Prop orientation and size

[BoredGuy]

The Power pod has a tilt in it to compensate for prop torque, right? Some time ago, I found a thread which discussed which way the motor would spin for a specific tilt on the power pod, but I can’t find it again. So, which direction (and from the front of the plane or the back) should the motor spin in for a left or right powerpod tilt, the tilt being seen from the top?
Also, for a 132% ft commuter, would a 6 inch prop be too small? 132% would give a wingspan of 1meter.

 

[PsyBorg]

Standing at the tail of the plane looking forward over the cowl the motor should be turning clock wise. Looking straight down over the cowl the motor should tilt down and to the right by what ever angles were designed in the build. If you did a speed build kit it should already be formed. If you are cutting from plans then be sure to get the correct end facing forward as one end is square and the other has the down thrust.

I am not sure on how much the power train would need to be scaled up to meet your needs but I am sure someone else with more knowledge in all that will appear in here shortly to answer.

 

[Merv]

The Power pod has a tilt in it to compensate for prop torque, right?

Yes, the right or left thrust angle is to compensate for the P-factor, some will call it prop torque, some prop wash. There is a debate over the proper term.
The bottom line, if you are using a CW (normal) prop and stitch to a to CCW (pusher) prop, your thrust angle will change from right to left.

So, which direction (and from the front of the plane or the back) should the motor spin in for a left or right powerpod tilt, the tilt being seen from the top?

I agree with @PsyBorg, if you are using a CW prop the thrust angle is to the right.
If you are using a CCW prop, the thrust angle needs to be to the left.
The up or down thrust remains the same with a CW or CCW prop.
When set up correctly, the plane will fly equally well with a CW or CCW prop.

Also, for a 132% ft commuter, would a 6 inch prop be too small? 132% would give a wingspan of 1meter.

I believe a 6" would be too small. You need to look at how much of the prop arc will be outside of the fuse.

The prop size if mostly determined by the motor you are using and how you want to fly. If you want to fly very fast, use a smaller prop spinning very fast. If you want to fly 3D, use a large prop spinning slowly. You need to match the prop to the motor and flying stile.

Larger planes will need a larger motor & prop.

 

[BoredGuy]

I believe a 6" would be too small. You need to look at how much of the prop arc will be outside of the fuse.

Thanks for clearing that up. What proportion of the prop diameter should be out of the fuselage? Also, just a bit curious, what happens if the entire prop arc is within the fuselage? Does it still generate thrust but less, or not generate thrust at all?

 

[Timmy]

Thanks for clearing that up. What proportion of the prop diameter should be out of the fuselage? Also, just a bit curious, what happens if the entire prop arc is within the fuselage? Does it still generate thrust but less, or not generate thrust at all?

pretty much no thrust will be hapening

 

[Merv]

Thanks for clearing that up. What proportion of the prop diameter should be out of the fuselage? Also, just a bit curious, what happens if the entire prop arc is within the fuselage? Does it still generate thrust but less, or not generate thrust at all?

I don’t have an exact answer, that is a percentage of how much of the prop arc can be covered by the fuse. In my thinking, the less percentage covered the better. I'm with @Timmy, if you covered 100% of the prop arc with the fuse, you would have little to no forward thrust.

The area of a circle (A = Pi x R^2) that is critical. Example, take a 6 inch prop, it will make a circle of 28.27 square inches. A 3 inch disc from the center will cover 7.07 square inches. That is only 25% of the prop area. Most of the area and therefore thrust comes from the outer portions of the prop. The parts of the prop arc covered are important. I would much rather cover the inner parts of the prop arc than the outer parts

 

[BoredGuy]

I was asking about the 6in prop because the motor I'm using (d2826 2200kv) is most commonly tested with a 6in prop. However, there is a guy on youtube who tested it with a 7030 prop, with 32A current (the max for the motor is 35A). I can't seem to find a 7x3 prop on aliexpress, though, so would a 7035 work instead?

 

[Merv]

.... so would a 7035 work instead?

It's hard to say, when you start pushing the limits of a motor, small things start to make a difference. Things that worked at Denver, 5,000 feet elevation, will not work at Tampa, sea level. Things that worked when its 75 outside will over heat when it is 95 outside. You might be better off using a lower Kv motor, this will allow you to use a larger prop.

So how wide will the fuse on a 135% Commuter be?

 

[Timmy]

I'm with @Timmy

Team Tim!
Also the outer parts of the prop create more thrust because they move faster. Although the inner prop has more pitch I'm pretty sure the outer area still makes more thrust.

My friend uses a 7x3 on a 2280kv motor. It gets really warm but not hot. I told him to switch back to a 6x4 because it looked like he was stessing the motor. Could that also affect the ESC? he was having ESC problems too.

 

[Merv]

...Could that also affect the ESC? he was having ESC problems too.

It's possible, ESC's get funky when they get hot.

 

[Tench745]

Yes, the right or left thrust angle is to compensate for the P-factor, some will call it prop torque, some prop wash. There is a debate over the proper term.

