Anyone interested in makeing a 3 bladed prop ?

[asra]

Ingenuity and perserverance will often triumph over the mighty dollar,or the lack of it. Keep goin Bob. You are obviously a man that hearsthe music played by the little people at the bottom of the garden.To many folks these days dont and are blind as well.I wish you well.Robert DunnMackay. Qld.Growing old is good while it lasts.

[asra]

Good going, Bob!My employer made/bought/resold loads of conventional 2-blade wood props back in the '80s, sold several thousand of them as part of our thrust packs for microlights, but we always wanted a ground-adjustable prop and we (briefly) tried something similar to yours made up from two damaged standard props. It held together, too, despite balance problems. Much too much hand labour to be profitable!The root was made by turning down the 'half- prop' bosses much like yours. Then S-glass roving (Structural glass 'string') was laid up from partway along the blade, down to the root, around it, and back up the other side. The theory was that the continuous rovings would carry the stresses all the way to the root. Seemed to work.Had to taper back some blade surface to maintain the airfoil shape before/after the glassing - we made some estimation of the amount by calculating the stress in the blade, and then allowing more-than-enough glass to take that stress.The result was fairly rough, but cleaned up a lot with some filler and a final thin layer of glass cloth to keep the weather out of the structural stuff. (WX is rough here in the UK) I think we were using vinylester resin, but today I'd use epoxy. If you want to know the stress in your blade root, you need to add the weight of your blade to the guessestimated weight of glass & resin,& with the distance of the blade CG from the centre and the design prop RPM (engine RPM / reduction ratio) you can calculate the load placed on the root. Seem to remember we had to do this two or three times, since the estimate for the glass/resin was not enough to take the load, first time out. Our UK rules want -large- safety factors on things that fly, which makes sense, especially with composite props.The equations for root stress :F =( M x V^2)/R LbfM = wt of 1 blade lbs/32.2R = Radius in Ft to CG of BladeV= 2x Pi x R x RPM/60Take the load (we ignored the strength of the wood) and divide it by the rated strength of the glass you are using. (The wood may be strong, but it is more elastic than the glass, and the stiffer glass structure will be taking most of the load in most modes)So if you get (say) 800 Lbf of load, and the glass is rated at (say) 8000 Lbs/sq" for this duty, you need 800/8000 or 0.1 Sq" of glass cross-section. If the circumference of the blade root is (say) 5", then the layer of -glass- will be 0.1/5 or 0.02" thick - that's 20 thou thick.Equally, your rovings will have the x-sectional area specified by the maker, and you can work out how many you need to make 0.1 sq".These numbers are nonsense, of course, just an example of the calculation process. Be sure to add large safety factors to allow for vibration loads, precession loads, etc. Think we used 3x the calculated load bearing material. Better safe than sorry.Hope that helps, Ben.

[Greg Mitchell]

And plays Blues guitar!Welcome Ben. Mitch.www.thebutterflyllc.com

[asra]

Thanks Ben !Lots of good info there thank you ! I figured 2 layers of cloth and reson over the entire blade and an aditional layer of cloth and reson on the root end , going up about 8" or so from the root end ...... Right now I'm stopped on all my projects because of lack of meterial to work with ... so everything is on hold ...thanks for the info ! Bob......" Momm'a alwayse told me , Son the impossable is only a little bit Harder... and ya know I do believe She was RIGHT ! "

[asra]

Thanks folks, happy if it helps.Your cloth needs to give something like 1.5 mm of thickness per layer based on guesswork, Bob. If you can give me the RPM, the weight of a blade as it is and the place where it balances I'll try to work it out for you more closely. Sounds about right, anyway. Know what it's like when the money runs out. Back in the late 70s when Richard Douglas used to visit us in our Wolverton hovel we were living on beans. He could tell you all about that, I'm sure. That's when my beloved F3 racing hovercraft was called 'Overdraft' with good reason! [)]Hi Mitch! You another blues enthusiast? I'm pretty relaxed these days, anything with a relationship to the blues will do if I can get these decreasingly flexible fingers around it. Last public gig was in Sydney earlier this year, sat in with "The Festers" at the Glengarry Castle in Redfern. Had a grand time there! []Ooops, off topic, sorry. [:I]All the best, Ben

[Greg Mitchell]

Sorry to hear things have stalled a bit Bob. Same for me, money is always tight.Ben, could have had a little blues guitar session at Mentone this year, with Sonny Jeffers but found out to late. Good to have you on the forum. Rub some Emu Oil into those fingers....they reckon it works, it cant hurt.Mitch.www.thebutterflyllc.com

[asra]

Thanks for the suggestion Greg - it's surprising how many Emus there are in this region! [)]My neighbour's suggestion is unrepeatable, but it would keep the fingers warm, I suppose.I may not make it to Mentone next year, but the Wauchula boys have convinced me to do Bensen Days 2006. Love that swamp music!BTW, Ken Wallis will be 90 next year, God willing. Anybody planning a visit to the UK for Wallis Days should aim for August and plan on kipping at my place for part of the time. 100K north of London, can't miss it.Anecdotally Ken was responsible for a lifting of restrictions on Gyros in Australia when he did the 007 appearances in "Little Nellie" - any knowledge of that?Off topic again... [:I] All the best, Ben

[asra]

Bob, Have you ever seen a wooden prop constructed even remotely close to the composite configuration you are copying? There are sound engineering reasons that wooden props have the MOST material at the root of the prop.A least give this question some thought before you try to run this one.Brad KingN6372KMad Max II LTC

[asra]

OO7's "Little Nellie".I have some black and white photo's of this gyro on display at a shopping center near where I lived in the early 70's. It was reputed to have flown a few displays from the car park but I didnt see that.I will post them in "Photo's" when I can get them scanned.M Barker

[asra]

Hey Bob, Howz this. That outa keep them where there supposed to be.Good luckSonnyImage Insert: 5.65

[asra]

THANK YOU SONNY ! How bout that a Wood adjustable prop being manifactured ! .... who sells that 'n Sonny ? I see its 2 blades or 3 bladed as well...... just like mine ..... heheheheh htanks for the pics ! Bob......" Momm'a alwayse told me , Son the impossable is only a little bit Harder... and ya know I do believe She was RIGHT ! "

[asra]

So bob k it apears as though wood adjustable props can succeed best of luck! copy manufacturing process & test carfully by the way what do you weigh looks like 6ft & 187ponds is this plus fuel realistic payload for your 40hp motor?

[asra]

Nope Butch ...5'10" 202lbs 42hp rotex at 4800ft elevation..... and it does get itself off the ground.... !see ya !Bob..." Momm'a alwayse told me , Son the impossable is only a little bit Harder... and ya know I do believe She was RIGHT ! "

[asra]

This is 91kg blokes in my area of your weight have comented that with a 503 rotax & a light gyro thay were very marginal you may fly down the runway in ground effect with a headwind but your first crosswind turn may tell the tale.test fly with minimum fuel!

[asra]

Hey Bob! There will always be doomsayers, but to truly know what's on the other side of the hill YOU have to go there yourself. It was people like you who made flight possible. Yeah, you might break something, even yourself, but nothing is forever, so keep up the (new) pioneering work. I, for one, would like to know a tried and true way to build a wooden prop.Avoid strong drink! It makes you shoot at tax collectors ....and miss!(Robert Heinlein)R.J.W.S.