mickey-gem

I have done a few electric conversions but mostly high wing airplanes.
These high wing designs are alittle more forgiving if the CG is not perfect,
I usually go by the manufacturers suggested CG in the manual.

I am currently doing a Hanger 9 P-51 .60 size Mustang. I am a bit worried
about getting the CG just right. It tends to make quite a bit more difference in
low wing planes, especially warbirds.

Should we be compensating for the fact that we do not have gas tanks in our
planes? In glow planes, ten ounces of fuel makes a big difference in weight from
takeoff to landing, does the CG change that much in mid flight?

Is it safe to balance as listed by the manufacturer?


Kind Regards,

Jesse

jooNorway

This is not a problem in electrics. It is the gassers which are not the ideal thing
In a gasser we usually adjust CG with empty tank and have to live with a plane being noseheavy when the tank is full. Not ideal, but of course the fueltank can be placed at CG and use pump-systems...

When it comes to the question if it is safe to balance as listed by manufactorer an other issue occurs; sometimes the CG recommended by manufactorers is not the best. It both depends on your personal taste, flying style and some manufactorers really (surprisingly!) don`t know. Lot of examples on this...

Search for threads on the Mustang and you probably will find other pilots experiences on this model.

red_z06

My Feedback: (11)

When you convert Glow model with tank behind firewall to Gasser ( typically with built-in pump ) with tank mounted on CG you adjust initial CG forward a little to compensate for the lack of fuel weight in the nose. I apply same on electric conversions. It is always good idea to use forward recommanded cg until u become familiar with the models characteristics.
You alway adjust your cg rearward after initial flight (in most cases) as the plane is simply too stable as a trainer ( in aerobatic planes ).

Here is typical example of initial adjustments used.

GP Patty Wagstaff Extra 78" wingspan 3 5/8" to 3 3/8" initial.
H9 Funtana 90 Electric 69" wingspan 7 1/8" to 6 3/4"

In mosts cases with 60-80" wingspan birds I use 1/4-3/8 shift initially.
Generally, your glow CG is set such that landings are manageble with empty fueltank. If you like the way the glow plane flys during 4th quarter of flight ( near empty ) then you can use that CG setting as your electric CG. However if you prefer how it flies during 1st quarter of flight, you can easily duplicate this in electric by taping the tank that comes with the plane in original location and fill it with 3/4 fuel and start shifting the battery until balance is achieved. Afterwards, make the batt tray so that you can shift the batt in both direction about 2" to compensate for further correction after maiden.

Hope this helps

mickey-gem

Thank you gentlemen! I appreciate you shedding some light on this area for me. I am leary about
maidening the mustang because I converted the H9 Corsair .60 to electric. During the maiden, takoff
was fine jumped into the air after about 15 ft. (with a good headwind) I had to add about 15 clicks of down
trim to level it out. I flew two relatively high passes for trimming, when I retracted the stock mechanical retracts
on the third fly by, she locked into a spin that I could not correct. I feel that by retracting the gear it causes my
other servos to freeze up. Any way that is still fresh in my mind! I really want to do the corsair again, it fleww so
well that first few minutes, and looked fantastic in the air.

On the P-51 I have Century Jet Pneumatic retracts to eliminate any servo lock up issues, if indeed that is what
happened to my Corsair. I just want to make sure I am covering all the bases before I send this one up!


Kind Regards,

Jesse

thunder21

My Feedback: (2)

If you had balanced the Corsair with the gear in the down position, then when you raised the gear your CG would have shifted towards the rear. Since you said you needed down trim for level flight I'd assume you were already a little tail-heavy.

You won't have the same problem with the P-51 since the wheel location relative to CG doesn't change drastically when the gear is raised. With the Corsair, the wheels go from being in front of the CG to behind the CG. So you want to set the CG to be correct with the wheels up.

altacom

My Feedback: (3)

I built a Corsair a few years ago with Retracts. And that mistake took it out for me as well. As soon as the gear retracted, the plane went out of control nose up and stalled into the ground. Balanced it with the gear in the down position. The second one, I balanced with the gear in the retracted position, and lo and behold, it flew great. A bit hot on landing due to being pretty noseheavy, but totally controllable.

Henke Torphammar

also be sure to check so that the retract servo does´t stall = no power to the other servos