Calculating Basic Empty Mass

[Aytonace]

Hi

Having trouble working out the following for BEM. So far I've been able to calculate the BEM and CG with no trouble, using the datum as a reference for plus or minus the arm for the weight at each wheel depending on where the datum is taken from, but I'm usually given the datum (which is not included in the question here). Am I missing something simple here? Q and A below.

Q. An aeroplane with a two-wheel nose gear and four main wheels rests on the ground with a single nose wheel load of 725kg and a single main wheel load of 6000kg. The distance between the nose wheels and the main wheels is 10 metres. What is the BEM and how far is the centre of gravity in front of the main wheels.

A. BEM of 25,450kg and CG is 57cm in front of the main wheels

Any help appreciated!

[RichardH]

You can put the datum anywhere you like. So in this case I am going to make the datum on the main wheels.

2 x 725 = 1450 kg x arm to main wheels 10 m = -14500
4 x 6000 = 24000 kg x zero arm = zero moments = 0

BEM = 25450 CoG 14500/25450 = .57 metres (57 cms in front of main wheels)

[Aytonace]

Awesome thanks the reply!

[Beethoven]

I’m sure you’re aware but just in case, beware of questions where they ask for the position of the CG in relation to the nose wheel rather than From the datum. Read the answer options very carefully. I did the exam last week and finished with 20 seconds to go so make sure you are VERY quick with the calculations. Also I seemed to spend a lot of time extracting the numbers required from very “wordy” questions.

There also seemed to be way more calculation-type questions in the real exam compare to the typical question bank mock exam, which I was finishing in an average of 30-40 minutes or so.

Best of luck.

[Tinstaafl]

Exam technique: RTFQ ie read the question carefully so you work out what you're supposed to work out.

Better exam technique: RTFQ + ATFQ ie as before but make sure you answer what the question asks eg distances given from one reference point but the question asks for an answer from a different reference point

Even betterer technique: As before + CYFA ie go back (if you have time) and check you answered everything, and your answers were as per the question.