Putting Wings or Winglets on a Mavic?

[grizzard]

No. These are not wings. They are propellers. And there's a huge difference.

In fact the main reason quads are feasible and so stable is because RPM is variable. Helicopters keep the RPM pretty rock steady and control power with angle of attack balanced by torque.

Quads are thrust machines. Helicopters are lift (wing) machines.

Sorry to refute - it's just so.

Actually, they are wings. And no, there is not a huge difference. A propellor is a wing. These propellors are wings. The curvature and angle of attack create a vacuum over the top giving it lift. Who told me so? My Instrument and Commercial license told me so. But you're right about the varying speed that gives it motion control.

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[AlanTheBeast]

Actually, they are wings. And no, there is not a huge difference. A propellor is a wing. These propellors are wings. The curvature and angle of attack create a vacuum over the top giving it lift. Who told me so? My Instrument and Commercial license told me so. But you're right about the varying speed that gives it motion control.

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In most modes of flight these are "fans", not wings. Indeed, on an airplane, the old correct term is "airscrew" as the "efficient" use of them is to "pull" the aircraft through the air as a screw through wood. Alas, not quite that perfectly efficient. In that mode, yes, they are quite like wings except during the beginning of the takeoff roll.

On a drone, they are "thrusters" in almost all modes of flight - pushing air down to repel the earth. I'll grant that at higher speeds forward, the advancing blade is providing conventional "winglike" lift. But it's still thrust/reaction through most of the flight as these flying cameras are used.

(CFI here if that's really important to you).

 

[cobra46]

The sole way to determine CofG (Shy of the entire parts list and their weights and positions) is by suspension, not balance.

• Get a piece of string with a weight on it.
• Pinch one of the rear rotor heads between thumb and finger
• Dangle the drone so it is hanging freely from your (tightly) pinched finger and thumb.
• Dangle the string from the same point.

Where the string crosses the centre line is the longitudinal CofG.

Verify by doing this with a front rotor - warning: harder to hold - so just hang the antenna over your finger.
Dangle again. String crosses the center line at the same point.

That is the CofG. The MP is only slightly nose heavy.

View attachment 6877 View attachment 6878

You absolutely can determine the CG of an object by measure the mass and location of it's points of ground contact. This is how the weight and balance is done on a jumbo jet.

 

[Gernby]

Here is a video I just made in my living room. While hovering, the body seems to be higher than the rear (not just the front props). The front and rear props clearly oppose each other by a few degrees. However, they do not oppose each other from side to side. If it was for stability, I would think they would all oppose each other by some amount.

I suspect that the MP is wasting a lot of energy while hovering (or flying sideways) due to the opposing thrust. The front motors are providing thrust against the rear, and vice versa. However, when flying straight into or away from the wind at enough pitch for either set of props to be level with the ground, they no longer oppose each other. All of the thrust would be providing either lift OR velocity.

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[Gernby]

**** ... did everybody go to bed at 7:52 PM Central Time?

 

[Wombat55]

Here is a video I just made in my living room. While hovering, the body seems to be higher than the rear (not just the front props). The front and rear props clearly oppose each other by a few degrees. However, they do not oppose each other from side to side. If it was for stability, I would think they would all oppose each other by some amount.

I suspect that the MP is wasting a lot of energy while hovering (or flying sideways) due to the opposing thrust. The front motors are providing thrust against the rear, and vice versa. However, when flying straight into or away from the wind at enough pitch for either set of props to be level with the ground, they no longer oppose each other. All of the thrust would be providing either lift OR velocity.

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Yeah, I've noticed that the front and rear propellers seem to be tilted a tiny bit relative to each other, too. My thought was that doing so gives the Mavic more ability to move forward (or backwards) at very small speeds, but that's just a guess. I'll have to test the control sensitivity of the Mavic to forward-to-backwards movements versus side-to-side movements to see if there is any merit to that idea.

 

[Logger]

...CofG does not change w/o something moving onboard (like fuel on a 747-400 being pumped into the vertical stabilizer to reduce tailplane induced drag (since it lifts "down", not up) in cruise)..

Pucker factor of the crew would change quicker than the CofG, if you found a means to pump fuel into the vertical stabilizer on a 747-400

 

[CactusJackSlade]

Most all motors on quads are tilted one way or another... it typically makes for better yaw control... I just looked at the Mavic and the rear motors are tilted WAY forward relative to the front motors axis plane... Again another surprise, usually the motors are tilted in or outward relative to the radius of the four motors... on a Phantom this is very easy to see.

 

[AlanTheBeast]

Pucker factor of the crew would change quicker than the CofG, if you found a means to pump fuel into the vertical stabilizer on a 747-400

Yet, there it is. In cruise, on a 747-400, fuel IS pumped into the vertical stab of the airplane to move the CofG aft and unload the horizontal stabilizer (which pushes down). This reduces induced drag on the horizontal stabilizer thereby saving fuel. Before descent that fuel is pumped back forward.

