HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Sep 17, 2012, 04:55 PM
Registered User
North London ENGLAND
Joined Dec 2006
1,666 Posts
Discussion
Build log; Twin rotor Autogyro with Klein-fogleman blade sections.

Having finalised design, started construction.Twin rotors side-by side, rotor dia 24 inch each. Blade chord 2.5 inches, top layer 1.5 inches, both layers from hard 3/32 inch balsa. Hubs; made a strip of hard balsa 1 1/4inch wide, tapered it in section like a solid trailing edge strip from 3/32 to 1/16 thick. Cut 1 inch pieces, mounted them on 1/16 birch ply cross-shaped pieces. Made 4 such hub plates, mounted shaped and sanded blades on hub plates,mounted second plates on top. Result, 4 bladed rotors with 5 degrees negative angle of attack. They will be mounted on spindles raked back at 11 degrees to datum. This will give max angle of attack to forward going blade of 6 degrees. Rearward going blade max angle 16 degrees negative.
The configuration has two motors with 8x6 counter-rotating props mounted ahead of the rotors.Thus they will get "blown" round whatever forward speed, and will hopefully result in very short take-offs and slow forward speeds. Tailplane will have twin fins/rudders in slipstream to aid control at slow speeds. Pics will follow as construction proceeds.
macboffin is offline Find More Posts by macboffin
Last edited by macboffin; Sep 18, 2012 at 01:29 PM.
Reply With Quote
Sign up now
to remove ads between posts
Old Sep 17, 2012, 05:23 PM
Registered User
Joined Oct 2009
127 Posts
Quote:
Originally Posted by macboffin View Post
Result, 4 bladed rotors with 5 degrees negative angle of attack. They will be mounted on spindles raked back at 11 degrees to datum. This will give max angle of attack to forward going blade of 6 degrees. Rearward going blade max angle 16 degrees negative.
Interesting project. I was thinking of making some of the Klein-fogleman blades to try on a Fire Fly.

With the flapping blades though, do those AOAs apply? I would have thought once the disc was spinning, and the autogyro was flying, the AOA would be less on the advancing blade than the retreating blade, otherwise it would pitch the nose up.
Lazygit is offline Find More Posts by Lazygit
Last edited by Lazygit; Sep 17, 2012 at 05:35 PM.
Reply With Quote
Old Sep 17, 2012, 05:36 PM
Registered User
North London ENGLAND
Joined Dec 2006
1,666 Posts
Being a twin rotor, the blades don't flap, or need to. Blades at negative AOA generate no lift.The blade "facing back" gets blown back/round by airstream or slipstream, has more drag than the forward facing blade which is generating lift. This is how the rotor spins after all!.
macboffin is offline Find More Posts by macboffin
Reply With Quote
Old Sep 17, 2012, 05:43 PM
Registered User
Joined Oct 2009
127 Posts
Now even more confused, surely if lift increases, so does drag.
Lazygit is offline Find More Posts by Lazygit
Reply With Quote
Old Sep 18, 2012, 01:28 PM
Registered User
North London ENGLAND
Joined Dec 2006
1,666 Posts
Of course. But the drag of the advancing blade which is generating lift is very much less than the drag of the retreating blade.
What do you suppose causes the rotor to spin?
It is the greater drag of the retreating blade. Autogyros are distinct from helicopters because the rotor or rotors are not powered.
macboffin is offline Find More Posts by macboffin
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Build Log FnT 'Twins' 50% build log nemoskull Parkflyers 5 Sep 27, 2012 01:24 AM
Discussion Klein-Fogleman Airfoil > Step on top or bottom? GB57 Foamies (Scratchbuilt) 5 Feb 26, 2008 01:20 PM
Yippee! GWS twin rotors Autogyros Slow-Stick, PT-17, TM400... GWS4CEO Auto Gyros 41 Jan 09, 2006 01:17 AM
Slow-G Twin Rotor Autogyro build thread Robert Stinson Auto Gyros 13 Sep 21, 2005 04:32 PM
Dihedral in twin-rotor winged autogyros iter Auto Gyros 4 Feb 28, 2005 06:06 PM