A question about rotors

[timezone]

Lets just imagine that cost is not an issue for this discussion. Why wouldn't one want rotors with a large chord on his gyro? I seems 7 inch is an average size for many gyro pilots. I see 8 inch chords advertised and somewhere I saw 8.5 inch cords I think. It seems a larger cord would equal more lift? More lift equals shorter take off, better glide ratio? Weight issues would be less critical. OK OK I know more cord equals more drag. Is drag that much worse with a wider cord? Do you need more power with a wider cord? Would take off rrpm be less with a wide cord? Kindly let me know what I am missing here. Thanks.

Timezone

[Brian Jackson]

Burt Rutan gave a very nutshell explanation of this on a Discovery program I saw recently... He described that it was much easier for a wing to deflect a lot of air by a small amount than to deflect a little air by a large amount. I don't fully understand all the physics behind it, but essentially that is why gliders typically have such high aspect ratio (long & slender) wings.

I'd be interested to hear other designers' comments on this thread.

Regards,
Brian Jackson

[animal]

Lets just imagine that cost is not an issue for this discussion. Why wouldn't one want rotors with a large chord on his gyro? I seems 7 inch is an average size for many gyro pilots. I see 8 inch chords advertised and somewhere I saw 8.5 inch cords I think. It seems a larger cord would equal more lift? More lift equals shorter take off, better glide ratio? Weight issues would be less critical. OK OK I know more cord equals more drag. Is drag that much worse with a wider cord? Do you need more power with a wider cord? Would take off rrpm be less with a wide cord? Kindly let me know what I am missing here. Thanks.

Timezone
All I know about wide chord blades is when I was building my TH-135 Dusty2 helicopter prototype I had some cut down agusta 109 blades, they where 13" chord. and weighed 40 pounds each.
what I can tell you is that it was impossable for me to get them tracked and balanced,I had a full gimble semi rigid hub and what would happen is the hub would sling to one side and just about shake the machine apart, when i sold it the new owner had use install a set of Vortech blades and they balanced almost perfectly the first time we ran it up.

[raghu]

Why wouldn't one want rotors with a large chord on his gyro?

Timezone

For one thing, all else being equal, (seesaw type) blades with larger chords (>8inch) would suffer from severe 2 per rev shake.

[KenSandyEggo]

Raghu,

Why? If they were properly made to begin with, why would the 2-pers be any worse than an equally well-made set of smaller chord blades? I think that a larger chord would amplify vibes caused by badly designed or made blades, but not cause them. I have the 8.5 inch chord Sportcopter blades and the 2-pers disappeared as soon as I installed and flew them. The 2-pers with the RAF blades were persistent and unremovable.

P.S. You've been around here awhile, how come your profile lacks even a name or a signature in your posts? I thought that was a mandatory requirement in order to post here, for us to know who we're communicating with.

[Victor Duarte]

All I know about wide chord blades is when I was building my TH-135 Dusty2 helicopter prototype I had some cut down agusta 109 blades, they where 13" chord. and weighed 40 pounds each.
what I can tell you is that it was impossable for me to get them tracked and balanced,I had a full gimble semi rigid hub and what would happen is the hub would sling to one side and just about shake the machine apart, when i sold it the new owner had use install a set of Vortech blades and they balanced almost perfectly the first time we ran it up.


hi animal, have kept some traces of your experiment ? have you stopped it?

regards
victor

[animal]

hi animal, have kept some traces of your experiment ? have you stopped it?

regards
victor yes I sold the prototype dusty2 and design rights to a guy in Pa., to bad he has no clue about what he bought.so I dought we will ever see it fly. I now have a rotorway Scorpion with the Exec 162 engine in it that I am working on.just finished the insturment console tonight,hope to start doing run up tests soon. bought is as a partly built project, but it was complete parts wise

I think it is going to be alot of fun to play with,plenty of power,but still has the old style cable head and has vortech blades.

[Victor Duarte]

congratulations ... hope you gonna have lots of fun and exitement !
a pity you stopped your own design.. must i understant you became wiser after that experience ;) ( did you wonder what happened to the guy ?) would you say it was a good venture, not to do again, or would you like to try again if you had appropriate tools, bucks etc ?
i m going for my own rotor (yes just call me mad man), so i carefully read every post..
thank you
victor

[animal]

congratulations ... hope you gonna have lots of fun and exitement !
a pity you stopped your own design.. must i understant you became wiser after that experience ;) ( did you wonder what happened to the guy ?) would you say it was a good venture, not to do again, or would you like to try again if you had appropriate tools, bucks etc ?
i m going for my own rotor (yes just call me mad man), so i carefully read every post..
thank you
victor
I had ran out of funds was the main reason and at the time wanted another harley in hopes i could get my bike shop going again.but the county here shut my shop down again,and around here every one and there brother is trying to have a bike shop,so i decided if I could find a good scorpion project with a 152 engine and most the parts i would sell or trade my bike. I found better then what I was looking for. alway have liked the Scorpions.

