Re: Light-Sport Aircraft Yahoo group WSC Weight and Balance

Hi Gary,

Trikes often have some fairly vague things in the POH like, "CG should be in the vicinity of the rear seat."  And if it is, quite honestly that is fine.  As you know, in fixed wing as well there is some leeway even though the W&B chart is very black and white.  If you find yourself in the upper right corner of the chart (like the typical FAA test example. haha) and then you add just 2 more pounds and you're outside the line, it doesn't mean the plane will automatically crash.  The really critical thing in trike CG is that it result in the mains being lower than the nose wheel so you don't land on the nose. 

 

As far as the wing position, sometimes I find it more clear to think in extremes.  If you hang the trike from the nose of the wing, it would fly very fast and very straight down.  If you hang it from the trailing edge, the wing would go nose up and stall.  But somewhere in the middle is the magic spot where everything is in balance and it flies perfectly.  That occurs at probably in the vicinity of 20-35% MAC just like an airplane.  (Somewhere forward of center of the wing.) Don't get hung up on the precise numbers, just the concept.  (I'm not trying to set up some quibble thing.)  The manufacturer sets the wing up so you have a range in which to hang the trike from it.  And that range usually isn't very large.  Like 1 1/2" or so.  Can you go outside that?  Usually, but you're now experimenting.  My Aerotrike flew much better when I drilled a new hole about an inch forward of the former most forward hole.  You just can't get too carried away. 

 

All of this stuff is why you do W&B on an experimental before you even fly it.  If you design and build an airplane in your garage (perfectly legal) the FAA will come inspect it for you and look at your W&B calcs as part of your required paperwork.  If the CG is way outside the normal range of where it normally lies in relation to the MAC of the wing, they will do you the favor of letting you know your craft will most likely crash.  This is something you'd like to know before flying the thing.  Keep in mind, this whole thread started because an individual brought up the fact he had hit on the nose wheel a couple of times and that causes real control problems.  This is why CG is important.

 

Jim

 

----- Original Message -----

From: Gary Orpe

To: Sport_Aircraft@yahoogroups.com

Sent: Sunday, October 04, 2009 9:55 AM

Subject: RE: Light-Sport Aircraft Yahoo group WSC Weight and Balance

 

Does it make any difference what position the wing is in? I know that you have to have a known position on fixed wing and then measure. Also CG doesn't mean anything unless you have the manufacturers data on what the CG should be and the way to measure it.

 

Are trikes different than this?

 

 Gary O.
 N181RL
 661 746-4780

-----Original Message-----
From: Sport_Aircraft@yahoogroups.com [mailto:Sport_Aircraft@yahoogroups.com] On Behalf Of Jim Bair
Sent: Sunday, October 04, 2009 6:58 AM
To: Sport_Aircraft@yahoogroups.com
Subject: Re: Light-Sport Aircraft Yahoo group WSC Weight and Balance

 

> >More likely W&L Weight and Loading.

> Not really. The Weight and loading is easy.
> We add your weight, my weight, the fuel, and the trike,
> and see if it adds up to less than 992. It does.
> I can do that in my head.
> No, our concern is what you mentioned about the
> nose wheel hanging lower.

You must have done this plenty of times Jim,
... it must be quick and easy for you.

How about doing just one more for the considered
loading (Richard doing his checkride with you),
and put it in the group files?
front seat 300
rear seat ~178
fuel 30

I've never seen a sample of a WSC weight and balance
in any text book.
(showing as you promise "nosewheel height")

Thanks,
Mike

WSC W&B is like any other W&B, so there doesn't have to be a sample of WSC
specific W&B in the textbook. In almost every textbook I have seen there is
the generic teeter totter examples so that the pilot understands the concept
of weight x arm = moment and that when all the weights are added up and all
the moments are added up, you simply divide the total moments by the total
weight and you have the CG. In trikes, the CG is typically "in the
vicinity of" the rear seat, and simply has to be behind the hang point for
the rear wheels to hang lower than the nose wheel. Once the CG of the
trike is determined (this involves weighing the trike with scales at each
wheel) it is simple to measure out the locations of the front seat, rear
seat, fuel tank, baggage area, etc., and plug in the numbers. I made a
spreadsheet for my W&B worksheet (or W&L worksheet, I don't care what you
call it. Same math.) for each trike so I could plug in the numbers for each
one with some various loading scenarios. I don't have the DTA one here at
the house, but I do have a copy of my old aerotrike paperwork and for a 300#
guy, which I happened to choose for the worst case scenario, the math showed
that the CG was still aft of the hang point location, meaning the trike
would hang lower in the rear than the front.

I did look in the SP written test study guide and you are correct, the
chapter on W & B is really lame. Even for fixed wing people there is almost
nothing on W & B. Probably because at the LS level, our loading options are
so limited that there is more concern with weight than with the balance
part. However, when we have a triker say he'd had a problem with landing on
the nose wheel a couple of times and it wasn't very pleasant, that should
tell him that he should figure out what's going on. Any textbook at the
Private Pilot level and above will have some info on how to do basic weight
and balance and certainly an instructor textbook should have it so when you
say you haven't seen WSC specifically addressed, I believe you. However,
you will be able to figure it out for a trike because the concept is no
different.

Personally, I didn't use the EAA supplied W&B paperwork. I made my own
because it was more complete and had examples of a variety of loading
scenarios to cover about any contingency. A story that was related to me
once underscored the importance of understanding this and knowing how to
calculate it. Triker is approached by a cameraman wanting ot attach a movie
camera to nose. Triker says OK. Next day, cameraman shows up with a camera
twice as big and attached to about a 3' boom to attach to the nose. Warning
bells go off in triker's head. He understands W&B and does a calculation
and determines nose will be hanging low. That's why every triker should
understand the concept. So when someone comes out with something out of the
ordinary, be it a camera on a boom or a 320# student in front, he knows to
do the WxA=M thing and figure his CG. Only tools needed are a tape measure,
scales, and some sort of plumb bob for extra accuracy.

Jim

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