"Modern" wooden gyro rotorblades

[Norm Mareeba]

Hi All,

I’ve been trying to find a ”modern” set of gyrocopter rotorblades. They just don’t seem to exits.

BW-19/BW20 plans have a set of rotorblades made out of solid Douglas Fir. They have a rectangular steel spar (1 1/2" x 1/ 8” x 10’). This spar sits in a routed channel and is held in place by wood screws.



Bensens B-8 rotorblades are made out of a combination of solid wood and plywood. They also have a steel spar that is held in place with wood screws. The spar is not rectangular, instead it is tapered from 2” to 1/2” at the blade tip.



I have not seen Monte Hoskins blade plans but I understand that they are made of plywood (simular to Bensens) but have a rectangle spar like the BW-19/BW-20. I don’t know if they are different in any other way.

These blades are fine but they are pretty low-tech and old fashioned. I also understand that they are not very efficient although I’m not quite sure what that means…

I’m thinking that with our modern power tools and modern glues we could turn out a much better rotorblade.

Before I go any farther, I’m not an engineer in any sense nor am I trying start any sort of business. I’m just trying to get a good set of blades at a price I can afford – that is all.

My first thought is that the blades should be glued together with Epoxy glue. Two of the aforementioned blades use weldwood glue – a bit unforgiving.

My second thought is forget the wood screws – bond the steel spar to the wood blade with epoxy.

On the steel spar subject, surely there is more strength than needed. Couldn’t you put lightening holes in it? Is it a good idea to have a light rotorblade? Do you need a steel spar? Couldn’t you laminate fibreglass between layers of plywood and end up with the same strength.

The above blades are balanced, front to back, with an airfoil shaped hunk of lead near the tip. Wouldn’t it be better to route a channel down the leading edge and fill it with lead shot (or the like) and held in place with epoxy. The whole blade would be balanced rather than just the tip…



Could the blades be made out of plywood stacked one piece onto of another, unlike Bensens jigsaw puzzle. EG. Take a sheet of plywood, 1/4” thick, rip it lengthwise into an 8” board, 6” board, 4” board, and, finally, a 2” board. Stack these boards one on top of the other and you almost have an airfoil shape. A power plane could quickly take off the excess…

I’m putting these ideas out into cyberspace in the hopes that someone will take up the challenge and design a modern wooden rotorblade. Please jump in with ideas, criticisms, numbers, drawings, whatever…

Thanks,
Bladeless in the third world

[Ga6riel]

I am aware that the famous Gougen Bros
boat designers and builders used to make wooden blades for windmills
they used their famous W.E.S.T. epoxy system that pioneered a revolution in wooden boat design. Wood cores can make sense from a structural point of view with glass or exotic skin and epoxy. Likewise wing spars for fast sailboats have become common place

[Bob]

Howdy !
Well you raise alot of good points.
why couldn't plywood be cut and stacked and glued and cut into a
rotor blade ...? it could but it would be very heavy !
....
I am in the proccess of building Monty's blades ( still waiting on the money for the meterials) but i will start them soon.
....
if you want High tech blades then do as Monty sujests and build the blades with a twist in them... I have a 4 degree twist cut into my blade bench already and that is all it takes.
...
Montys plans are almost exactly like the benson's plans except that he uses a plane steel bar not tapered that runs the length of the blade... and I agree that the screws are a pain...but NESSARRY !
there is alot of force out there and alot of weight ... it needs all the GRIP it can get ! I personally wouldn't trust an epoxie to hold the wood to the steel at rotor rpms !
....
Ballanceing the blades the way they have done I agree is a totally screwed up method ! I havn't tackeled that aspect of it yet but I do have a container of BB's here and fiberglass reson
so I may well attempt another method... but if you look at the blade and the weight simply mounting the blade a bit diferent may well cure the ballance problem of haveing to have the weight way out in front of the blade, because they are mounted about 1/3 the distance from the leading edge ... mounting them at the ballance point would be a better choice I think , I dunno I'm no engineer eather but it seams silly to mount them the way they did and have to ADD a big weight to correct it !
...
anyway, makeing the plywood blades seams the easiest way to go (and no doubt the cheepest) but I would take the time to put in all the screws ! its over kill no doubt ! but better to be safe than sorry !
as far as better blade plans ...I havn't seen any !
dollar per dollar their probly the cheepest way to go... albeit
not the safest... no doubt that buying Dragon blades or Rotodyne
blades is SAFER ... giveing that you have no idea weather the plywood YOU have will have voids in it or the steel you buy have a brittle spot... of if the glue will hold ...or if you did it all right in the first place....
but if you trust yourself then by all means go for it ...I am !

my 2 coppers !

Bob...........

[BUD ONEAL]

Don't use "cdx" or roofing plywood. If you buy plywood from aircraft spruce along with the spar and expoy,straps, bolts,materail for the rotor hub,for the rotor head,Then you have to have a press long enough to hold the blades together so that the glue can bond properly. Mess up one time then "dragon wings" become a real bargan.The wheel has allready been invented.You cannot do better that Dragon Wings.

[BUD ONEAL]

PS,
Even Dr. Bensen quit messing with wooden blades before his death.I had a long talk with him the last time that we flew him to "Bensen Days"and his thoughts were that the weather,moisture, was the death of wooden blades and would not go back to them.

[C. Beaty]

Below is a drawing showing the construction of the Bell-47 rotorblade.

The steel bar is solely a balance weight and serves no structural purpose. It is tied to the blade at the steel root fittings.

The laminated bitch/spruce serves as the spar and carries all loads.

I know of at least one individual who used concrete rebars near the leading edges as balance weights. Here again, the rebar must be carefully tied in at the root end doublers to be safe.

