|
A i r c r a f t S
u p e r C a
l c u l a t o r 7.0
calculation bug fixes with optimizations
for the Weedhopper ultralight © 6/20/2008, all rights reserved. |
| MAC
And Neutral Point
|
use the same units of measure for all entries!
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 generated by the wing and tail are
balanced.
25% - 35% MAC is generally
accepted as a good range for the CG of a conventional tailed
aircraft .
Placing CG 5% - 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. Too high
of a static margin results in elevator stall at take off and
landing.
|
The Equations
|
Wing Sweep, C = |
(S * (A + 2B)) / (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 = |
Y * (A + B) |
| tail area, TA = |
YY * (AA + BB) |
| wing aspect ratio, ARw = |
((Y * 2) ^ 2) / WA |
| tail aspect ratio, ARt = |
((YY * 2) ^ 2) / TA |
| Tail Arm = |
(D - wing AC) + tail AC |
| tail volume, Vbar = |
(TA / WA) * (Tail Arm / MAC) |
| NP (%MAC) = |
0.25 + (0.25 * sqr(sqr(ARw)) * Vbar |
| ideal CG (%MAC) = |
NP - Desired Static Margin |
| Moment (total) = |
(Lt wheel Wt * Lt Arm) + (Rt Wheel Wt * Rt Arm) + (Ctr Wheel Wt
* Ctr Arm) + (Pilot Wt * Pilot Arm) + ( Psngr Wt * Psngr Arm) + (Fuel
Wt * Fuel Arm) |
| actual CG (%MAC) = |
((Moment / Total Wt) - (Datum2LE + C)) / MAC |
| actual static margin % = |
(NP - actual CG) / MAC * 100 |
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 -
2008, all rights reserved. Unauthorized use of the codebehind,
html, or content is strictly prohibitied.
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.
|
|
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 |
|
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) : |
|
| Enter
1 for Weedhoppers, 0 for all others : |
|
| Desired Static Margin
(5% = twitchy 15% = mushy 10% recommended) : |
|
| |
| Weight And Balance
|
| |
Weight |
Arm |
| Left Main Wheel : |
|
|
| Right Main Wheel : |
|
|
| Nose or Tail Wheel
: |
|
|
| Pilot : |
|
|
| Passenger : |
|
|
| Fuel Tank (gallons
of gas) : |
|
|
| Datum
Point from Wing Root LE (neg is aft):
For Weedhoppers, this is the LE bracket bolt hole! |
|
| |
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 Apsect = |
|
Tail Aspect = |
|
| Wing Taper = |
|
Tail Taper = |
|
| W sweep C = |
|
T sweep CC = |
|
| Tail MAC = |
|
T MAC dist = |
|
| Tail Arm = |
|
Vbar = |
|
| Lt wheel mnt = |
|
Rt wheel mnt = |
|
| Center wheel mnt = |
|
Pilot mnt = |
|
| Passngr mnt = |
|
Tank mnt = |
|