 

[AlanTheBeast]

Most all motors on quads are tilted one way or another... it typically makes for better yaw control... I just looked at the Mavic and the rear motors are tilted WAY forward relative to the front motors axis plane... Again another surprise, usually the motors are tilted in or outward relative to the radius of the four motors... on a Phantom this is very easy to see.

At first I thought it was a stability thing, but I'm now leaning that it's to keep the rotors from showing in the video.

It could also be related the the folding of the drone so the blades lie so snug against the body...

 

[Logger]

Yet, there it is. In cruise, on a 747-400, fuel IS pumped into the vertical stab of the airplane to move the CofG aft and unload the horizontal stabilizer (which pushes down). This reduces induced drag on the horizontal stabilizer thereby saving fuel. Before descent that fuel is pumped back forward.

Wanna bet?

 

[AlanTheBeast]

You absolutely can determine the CG of an object by measure the mass and location of it's points of ground contact. This is how the weight and balance is done on a jumbo jet.

Of course. Go ahead. Not like I have a small, accurate scale to do so. Sorry I worded that so absolutely. I've amended that post for you too.

 

[AlanTheBeast]

Wanna bet?

No. Can't find source material - so I may be confusing it with another type. This -does- exist on some types.

 

[Logger]

You were on the right track. Just not in the vertical stab on the 744. The tanks are in the horizontal stab.

 

[AlanTheBeast]

Here is a video I just made in my living room. While hovering, the body seems to be higher than the rear (not just the front props). The front and rear props clearly oppose each other by a few degrees. However, they do not oppose each other from side to side. If it was for stability, I would think they would all oppose each other by some amount.

I suspect that the MP is wasting a lot of energy while hovering (or flying sideways) due to the opposing thrust. The front motors are providing thrust against the rear, and vice versa. However, when flying straight into or away from the wind at enough pitch for either set of props to be level with the ground, they no longer oppose each other. All of the thrust would be providing either lift OR velocity.

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I'm not sure what you're getting at. In hover it's simply sitting at the pitch angle where all horizontal vectors cancel out with the appropriate RPM's. (We don't know that the RPM's are nominally the same).

In your video I couldn't find a point where the camera (filming) was level with the laser horizontal line. It would have been interesting to see where the laser line was relative to the rotor planes.

I'd amend your last two sentences as:

IF all RPM's are the same (nominally) then:
There will be one slightly nose down attitude where the rear rotors supply lift+FWD horizontal thrust and the front rotors lift only; and
one slightly nose up attitude where the front rotors supply lift+RWD horizontal thrust and the rear rotors lift only. (edited).

But again that assumes the same RPM.

 

[AlanTheBeast]

You were on the right track. Just not in the vertical stab on the 744. The tanks are in the horizontal stab.

But I think those are raw range extending storage, not trim. What I was describing was a dynamic effort to trim the CofG in order to reduce induced drag.

 

[Logger]

That describes the system found on airbus aircraft such as the a330/340 and a380. Transfers fuel forward and aft to optimise CG improve fuel economy, I gather.

 

[AlanTheBeast]

That describes the system found on airbus aircraft such as the a330/340 and a380. Transfers fuel forward and aft to optimise CG improve fuel economy, I gather.

It does - at the expense of stability. The notion is that in cruise there will be little in the way of control inputs or disturbances so sacrifice some longitudinal stability for reduced drag (by unloading the horizontal stab which pushes down in flight).

 

[BadBob]

When forward speed and rpm are added together the props become much more inefficient at the blade tips since the blades operate horizontally in the direction of flight instead of vertically like in a fixed wing. This is why good efficient helicopter blades are shaped to control the vorticity at the blade tips. Now if only we had after market blades made for rotor wings instead of fixed wings then the flight time would increase.


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[AlanTheBeast]

When forward speed and rpm are added together the props become much more inefficient at the blade tips since the blades operate horizontally in the direction of flight instead of vertically like in a fixed wing. This is why good efficient helicopter blades are shaped to control the vorticity at the blade tips. Now if only we had after market blades made for rotor wings instead of fixed wings then the flight time would increase.

The stock props have to work well enough across the flight range. Unlike helicopter blades there is no pitch adjustment over the course of one turn in forward flight. Unlike helicopter blades the RPM is very variable.

They (DJI or 3rd party) could add tip fences or other clever anti-vortex changes - but in the end, this is a flying camera, not a fuel gulping revenue machine. (Note the fence can go upward to pretty much the same effect like winglets on an airplane to avoid the down tip hitting the drone...).

I even wonder if a ducted fan could be more efficient - while providing more protection to the rotors and people...