Putting Wings or Winglets on a Mavic?

[Chase R]

Well ****. I expected to fast forward and see someone with a wing mounted to this thing flying around.

 

[Gernby]

Here is another video I took last night at 120 fps with various resolutions to capture the prop speeds. In all views, there seems to be an apparent difference in RPMs in the front.

 

[AlanTheBeast]

Here is another video I took last night at 120 fps with various resolutions to capture the prop speeds. In all views, there seems to be an apparent difference in RPMs in the front.

Given the difference in angle that's not surprising - could you shoot video from the side in the same plane as the level laser? See sketch. I want to see if the rear rotor plane is horizontal.

 

[Wombat55]

Perhaps the way to extend the range and flying time of a Mavic would be to add wings or winglets AND enable the axes of the propellers to turn in flight like one of those US Marine Osprey tilt-rotor aircraft so that the Mavic could transition to flying more like a normal RC aircraft. Of course, that would be a big engineering effort. Also, the rate of Mavic crashes would probably be at least 10-times higher than they are now.

 

[CactusJackSlade]

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.

.

Huh? Hows that?

 

[Gernby]

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).

Sure, the vertical vectors while hovering will add up to the total weight of the MP, and the opposing horizontal vectors will cancel out (wasted energy). However, if the center of gravity while hovering is relatively closer to the front rotors, the front rotors will have to spin faster than the rear. Since the horizontal vectors must cancel out, the average pitch of the front and rear would need to tilt more forward, so that the horizontal component force of the front (spinning faster with less rearward pitch) is equal and opposite to the horizontal component of the rear (spinning slower with more forward pitch).

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.

See 0:45 - 0:50

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.

I disagree with the amendment, since I don't think the RPMs would necessarily be the same (nominally) when that "ideal" attitude is achieved (ideal meaning perfectly horizontal front OR rear rotors). Maybe they would, but maybe not, due to the CoG relative to the props at the given body pitch. The CoG is way below the props, so body pitch will have a large impact on the location of CoG relative to the props, which will have a large impact on rotor speeds.

As I'm sure you know, CoG is 3 dimensional, and the string test you illustrated identifies only 2 of those dimensions (ignoring the vertical dimension). It seems that a more relevant test would be to suspend the MP from the front pair of rotors (not prop stands), capture the angle of the MP relative to vertical (using a string or laser level), then do the same while suspending the MP from the rear props. It's been 33 years since I took Trigonometry, so I'm really rusty on my theorems, but I'm sure there would be some strong correlations between the body pitch (attitude?) while hovering, front / rear rotor RPMs while hovering, and the difference in angles measured above.

 

[AlanTheBeast]

Sure, the vertical vectors while hovering will add up to the total weight of the MP, and the opposing horizontal vectors will cancel out (wasted energy). However, if the center of gravity while hovering is relatively closer to the front rotors, the front rotors will have to spin faster than the rear. Since the horizontal vectors must cancel out, the average pitch of the front and rear would need to tilt more forward, so that the horizontal component force of the front (spinning faster with less rearward pitch) is equal and opposite to the horizontal component of the rear (spinning slower with more forward pitch).



See 0:45 - 0:50



I disagree with the amendment, since I don't think the RPMs would necessarily be the same (nominally) when that "ideal" attitude is achieved (ideal meaning perfectly horizontal front OR rear rotors). Maybe they would, but maybe not, due to the CoG relative to the props at the given body pitch. The CoG is way below the props, so body pitch will have a large impact on the location of CoG relative to the props, which will have a large impact on rotor speeds.

As I'm sure you know, CoG is 3 dimensional, and the string test you illustrated identifies only 2 of those dimensions (ignoring the vertical dimension). It seems that a more relevant test would be to suspend the MP from the front pair of rotors (not prop stands), capture the angle of the MP relative to vertical (using a string or laser level), then do the same while suspending the MP from the rear props. It's been 33 years since I took Trigonometry, so I'm really rusty on my theorems, but I'm sure there would be some strong correlations between the body pitch (attitude?) while hovering, front / rear rotor RPMs while hovering, and the difference in angles measured above.

Identifying the middle (3d) CofG is not quite as easy. On a "sight" hang I see it as about 1 cm above the bottom of the heat sink. But lot's of chance of error there.

I'll take another look at the video ... but can't find it anymore (1st video) - got a link.? NEVER MIND - FOUND IT.

As to the amendment, that is _with_ forward (or rearward) movement if the RPM are equal, From your video, in hover, it does appear to have a difference in speed, but can't tell if it's significant.

 

[AlanTheBeast]

Huh? Hows that?

The blades point up a little wrt to the level camera view. Less likely to be seen by the camera.

Another reason for the angle may be for folding and having the blades lie flat when folded.

Or longitudinal pitch stability. Or to offset the pitch moment due to the slightly forward CofG as Gemby proposes. Or because it looks cool.

(Why don't I think it's for pitch moment correction? because it would have been far simpler to correct the CofG by distributing the parts inside correctly).

 

[AlanTheBeast]

Gembey. See annotated photo from your first video. (Revised, better position to see the front legs in full)

The dark blue line is the "rest line" when the drone is sitting on the ground. Yellow box; divide the line between the two front legs.

The magenta is your laser line.

The green lines are the rotor planes as best I can see.

The light blue is a copy of the forward rotor line (same angle)

As you can see the fore rotor plane tilt and the aft rotor plane tilt are near mirrors of each other in hover.

If you could repeat this with the camera "in plane" and on a stand (so it doesn't move) and with a lighter and even coloured background, then I think we'd have a great means to check this out.

