flies apart and hurts someone. It would be the same with tail rotor blades, a touch on the ground in an auto and one gets slightly bent. No problem, just straighten it up. Then it fails.

So, the AMA bans them, now you cant do it.

I heard that aluminum blades didn't break and was going to to go to the AMA wth the proposal that they should be allowed as they were inherently safer than carbon blades in a crash, however, I found out the hard way that they do break so I cant go to the AMA with that proposal. I still think they are safer in a crash than carbon blades. If you got hit by a blade end which flew off a crashed heli, would you rather pick a piece of metal out of yourself or spend the rest of your life trying to pick carbon fibers out. They will both do the same damage to your body, but the after effects from Aluminum would be much less.

As for why aluminum blades are better, well, they are extremely rigid, precisely matched in CG and weight and dont melt when used in a turbine. I liked the ones I used and I think if they were allowed, they would be the blade of choice for hard core 3D pilots. The manufacturers have been selling these blades in Germany for many years and have tested them in the lab and field under all sorts of extreme conditions so I would be very confident putting them on helicopter.

However, its all moot as the AMA is still run by plank pilots and there would be no good reason why they should change their opinions just because a few guys would like to use them. So, we cant import certain Vario models as they have to have metal blades. Somehow I dont think the AMA will care very much.

[mdelzer]

Ironic how a special interest group would have not interest in it's own special interest groups :)

Mark

[Laurens]

I'm with Peter, if your going to get hit by a 90 sized blade (smallest size for turbines I think?) You don't really care if its carbon or aluminum

[mdelzer]

Honestly that is kind of the whole reason I posted this to begin with. Sure it's dangerous, but is it anymore dangerous then a carbon blade? Probably less in fact, but it probably will never matter over here.

Mark

[sgil123]

You guys kill me! Peter Whales gives you a great explaination as to why you cannot use metal blades in the US. After that the next post sends a slam. OK so If you would like to have a copter with metal blades why wouldn't you or a group of you go out and get an insurance underwriter start a new chapter and call it the AHA (American Helicopter Assoication) start your own flying feilds and sanctioned events.

The thing is you can fly aluminium blades in the US, the AMA Will not cover them and you cannot fly on there fields

[mdelzer]

You guys kill me! Peter Whales gives you a great explaination as to why you cannot use metal blades in the US. After that the next post sends a slam.

What are you talking about? Perhaps I should explain, I meant it was ironic that the AMA (special interest group) doesn't have any interest in supporting the special interests of it's members. I have great respect for Peters opinions as they probably have more merit then most people when it comes to scale, turbine, and global aspects of the hobby.

Mark

[sgil123]

My apologies to you! I was assuming (and you know what happens when we assume) that the way your reply was written you were refering to Peter, again I apologize

[mdelzer]

No problem, my intial reply was a bit ambigious.

Mark