Putting Wings or Winglets on a Mavic?

[AlanTheBeast]

I think that's the one part he's missing. It's not a lifting "disc" so much as it is the forward sweeping blade acting as a wing.

Which is fine for helicopters but doesn't translate well to quads as it's a "reaction" machine rather than a "lift" machine. To be sure the props do behave like wings to some degree - just not to the degree they do on helos.

As to the "lifting" body in forward flight, no, the nose is pitched down - if anything it makes a downward thrust.

 

[AyeYo]

As to the "lifting" body in forward flight, no, the nose is pitched down - if anything it makes a downward thrust.

For sure.

 

[rydfree]

That explanation started out as "Let's make it simple" so it was a dumbed down way to go about it but was solely to explain the rotor becomes a wing basically which was what I didn't think he was getting at all . They do provide extra lift in forward motion even if pitched down somewhat . Rotors do not stay perfectly flat as they are lifting the weight of the craft. The forward advancing blade is doing the work and you can fly with that one blade only just fine if you counterbalance the other side to compensate for the missing blade . I have a single bladed RC heli in 450 size . Anyway , on to more aerodynamics principles people argue over so , Can a plane take off from a moving conveyor ? LMAO

 

[Gernby]

I disagree with all of you guys!

I think it has everything to do with weight distribution! The Mavic is very nose-heavy, which means that the front props have to run at a higher RPM than the rear when hovering. However, when it's pitched forward, the center of gravity moves in relation to the props, allowing the rear props to do more of the work. At the perfect pitch angle (air speed), the 4 props should all be turning about the same RPM, which I assume would be an optimal RPM for this prop design.

It shouldn't be hard to test. Don't the flight logs show RPMs and motor current draw? If so, then hovering in a steady wind should result in the RPM and / or current draw changing based on the relative angle of the MP vs. the wind.

 

[rydfree]

IS the mavic nose heavy ? Wow that's a bad design . I haven't checked that since I didn't build it from scratch but I will tonight !

 

[CyberNate]

The Mavic will use less energy moving at a slow speed because it stays out of it's own prop wash. It takes more energy to stabilize itself in turbulent vs non-turbulent air that it is continuously moving into while in motion. Any variation in motor speed for stability corrections takes more energy. You will see that the craft is more stable when moving slowly versus when standing still.

Regarding the idea that the Mavic body acts like a wing, then the force would be in the wrong direction. The mavic leans forward to move forward. A wing with the leading edge lower than the trailing edge would generally result in a down force unless there is exaggerated shaping of the wing to give great air speed on the underside of the wing. The Mavic is not shaped in a manner that would induce lift.

 

[Tas47]

According to the work of these Melbourne University (Aus) engineering students the best way to increase the endurance of a multicopter is to reduce weight and improve airflow by modifying the arms to a vertical airfoil design.
Ultra-light 3D printed titanium firefighting drone to aid in bushfires
The improvement is pretty impressive.
"The clever 3D printed design has been a great success, with the airfoil shaped arms helping to reduce drag by 60% and increase flight time to around 45 minutes, double that of the previous design."

 

[Qoncussion]

I dont think the Mavics body produce any significant lift wings might help but as other explained there are other physics which are affecting the craft

Additionally, the wings would add weight. The additional lift offered from the airfoil of the wings would only be noticed when moving forward, at speed. The wings would also block the downdraft of air produced by the props. In the end, I think it would cost more battery than it's worth. Come to think of it, wings would probably attribute to VRS (Vortex Ring State), creating turbulent air below the craft.

 

[AlanTheBeast]

I disagree with all of you guys!

I think it has everything to do with weight distribution! The Mavic is very nose-heavy, which means that the front props have to run at a higher RPM than the rear when hovering. However, when it's pitched forward, the center of gravity moves in relation to the props, allowing the rear props to do more of the work. At the perfect pitch angle (air speed), the 4 props should all be turning about the same RPM, which I assume would be an optimal RPM for this prop design.

It shouldn't be hard to test. Don't the flight logs show RPMs and motor current draw? If so, then hovering in a steady wind should result in the RPM and / or current draw changing based on the relative angle of the MP vs. the wind.

The MP is not very nose heavy. The CofG is right about the 2nd light from the front on the battery - so only very slightly nose heavy. So the 4 rotors should have very close speeds in forward flight - the forward ones working a bit harder perhaps because there may be a down moment due to airflow against the wide front when pitched nose down.

(Easy to find the CofG: hold the drone by an extended arm rotor (thumb and finger). Imagine the line down to the floor. Same with another rotor. Where those lines cross is the CofG (longitudinally). In fact a single "hang" is enough because it has to cross the longitudinal centreline of the drone.

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). Centre of lift is something else and obviously changes on the MP to effect changes in pitch.

I wish the logs had RPM for each motor and better yet volts/current averages (per second) for the flight - that would give me GREAT data for a project of mine.

 

[AlanTheBeast]

According to the work of these Melbourne University (Aus) engineering students the best way to increase the endurance of a multicopter is to reduce weight and improve airflow by modifying the arms to a vertical airfoil design.
Ultra-light 3D printed titanium firefighting drone to aid in bushfires
The improvement is pretty impressive.
"The clever 3D printed design has been a great success, with the airfoil shaped arms helping to reduce drag by 60% and increase flight time to around 45 minutes, double that of the previous design."

Notice they said reduce weight. That is important in a device the derives lift from straight out bashing air down to fight gravity. (reaction). F=ma, after all, so reduce m and less F is needed. a is constant.

It is, though, nice that they've improved the downward flow as it's not pushing against a square surface as on the MP. That helps too, to be sure.

That said I'd like to know how much of the time improvement is due to weight and how much to streamlining the arms.

