twisting rotorblades
twisting rotorblades
(OP)
i plan to build rotorblades by machineing a main spar and have a ribbed tail section.how to twist? my original plan was to twist the billets befor machineing and let them return to there natral state. but i beleive this would be difficult to yeild reliable results. can they be made strait and then bent? would that comprimise the strength? many production blades almost all are twisted. how is this done? any thoughts sugesstions or knowlage would be awsome thanks
RE: twisting rotorblades
Mike Halloran
Pembroke Pines, FL, USA
RE: twisting rotorblades
CODE
Propellers are made normally of wood, aluminum or composite with optional angle pitch adjustment in the hub.
Helicopter blades are mostly made of composites due to thier length. Are shaped like a plane wing and are pitched by a swashplate at the mast.
CODE
I think the short answer you want is: "they are forged"
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RE: twisting rotorblades
The process is extremely difficult and costly and is probably why composite blades are all the rage - much easier to lay up than twist :)
RE: twisting rotorblades
RE: twisting rotorblades
Rotor - Blade - NACA 00xx - IRAT - Torque Tube Method
http
Dave J.
RE: twisting rotorblades
This page is the best CH-47 resource on the net and has a good decription of the make up of the rotors. The decriptions and pictures are about half way down.
http://www
RE: twisting rotorblades
Nowadays with composites there are a bunch of different techniques used. I am not sure of the scale of your blades but I have fabricated smaller blades using Rohacell Foam and Pre-preg carbon fibre. Though the process is fairly lengthy it is still the easiest. First, and most expensively you design a mold that incorporates the blade twist. You then use the foam to shape the blade and cover this with the pre-preg C-F. You then bake the mold in the oven (not normal home oven obviously) and out pops a blade. There is a lot of very specifid other things you must do but that is the gist of it.
If you are planning on machining an aluminum (or whatever) spar I would recommend doing that without the twist and then twisting it after. You will have to be very careful to apply the same twist to each blade.
You have your work cut out for you.
RE: twisting rotorblades
Also ours only have a hollow metal core made from a flattened tube with composite for the rest.
Dave
RE: twisting rotorblades
How can you say that helicopter main rotor blades are not twisted? This is one of the easiest ways to improve the Figure of Merit of a rotor and some degree of linear twist is used on pretty much every main rotor blade in use today. Almost all of the have a linear twist of somewhere between 8 and 12 degrees from root to tip always, to my knowledge, in the form of a nose down twist (negative).
I know for a fact that the Blackhawk has a substantial amount of blade twist (somethign like 11 to 15 degrees) though those blades use a non-linear twist distribution.
For Tail rotors it is more likely that the blades are not twisted but even then a good number incorporate some degree of twist.
Where are you getting your facts?
RE: twisting rotorblades
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Greg Locock
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RE: twisting rotorblades
RE: twisting rotorblades
We have CMM'd an original spar and it does not match what the drawing specified, but it is a timed out blade so perhaps I should not take that too harshly.
RE: twisting rotorblades
Is this for aerial firefighting use?
RE: twisting rotorblades
RE: twisting rotorblades
These blades are going on a restricted category a/c. Fires are one opf their tasks but they do construction and lift jobs also.
RE: twisting rotorblades
I think you will find that "We have pretty much solved all the problems in resurrecting the parts except for the twisting of the aluminum spar" means you have not solved a vast majority of the problems. How can you attempt this without the type data to dictate tolerances, spar wall thicknesses etc? You will surely have to certify the bonding process via significant coupon fatigue testing too.
Couldnt you more easily buy them from Sikorsky?
RE: twisting rotorblades
As to the second comment, we have all the necessary data to do the project. Our customer has 95% of the original Sikorsky data/draings, including the spar and titanium cuff. The remainder we have had to purchase or reverse engineer. There is significant testing that will still be required for the PMA, but we have built the metal bonded items of the blade(pocket and fairing) for some time. The relevant Sikorsky bonding processes we have accomplished in the past and include peel/shear/fatigue tesing.
Sikorsky has not supported the aircraft these are going on (CH-54B/S-64F)since they sold the type certificate to Erickson Air Crane in the 90's. A VERY similar blade is currently used for the CH-53D and MH-53J. I assume Sikorsky still supports these. Besides, our customer is looking at long term supportability of their aircraft. Their fleet is growing.
RE: twisting rotorblades
Interesting how your customer has 95% of the drawings since Sikorsky sold the whole package to Erickson. They certainly shouldn't have the reports necessary either since they too were part of the deal.
So which route are you taking? Similarity??
RE: twisting rotorblades
I should have differentiated the F and B models. Our blade project is for a different customer who operates seven B models and three A's. They are all restricted category. The drawings they have are all Sikorsky and pre-date the Erickson purchase of the type ceritficate. The blade drawing effectivities "generally" show that blades and parts for the CH-54B also apply to the S-64F. Since the CH-54 was military, a lot of info is available through FOIA.
We are doing the STC by similarity. A few minor changes to detail parts that are being blessed by our blade DER and testing.
RE: twisting rotorblades
The twist is very beneficial in load lifting. Ray Prouty has told one helicopter manufacturer that an 8 degree linear twist would allow them to pick up 43# more than the straight blades, with all else being equal. This is on an 1500# gross wt. helicopter.