 

[Helo]

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.

Boy that brings back memories, fortunately I was flying and didn't have to run. The old C model (huey) gunships when loaded with ammo and fuel would not hover so we would hop them to the runway then get them light on the skids and slide down the runway and as you said the crew chief and gunner would run beside. When they were out of steam they would jump aboard and by then you would have enough speed to hit "transitional lift" (clean air through the rotar system producing greater lift) and you would lumber off,

This has been one entertaining thread to read!

 

[Helo]

A S-58 (and former snake) pilot friend of mine mentioned doing pedal turns to reduce torque on the tail rotor, making more power available to the main rotor, to power out of hot and high locations with sling loads in Vietnam.

More memories of the old days.

 

[cobra46]

Boy that brings back memories, fortunately I was flying and didn't have to run. The old C model (huey) gunships when loaded with ammo and fuel would not hover so we would hop them to the runway then get them light on the skids and slide down the runway and as you said the crew chief and gunner would run beside. When they were out of steam they would jump aboard and by then you would have enough speed to hit "transitional lift" (clean air through the rotar system producing greater lift) and you would lumber off,

This has been one entertaining thread to read!

Thanks for your service in the unpopular war.

I was at an AVIM repair facility in Germany and then a crew chief at the maintenance test pilot school...all on Cobras. My screen name is from my Ford Cobra but fits nicely with my service as well.

Fortunately, I was in well after Vietnam and ETS'd before Gulf 1.

 

[Wombat55]

Boy that brings back memories, fortunately I was flying and didn't have to run. The old C model (huey) gunships when loaded with ammo and fuel would not hover so we would hop them to the runway then get them light on the skids and slide down the runway and as you said the crew chief and gunner would run beside. When they were out of steam they would jump aboard and by then you would have enough speed to hit "transitional lift" (clean air through the rotar system producing greater lift) and you would lumber off,

This has been one entertaining thread to read!

Gee, didn't know that there were so many old-timers on these boards. Maybe you old guys can tell us about what it was like fighting with muskets in the Civil War days next?

Just kidding. I'm an old 56 yo myself. I imagined most of the people on these forums being teens or 20-somethings, though, although it did leave me wondering where all of those youngsters got enough money to so frequently crash Mavics like described on these forums.

 

[stratos]

Here is another video I took last night at 120 fps with various resolutions to capture the prop speeds. In all views, there seems to be an apparent difference in RPMs in the front.

of course there is a difference in RPM.... how do you think the craft is perfectly balancing in the air , is not magic buddy, is physics , engineering and aerodynamics

 

[AlanTheBeast]

More memories of the old days.

of course there is a difference in RPM.... how do you think the craft is perfectly balancing in the air , is not magic buddy, is physics , engineering and aerodynamics

Nobody's claiming magic that I can see.

The purpose of the discussion is trying to determine if the difference in RPM is due to CofG position, thrust vectors (due to the difference in angle between the rotors) or what in particular.

I took a frame of Gembey's earlier video and it shows that the rotor angles are tilted almost the same (fore tilted back, aft tilted fore) v the laser horizontal on that image (somewhere above).

 

[grizzard]

Thanks for your service in the unpopular war.

I was at an AVIM repair facility in Germany and then a crew chief at the maintenance test pilot school...all on Cobras. My screen name is from my Ford Cobra but fits nicely with my service as well.

Fortunately, I was in well after Vietnam and ETS'd before Gulf 1.

Oh yes .... there are some old timers here. I was a helicopter mechanic in Japan in the late 50s ... on H21 Piaseckis and Sikorskys as well has H19s and H13s. Half of my company (6th Transportation) went to Korea and the other half to Hawaii. I guess once you fall in love with aircraft ... you don't give them up easily.

 

[Gernby]

Gembey. See annotated photo from your first video. (Revised, better position to see the front legs in full)

The dark blue line is the "rest line" when the drone is sitting on the ground. Yellow box; divide the line between the two front legs.

The magenta is your laser line.

The green lines are the rotor planes as best I can see.

The light blue is a copy of the forward rotor line (same angle)

As you can see the fore rotor plane tilt and the aft rotor plane tilt are near mirrors of each other in hover.

If you could repeat this with the camera "in plane" and on a stand (so it doesn't move) and with a lighter and even coloured background, then I think we'd have a great means to check this out.

I plan to repeat that video tomorrow evening (my daughter is here tonight), without the couch behind it, and with a better camera. I also plan to get a better video of the props from above, with more light and a 360 degree view.

 

[Gernby]

If I have time, I also plan to drop paint balloons into each prop, so we can observe the resulting spatter patterns. I theorize that the front rotors will produce smaller paint spots on my walls and furnishings than the rear rotors. Of course, I need to use 4 different high contrast paint colors to differentiate the spatter patterns...

 

[Gernby]

Aside from the science talk, I totally agree with AlanTheBeast's comment about packaging. If the "interesting" design choices about the Mavic were based on physics and flight characteristics alone, then I would expect the Phantom 4 to share those design choices. I am sure that the Mavic missed out on many ideal design parameters, so it could achieve its obvious objective (compactness).

 

[Gernby]

of course there is a difference in RPM.... how do you think the craft is perfectly balancing in the air , is not magic buddy, is physics , engineering and aerodynamics

Ummm ... thanks for being the first person to agree with me, buddy ... I think. I'm confused by your statement about magic, since I'm pretty sure my 1st post in this thread mentioned the apparent RPM difference as a supporting point to support my scientific theory about flight time (as an engineer).