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Center of Gravity For an RC plane with no steering

#1
I am working on a diy foam board RC plane project. I am new to building RC planes and would like some input. I want this plane to fly as far as possible. I have a motor battery and esc. Wings are fixed and so there will be no steering mechanism. I do have the ability to control engine speed, which should be enough to control the planes lift and decent. What should the Center of gravity be for this plane to function but not be so sensitive when giving it throttle?


Here are some pics of my build.
The shoe strings were my idea to make the wing adjustable forward and backwards to change center of gravity.

Thanks for your help!
planesideview.jpg
plane3.png
 

FDS

Well-known member
#2
I would add an elevator and rudder to that set up. If you only have one more servo channel then put ailerons on with a single servo in the middle of the fuselage. There’s lots of how to‘s on that.
If you want to fly far then you need a larger wing, that one is very short.
Why not try building a simple soarer or Tiny Trainer as a GLIDER first, they will use 2 channels, rudder and elevator, and give you a great chance of success. You can even try using a Tiny Trainer basic wing on your design, it has a great shape for stability and lift.
Elastic bands and BBQ skewers are a good way to secure the wings, a bit easier and with less holes than your innovative laces!
Well done for getting something built, now to get it flying.
Have you throw tested it?
 
#3
Thanks for the reply! Yes it goes pretty good! For this project I am only allowed to use a motor as a source of control. I tested a heavier plane (twice as heavy) that I had previously built with the same motor combo and when throwing it at half throttle then ramping up to full throttle it went straight up and stalled then crashed. Is there any key to finding the perfect center of mass to get it to not be so sensitive when giving it throttle? I also made this plane 6 inches longer in total length to hopefully help with controlling it. Have not tested this new design with the motor yet.
 

Merv

Well-known member
#4
I'd recommend a CG @ 25% of the wing.
To me, it looks like the thickest part of the wing is too far forward, I'd move it back to about 30% of the wing. I'd also recommend adding some dihedral or polyhedral to the wing to improve stability.
 

Piotrsko

Well-known member
#5
Can you define the task a little better?

You can add a stability effect by by trimming the outside edges of the wing with a table saw and adding end plates so the wing looks like this : \______/ shape and size is non critical. Square to the flight path is, which is why I suggest table saw with good fences. Keep the center of mass as low as possible. If the plane flies well as a glider, then you need down and left thrust (assuming ccw rotation viewed from the nose looking back). Perhaps 5 degrees down, 2 degrees left. Make the rudder/vertical stabilizer bigger in area. Wouldn't hurt to make the horizontal stabilizer bigger also preferred using a jack screw trim system like a super cub.
 

mrjdstewart

Well-known member
#7
ok, sorry i need to actually answer your questions... :sneaky:

it looks like you may be a bit nose heavy but the best test is a test glide. take it some place it can land w/o damage and chuck it a few times. adjust the CG and see what works best.

the advice of 2.5 left and 5 degree down on the motor mount will certainly help with on throttle lift, but if lift is what you want...
when setting up a new plane the first thing i do after getting it trimmed is roll inverted and neutral sticks. if it stays level you got your CG spot on.

are any limitations placed on the wing size? your wing is very short for you airframe. if i was you i would double it if efficient flight is your plan.

good luck,

me :cool:
 
#8
So for this project the main limiting factor is weight. My origional design weighed around 3 pounds this one is 2. It was suggested that the plane be lighter than 2 lbs inlcuding the motor/battery pack and esc all will be placed in the front as we are given the pack as a unit.
motor.JPG
 
#9
Current plane specs:
weight empty plane = 23.1 oz
simulated weight of motor and battery = 11 oz (which is that grey box you can see in the front of fuselage)
wingspan= 28 inches
fuselage= 33 inches
plane has two carbon fiber arrows in fuselage on roof will include a picture below.
also has two in the wing.

IMG_6684.jpg
 

Attachments

#10
I think I going to try and keep the fuselage as is maybe remove more material since it has two carbon fiber arrows in it. the box in the front only serves as a holder for battery and esc. have bolts with the right thread pitch to connect arrows together to make a wider wing. any suggestions on a good starting point for width? Requirements for this project are kind of stiff. Thanks to all of you for the awesome tips!
 

Merv

Well-known member
#11
Weight is the enemy and you need to lose a lot. My flite test planes come out weighing 26-28 oz, including everything, motor, battery, etc. Only 1 arrow shaft is needed in the wing. Don’t use any duck tape, it’s way too heavy, use packing tape instead. Use hot glue sparingly, it’s heavy and adds weight. I have had great results with a wing loading of 10-12 oz/sqft. So a wing 45x8 would give you a target weight of 25-30 oz.
 

Piotrsko

Well-known member
#12
Requirements for this project are kind of stiff. !
Hate to be picky, but: what EXACTLY ARE THE REQUIREMENTS? what I have seen so far is some sort of plane that flies with a variable speed drive plug in module. And for a non-areobatic plane under 4lbs, there is NO NEED for carbon fiber anything, foamboard structure and string tape is more than adequate. If you get to use a "C" pack you get 3.5 lbs thrust.