It's a bit of a divergence, but I thought it was worth noting that P-factor (propeller disk asymmetric loading), prop wash, and prop torque are all different phenomena which contribute to the larger whole.
In an aircraft with a standard Clockwise rotating prop the following is true. In the following examples, Left and Right refer to a pilot in the cockpit's left and right.

P-factor is usually encountered when the aircraft is in a constant positive angle of attack, such as in a climb. The downward moving blade, on the right side of the plane, has a higher angle of attack and higher thrust than the upward moving blade on the left side, resulting in a left-turning moment. (Causes a yawing moment in climbs or decents)

Prop Torque stems from the drag on the prop as it rotates. The drag resists the prop's rotation and imparts a left-rolling tendency to the aircraft. (Causes a rolling moment, especialy with power changes)

Prop Wash, or slipstream, is the force of the the air spiraling around the fuselage and striking the left side of the rudder, pushing the tail to the right and causing a left-turning tendency. (Causes a yawing moment that increases with prop speed)

There is one more factor we don't talk about much in model aviation:
Gyroscopic Precession acts during attitude changes such as pitching up and down, or yawing left and right. Basically, the prop acts like a giant gyroscope, and any time you try to displace a gyroscope from it's plane of rotation, it reacts as if the force was applied 90° around the disk in the direction of rotation from where it was applied. The faster the change, the bigger the force. For example, if you force the nose down suddenly causing a forward force on the top of the prop arc, the plane would react like that force was applied to the right side of the prop arc and the plane would yaw left. (Causes yawing or pitching moments with attitude changes)

TLDR, Each term refers to something specific, and they're each only one part of the picture of why an aircraft may have a left-turning or right-turning tendency.

 

[BoredGuy]

From just

You might be better off using a lower Kv motor, this will allow you to use a larger prop.

So how wide will the fuse on a 135% Commuter be?

Lol, already brought the motor, I guess I'll learn things the hard way eventually. Anyway, the prop is a GWS prop, so it uses less current than the EMP prop the guy on youtube was using. From eyeballing the plans, the fuse on the 100%scale seems to be about 2.5-3 inches (at the prop, it curves out later), so the 132% would be maybe 4-4.5 in thick. I'm conisdering making the plane at 120% instead as well.

 

[shadeyB]

It's a bit of a divergence, but I thought it was worth noting that P-factor (propeller disk asymmetric loading), prop wash, and prop torque are all different phenomena which contribute to the larger whole.
In an aircraft with a standard Clockwise rotating prop the following is true. In the following examples, Left and Right refer to a pilot in the cockpit's left and right.

P-factor is usually encountered when the aircraft is in a constant positive angle of attack, such as in a climb. The downward moving blade, on the right side of the plane, has a higher angle of attack and higher thrust than the upward moving blade on the left side, resulting in a left-turning moment. (Causes a yawing moment in climbs or decents)

Prop Torque stems from the drag on the prop as it rotates. The drag resists the prop's rotation and imparts a left-rolling tendency to the aircraft. (Causes a rolling moment, especialy with power changes)

Prop Wash, or slipstream, is the force of the the air spiraling around the fuselage and striking the left side of the rudder, pushing the tail to the right and causing a left-turning tendency. (Causes a yawing moment that increases with prop speed)

There is one more factor we don't talk about much in model aviation:
Gyroscopic Precession acts during attitude changes such as pitching up and down, or yawing left and right. Basically, the prop acts like a giant gyroscope, and any time you try to displace a gyroscope from it's plane of rotation, it reacts as if the force was applied 90° around the disk in the direction of rotation from where it was applied. The faster the change, the bigger the force. For example, if you force the nose down suddenly causing a forward force on the top of the prop arc, the plane would react like that force was applied to the right side of the prop arc and the plane would yaw left. (Causes yawing or pitching moments with attitude changes)

TLDR, Each term refers to something specific, and they're each only one part of the picture of why an aircraft may have a left-turning or right-turning tendency.

Nice information thank you, however none of my planes have any of that, or affected by any of the above nor do they even bother or understand that, is that why they crash a lot ?
Asking for a friend 😂

 

[Merv]

....so the 132% would be maybe 4-4.5 in thick. I'm conisdering making the plane at 120% instead as well.

A 4 inch disk would cover 44% of a 6” prop & 4.5 inches 54%.

Is there any rule saying you must increase all of the dimensions the same? Make the fuse length & wing any size you want, but slim down the fuse width.

 

[BoredGuy]

A 4 inch disk would cover 44% of a 6” prop & 4.5 inches 54%.

Is there any rule saying you must increase all of the dimensions the same? Make the fuse length & wing any size you want, but slim down the fuse width.

Oh yeah, that’s a great idea! Decided on scaling down to 120% but keeping the wings and stabilisers 125%. Is there anyway to stretch the plans so that the width of the fuse is 120% and the length is 125%? Your tip on tiling the plans on acrobat was awesome, can it be done on that? Now that I think about it, would it look too bad if the entire plane was 133% but the fuselage is only 120%?