What prop should i use?

[norvin20dV2]

Hey guys, i made a simple glider that has a 1200mm wing span, 840mm length and weighs in around at 800-900 grams with all the electronics including the battery. the shape and design is a mix of the FT explorer and FT simple storch. I currently have a 40a ESC and a 2212 2200kv motor and do not know what prop to use. Are there any props that i can use with this motor to give me enough thrust to make my model fly. Should i buy a 1000kv motor to run a bigger prop and will that give me enough thrust?

 

[Merv]

...I currently have a 40a ESC and a 2212 2200kv motor and do not know what prop to use....Should i buy a 1000kv motor to run a bigger prop and will that give me enough thrust?

With the 2200 Kv motor I would start with 5 or 6 inch prop. with a 1000 Kv motor I would start with a 9 or 10 inch prop. The 1000 Kv will have more thrust at low speeds & the 2200 will have more top end speed. I'm not sure your current motor will give enough thrust for a plane that heavy. If you could get the weight down to 600 grams or so, your current motor would work. Your plane is too heavy for it's size, too many 3D printed parts & spars that are too heavy. You would be far better off building a FT tiny trainer or some other known design. If you plan of buying a new motor, I would step up a size, & get a 2218 1000Kv, then you will have plenty of power.

When considering Kv & props, think transmission. Low Kv & large prop are similar to low gear. Lots of lugging power but limited top speed. High Kv & small prop are similar to high gear. Limited lugging power but higher top speed.

 

[norvin20dV2]

So let me get this straight, the 1000kv motor with a larger prop is like a semi truck with more power at lower speeds, and the 2200kv motor with a smaller prop is like a supercar with more power at higher speeds. I have also seen people use 1400kv motors, do you think i should use that for a glider, or use a 1000kv motor with a 10 inch propeller? what do you think is the best for a glider?

But thanks for ur reply ill start looking for 1000kv motors

 

[quorneng]

norvin20dV2
Your analogy about power and kV only applies if the motors are otherwise identical.
Remember kV is simply the speed the motor turns for each volt applied. It is not a indicator of motor power.
The power an electric motor produces is down to its physical dimensions and the applied battery voltage.
Motors with the same kV number can range from delivering 140W to 600W. You have to check the motor specifications.

 

[Merv]

... do you think i should use that for a glider,...

Your plane is way too heavy to be considered a glider. With enough power it will fly, just not as well as it would if it were lighter. If you build it out of foamboard, you have no need for the frame. If you want a frame, you have no need for the foamboard, use some kind of film covering instead. The plane should be build with a frame OR foamboard, not both. Using both is just unnecessary weight.

I agree with quorneng, don't confuse power & Kv. A farm tractor and a race car can both have the same Hp. Put both on a road, the race car will win every time. Hook both of them to a plow, the tractor will win every time. The question is at what speed do you want the power. With electric motors power is measured in watts. When two motors have the same watts, if you want to fly fast, chose the higher Kv motor. If you want to lift a heavy load, chose the lower Kv motor.

Only you can decide if you want to fly fast or lift a heavy load.

 

[quorneng]

norvin20dV2
Just to give you an idea about size and weight this plane is a power conversion of a cheap moulded foam chuck glider. It is supplied with carbon tube reinforcement for the wing and rear fuselage.

1.2m span it weighs 325g ready to go. It uses a 5.3 x 3.3 folding prop with a small 120W motor powered from an 850mAh 3s LiPo.
It glides really well and can fly under power for at least 20 minutes.
The heavier a plane becomes the more power is required and doing that adds still more weight.

 

[norvin20dV2]

With the 2200 Kv motor I would start with 5 or 6 inch prop. with a 1000 Kv motor I would start with a 9 or 10 inch prop. The 1000 Kv will have more thrust at low speeds & the 2200 will have more top end speed. I'm not sure your current motor will give enough thrust for a plane that heavy. If you could get the weight down to 600 grams or so, your current motor would work. Your plane is too heavy for it's size, too many 3D printed parts & spars that are too heavy. You would be far better off building a FT tiny trainer or some other known design. If you plan of buying a new motor, I would step up a size, & get a 2218 1000Kv, then you will have plenty of power.

When considering Kv & props, think transmission. Low Kv & large prop are similar to low gear. Lots of lugging power but limited top speed. High Kv & small prop are similar to high gear. Limited lugging power but higher top speed.

So im not going to use the frame, but can i still use the wing ribs in the wing to form the shape of the airfoil and also the spar. since there are 13 ribs can i cut down to 5 or 7, and can i stil use the 3D printed motor mount, as including the motor it weighs 75g. I am using the Spar for the main wing and the Tail plane, or do you think i should make a whole closed fuselarge, or keep a boom in the back like a FT exlporer. I am in australia and Foamboard here is very scarce, unlike the USA. Foamboard here is heavier, and much more smaller and harder to find a lot more expensive, so i am trying to save weight and money as well. the Foamboard size is a normal A2 size (420 x 594 mm) and one sheet weighs in at around 121g. i am planning on using 2 for the wing, which is 242g, and around another sheet for the fuselarge and the V tail, which is around 363g for the foamboard. With everything else it is estimated to be around 700g without the battery and some parts of the frame and reducing the amount of 3d Printed parts. I think i might just buy the 1000kv motor just to be safe.

 

[Merv]

...I am using the Spar for the main wing and the Tail plane, or do you think i should make a whole closed fuselarge, or keep a boom in the back like a FT exlporer....

Either one will work, I have built planes with FB tails and some with tail booms. Use whatever lightweight materials you have on hand.

..I am in australia and Foamboard here is very scarce, unlike the USA. Foamboard here is heavier, and much more smaller and harder to find..

We use FB in the USA because it is cheap, light weight & widely available. Before I stumbled across FT, I built planes from flat fan foam or corrugated cardboard, the stuff your amazon package comes in. Either will make a great flying plane, I switched to FB because the planes look better, they have a smother finish. If they quit making FB, I would go back to those materials.

Here are 2 videos from Australia building planes from depron. BTW, no ribs were used.
In the USA depron is very hard to get & very expensive, the shipping is far more than the material. I have no idea of your access to it.
Use whatever lightweight materials you have on hand.

 

[Piotrsko]

Late to the party, but: one sheet of your foamboard will build a wing made of 4 panels about 100 mm by 1180 mm. Use a carbon fiber arrow shaft for the spar, no ribs required, flatbotton clark "Y", spar at 30% of chord, CG at high point. 10% of wing needs to be tail area, ruleof thumb engineering