dsercflyer

I have a "new" ESM P-51B which I've flown 5 times, each flight as horrifying as the last. Flight characteristics are that of a tail heavy model.

I have Saito 180 power and have tried 5 different CGs.

The mfgr says 157mm from the leading edge (using the wing LE where the dowels are placed, where the LE fits into the wing saddle). That was tailheavy - bad flight

I was told to use 33% of the "mean chord" (chord hereafter defined as thedistance from where the long LE of each wing half intersect, not from the central extension of the LE -to the center of the TE). In other words, chord ignores the LE "wedge extension" on the front/center all P-51 wings. That was also tailheavy.

Arfpros (from whomI purchased the model) says use 28 - 30% behind the LE. Still tail heavy.Lousy flight.

My last flight I used an arbitrary CG 1/2" ahead of the 28%CG and it was no better.

I have since added 14 oz of lead to the nose which places the CG at 22% (3.75" behind the mean LE) and haven't tried it yet.

Is anyone out there familiar with my experiences with this aircraft and have any suggestion ao comment??

Dan

Props4ever

What scale and wingspan is your model?

My Nosen P51B is some nose heavy and it's CG is 6"-7" on the fuselage, behind the LE on wing saddle...

Juss checked, it's 6.5" to be exact on mine..

91zulu

My Feedback: (2)

A tail heavy plane will be pitch sensitive. So are you saying when flying it is flying nose high and you have to give a lot of down trim in order for it to fly level and any little input of the elevator it pitch up sharply or down? Explain what is happening when you fly so we could tell if it is tail heavy or an incidence or engine thrust problem. Pics will help too with a mark of the CG. If you keep pulling the CG forward as much as you say, the elevator should be heavy by now. I other words more elevator is needed to lift the nose.

dsercflyer

All Day Dan

My Feedback: (5)

Dan, use this website to calculate the correct position of the CG if no one knows the point. Put the CG at the 25% point of the MAC. If that does not work, then your incidences may be wrong. Measure them. A good starting point is 0-0. Dan.

Dash7ATP

How are your control throws set up?  If your throws are set too high it will be quite sensitive also.

Dash

oldtimer4759

hello Dan,
I have the ESM P-51B, set the CofG at 130mm max back from the glue joint at the centre of the wing, set your high elevator rates at maybe 5/8" and your low rates at about 3/8" depends on how sensitive you like your models to be, about 40% expo to start with will help as well, here are a couple of threads to look at.
that CofG is still marginal, I would go to 125 mm to start with,
how some of these companies come up with their recommended CofG and control throws has to be pure guess work, this is a typical example of it, the kits are great, I also have the ESM P-47, it is one of the nicest models to fly, the book CofG for that was also wrong.
http://www.rcgroups.com/forums/showt...141908&page=38
http://www.rcgroups.com/forums/showthread.php?t=1426316
Oldtimer.

All Day Dan

My Feedback: (5)

Oops! Here's the website. Dan.
http://www.geistware.com/rcmodeling/cg_calc.htm#mac

dsercflyer

Thanks for your reply. Could you be mure specific about where the 130mm is measured from? Do you mean from the flat front edge (with the dowels) that sits in the very front of the wing saddle? The mfgr says 157mm from this front edge, and I have tried several CG's forward of this mark and still can't get her to settle. I have a Saito 180 installed, so I'm a little heavy in front anyway.

kahloq

I have this plane also. CG is 126mm from the leading edge of the wing against the fuse on mine and she flies rock solid.

I had read several ppl on rcgroups lose their model cuz they went with the 157mm manual cg setting...then I found someone mention 130mm somewhere. I put it at 126mm to be safe and it flies very well. I didnt use control throw inches measurements. I put low rates at 50% on aileron and elevator and 80% for rudder with 50% expo on each using a JR radio.

Some ESM planes require a lot of weight up front to balance. If you can move RX battery over the engine, do so.....or somewhere ahead of the firewall. If using onboard glow, you can put that up front also.

I have several ESM planes and most dont have the Cg right in the manual. Some are too tail heavy and some like the b-25 and me-110 and way too nose heavy. The only one so far that I have that was correct was the ME-109E. But i dont own all of them so cant report on cg bad,good on ones I dont have.