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Old Jul 26, 2004, 04:11 AM
Douglas Kaip
Guest
n/a Posts
Symptoms of CG being too far back.

Hello all,

I have a plane that is hopefully going to take its maiden flight in the
next couple of days. The CG is set according to the plans, however, because
of the design of the plane I expect the CG to be very attitude sensitive.
(The engine is on a pod above the plane.) What kind of behavior should I be
watching out for? Will it tend to be very pitchy?

Thanks,

Douglas Kaip


Old Jul 26, 2004, 05:59 AM
It flies? I like it!
Joined Apr 2004
868 Posts
An aft CG causes pitch sensitivity... touch of up... Woops!, down... Woops! quite unpleasant, actually. I had a brain fade today with a newly renovated Midwest Electric Hots and the CG was about 1" too far back (new brushless setup was much lighter than the old can motor and car NiCd's which caused the nose to be MUCH lighter)... anyhow, it is very fresh in my memory how hard it is to hang on and land.
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Old Jul 26, 2004, 08:11 AM
Ted Campanelli
Guest
n/a Posts
Re: Symptoms of CG being too far back.

On 7/26/2004 4:02 AM Ted shuffled out of his cave and grunted these
great (and sometimes not so great) words of knowledge:

> Hello all,
>
> I have a plane that is hopefully going to take its maiden flight in the
> next couple of days. The CG is set according to the plans, however, because
> of the design of the plane I expect the CG to be very attitude sensitive.
> (The engine is on a pod above the plane.) What kind of behavior should I be
> watching out for? Will it tend to be very pitchy?
>
> Thanks,
>
> Douglas Kaip
>
>


Do to the sensitivity of the CG I would suggest, for the maiden flight
anyway, move the CG forward about 1/4".

Yes, this will make the plane nose heavy and sluggish. For your maiden
flight though, you will be expecting the sluggishness, however, after
trimming it it out and insuring that the engine pod thrust lines are OK,
you can move the CG back. I would suggest moving the CG back in 1/8"
increments.

A nose heavy plane flies sluggishly, a tail heavy plane flies once.

Old Jul 29, 2004, 12:11 PM
Robert A. Plourde Jr.
Guest
n/a Posts
Re: Symptoms of CG being too far back.

If you find it is tail heavy in the air, just keep the speed up and try and
land it hot. The speed helps out in a tail heavy situation.

"Douglas Kaip" <dkaip@net.e_a_r_t_h_l_i_n_k> wrote in message
news:JU2Nc.16625$Qu5.9047@newsread2.news.pas.earth link.net...
> Hello all,
>
> I have a plane that is hopefully going to take its maiden flight in

the
> next couple of days. The CG is set according to the plans, however,

because
> of the design of the plane I expect the CG to be very attitude sensitive.
> (The engine is on a pod above the plane.) What kind of behavior should I

be
> watching out for? Will it tend to be very pitchy?
>
> Thanks,
>
> Douglas Kaip
>
>



Old Jul 29, 2004, 02:11 PM
Don Hatten
Guest
n/a Posts
Re: Symptoms of CG being too far back.

Hmmm, I've found the opposite to be true. Overcontrolling on a tail heavy
plane is more likely with more airflow over the elevator. Or I
misunderstood what you are saying. If it zooms up, drop the nose to keep
it above stall speed, cut the throttle and go easy on the elevator movement
while you get it on the ground.

Having the engine above the wing will have a pitch down tendncy with
throttle and a pitch up as you remove power. Before the maiden flight, if
you're concerned about it, add more weight to the nose for the maiden but
make it removeable so you can move the CG back to the plans location as you
test fly the plane.

I mean, why risk the plane. If YOU think the CG is too far back, move it
forward for the maiden flight and then move it back as you fly it. A nose
heavy plane flies poorly, a tail heavy plane flies once.

