1029

Item 1029

DESIGN: UniCopter ~ Rotor - Disk - Downwash Intersection Azimuths - 3-blade

May want to produce a page for the 4-blade rotor and upgrade this one to 1150 GW UniCopter.

The location (azimuth and radius) where the lower rotor is struck by the downwash from the upper rotor. This is not exactly true since the lower blade will have move along a bit before the downwash gets to it.

The radius at 75% R is 0.75 * 100 = 75". Circumference at 75% of R is 2 * (22/7) * 75" = 471". The blade chord at 75% of R is 7". The rough blade-blade interaction will be 360º * (7/471) = 5.3º.

In Hover:

	Starting Azimuth & Radius:	Finishing Azimuth & Radius:	Duration:
A/	150º @ root. Start @ cut-out	202.5 @ .85R	202.5-150+5.3 = 58º
B/	275º @ root to (tip - stagger). Downwash from upper blade may strike all the elements of the lower blade at the same moment The downwash at the outer portion will have further to travel but it will have a higher velocity.		5.3º
C/	337.5º +/- @ .9R	30º @ root. Start @ cut-out	22.5+30+5.3 = 58º

Gray values are temporary approximations.

It appears that there is some blade-blade interaction for about half of the rotation.

For plan view of rotor disks see: DESIGN: UniCopter ~ Rotor - Disk - Blade to Blade Clearance

With ABC the lower blade will be generating less thrust than the upper. In addition, the upper segments are above segments on the lower blade that are closer to the root and therefor have even less thrust. This is a strong reason for twist; as long as it is too much and is detrimental to autorotation.

In Forward Flight at ?? MPH:

	Starting Azimuth & Radius:	Finishing Azimuth & Radius:
A/
B/
C/

In forward flight it appears that A & B will take longer than 52.5 of rotation since the free air stream is moving aft whereas the scissors action is moving forward.

Viewing the helicopter in plan view and having 12:00 representing straight ahead, the sequence and locations of blade crossing is;

Location:	Orientation:	Crossing Passage:
3:00	Port above Starboard	All of span at same time
7:00	Starboard above Port	Tip --> Root
1:00	Port above Starboard	Root --> Tip
9:00	Starboard above Port	All of span at same time
5:00	Port above Starboard	Tip --> Root
11:00	Starboard above Port	Root --> Tip
repeat.

In Hover:

Approximate azimuths where .75R aerodynamically interact. 45º, 92º, 140º, 200º, 272º & 345º.

Degrees between aerodynamically interaction azimuths. 47º, 48º, 60º, 72º, 73º, & 60º.

Positioning for 60º intervals and giving preference to the lower blade. 32º, 92º, 152º, 212º, 272º, & 332º.

A 'hump' may be needed at azimuth 270º on the two swashrings, to increase the pitch slightly.

A 'hump' may be needed at azimuth 90º on the two swashrings, to increase the pitch slightly.

The azimuth of the 'humps' and 'dips' will increase when the forward speed increases.

Note: The 'dip' on the upper blade will reduce the lift on the helicopter slightly. The lower blade extends out beyond the upper blade and thereby has two regions. The outer region is in free air and therefor the 'hump' will allow it to offset the loss of lift that is experienced by the upper blade. The 'hump' will allow the inner portion of this blade to reduce the effect of the downwash from the upper blade.

In Forward Flight:

The upper 'dip' must be advance to greater than 90º and the lower 'hump' must be increased to greater than 270º. This means that the swashrings must be advanced by about 30º in fast forward flight.

Two Possibilities for Producing HHC:

Humps and Dips in the swashring:

At present, I do not know how to rotate the swashring, which contains the 'hump' and the 'dip".

See: DESIGN: UniCopter ~ Control - Flight - Swashring

Hydraulics Incorporating 'Spikes':

See: OTHER: Aerodynamics - General - Higher Harmonic Control See Idea: on this page.

This page is currently showing the required period for the HHC: OTHER: Aerodynamics - General - Rotor Induced ~ Frequencies

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Last Revised: January 24, 2004