 

[Gernby]

If you try to balance the MP on your fingers from 2 corners, it will tilt its nose down. That indicates that it is nose heavy. Also, if you video the MP while it is hovering at a high frame rate, the captured pattern indicates that the fronts are spinning at a different RPM than the rear.

 

[AlanTheBeast]

Additionally, the wings would add weight. The additional lift offered from the airfoil of the wings would only be noticed when moving forward, at speed. The wings would also block the downdraft of air produced by the props. In the end, I think it would cost more battery than it's worth. Come to think of it, wings would probably attribute to VRS (Vortex Ring State), creating turbulent air below the craft.

The design of such wings would have to avoid being hit by downflow - (mid body struts?). Other consideration is the Reynolds number which essentially means for small air vehicles you need a lot of speed to get lift from a small wing. I have no WAG number for that, but probably not until at least 50 km/hr - and probably faster - and then I wonder if that lift would pay by less energy from thrust. Said wing would have to have quite a + incidence angle v. the body since thrust is by pitching the nose down. Air impinging the top of the drone is actually pushing the drone down in forward flight with the MP as it is - more for the motors to fight!

VRS is particular and I've wondered if the max vertical speed programmed by DJI for these drones prevents VRS. In a helicopter, in still wind, if you descend perfectly vertically and attain a certain vertical speed you're very likely to create a VRS. This is a concern to me as I've made some pretty aggressive vertical descents - I guess I better back off!

I see a few videos out there describing VRS for drones - including a Phantom.

 

[ATXdrone]

Let me make it simpler. AlanTheBeast is stating this (with my wording): Imagine flying a waterproof helo, under a column of falling water (a waterfall). Yes of course it would get knocked out of the air. But IF it could fight back, with more power, it would hover in the waterfall. In real life an impossibility due to the mass of water. But think of how much power it would require!

Now replace the water with air. You fly under a downrush of air, an "airfall". This pushes the entire aircraft down. To compensate you add lift (more thrust). This is possible because air is so much less dense than water.

AlanTheBeast and rydfree, in their own ways, are both saying that while hovering, the quad creates its own column of air, a "waterfall of air" that it is fighting. In moving foward, it is getting fresh, clean air into its props that has no downward momentum (that it has to compensate for), providing better lift at a given torque.

 

[AlanTheBeast]

If you try to balance the MP on your fingers from 2 corners, it will tilt its nose down. That indicates that it is nose heavy. Also, if you video the MP while it is hovering at a high frame rate, the captured pattern indicates that the fronts are spinning at a different RPM than the rear.

Edited for Cobra: One sure way to determine CofG (Shy of the entire parts list and their weights and positions or using a small, accurate scale) 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.

 

[AlanTheBeast]

Let me make it simpler. AlanTheBeast is stating this (with my wording): Imagine flying a waterproof helo, under a column of falling water (a waterfall). Yes of course it would get knocked out of the air. But IF it could fight back, with more power, it would hover in the waterfall. In real life an impossibility due to the mass of water. But think of how much power it would require!

Now replace the water with air. You fly under a downrush of air, an "airfall". This pushes the entire aircraft down. To compensate you add lift (more thrust). This is possible because air is so much less dense than water.

AlanTheBeast and rydfree, in their own ways, are both saying that while hovering, the quad creates its own column of air, a "waterfall of air" that it is fighting. In moving foward, it is getting fresh, clean air into its props that has no downward momentum (that it has to compensate for), providing better lift at a given torque.

Nicely put.

 

[rydfree]

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 probably have a partially discharged battery ,LOL

 

[Robbyg]

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

Yes that's the only easy way to check it and as expected they designed it slightly nose heavy. I wonder how many grams of extra nose weight it has?

 

[Wombat55]

Let me make it simpler. AlanTheBeast is stating this (with my wording): Imagine flying a waterproof helo, under a column of falling water (a waterfall). Yes of course it would get knocked out of the air. But IF it could fight back, with more power, it would hover in the waterfall. In real life an impossibility due to the mass of water. But think of how much power it would require!

Now replace the water with air. You fly under a downrush of air, an "airfall". This pushes the entire aircraft down. To compensate you add lift (more thrust). This is possible because air is so much less dense than water.

AlanTheBeast and rydfree, in their own ways, are both saying that while hovering, the quad creates its own column of air, a "waterfall of air" that it is fighting. In moving foward, it is getting fresh, clean air into its props that has no downward momentum (that it has to compensate for), providing better lift at a given torque.

Hmmmm. OK, now my new wild idea is some sort of contraption in which, say, each of the four propellers is not only spinning around at high speeds due to its own electric motor, but each propeller is also slowly rotating around another, separate vertical axis so that each propeller is constantly being supplied with relatively "fresh", non-moving air even though the drone as a whole may be hovering in one fixed location in the air. But maybe that's all starting to get a bit complicated....

 

[cobra46]

Unless I'm not understanding either one of you, you both failed to mention the biggest reason for the higher flight times when not hovering. It has to do with how clean the air is that the blades move through. When hovering each blade is moving through the rotor wash of the previous blade which is highly inefficient. When any rotary winged aircraft moves forward with sufficient speed, the blades are moving through relatively clean air which greatly improves efficiency. This is only advantageous up to a point where parasitic drag becomes large and efficiency drops back off again.

Back in Vietnam, they would regularly fly helicopters overloaded but to take off the crew chief would run next to the bird until it had some forward speed and then jump on.

I was a helicopter mechanic in the Army and hold a degree in aeronautical engineering although I work as a mechanical engineer.

 

[Gernby]

I would bet that we could come up with many ways to prove that the MP is nose heavy, but thankfully, it seems we agree it is. However, another factor that I just noticed is that the front props are pitched toward the rear a few degrees, but the rear props are not. I suspect the pitch in the front motors is required to offset the heavy nose.