Author Topic: PP Ground School help.  (Read 1066 times)

Offline MK-84

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Re: PP Ground School help.
« Reply #15 on: February 06, 2012, 04:40:36 PM »
I always remembered it as WAM! (Because if you dont do your W&B that is the sound your airplane will make when it kisses the ground)

Weight+Arm=Moment.

As you can see on the top part of the graph you have different stations with lines. Figure out how much everything weighs. Say you and your instructor combined weigh 250 pounds, so your moment is 8,500 for the front. You have 30 gallons (180 pounds) of gas and nothing in the baggage compartment or back seat, so your moment is 7,500 for the gas. Say empty moment on the airplane is 52,910, So you should get 68,910. Now look at your moment envelope down on the bottom and find where you are (use 1450 as your empty weight in this case) 1,880 pounds and essentially 69k on the moment.

You should be in the upper middle of the utility category

Any chance you could describe this more in detail?  I am having trouble trying to wrap my pitiful brain around it.  :uhoh

Offline Tupac

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Re: PP Ground School help.
« Reply #16 on: February 06, 2012, 04:45:16 PM »
Any chance you could describe this more in detail?  I am having trouble trying to wrap my pitiful brain around it.  :uhoh

Are you looking at the graph in conjunction with it?
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Offline MK-84

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Re: PP Ground School help.
« Reply #17 on: February 06, 2012, 04:56:10 PM »
Possibly, and maybe a real world example...I'm not really sure, I understand what the purpose is, but I cant get seem to get my brain to "understand it"

Offline Tupac

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Re: PP Ground School help.
« Reply #18 on: February 06, 2012, 05:04:20 PM »
Possibly, and maybe a real world example...I'm not really sure, I understand what the purpose is, but I cant get seem to get my brain to "understand it"

I'll see if I can post a more detailed explanation of what a W&B is when I get home. I'm out running errands right now
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Offline MachFly

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Re: PP Ground School help.
« Reply #19 on: February 06, 2012, 06:00:55 PM »
Let me know what you guys think and what you found in the real world.
What is the difference between the utility category and the normal category.

How would it apply in real life.

Looks like you pretty much got it. I do recommend you use the weight x arm to get the moment as it is more accurate and I think the method is easier in general. After I get the the final numbers I match them to the center of gravity chart (the 2nd one that Tupac posted) and make sure that it all works out. Right now I got tired of doing all the math myself and just do it on the (electronic) E6B. However I recommend you do everything manually until your 100% sure that you understand the way it works and how to do it. Another thing you can do (later on) is make a .xls file that will do all the calculating for you.

I don't remember the exact regs but if the aircraft is in utility category your allowed to practice spins. See by calculating W&B you get your CG (center of gravity), that is the point around witch your aircraft will move.
Here is the difference between having a forward CG and an aft CG:

ForwardAft
Longer T/O rollShorter T/O roll
Longer Landing distanceShorter Landing distance
Harder to rotate & flareEasier to rotate & flare
Slower cruise TASHigher cruise TAS
Higher fuel burn rateLower fuel burn rate
More stableLess stable
Easier to stallHarder to stall
Easier to recoverHarder to recover
Less maneuverableMore maneuverable



MK-84, I think this explanation should help you out as well.
« Last Edit: February 06, 2012, 06:16:36 PM by MachFly »
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