RAF rotor blade cracks

b.charlton

Junior Member
Joined
Apr 27, 2004
Messages
13
Location
dunedin new zealand
Noticed several cracks on my RAF blades last week, after the paint was removed it was confirmed that the cracks were in the fiberglass. The blades have done 350hrs and were probably manufactured about 1996. I had a 1" crack appear on the trailing edge about 8" ftom the root at 150 hrs , I had it repaired and it hasnt cracked again. These new cracks are futher out and originate from the trailing edge. I;m not keen to replace the blades with RAF ones, even if i can get them, anybody else flying with non RAF blades----How about you Birdy--i was thinking of using Jeff Henley Smiths Blades ?
 
have fix them

have fix them

send some piuc I fix mine every year. Do you let them stand freely when hangarred? I have a hosit device and I keep them pull and straight when in the hangar.

ChuckP
 
Chuck beat me to my question, Barry.

Have you supported your blades, to remove the droop, when not used?


Cheers :)
 
Barry, I had a similar experience last August as I was packing my gyro to trailer it to Mentone. I discovered a 1" crack on the trailing edge about half way down the blade. At Mentone, the experts said : sand through the paint and gel coat and patch with fiberglass. I made a three-ply patch; a narrow ply ( 1" wide ) then 1 1/2 " followed by a 2" layer. I sanded smooth and flew. It flew fine, but I wondered " when would it crack again ". I sold the blades to a willing buyer and bought a set of Sportcopter blades and hub bar. It sounds like your crack is not in a high pressure area ( lbs. / sq. ft. ). Some would say the repaired blades will fly fine; others may say " Cracked once, will crack again . " Tom T. Hall in MN
 
I used carbon fibber. also the crack problem is acentuated when you tight them down. we tend to tro a rope at the front pull them down and creat a bigg stres load. I now tight them to the front but I let them more loose . So if the wind wnat to move them side to side will be much free to do so.

Also I found that if you try to sand the repair to a perfect smooth line you eat up alot of fiber and resin. Leaving again a week repair for the crack to appera.

so if thiere is a small bump is not an issue.

Also you will need to do a static balance. This is what I am doing right now since I repair mine a month ago . I have it tracking almost equal. I think I have 1 blade with too much paint in the tip.

ChuckP
 
known problems

known problems

There are so many known problems with the raf blades it is a miracle that more pilots have not been killed. Their original time was over 2000 hours then cut in half, then after the Ortmayer accident someone said that time was cut in half again to 500 hours. The hub bar itself has been updated and the bolts used to secure the winglets to the center section I think have a 100 hour time limit.

Jonathan
 
I'm puzzled as to this statement, could you tell me how and why please?

Hello Charles,

Not easy to answer. Best thing is to look up the characteristics of the type of epoxies that are supposed to be used and compare them with the vinylester of the days when RAF was building blades.

I remember the first time I squeezed the trailing edge of an RAF blade, and it bent surprisingly easy. Elasticity seems like a good idea in a rotor blade, but in reality, the resin may be elastic, but the glass fibers used may not be the correct type, and they are not so elastic.
 
Hello Charles,

Not easy to answer. Best thing is to look up the characteristics of the type of epoxies that are supposed to be used and compare them with the vinylester of the days when RAF was building blades.

I remember the first time I squeezed the trailing edge of an RAF blade, and it bent surprisingly easy. Elasticity seems like a good idea in a rotor blade, but in reality, the resin may be elastic, but the glass fibers used may not be the correct type, and they are not so elastic.

There are lots of arguments for using VE versus Epoxy and visa versa. The statement Epoxy, Vinyl Ester means very little except describing generic materials, there are many categories especially with the epoxy. Epoxy can have much higher mechanical strengths than VE but generally requires post curing to get really good properties. The VE wets the fibre better cures at even low ambient and is less humidity sensitive during cure and can get good mechanical results without post curing. The VE is less succeptible to stress cracking and more resistant to UV degradation, it can be controlled in pot life quite readily unlike the epoxy. There are many considerations and arguments either way Epoxy - Unsaturated Ester (VE) but if I were to be constructing without a sophisticated set up I think the VE would be the choice. I don't actually know if the resin used by RAFwas VE or Epoxy but I too think the former.
Having disected two different sets of RAF blades I would make the following observations. The aluminium spar is constructed like the proverbial brick s--t house. The wrap around GRP is sufficient unto the day but I think I would observe workmanship as a problem. On one set of blades received brand new there was already seperation of the trailing edge on one blade which had not been glued correctly. The same set of blades were later damaged due to my inability to remember a gyro is not a helicopter!! On examination of the blades I found that the GRP was not bonded to the aluminium spar. The surface had been roughened by what looked like wire brushing or disc grinding but this is not really acceptable without a specialist primer for the VE (this is an area where the right epoxy would be of advantage), or it should have been sand (grit) blasted. The foam filling was incomplete. The other set of blades had delamination between the plies as if overcoating time had been exceeded or there had been some contamination between the plies being laid.
I personally would not worry too much about the cracking of the upper surface of the outer skin as it is likely to be surface stress cracking due to creep and the blades being unsupported for significant periods of time. Of course if that skin debonds and falls away there may be some interesting flight characteristics to cope with but the idea that the crack will propogate and the blade fall in half is in my view a total nonsense. Carefully manufactured I would have no problem with these blades and I think even when not entirely correct there is sufficient leeway for them to be acceptable for their promulgated life.
 
I thought the only use for vinyl ester these days was to repair wrecked corvettes. Am I wrong? Cause I wouldnt build a set of blades with VE if you paid me double. Besides....it stinks.
 
There are lots of arguments for using VE versus Epoxy and visa versa. The statement Epoxy, Vinyl Ester means very little except describing generic materials, there are many categories especially with the epoxy. Epoxy can have much higher mechanical strengths than VE but generally requires post curing to get really good properties. The VE wets the fibre better cures at even low ambient and is less humidity sensitive during cure and can get good mechanical results without post curing. The VE is less succeptible to stress cracking and more resistant to UV degradation, it can be controlled in pot life quite readily unlike the epoxy. There are many considerations and arguments either way Epoxy - Unsaturated Ester (VE) but if I were to be constructing without a sophisticated set up I think the VE would be the choice. I don't actually know if the resin used by RAFwas VE or Epoxy but I too think the former.
Having disected two different sets of RAF blades I would make the following observations. The aluminium spar is constructed like the proverbial brick s--t house. The wrap around GRP is sufficient unto the day but I think I would observe workmanship as a problem. On one set of blades received brand new there was already seperation of the trailing edge on one blade which had not been glued correctly. The same set of blades were later damaged due to my inability to remember a gyro is not a helicopter!! On examination of the blades I found that the GRP was not bonded to the aluminium spar. The surface had been roughened by what looked like wire brushing or disc grinding but this is not really acceptable without a specialist primer for the VE (this is an area where the right epoxy would be of advantage), or it should have been sand (grit) blasted. The foam filling was incomplete. The other set of blades had delamination between the plies as if overcoating time had been exceeded or there had been some contamination between the plies being laid.
I personally would not worry too much about the cracking of the upper surface of the outer skin as it is likely to be surface stress cracking due to creep and the blades being unsupported for significant periods of time. Of course if that skin debonds and falls away there may be some interesting flight characteristics to cope with but the idea that the crack will propogate and the blade fall in half is in my view a total nonsense. Carefully manufactured I would have no problem with these blades and I think even when not entirely correct there is sufficient leeway for them to be acceptable for their promulgated life.


OK.

But they cracked.

There is no argument. Don't use vinylester, or pay the price later.

You will never make a composite rotorblade with a frequency above 100 CPM with vinylester. You must use epoxy and you must post cure it to achieve a rotorblade stiff enough.

Also, sanding a spar with course grit sandpaper is only going to get you a mechanical bond. Not good enough. You must make a chemical bond to the aluminum.

I have never had a set of composite blades I made using epoxy ever, ever crack, and most of those were for helicopters.
 
I thought the only use for vinyl ester these days was to repair wrecked corvettes. Am I wrong? Cause I wouldnt build a set of blades with VE if you paid me double. Besides....it stinks.

Yes you're wrong! Anyway you can get addicted to the smell of styrene, the peroxide's great for making bombs and using acetone for cleaning is cooling but can get you arrested in some countries as they seem to have other uses for it. Mind the MEK and Xylene can be fun too not to mention the highly carcinogenic hardners. Just so you know I'm not biased!
 
Thanks guys, but the bottom line is the blades have cracks in them and when i'm flying with cracks in my blades it makes me nervous, i feel i should buy blades that dont crack after a few hundred hours whether i support them or not.
So what other blades are we flying succesfully in our RAfs?
Barry
 
Barry,

If you want to stay with composite Patroney makes a great blade.

Mitch
 
I would suggest getting a set of Sportcopter Blades......I own a set of 28' x 8.5".

They are beautiful blades. Most guys switch over to them & they are also supplied with the Sparrowhawk gyro.

http://www.sportcopter.com/sport-rotors.php
 
I won'y get any deeper into the merits of Epoxy/VE resins it's too complex for this forum and bland meaningless statements.
The sportcopter blades look good, anyone got an idea of the weight difference and rotor speed differences for same lift?
 
I won'y get any deeper into the merits of Epoxy/VE resins it's too complex for this forum and bland meaningless statements.
The sportcopter blades look good, anyone got an idea of the weight difference and rotor speed differences for same lift?

Yes, I do. Also, I'm sure you'll find that there really isnt any subject too complex for this forum or the people who use it. We have people here who can teach you many things...try listening.

I don't think you really understand the danger of using VE in rotor systems otherwise you wouldnt be touting it's benefits. Do some research.

How do I know? I build the damn things. I wouldnt risk it. VE has proven itself unreliable and dangerous.....why even suggest that it can be used?

Jon
 
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