Your mileage may vary.
Don


"Robert A. Plourde Jr." <noone@hotmail.com> wrote in message
news:O%9Oc.32$Yr.30@okepread02...
> If you find it is tail heavy in the air, just keep the speed up and try

and
> land it hot. The speed helps out in a tail heavy situation.
>
> "Douglas Kaip" <dkaip@net.e_a_r_t_h_l_i_n_k> wrote in message
> news:JU2Nc.16625$Qu5.9047@newsread2.news.pas.earth link.net...
> > Hello all,
> >
> > I have a plane that is hopefully going to take its maiden flight in

> the
> > next couple of days. The CG is set according to the plans, however,

> because
> > of the design of the plane I expect the CG to be very attitude

sensitive.
> > (The engine is on a pod above the plane.) What kind of behavior should

I
> be
> > watching out for? Will it tend to be very pitchy?
> >
> > Thanks,
> >
> > Douglas Kaip
> >
> >

>
>




Old Jul 29, 2004, 02:11 PM
PaulBK58
Guest
n/a Posts
Re: Symptoms of CG being too far back.

you are both right, but you are talking about differeent things. yes, a
rearward CG makes the airplane more pitch sensitive. but airspeed is the only
thing that might keep the tail from tucking, so flying fast, especially on
landing, may be the only prayer. for example: a few years ago a guy came out
wiht a .40 ARF something, the field experts told him it was really nose heavy
and he proceeed to put lots of weight in the rear. everything was more or less
okay until he throttled back, at which time the tail basically pointed towards
the ground, and that was that.
Old Jul 29, 2004, 06:11 PM
Paul McIntosh
Guest
n/a Posts
Re: Symptoms of CG being too far back.

Good points. You can go fairly severe with nose heavy before the plane
becomes unflyable. When in doubt, start at about 20-25% from the leading
edge and work back.

--
Paul McIntosh
http://www.rc-bearings.com
"Don Hatten" <hattend@starband.net> wrote in message
news:V9bOc.80$qB1.59@fe25.usenetserver.com...
> Hmmm, I've found the opposite to be true. Overcontrolling on a tail heavy
> plane is more likely with more airflow over the elevator. Or I
> misunderstood what you are saying. If it zooms up, drop the nose to

keep
> it above stall speed, cut the throttle and go easy on the elevator

movement
> while you get it on the ground.
>
> Having the engine above the wing will have a pitch down tendncy with
> throttle and a pitch up as you remove power. Before the maiden flight, if
> you're concerned about it, add more weight to the nose for the maiden but
> make it removeable so you can move the CG back to the plans location as

you
> test fly the plane.
>
> I mean, why risk the plane. If YOU think the CG is too far back, move it
> forward for the maiden flight and then move it back as you fly it. A nose
> heavy plane flies poorly, a tail heavy plane flies once.
>
> Your mileage may vary.
> Don
>
>
> "Robert A. Plourde Jr." <noone@hotmail.com> wrote in message
> news:O%9Oc.32$Yr.30@okepread02...
> > If you find it is tail heavy in the air, just keep the speed up and try

> and
> > land it hot. The speed helps out in a tail heavy situation.
> >
> > "Douglas Kaip" <dkaip@net.e_a_r_t_h_l_i_n_k> wrote in message
> > news:JU2Nc.16625$Qu5.9047@newsread2.news.pas.earth link.net...
> > > Hello all,
> > >
> > > I have a plane that is hopefully going to take its maiden flight

in
> > the
> > > next couple of days. The CG is set according to the plans, however,

> > because
> > > of the design of the plane I expect the CG to be very attitude

> sensitive.
> > > (The engine is on a pod above the plane.) What kind of behavior

should
> I
> > be
> > > watching out for? Will it tend to be very pitchy?
> > >
> > > Thanks,
> > >
> > > Douglas Kaip
> > >
> > >

> >
> >

>
>
>



Old Jul 29, 2004, 06:11 PM
Don Hatten
Guest
n/a Posts
Re: Symptoms of CG being too far back.

Never experienced a "tail tuck" due to weight being in the back and pulling
back on power. Sounds like the guy's thrust line was waaay off. We're the
field experts wrong... Did he make it tail heavy and just forgot to get the
nose down when it pitched up (got complacent since things were going "more
or less okay")?

Don

"PaulBK58" <paulbk58@aol.com> wrote in message
news:20040729143121.25422.00002403@mb-m29.aol.com...
> you are both right, but you are talking about differeent things. yes, a
> rearward CG makes the airplane more pitch sensitive. but airspeed is the

only
> thing that might keep the tail from tucking, so flying fast, especially on
> landing, may be the only prayer. for example: a few years ago a guy came

out
> wiht a .40 ARF something, the field experts told him it was really nose

heavy
> and he proceeed to put lots of weight in the rear. everything was more or

less
> okay until he throttled back, at which time the tail basically pointed

towards
> the ground, and that was that.




 


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