Help! CG problem with master series spitfire

[BobBurger69]

I scratch-built an ft master series spitfire and I have a dilemma with the CG, on their plans, it says the CG is 2 inches from the leading edge, but I do not think it's even close to that, its at least 2.7-3 inches.

If I follow with their suggestion of 2 inches, I will have to at least add another 2300 mAh battery to balance it out, unless Im just using a small battery?

Another problem could be is I'm not balancing it correctly which I doubt, I hold the plane with my thumb and middle finger where CG is indicated.

I maiden the plane with the 2 inch CG, but the nose just wanted to keep coming down, I'm not sure if that's an elevator issue, it was very straight when I pre-flighted it. Oh and I'm using the Ft aura gyro on top of this.

So my question is what would be the correct way of measuring the CG, and if anyone has this particular plane what CG do you use? Thank you.

 

[JasonK]

Did you use a kit or did you purchase foam and cut it out yourself?
Are you using a FT power pack or did you part out the power system yourself?
How much hot glue did you use building it? IE how many sticks?
How do you have the aura mounted? if it is slightly angled, depending on the mode your in, it could be 'leveling out' to that down nose attitude.

the store page is recommending a 4s 2200mAh lipo and 2218/1180kV motor

I would turn off the gyros 100% doing your initial testing to figure out if it is an air frame or FC issue, this will get rid of various trim/stick center/etc issues that can cause the FC to do something other then you expect. if it flies correctly with all of that disabled, then you know your issue is a settings issue, if it flies badly, then you have an airframe issue.

 

[leaded50]

https://www.flitetest.com/articles/balancing_your_plane

 

[Merv]

..... So my question is what would be the correct way of measuring the CG, and if anyone has this particular plane what CG do you use? Thank you.

Balancing the plane on your fingers is a perfectly acceptable way to check CG. I use a scrap piece of wood, usually a 2x4, drill some holes, put in some bbq squires & cut them to an appropriate length. Now you have a hands free balance stand.

Better question, how do you tell where the CG should be?

It should be between 25-30% of the wing area. If you want a stable plane set it at 25%, if you are like me & want a bit of instability, set it at 30%.

Here is an article that gives more information https://www.flitetest.com/articles/easy-aircraft-design

 

[Piotrsko]

Old man rule of thumb: on conventional single forward wing, CG is generally either where they put the main spar, OR, in front of the high point of the wing. 25% is a very conservative value tending for nose heavy but overly pitch stable so that's why FT uses it. If there is more than 5 degrees up trim to fly, it's too far forward or built wrong. My pizza pan wing is at 40% but don't try this at home.

 

[JasonK]

My pizza pan wing is at 40% but don't try this at home.

My vtail stick had the CG 40-50% of wing cord also... it had a really big tail that was quite a ways back.

 

[BobBurger69]

Did you use a kit or did you purchase foam and cut it out yourself?
Are you using a FT power pack or did you part out the power system yourself?
How much hot glue did you use building it? IE how many sticks?
How do you have the aura mounted? if it is slightly angled, depending on the mode your in, it could be 'leveling out' to that down nose attitude.

the store page is recommending a 4s 2200mAh lipo and 2218/1180kV motor

I would turn off the gyros 100% doing your initial testing to figure out if it is an air frame or FC issue, this will get rid of various trim/stick center/etc issues that can cause the FC to do something other then you expect. if it flies correctly with all of that disabled, then you know your issue is a settings issue, if it flies badly, then you have an airframe issue.

I figured out the problem, took it out for a flight turns out, the elevator servo could barely work, only pushed out like 2 grams, ended up crashing it /: