news of cloud dancer II

[Gyronaut]

It makes perfect sense to my aerodynamically uneducated mind that 4 shorter blades should generate the same amount of lift as 2 longer blades.

I would also imagine that 3 or 4 blades have less vibrational tendency than 2. ?? Shorter blades mean less ground handling effort and storage effort no?

The perfect solution would be 4 heavy blades that could spin up to a very high RPM, with a small pitch-change ability in order to do a jump-start, up to say 100', using the inertia in the blades, then accelerate into auto-rotation.

The biggest draw back of gyro's at present is being unable to get out of a tight (restricted) area. We can put them in there, we just can't get them out again.

Go on Volki, design one that works... We'll all buy it believe me!!

Keep up the good work.

Len

[t-bird]

Hi Jetranger

Magni-4-blade rotor in 2000

http://www.magnigyro.com/USA/magniday2000.htm

[Gyronaut]

Well I never! Thanks T-bird. So leer mens. I wonder why they didn't pursue the option?

Interesting that they say "The 4-blade rotors present some issues that we do not want to be concerned with in the sport Magni gyros. They are more difficult to hangar and they will be more expensive."

If they generate far more lift and provide extra maneuverability (as per the article) then one would have imagined it would be an option in spite of it being more expensive and more difficult to hangar?

[mak]

Would shorter 3 or 4 blade rotors with the same lift as 2 rotors increase gyro speed?

[Learjet]

Len pondered

I wonder why they didn't pursue the option?

Mak asked

Would shorter 3 or 4 blade rotors with the same lift as 2 rotors increase gyro speed?

Vittorio said

This prototype is much more blade than required for the M-16 with only Vittorio's weight aboard. Vittorio said he had to limit the
upper speed on his demo flight because the rotor is really intended for much heavier gyros.

Perhaps Vittorio's comments allude to the fact that the shorter 4-bladed rotor present a greater reduction in total drag compared to the longer 2-bladed rotor (assuming little difference in rotor profile drag i.e 4 short rotors = same profile as 2 long rotors - yes I know that wingtip[ induced drag also comes into play but I'm deliberately trying to keep it fairly simple *smile*). So because Total drag is primarily a function of airspeed - and the shorter 4-bladed rotors allow for a significantly reduced rotor rpm and wing airspeed! (Mak to answer your question - as per drag equation: the longer 2-blade rotor wingtip travelling at twice the speed {as a shorter one half it's length} has 4x the drag) Thus the resultant reduction in total drag offers increased overall airspeed. In a pusher configured gyro this probably brings about a whole new set of flight characteristic dynamics - specifically with increased cabin parasite drag and possible resultant yawing / pitching and even weathercocking actions - not to mention any offset thrustline dynamics coming into play. (this was probably far less of an issue in the early tractor / puller configured 4-bladed gyros with their CLT).

So in a nutshell I would speculate that Magni simply decided that introducing a 4-bladed rotor would most likely require a complete aerodynamic redesign of his existing gyro (M16 etc) to cope with the increased airspeed and change in handling characteristics. Of course by increasing the aircraft weight changes the lift coefficient requirements - and increasing the overall gyro weight is one way of taming the 4-bladed rotor beast! But as Magni says, "4-blade rotors present some issues that we do not want to be concerned with in the sport Magni gyros". I guess the old adage also stands - if it ain't broke... etc.

[gyrosa]

