I have never read this in any trike POH:
"CG should be in the vicinity of the rear seat."
Throw that trike out the window :).
And if its your DTA POH that says that. May be its a bad translation from French but throw it out anyway, and let me know when and where, I'll clean it all up for you :).
Abid
--- In Sport_Aircraft@yahoogroups.com, "Jim Bair" <JimBair@...> wrote:
>
> 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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