Prize Offered for Technical Solution
Thread Starter
Joined: Nov 2000
Posts: 452
Likes: 0
From: Vancouver, BC, Canada
Prize Offered for Technical Solution
The grand sum of $49.98, less amusement tax, is offered to the first person who comes up with a practical solution to the following very simple rotorcraft problem.
________________
The Problem ~ Rotor to Rotor Vibration:
How to eliminate the rotor to rotor induced vibration, in helicopters with overlapping twin-rotors by somehow temporarily increasing the pitch [and thereby maintain a consistent angle of attack] on the blade (or its individual elements) as it (they) passes through the downwash from an upper blade and through the downdraft from a lower blade.
The Solution
How to get rid of the problem.
________________
Contest Conditions:
1/ For reasons of economy, and cheapness, the prize is in Canadian dollars; 'cause they're half way between a US dollar and a Monopoly dollar.
2/ No more than 20 submissions per person.
3/ Second prize is $49.98, in Monopoly dollars.
Dave J
________________
The Problem ~ Rotor to Rotor Vibration:
How to eliminate the rotor to rotor induced vibration, in helicopters with overlapping twin-rotors by somehow temporarily increasing the pitch [and thereby maintain a consistent angle of attack] on the blade (or its individual elements) as it (they) passes through the downwash from an upper blade and through the downdraft from a lower blade.
The Solution
How to get rid of the problem.
________________
Contest Conditions:
1/ For reasons of economy, and cheapness, the prize is in Canadian dollars; 'cause they're half way between a US dollar and a Monopoly dollar.
2/ No more than 20 submissions per person.
3/ Second prize is $49.98, in Monopoly dollars.
Dave J
Last edited by Dave Jackson; 29th May 2002 at 00:38.
Moderator
Joined: Feb 2000
Aviation Qualifications: CPL
Posts: 14,479
Likes: 178
From: UK
Bifilar absorber on each hub - Westlands use them to save the trouble of fully balancing discs for flight test. Basically it's an annulus half full of mercury, which will establish itself relative to any vibration so as to balance it out.
Make sure it's well sealed, mercury eats aluminium.
G
Make sure it's well sealed, mercury eats aluminium.
G
Joined: Jul 2001
Posts: 82
Likes: 0
From: California
Overlapping rotors, not intermeshing, right?
(Two) 2 bladed rotor heads
Overlap blades less then 65%
Stack one higher by 3 feet or so depending on blade flex etc
The center portion will be retreating side
Reduce flapping and encourage dyssemetry of lift on each rotor
On lower head 90 degrees from blades fit two weighted stub blades that can lead/lag (tuneable)
Both xmsn assemblies mounted to allow left/right, fore/aft and vertical dampning (tuneable)
Use a third prop mounted aft and at the mean average of the discs for thrust, yaw control and to keep the disc setup above etl.
Install a very large ballistic recovery parachute.
Let me "hold your watch" while you test fly it.
Working on my second cup of coffee now !
(Two) 2 bladed rotor heads
Overlap blades less then 65%
Stack one higher by 3 feet or so depending on blade flex etc
The center portion will be retreating side
Reduce flapping and encourage dyssemetry of lift on each rotor
On lower head 90 degrees from blades fit two weighted stub blades that can lead/lag (tuneable)
Both xmsn assemblies mounted to allow left/right, fore/aft and vertical dampning (tuneable)
Use a third prop mounted aft and at the mean average of the discs for thrust, yaw control and to keep the disc setup above etl.
Install a very large ballistic recovery parachute.
Let me "hold your watch" while you test fly it.
Working on my second cup of coffee now !
Thread Starter
Joined: Nov 2000
Posts: 452
Likes: 0
From: Vancouver, BC, Canada
Granger,
The single rotor configuration may have reached its limits, particularly in respect to forward velocity. Small improvements will be 'tweaked' out, but no quantum leaps IMHO.
tgrendl,
Intermeshing, coaxial or tandem. Any configuration where the two rotors aerodynamically interact.
The biggest disadvantage of overlapping rotors is vibration. As technological improvements continue to be made in eliminating vibration (Higher Harmonic Control, Individual Blade Control, etc), it is the helicopters with overlapping rotors that will see the greatest benefits.
More coffee. This thread is a request for all 'wild & wacky' ideas. Thanks.
The single rotor configuration may have reached its limits, particularly in respect to forward velocity. Small improvements will be 'tweaked' out, but no quantum leaps IMHO.
tgrendl,
Intermeshing, coaxial or tandem. Any configuration where the two rotors aerodynamically interact.
The biggest disadvantage of overlapping rotors is vibration. As technological improvements continue to be made in eliminating vibration (Higher Harmonic Control, Individual Blade Control, etc), it is the helicopters with overlapping rotors that will see the greatest benefits.
More coffee.
This thread is a request for all 'wild & wacky' ideas. Thanks.
Last edited by Dave Jackson; 29th May 2002 at 21:59.
Joined: Jan 2001
Posts: 420
Likes: 0
From: AB, Canada
Dave, get the blades spinning the same way, one of them slightly lagging the other. Make sure forward velocity of the aircraft keeps any disturbed air from the lower rotor.
Okay, it only works for one rotation of the blades, but you didn't specify.
Okay, it only works for one rotation of the blades, but you didn't specify.
