MaxLoadFactor calculation?

[FrankD]

Hello modders,

 

would anyone know for sure how to calculate the Gear's MaxLoadFactor?

 

In the manuals I have read to date, the landing gear limitations are expressed as maximum rate of descent at touchdown (SCORE! ) for a given mass.

 

Simply converting the acceleration expressed in feet per second to G is more probably wrong since I'm obtaining atrociously high figures.

 

So, what's the trick gents? (Yup, Googled it, but no joy)

[Fubar512]

Maximum allowable descent rate at maximum gross weight x 1.5 per individual component should be good enough for gov'ment work (or for ThirdWire gameplay purposes, for that matter).

[FrankD]

Thank you Fubar512.

[FrankD]

Fubar, I thought that it would be easy but I must admit that it's tougher than that.

 

I've got a maximum allowable descent rate, for 13007 lbs, of 400 feet per minute.

 

So, and I may be totally wrong doing this, I convert the descent rate to g.

 

(400 / 60) * 0.03108095 = 0.207206333 , rounded to 0.21 g

 

Ridiculously low, isn't it?

 

 

So, without any (more?) logic, I converted ft/m to g and the figure were, while a bit high, closer to the figures usually seen.

 

400 * 0.03108095 = 12.43238 , rounded to 12.43

 

But I'm sure that it's an heresy.

 

Please Fubar, pimp my calc

 

(aka "how would you proceed, Fubar?")

 

 

 

 

 

 

Edited March 15, 2011 by FrankD

[+Dels]

FrankD,

 

You need to multiply your answer by acceleration due to gravity (making sure you use the same units)

 

So from your calulation: 0.207206333 x 32.1740486 ft/s^2 = 6.67 'g'

 

That's a bit closer to the mark.

 

Dels

[FrankD]

Thanks for answering Dels.

 

As I'm already dividing by the gravity (* 0.03108095), I should simply use the feet per minute figure converted to feet per second?

Edited March 15, 2011 by FrankD

[+Dels]

Ahhh, now I get it. Excuse my ignorance before.

 

Your answer of 0.21 g is correct, but that assumes that the aicraft decelerates from 400ft/min to 0ft/min over a 1 second period.

 

So the calculation would be rate of deceleration divided by acceleration due to gravity. (Hence a ratio between the two)

 

The rate of deceleration requires a time period. IIRC:

 

v = u + at

 

Where v is final speed, u is initial speed, a is acceleration and t is time.

 

Plugging in your figures: v=0, u=400ft/min (6.67ft/s), a=unknown and t=1

0=6.67+(a*1)

a=-6.67ft/s^2 (i.e. deceleration)

Therefore, 6.67/32.174=0.207 (as per you calculations above)

 

So to get an accurate 'g', you would have to know the time period that the aircraft decelerates over.

 

Dels

[FrankD]

Thanks again Dels.

 

Well, as it is landing, I assume that the descent rate actually go from 400ft/m to 0ft/min within a short moment as soon as it touch down, isn't it?

 

 

By converting the approach speed for the maximum landing mass, 140 knots, to m/s and then g, rounded to two decimals, I get 7.34 g.

 

A good looking figure, but does it have any relevancy from your point of view?

 

 

(It's a pity, I've got a manual full of figures but either it doesn't fit with the model, either I can't understand how to use them in the game, it's very frustrating. I would love to have an FM tutorial at hand!)

Edited March 15, 2011 by FrankD

[+Dels]

You could work out time using:

 

v^2 = u^2 + 2as, where v, u and a are as above, but s is displacement.

 

So, if we assume the tyre is rigid and the compression stroke of the struts is 0.3048m (1 foot to make it simple)

Rearranging the formula above we can get:

 

s = (0.5*(v+u))*t

1 = (0.5*(0+6.67))*t

1/t = 0.5*6.67

t = 1/3.335

t = 0.3 (rounded)

 

So, a = 22.23 ft/s^2 and the 'g' would be 0.691.

 

Still quite low, but a compression stroke of 0.3m is pretty long.

 

Dels

[+Dels]

I don't think airspeed should be in the equation because that will introduce all sorts of complications.

[FrankD]

If i got it right , the shock stroke would be 26-40mm (0.04 m) for the main gear and 85-103mm for the nose gear. (That are the value that have to be checked during the pre flight check).

 

 

 

 

Anyway, that's still pretty low for a gear max load factor, even multiplied by 1.5, isn't it?

 

 

(Roger about airspeed, I'm already on the edge of my math abilities, I don't need any complication more)

Edited March 15, 2011 by FrankD

[+Dels]

Well acctually, that would work.

 

Shock stroke 0.04m = 0.131ft

So, t = 0.131/3.335 = 0.0393sec

And a = 6.667/0.0393 = 169.64ft/sec^2

 

So, 'g' = 169.64/32.174 = 5.27

 

That looks good to me...

[FrankD]

Awesome!

 

Now I'm gonna try to elaborate an excel formula to smooth the process.

 

Thank you very much for your guidance Del, I wish I had your knowledge!

[FrankD]

Formulas for Excel (or Google if you omit the = sign)

Rate of Descend at touchdown: either in feet/s or meters/s

Shock stroke: feet or meter

Imperial measures

=(rate of descend/(Shock stroke/(0.5*Rate of Descend)))/32.174

 

Metric measures

=(rate of descend/(Shock stroke/(0.5*Rate of Descend)))/9.80665

Thanks again Dels!

[Fubar512]

I recall watching a documentary on the A-4 Skyhawk, and what I got out of watching it, was a new-found respect for the scooter, namely how incredibly well-built it was.

 

They showed early landing-gear fatigue testing, were an A-4 prototype loaded to simulate max gross weight was dropped onto a concrete pad from some 3 meters height. If my memory serves my right, the test model achieved 24 fps just before the tires hit the concrete, and they repeated this "torture" test several hundred times, in order to simulate a lifetime of carrier landings.

[Derk]

I recall watching a documentary on the A-4 Skyhawk, and what I got out of watching it, was a new-found respect for the scooter, namely how incredibly well-built it was.

 

They showed early landing-gear fatigue testing, were an A-4 prototype loaded to simulate max gross weight was dropped onto a concrete pad from some 3 meters height. If my memory serves my right, the test model achieved 24 fps just before the tires hit the concrete, and they repeated this "torture" test several hundred times, in order to simulate a lifetime of carrier landings.

 

 

Fantastic !!!!!!!

 

Derk

[+Dels]

Happy to help. I'm just glad we got somewhere with this and didn't hit a brick wall.

 

Good luck with your modding.

 

Dels