[Ga6riel]

personally I think the way to go is a core like balsa
glued pieces and machined to a profile, and inserted mass weight of rod
a lightweight skin of malleable ply with scarfed sections
and a final vacuum bagged epoxy/glass skin

the core keeps the skins appart and the skins are the real strength
its an engineered structure that needs to be carefully thought out
special consideration needs to be given to keeping the weight & ballance consistent

I think rather like high tech boat spars, they would be stiffer and perhaps a tad lighter

[Vance]

At the risk of bringing up something too fundamental, I believe the reason for the location of the weight is to put the center of gravity of the blade at the center of lift. That is generally near the 25% chord line.

A lot of ugly things can happen if this isn’t done. Some balance their blades a little further forward and got what they feel was a stability benefit, but I believe that moving it back is a particularly bad idea.

Attaching the weight well is particularly important because there is more than 300 Gs at the tip trying to pull that weight out of the blade. If it even slips a little I believe it will unbalance the rotor blade enough to tear the machine apart.

I feel wood is still the best composite out there and I understand the allure of the wooden blade.

Thank you, Vance

[C. Beaty]

The most setious shortcoming of wood rotorblades is that they're more expensive than metal blades. At least in the market driven commercial world where labor has value.

Bell switched over to metal blades toward the end of the long production run of B-47s to control costs, a move that upset many helicopter operators.

The wood blades had better performance and unlimited life. The metal blades were aluminum scrap after runout.

[Doug Riley]

Bensen-style wooden blades will likely shatter if you hit a bird. I imagine this problem could be overcome with a sheet steel leading edge.

You might as well make the center of the blade aft of the spar either hollow or filled with a light core such as balsa. Simply glueing up a solid plywood blank and carving it like a prop will make a very tail-heavy blade, as Vance says. Tail-heaviness is especially evil with a limber material like wood; some amount of it is tolerable with stiff metal blades and with props.

The Bensen airfoil section for wood blades is modified away from the ideal section to make it easier to build. Better performance is possible, at the cost of more labor, if you accurately reproduce an 8H12 or other rotorcraft airfoil.

A nicely-made set of Bensen wood blades is a gorgeous piece of woodwork. I flew Ron Menzie's old set for awhile, then sold them back to him for (I think) $150 credit on the new "exotic" Bensen metal blades. I grew a little afraid of these woodies because the oldtimer who owned the airport I flew at claimed that a set had come apart on takeoff there, killing gyro pilot Andy White. The wreckage of his gyro was in the airport dump for me to see any time I wanted.

I now suspect that this accident was a PPO, and that the blades shattered because they hit the prop or tail, as usual.

[Bob]

I was seriously considering modifing the plans or for that matter comeing up with my own design and makeing the blades 10" wide and 12' long with a thickness of 1"
the reason for this change from the ordinary is my high elevation
5000ft ASL also instead of a steel bar in the front of the blade I was going to use a 1"x 12' x 1/8" wall alum tube or thicker wall..(screwed to the wood every 6" with 3" drywall screws.)
depending on what was available.... however I may be moveing soon and getting off the mountian top so the added width isn't needed as much
so I will probly make them the standard 8" wide havn't desided yet.
....
I will not use Plywood that i can't buy at a hardware store...
the cost for aircraft plywood is so outragious its silly !
useing plane old normal Plywood CDX for outside use will do me just fine... I have seen good quality wood and bad quality wood in plywood ... You can buy VOID-LESS plywood from the hardware store!
it is more expensive but worth it .you get what you shop for ...not what you PAY for ! <grin>
even I admit if i had to buy all aircraft quality wood to build the rotor blades , I'ed be better off ordering a set of New Blades from someone ! new Rotor blades can be had for $1500.00 pluss shipping probly another $300.00 ... the aircraft Quality wood would probly cost you about the same ! ... where I can build my rotor blades for about $200.00 to $250.00

no their not as good as...... but they work and are safe enough
to use.... if you don't have money growing on trees in your back yard its a good option for you !

....
My original rotorblades were made of a airfoil shaped alum spar as the leading edge with a blue foam core covered with fiberglass , they were quite strong and robust I put them back togather 3 times before finally totally destroying them
if I could find the alum spar i would probly just make the blades the way they originally were made.
....
However I make them I will no doubt give the blades a coat of Reson to make them weather proof... I am not a believer in Paint,
as I havn't seen a paint yet that lasts not to mention keeps out moisture... but fiberglass reson sure does !

thats my 2 cents worth !
C ya !
Bob........

[Vance]

Originally Posted by Bob

even I admit if i had to buy all aircraft quality wood to build the rotor blades , I'ed be better off ordering a set of New Blades from someone ! new Rotor blades can be had for $1500.00 pluss shipping probly another $300.00 ... the aircraft Quality wood would probly cost you about the same ! ... where I can build my rotor blades for about $200.00 to $250.00

no their not as good as...... but they work and are safe enough
to use.... if you don't have money growing on trees in your back yard its a good option for you !

....
C ya !
Bob........

Hello Bob, How do you know they work and are safe enough?

Thank you, Vance

[brett s]

I've flown Bell 47's on both - schools liked the wooden blades because of the unlimited life, but they also usually hangared them so they didn't have as many weather related issues. Ag or utility guys were usually the opposite - the machines lived outdoors 24/7, most used metal blades.

The wooden ones had a bit less inertia, only noticable when doing touchdown auto's. They were more difficult to track & balance (or at least to keep nice & smooth all the time) because they'd change slightly with the weather.

[gyromike]

Chuck,

Were the blades for your 3-bladed rotor constructed like the Bell 47 blades?

[Ga6riel]

despite my vaunting the how
i should hasten to add
i would use extruded alluminium blades

you would need to be a craftsman of the highest order with a great experience in composites to resolve some of the design and manufacture issues

the gougen bros qualify in both respects