Item 0903

DESIGN: UniCopter ~ Dimension, Area & Drag - Drag - In Hover

Reference: DESIGN: UniCopter ~ Dimension, Area & Drag - View - Front, X-Y plane

Note: The high horizontal stabilizer will have little effect during hover but it will have an effect during climb and descent. This may entail the use of a separate page.

 Vertical Drag (Download) in Hover:

Method is from Helicopter Performance, Stability and Control; page 278+

Disk Loading DL is 3.476 lb/ft2

 

Airframe Segment n

Radial Position r/R

Vertical Position Z/R

Dynamic Pressure Ratio (q/DL)n *

Drag Coeff. CDn

Segment Area An [ft2 ]

Multiple of last 3 columns.

Moment about Y-axis ** Previous column * r

 

1

.6

.21

0.7

.2

0.4

0.06

-0.036

 

2

.5

.11

0.6

.4

1.4

0.37

-0.185

 

3

.4

.03

0.5

.4

2.2

0.44

-0.176

 

4

.3

.02

0.3

.5

4.0

0.6

-0.180

 

5

.2

.02

0.3

2.0

2.0

1.20

0.240

 

6

.3

.02

0.3

.5

4.0

0.6

0.180

 

7

.4

.02

0.5

.3

1.0

0.15

0.060

 

8

.5

.02

0.5

.3

0.6

0.09

0.045

 

9

.6

.03

0.7

.3

0.6

0.13

0.078

 

10

.7

.03

0.9

.3

0.6

0.16

0.112

 

11

.8

.04

1.3

.3

0.6

0.23

0.184

 

12

.9

.05

0.2

.3

0.6

0.04

0.036

 

13

1.0

.06

0.0

.3

0.6

0.00

0.000

 

 

 

 

 

Totals:

18.6

4.07

0.358 ***

*** The download penalty is 2 * 0.358 / 1150 = 0.00062 = 0.062% of gross weight [Source ~ RWP1 p. 280 & 282]. My calculation must be out in left field. Mind you the fuselages relative footprint is a lot smaller than Prouty's; perhaps 1% would be a reasonable guess.

*** This value will probably be a lot lower because the dynamic pressure ration at segments 4 and 5 will probably be quite a bit lower. Also the drag coefficient at segment 5 will probably be less than 2.0. The value must be multiplied by 9.5 (ft) to give the actual moment. The downdraft on the HS might increase this value somewhat.

Note: The supports are not yet included in the above.

* [Source ~ RWP1 Figure 1.19]

This is the vertical drag but does not relate to the downwash from the rotor because each element will have a different thrust.

** This is in addition to Prouty's work. This will require an amount of forward cyclic stick to hover. If the center of gravity is ahead of the masts then this might help the balance in hover. I think that the information in this column belongs in 0906.

T = GW + DV The vertical download on a helicopter can be up to 5% of the aircraft's weight. Thrust recovery ~ The thrust increases (improves) as the fuselage is brought closer to the rotor. [Source ~ PHA page 218]

Fuselage:

xxx

 

Landing Gear:

xxx

Horizontal Stabilizer:

 N/A

Vertical Stabilizer:

N/A

 

Main Rotors:

N/A

Total Equivalent Flat Plate Area:

xxx

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Last Revised: July 4, 2004