|
A i r c r a f t S
u p e r C a
l c u l a t o r 7.5.1
© 2005 - Dean A. Scott, all rights reserved. |
| MAC
And Neutral Point
|
use the same units of measure for all entries!
The Equations
|
Wing Sweep, C = |
(S * ((2 * B) + A)) / (3 * (A + B)) |
| MAC (length) = |
A - (2 * (A - B) * (0.5 * A + B) / (3 * (A + B))) |
| MAC location, d = |
Y * ((A - MAC) / (A - B)) |
| wing area, WA = |
2 * Y * ((A + B) / 2) |
| tail area, TA = |
2 * YY * ((AA + BB) / 2) |
| wing aspect ratio, ARw = |
(2 * Y) / ((A + B) / 2) |
| tail aspect ratio, ARt = |
(2 * YY) / ((AA + BB) / 2) |
| Tail Arm = |
(D - wing AC) + tail AC |
| tail volume, Vbar = |
(TA / WA ) * (Tarm / MAC) |
| NP (%MAC) = |
0.25 + (.7 * Vbar * (As / Aw) * ( 1 - de / da)); |
| ideal CG (%MAC) = |
NP - Desired Static Margin |
| actual CG (%MAC) = |
((Total Moment / Total Wt) - (Datum to LE + C)) / MAC |
| actual static margin % = |
(NP - actual CG) / MAC * 100 |
Center of Gravity (CG) is the point where the weight of the aircraft is balanced.
Neutral Point (NP) is the point where the aerodynamic forces of the wing and tail are balanced.
25% - 35% MAC is the typical range for the CG of a conventional aircraft .
Placing CG 5% to 15% of MAC in front of NP creates a longitudinal (pitch) stability
called Static Margin. A lower margin (tail heavy) produces less stability and greater elevator authority, while a
higher margin (nose heavy) creates more stability and less elevator authority. A static margin that's too high
may result in elevator stall at take off and landing.
Vbar is a unitless volume coefficient, based on the ratio of the wing surface area to the horizontal tail group (stabilizer and elevator)
surface area and the distance between the wing's AC and the tail's AC. It quantifies the tail's aerodynamic effectiveness and is used to calculate NP. Typical values range from
0.35 (smaller or closer to the wing, thus less effective) to 0.6 (larger or farther from the wing, thus more effective).
|
COPYRIGHT NOTICES:
- CG & MAC
equations adapted from the Public Domain.
- NP equations courtesy Alasdair Sutherland (see C.G.
Position article on Bloobird
Radio Flyers)
- Neutral Point and
Weight & Balance
Calculators developed by Dean A. Scott and are (c) 2005 -
, all rights reserved. Unauthorized use of the codebehind,
html, or content is strictly prohibitied.
Additional thanks to Geoff Haynes, vice-president, HMAC, for refinements to the code.
Email the author at dascott / at /
chrusion / dot / com to obtain copyright clearances to redistribute,
repurpose, and/or reuse all or parts of the code and content
herein.
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TESTIMONIALS:
|
|
I have been using your software/calculators to set up the
RC gliders that I build for myself. I had two planes go down
because of the lazy calculators that are out there. Since I
have found your calculator I have had nothing but success.
I just want to say, THANK YOU VERY MUCH!!!
David Field |
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|
Enter the following data: |
Wing |
Tail |
| Root Chord (A, AA)
: |
|
|
| Tip Chord (B, BB)
: |
|
|
| Sweep Distance (S,
SS) : |
|
|
| Half Span (Y, YY)
: |
|
|
| Distance between wing & tail
root LE's (D) : |
|
| Desired Static Margin
(5% = twitchy 15% = mushy 7-10% recommended) : |
|
| |
| Weight And Balance
|
| |
Weight |
Arm |
| Left Main Wheel : |
|
|
| Right Main Wheel : |
|
|
| Nose or Tail Wheel
: |
|
|
| Pilot : |
|
|
| Passenger/Cargo/Accessory : |
|
|
| Fuel Tank (gallons
of gas) : |
|
|
| Datum
Point from Wing Root LE (neg is aft): |
|
| |
Calculated Results
|
| Mean Aerodynamic
Chord (MAC) = |
|
| MAC distance from
root chord (d) = |
|
| Wing Aerodynamic Center
aft of root LE = |
|
| Ideal Center
of Gravity %MAC = |
|
| Ideal CG
aft of root LE = |
|
| Actual Center
of Gravity %MAC = |
|
| Actual CG
aft of root LE = |
|
| Actual CG
from main axle (neg. is aft) = |
|
| Neutral Point %MAC
(NP) = |
|
| Neutral Point aft
of Wing's root LE (NP) = |
|
| Distance between Ideal CG
and NP (E) = |
|
| Distance between Actual CG
and NP = |
|
| Desired Static
Margin % = |
|
| Actual Static
Margin % = |
|
| Gross Takeoff Weight
of Aircraft = |
|
| Empty Weight of
Aircraft = |
|
| Total Moment of
Aircraft = |
|
| |
Wing Area = |
|
Tail Area = |
|
Wing Aspect = |
|
Tail Aspect = |
|
| Wing Taper = |
|
Tail Taper = |
|
| W sweep C = |
|
T sweep CC = |
|
| W sweep Angle = |
|
T sweep Angle = |
|
| Tail MAC = |
|
T MAC dist = |
|
| Tail Arm = |
|
Vbar = |
|
| Lt wheel mnt = |
|
Rt wheel mnt = |
|
| Ctr wheel mnt = |
|
Pilot mnt = |
|
| Passngr mnt = |
|
Tank mnt = |
|