Hi Learjet
I actually saw the rotor head that Magni produced for the 4 blades. They were actually 2 sets of blades, each on it's own teeter system, which made the rotor system expensive and complicated. If each blade was on it's own drag and teeter hinge, it would have made more sense and it could have allowed the blades to fold back and be hangered in possibly a smaller area than the present M16.
The 3 or 4 bladers of yesteryear had very simple heads as far as rotor heads go and similar to Alhoette choppers, actually had a cable keeping them 120 degrees apart ( in the case of the 3 blade systems) and 90 degrees apart ( in the case of the 4 blade gyro copter systems).
The idea that Magni persude was to be able to carry heavier loads e.g. for crop spraying. If I remember correctly, the blades were something like 24 feet in diameter and on climb out, it scared him a bit because of the vicious climb rate. They were however a lot smoother than the standard 28 footers. Why he did not carry on - I really do not know as I think it was a great idea and one that could have been beneficial in Africa in the agricultural as well as police applications.
My Bensen has 24 footers and they are extremely smooth to fly, so my conclusion is similar to that which Vitorrio made a few years ago - the shorter the blade on a standard 2 blade system, the smoother it goes but you will loose the benefit of other factors such as lift, performance and possibly even top end. This was my comparison to the Bensen 22 footer blades which was faster than the 24 footers but lacked the lift and climb rate. The 24 footer flew at 35mph (almost top end) where the 22 footer easily went over 50mph - big difference. Drag on the bodies was the same.
Unfortuneately, we have to compromise. I think Len will also agree that a 3 blade chopper also flies smoother than the old 2 bladers such as the Roby 22 and 44.
My own preference goes to 3 blades without a doubt, if they can be swung backwards in the event of parking and hangers.

[t-bird]

Hi Learjet

On the rotary forum they mention rotor solidity also as a factor when calculating the lift, drag ratio.
Attached are some of the calculation

From calculations:
1330lbs...85mph.
2 blades 30'X8.75'' (solidity ratio=0.0309) give L/D rotor=8.8...
4 blades 25'X7.5'' (solidity ratio=0.0636) give L/D rotor=10.0...

This also proofs that the lift, drag ratio is higher with shorter 4 blades than longer 2 blades

[Learjet]

Thanks for the info T-bird. The more I read up on rotor aerodynamics the more it seems like a dark science to me! and of course the sales pitch info often doesn't help - I recently read in a certain gyro manufacturers brochure that their extruded aluminium rotors were (and I quote) "made of aviation aluminum Naca 8H12" - a little misleading I thought, as further exploration revealed that Naca 8H12 is simply an aerofoil shape design and has absolutely nothing to do with the grade of aluminium used.

[rotortec]

Hi Learjet,

Yes you are absolutly right, It shoud say " made out of Aircraft Aluminum" "Profile used is Naca 8H12"
But we never put this mentiond statment in to our Brochures. Presently we are only using "Dragon Wings"
on the 2 Bladed System (single seater) and on the new 4 Bladed System we will use them to.

John Steinbeck
Rotortec Germany

[Learjet]

Hi John - Sorry I went a bit off topic there and apologies if you thought I was referring to Rotortec - it's actually another manfucturer's brochure I was referring to.

[peterb]

Hi John - Sorry I went a bit off topic there and apologies if you thought I was referring to Rotortec - it's actually another manfucturer's brochure I was referring to.

Hi John I read the same brochure Leerjet is refering to. I did not Know that brochures for Cloud Dancer II is available. If so where can I obtain one?

[rotortec]

Hi Peter,

presently we have only Brochurs for the Single Seater. We will produce new once at the End of the year,
for the New 2 Seater Cloud Dancer. A PDF File will be availeble on our Web Pages at the same Time,
for you to dounload. As soon as testing for the new Motor and Gearbox is compleated we will supply
more Pictures here on this Forum for you. If you instrested in Pictures of the Status reached so fahr,
let us now and we will provide them to you on your PN

Regards
John
Rotortec Germany

[rotortec]

We have promissed Updates to the project but it made us very bussy over the last. We will finalise the Gyro
by beginning of the year 2010 and so fahr (Okt 2009) we have the recieved the "Provicinal Certificat of Airworthiness" from
the German Dep. of Aviation.

See encolsed a Drawing of the new Rotortec Powerplant 135 Hp with direct Planatery Drive. Powering a 1800mm Prop
at top speed of 1920 rpm for low noise.

Rotortec Powerplant 135 HP

[rotortec]

Small Update.... The new "2 in one" Glass Panal for the Cloud Dancer II
Size 10,4" Tutch Screen , High Britness Display

John