[Victor Duarte]

alway have liked the Scorpions.
i guess you love it to trade your bike ! i hope you will reach your goals.
thats really a good thing you can fly it! here thats impossible (thats why i wanna do it :D), keep it going ! sorry i cant help you except with my best regards :D

victor

[timezone]

Ken, I guess I didn't sign up right or maybe I just didn't do the signature correctly. Sorry. Timezone aka Dale Nalder Boise, Id.

I'll include all information manually on future posts.

[rehler]

To change or add to you personal information just click on "user CP" in the top left corner of this page. Then you can edit what ever you want - list on the left side of the page.

[nicklappos]

Let me weigh in on the value of diameter and chord:

The efficiency of the rotor (power needed to fly, or for a helo, power needed to hover) is very much determined by the disk loading - the weight of the machine divided by the rotor disk area. If the disk is lightly loaded, it is like a big wing, and it means that a large volume of air is being moved a little bit. Think of the disk area as a pipe, where the bigger the pipe, the more air we can move. Rotopix gave the quote from Burt Rutan about this. Move lots of air a little bit, and it takes little power to fly. Think of it like a water ski, if you have a big ski, you can climb up while beng pulled slowly, and you won't waste much power making a deep wake. You are moving a big bunch of water a little bit.

Since lift is made by accelerating a bunch of air, if we can accelerate a big bunch of air just a little bit, we can develop lift without a lot of power. Power is used to make the air have more speed. More speed, more power. If the rotor disk is small, than we have to move less air, and move that air faster. This uses more power.

So, for less power to fly, use a bigger rotor.

How about chord? The chord determines the solidity, which is the amount of blade area as compared to the amount of dsk area. This is what make s the peak thrust of the rotor, which means this is the thing that makes us able to amneuver without blade stall. The more blade area, the less the angle of attack needed for a maneuver, and the more the thrust before we experience blade stall. Big blades take more power to spin them, because they have more parasite drag (more area with wind going past them).

Put this together and we see that a big rotor diameter means less power needed to fly. A wide blade means more maneuvering capability, but the wide blade eats power. So for efficient lift, long skinny blades are nice. For maneuvering without blade stall, wider blades are nice.

[Ted Eggleston]

So the rule of thumb here is....Thinner chords for distance flying and wider ones if I wanted to chase cows like Birdy?

[birdy]

Hmmmm............Nik has just shot my oppinions down in flames.
I'v found that long ,narrow ,high rpm[low pitch]blades are best for wot I'm do'n coz they have a faster responce time to inputs and are generaly more efficiant with more stored inertia.

[nicklappos]

birdy,

I agree with you, the faster rpm makes a sportier handling aircraft. The response time is driven by the rpm, so fast systems make snappier handling.

Also the thinner blades flap more easily (less resistance flatwise) so they assume the new flapping position faster.

The rotor design is also a very important contributer. If the rotor has a teetering head, it will be softer and slower to respond. A head with offset hinges will respond faster, and one that is rigid will be faster yet.
Where thin blades are less effectve is the max G they can create. This can be offset by spinning them faster (less area, but more equivilent airspeed).

[Hognose]

Nick!

Good to have you in the forum. Your posts were always the best part of the rotorcraft newsgroup on usenet. Sorry about Comanche.

cheers

-=K=-

[Mayfield]

Although I have not had the pleasure of meeting Nick in person, I have followed his career with great interest and read as many of his writings as possible.

For those of you that do not know it, Nick has a long and impressive test and, I suspect, design career behind him.

He will be an extremely valuable addition to the knowledge base on this forum and can answer almost any flight testing question you might have.

Jim Mayfield

[birdy]

Well,....... it don't half make me stick me chest out to learn who Nik is,and have him agree with me. ;) :D :D

[Chopper Reid]

Well, I'm still a bit in the dark who "Nick" actually is so could someone please enlighten me ?
Birdy, obviously your gyro is fairly light [compared to mine] and this has a big bearing on the performance of your blades. How you fly and what you want the gyro to do makes blade selection important. I'm finding the big wide chord rotors [slow reving] keep my gyro from reacting so quickly to whirly winds and also keep their inertia for longer .

[MattPearson]

There is a point to which disc loading becomes secondary to blade loading. Blade loading is what determines tip speed and too high a tip speed is what induces high drag; also the blades are having to fly at a greater AOA to do the same work as a multi-blade rotor with lighter blade loading, but the same disc loading. Not to mention the two-per-revs go away!