Four Blade rotor

Scorpion

Junior Member
Joined
Jan 13, 2007
Messages
41
Location
Pacific Haven (Australia)
Hi all,

Does any one know what the pro's and con's are for using two sets of rotor blades on seperate teeter bolts and set at 90 deg to each other?

Could the total rotor diameter be reduced when using 4 rotor blades?

Looking for some honest answers.

Graeme
 
If you don't allow for individual blade lead/lag things will start cracking in very short order (in just a few hours). It's been tried by a bunch of folks...

Allowing for individual blade lead/lag means a much more complex rotor system. That combined with needing more blades means it costs a lot more.
 
Four Blade rotor

Hi Brett,

I found the pic some time ago. It is crudely constructed, but I thought the principle would work.

Graeme
 

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No, that one has a design flaw. The axes don't allow scissor movement. Assume, in horizontal position the blades have an angle of 90 Deg. If you could tilt them down all the way, parallel to the rotor axis, the angle would be 0 degrees at the bottom and top and 180 deg left and right, correct? Although you never get all the way down, of course, you can imagine, that a change of angle would occur every time the blades teeter.

The Rotortec 4-blade rotor therefore has a rubber joint, which allows scissor movement between the two rotor-pairs. (see my aero thread).

Kai.
 
Four Blade rotor

I found these two gyrocopters that are using four bladed rotors.

The Magni M16 and the Cloud Dancer.

Seems the smaller diameter four blade rotor has better weight lift capabilities even though it may be more expensive.

It also allbut eleminates stick shake!

Graeme
 

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  • Gyro Cloud Dancer 4 blade.jpg
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It's not that a multi-bladed rotor is impossible to make, it's just more complicated & expensive to do it correctly. Simply stacking a couple of teetering ones definitely will not work.
 
Four Blade rotor

Hi Brett,

Yes, I do understand that and the photo of the double teeter hub was one I found on the net.

I was not proposing to build one like that at all.

I would like to find out, from the many experts on this forum; what the benifits would be (expense and complexity excluded) compared to the standard 2 blade rotor system.

From what I am finding, it appears that the extra expense would be worthwhile.

Here is another 4 bladed 2 seat tandem Gyro which is under construction now, in Europe.

Graeme
 

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four blade rotor

four blade rotor

it is possible to build a rotor with any number of blades within reason if you need it but for a single place there is no need as the two blade works just fine but if you go to a very heavy machine then more blades may be needed, at one time I was going to build a large tractor gyro and was planing to use a five bladed rotor but the engine deal didn't work out( 600 hp P&W radial with gear reduction to the prop) a two bladed rotor would not work on gyro of that size. I am working on a tractor that will use a three blade rotor but not because of weight but I need a shorter rotor for float operations, longer two blade rotors get more spray damage , with three blades it won't fit through an 8ft door but there is lots of room on the beach.
 
Right, the advantages will only come into play with heavier ships where you really can't get enough blade area with 2 blades (or at least not enough without the vibration becoming an issue).

Ideal blade loading is around 35 lbs/square foot, you can see where heavier ships would like more blades.
 
Don't you mean 3.5 lbs/Sq.Ft.

I would like to have a four rotor diameter of about 18' and have 2 of the blades being able to be folded to the front or back to minimise storage space and have the ability to trailer the gyro without removing the rotor blades for transport.

I can't see why this would not work for a single seat gyro of less than 600lb.

Graeme
 
Graeme: No.....Brett said "blade loading", which should be ~35 lb/sq.ft.. The ideal "disk loading" is 1.3 lb/sq.ft, which you may be thinking of.....
 
For a single seat gyro, the disk loading should be 1.3 lb/sq.ft.....regardless of the number of blades. A 600 lb AUW with an 18' dia. rotor would be ~2 lb/sq.ft. and ~28 lb/sq.ft. of blade loading (with a 7" chord on the four blades). I think your rrpm would be too low. As stated in another post, four blades would work better on heavier machines. I suppose you could reduce the chord….if you can keep the same strength.
 
Diskload

Diskload

Do not understand this... with shorter Blades you get less Rotordisk and therfore higher Diskload ... i,m wrong on this?? 1102 pound Gyro with 334.7
diskarea would get a diskload of 3.2 p/sf Where is my mistake ??

Steven
 
Here is another 4 bladed 2 seat tandem Gyro which is under construction now, in Europe.

Graeme

Graeme, the gyro project (and the first to fly) is with 2 blades. The one on the picture is "more" than a gyro and the 4 blade is not a tilt head but with a swash plate for a specific reason...... :tape:
 
Four Blade rotor

Hello Nicholas,

Thank you for your clarification.

I'll be looking forward to your progress with the design.

It's good to see these advanced designs being produced.

Graeme
 
you are welcome. Progress is slow but steady.
 
Do not understand this... with shorter Blades you get less Rotordisk and therfore higher Diskload ... i,m wrong on this?? 1102 pound Gyro with 334.7
diskarea would get a diskload of 3.2 p/sf Where is my mistake ??

Steven

That's way too small a rotor for a 1100 lb gyro - just under 21' diameter. Sure you did the math right? Now, for a helicopter that's a different story...
 
That's way too small a rotor for a 1100 lb gyro - just under 21' diamThat's way too small a rotor for a 1100 lb gyro - just under 21' diameter. Sure you did the math right? Now, for a helicopter that's a different story...

Thank you Brett,s ... I whas working this for a 4 blade System not 2 blades

Steven
 
The number of blades doesn't change the disk loading you should aim for.
 
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