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Mini Arrow Too Far Aft CG

#1
Okay, obviously I'm doing something wrong here. I built 2 mini Arrows out of Dollar Tree foam board and they came out perfect! Once I mount the recommended Emax 2300 motor, 30A ESC, Lemon Receiver, and a 3S 1300mAh battery shoved all the way forward, that's where it all goes bad. The CG is about 1 inch from the firewall instead of the 1.75 inches. I had to add 50g of weight in the nose just to get it to balance. I also placed the receiver and ESC in the compartment bays trying to move as much as I can forward. The AUW is now 509g.
The CG seems to be perfect until I put the vertical fins on, which is way aft of the CG. I used foam board to make one set of fins and 3-D printed another set (which is actually lighter) and with either one, the CG is too far aft without adding 50g of lead weight. Does anyone have a clue as to why??
Thanks!
 

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SlingShot

Maneuvering With Purpose
#2
Okay, obviously I'm doing something wrong here. I built 2 mini Arrows out of Dollar Tree foam board and they came out perfect! Once I mount the recommended Emax 2300 motor, 30A ESC, Lemon Receiver, and a 3S 1300mAh battery shoved all the way forward, that's where it all goes bad. The CG is about 1 inch from the firewall instead of the 1.75 inches. I had to add 50g of weight in the nose just to get it to balance. I also placed the receiver and ESC in the compartment bays trying to move as much as I can forward. The AUW is now 509g.
The CG seems to be perfect until I put the vertical fins on, which is way aft of the CG. I used foam board to make one set of fins and 3-D printed another set (which is actually lighter) and with either one, the CG is too far aft without adding 50g of lead weight. Does anyone have a clue as to why??
Thanks!
Can we see a straight up and down top view please? From here, it looks like your motor is sticking out too far. The firewall should be flush (or nearly so) in the back.
 
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buzzbomb

I know nothing!
#3
Okay, obviously I'm doing something wrong here. I built 2 mini Arrows out of Dollar Tree foam board and they came out perfect! Once I mount the recommended Emax 2300 motor, 30A ESC, Lemon Receiver, and a 3S 1300mAh battery shoved all the way forward, that's where it all goes bad. The CG is about 1 inch from the firewall instead of the 1.75 inches. I had to add 50g of weight in the nose just to get it to balance. I also placed the receiver and ESC in the compartment bays trying to move as much as I can forward. The AUW is now 509g.
The CG seems to be perfect until I put the vertical fins on, which is way aft of the CG. I used foam board to make one set of fins and 3-D printed another set (which is actually lighter) and with either one, the CG is too far aft without adding 50g of lead weight. Does anyone have a clue as to why??
Thanks!
Nope. No clue. Aren't I helpful? Really though, I'm new here, and I haven't a single clue as why your CG is messed up. There are some very experienced people, and some not so much who will chime in soon, with some helpful advice. I hope.

So why did I post? Do I just like to read my own posts? Well, yes I do actually. I also wanted to say that those are some great looking bevel cuts! I'm working really hard to get to that level and I am nowhere close. Good job, man!
 
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Keno

Well-known member
#6
What you have here is a CG point and a reflex problem. I just launch my new Arrow and it required adjustment to its reflex or up elevon in my case. Keep the plans CG point and make sure the nose drops slightly when you check it. Then add a little bit more up elevon reflex. Building weight forward and aft has been a problem for all and it take time to learn how unwanted weight is added wither it be for or aft. My experience is when you bring a new wing to the field be ready for up elevon. Happy flying
 
#9
Nope. No clue. Aren't I helpful? Really though, I'm new here too, and I haven't a single clue as why your CG is messed up. There are some very experienced people, and some not so much who will chime in soon, with some helpful advice.

So why did I post? Do I like to read my own posts? Well, yes I do actually. I also wanted to say that those are some great looking bevel cuts! I'm working really hard to get to that level and I am nowhere close. Good job, man!
Nope. No clue. Aren't I helpful? Really though, I'm new here, and I haven't a single clue as why your CG is messed up. There are some very experienced people, and some not so much who will chime in soon, with some helpful advice. I hope.

So why did I post? Do I just like to read my own posts? Well, yes I do actually. I also wanted to say that those are some great looking bevel cuts! I'm working really hard to get to that level and I am nowhere close. Good job, man!
 

Mode 1

Active member
#11
I'm impressed that you got all of the electronics inside. On my arrow with the 2205 I had to move the rx into the wing to accommodate the 30amp esc and only a 850mah 3s battery. Well done!
 

SlingShot

Maneuvering With Purpose
#14
It is a bit, I did a 3-D print, which fits beautifully! Even on the other plane, I used the 3/16 plywood and it was flush. Still the same results.
That is a LOT. Your fancy motor mount is screwing you my friend. It has the motor WAAAAY too aft. Use a standard firewall and you should be much much better.
 

buzzbomb

I know nothing!
#20
I see what you did there. Awesome!! o_O:D You sir, rock! Mentally Jimmy Hendricks level kind of rock. Seriously, on my best day, I might could have come up with that. Reading Comprehension 101.
Denny H. said:
Thanks! Here is the foam board cutter I use.
What makes that better than a utility knife? The handle?

I don't know why I can't quote where you quoted me twice to make the point of me liking my quotes. Isn't the internet awesome? Regardless, the question still stands.