Tapered Blades

I forgot to explain that I had to take care of my customers first. That's why it's taking a little longer. Sorry.

PRA 73 will be here Saturday, so they will be the first to see them. If I have definite results by then, I will post. I'll post anyway, what the heck.
 
Welllllllll??? How did they fly?


If you are asking re me................they were definately different, good different.
Could feel better lift, less power for same cruise........downside..........they just wanted to keep flying on roundout / flare, but with more time, one would adjust technique to control that.
My main concern with blades in general, is weight..........big blades are getting damn heavy ( 30 footers and bigger ) composite is even heavier than same alloy.
This "heavy" getting into our perameters now, is possibly entering into the unknown, we could rue this venture............maybe not:noidea:
 
[ This "heavy" getting into our perameters now, is possibly entering into the unknown, we could rue this venture............maybe not ]

Russ, once you get past centrifigal force and coning flex in the book on 2 blade rotors its like the rest of the pages are missing.
There's a lot of different thoughts and theorys, none of them proven - mine included.

I am hoping to get my theory tested by maths and strain gauges so it can be laid to rest or proven.
If it is disproven there will still be a black hole in rotor theory.
 
Possibly the wrong thread for it but if you can nail down the exact cause of a number of low hour hubbar failures due purely to fatigue, I would consider that solid ground.

Some common factors appeared to be heavy machines, heavy blades, take off and landings. From what I make of the way the cracks developed it was due to both cone flex and inplane flex. Some possibly just inplane flex.
 
Well Peter, since you asked......

I believe the problem to be a combination that involves resonant harmonics. The material simply cannot dissipate the energy frequency. What I mean is, if you vibrate something at it's resonant frequency, it will tear itself apart. This is pure speculation.

And, yes this is the wrong thread....albeit a good one. You should start one.
 
Would like to add........i was privy to limited information the other week, A chap here is doing a thesis on metal fatigues, all part of his "degree"
Anyway a gyro buff got onto him to maybe look into our situation, chap agreed to include our hub bars in his research..........cut a long story short, already he has identified matters we must address, will be interesting to see the final outcome of his research.
His access to knowledgable folks, equipments, etc, and all for zip...for us, is great news indeed.

Stay tuned.................
 
Hi Kai - Check out posts #9 & #10. If the outboard 1/3 of the blades have the same area, all other parameters being equal, they will have about the same lift. In my humble opinion the taper both in chord and span, compared to a rectangular blade, will produce higher Reynolds numbers for each chord station. At the correct taper angle the lift will be linear along the span and not logarithmic as with a rectangular blade. This will give more drive to the middle 1/3 of the span and more able to power the outboard 1/3 driven lifting section. Also a wider chord at the inboard 1/3 will stretch out retreating blade stall.

Hello,

if you taper, than you have less surface area per running length, don't you. Again, I would achieve a similar effect with down-twisting the tips wouldn't I?

Kai.
 
Kai - It depends on what chord length you start with at the tip. If you have two 9' blades, one an 8" rectangular blade and one tapering blade that starts at 8" at the tip and ends at 12" at the root, the tapering blade will have more lifting area. Comparing the lift these two blades I found I could reduce the span of the tapering blade by about 1'.
 
..we got a guy here in Oz, makes composite blades and props etc........guys swear by them, he produces a "twisted....tapered" blade for those wanting the characteristics of that "type".
As well he makes the conventional profile. Even moulds into the leading edge a " protector thingo"........great for rain damages.

This same guy was approached by "Robinson" re him making blades for helos...

Certain fibres go into certain sections of the blade, and certain resins go into particular areas of the blade...........it was a real eye opener.

I know that Robinson had a bad problem with outsourcing when it came to rotor blade manufacturing, so much so that now Robinson makes his own blades. If the individual is NOT the one Robinson had problems with, who is this fellow? What is his business/mailing address?

tyc
 
Not the same guy..........he said no to Robo ( too busy with what's on his plate in general )

Re contact..........drop me a "PM"
 
Moved this post here, from the "Skinny Blades" post.

These 0012 blades start tapering from 7" at the tip (for the reasoning in this thread and Peter's post #28), and .5" per foot to the root at 11". I have found this shape will lift as much at 22' dia. as a 24' rectangular blades and the autorotative vector forces are also higher. The rotor is rigid and the blades are fixed at zero degrees. The collective and cyclic controls cause the servo tabs to twist the blades. The collective controls the amount of positive pitch and the cyclic controls both positive and negative pitch. This allows for higher pre-rotation rrpm, jump takeoff, soft landings, etc.

This will give those that asked, some idea of what these tapered blades look like…. Note that you can zoom in and out....
 
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Welcome Jordan, to the club of getting your head around it!

I look at failure of the servo-tabs in the same way I look at FW aileron failure….chances are good that there will be some exciting moments. The servo-tabs are interconnected to the swashplate and on to the flight controls. The inside blade control path is by two bellcranks and cables. The cables are run inside UHMW urethane tubing. I'm using four Morse cables from the flight controls to the swashplate and control rods for everything else.
 
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