Aerodynamics

[John Shaw]

Drag also goes up with pitch angle as the top of the fuselage is exposed to the oncoming air.

 

[flyNfrank]

Interesting... That make me think that 30 degrees is all they can handle for level flight. They initially go to 35 degrees to get initial acceleration, accept a slight sink, and then come back to 30 degrees for sustained flight.

That 30 degrees would be as long as it was still full throttle. It would also be determined on if the Mavic was flying into a head wind, and how strong that head wind was at the time. I have seen dji program up to -45 degrees in some instances.

 

[RFaust]

Sorry for changing direction back to the prop sanding and balancing idea, but can you actually balance these props with a DuBro or similar balancer? I haven't seen them yet- do they just flop over?

 

[Bivalve]

Good question!

They are not rigid, by any means, but they do not flop over.
HOWEVER, it is vital to get them absolutely straight before balancing.
After sanding a set, the only difference I can tell is that they might be a smidge quieter. Maybe.

I work in a company with helicopters, and the tips of their rotors are swept back at almost a 45 degree angle. I asked why, and was told that this was to make them quieter by reducing the tip speed below mach 1.

I thought about cutting mine that way, but decided that the mavic just doesn't have that much juice. Still, they look cool, so I'm tempted.

I guess doing so would void the guarantee on the props. Oh well.

 

[RallySoob]

Being it doesnt go fast that often you would think a little drag is ok but i wonder if better aero would help its ability to cut thru higher speed wind than it does now ... doubt it would be noticable huh. In the car world, spoilers are starting to get effective over 50-60mph and very effective after 80-120 but cars are heavy . Some wind tunnel testing would be neat to see


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[RFaust]

Good question!

They are not rigid, by any means, but they do not flop over.
HOWEVER, it is vital to get them absolutely straight before balancing.
After sanding a set, the only difference I can tell is that they might be a smidge quieter. Maybe.

I work in a company with helicopters, and the tips of their rotors are swept back at almost a 45 degree angle. I asked why, and was told that this was to make them quieter by reducing the tip speed below mach 1.

I thought about cutting mine that way, but decided that the mavic just doesn't have that much juice. Still, they look cool, so I'm tempted.

I guess doing so would void the guarantee on the props. Oh well.

Yes I read an article about that blade design - it makes a big difference in noise.
Maybe the floppy blades need to be dynamically balanced (while spinning).

 

[RFaust]

Listen to the difference:
http://gizmodo.com/5481081/the-blade-that-would-make-helicopters-almost-silent

 

[F6Rider]

I don't think you are going to be able to balance these blades without a lot of work, the blades are riveted individually to the hub, so no disassembly. Due to the design good luck getting them straight enough to static balance, and dynamic balancing is not possible. In the Army we had trim tabs on the tip of each blade to do a vertical trim to get both blades swinging in the same arch, but with the short throw of these it's not needed. After inspecting my blades in a strong magnifying glass it seems there is very little to sand, just a tiny mold line, I am thinking you would not help much by sanding it. And talking about this drone doing 100mph is nonsense, neither the battery nor the motors will support that. If you want to go that fast you bought the wrong drone.

 

[RFaust]

I don't think you are going to be able to balance these blades without a lot of work, the blades are riveted individually to the hub, so no disassembly. Due to the design good luck getting them straight enough to static balance, and dynamic balancing is not possible. In the Army we had trim tabs on the tip of each blade to do a vertical trim to get both blades swinging in the same arch, but with the short throw of these it's not needed. After inspecting my blades in a strong magnifying glass it seems there is very little to sand, just a tiny mold line, I am thinking you would not help much by sanding it. And talking about this drone doing 100mph is nonsense, neither the battery nor the motors will support that. If you want to go that fast you bought the wrong drone.

Oh well, guess I won't be using my DuBro much anymore. Hope they have good motor bearings

 

[F6Rider]

Oh well, guess I won't be using my DuBro much anymore. Hope they have good motor bearings

I will keep mine for my Phantom blades but after one look at the Mavic's I knew they wouldn't need balancing. The hub will pivot to balance weight distribution between blades as soon as RPM builds up, acting like a swash plate on a helicopter.

 

[Tomdog]

Also sanding off the raised numbers on top of blades could clean things up a little.
Realizing these numbers are close into the blade pivot center so relative air speed isn't as great as out at tip. Small efficiency improvement perhaps?


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[erkme73]

There was a video showing a guy who used his DuBro to balance the Mavic blades. He spun them on a drill first to get them to straighten completely. Then, after mounting them on the DuBro, he was able to verify their balance. He did state that 100% of the blades he tested were completely balanced right out of the box. So it's probably not worth it. Now, if you're sanding off material, I think that changes the equation.

Here's the video...

 

[RFaust]

There was a video showing a guy who used his DuBro to balance the Mavic blades. He spun them on a drill first to get them to straighten completely. Then, after mounting them on the DuBro, he was able to verify their balance. He did state that 100% of the blades he tested were completely balanced right out of the box. So it's probably not worth it. Now, if you're sanding off material, I think that changes the equation.

Here's the video...

Thanks for posting that video. I like the results of his test. Now I won't have to toss out my DuBro after all.

 

[awake1563]

I hope someone makes an extended battery that takes advantage of your thoughts on improving the aerodynamics. Also, I'm no expert on pitch angles etc, but I can tell you that I had my mavic in the first batch of shipments and it was regularly hitting 60mph (regardless of wind) before the first firmware update. Now I'm lucky if I can top 45 with a 30mph tailwind. It is funny and disappointing to see the drone at "top speed" while the rotors are only turning aroun 4k rpm when they are capable of 9800...

 

[John Shaw]

I hope someone makes an extended battery that takes advantage of your thoughts on improving the aerodynamics. Also, I'm no expert on pitch angles etc, but I can tell you that I had my mavic in the first batch of shipments and it was regularly hitting 60mph (regardless of wind) before the first firmware update. Now I'm lucky if I can top 45 with a 30mph tailwind. It is funny and disappointing to see the drone at "top speed" while the rotors are only turning aroun 4k rpm when they are capable of 9800...

There was much discussion earlier that the speeds displayed in the early firmware were way high. It was about the numbers you mentioned - like measured as kph and reported as mph. That may have been corrected but I'm not sure.

 

[voxelman]

It seems to me that the surest way to increase flight time or speed is to rebuild the aircraft and batteries with ultra light materials. A complete tear down and analysis of the airframe would give insight into where the greatest gains are to be made. I wonder if the heat sink could be lightened significantly? Of course this would be a significant undertaking but it could lead to some fairly spectacular gains; sort of like overclocking a computer.

 

[Guitarzan]

For those that don't know, the FAA allows hobbyist aircraft to fly up to 100mph.

There are jet powered R/C planes that easily exceed that.

 

[Deluge2]

<snip>

For those that don't know, the FAA allows hobbyist aircraft to fly up to 100mph.

That is not correct. Check out the most recent FAA advisory circular on 'model aircraft operating standards' (AC 91-57A) dated Sept 2, 2015. This document says nothing about max speed.

OTOH, Part 107 regs covering *commercial* use includes the limit of 100 mph. So it is commercial use, not hobby use that has the speed restriction.

 

[LakeTravis]

Some considerations...
This isn't an airplane. The airflow is not front to back. This is a quad where the body is immersed in the downwash from the props. I also suspect it isn't laminar flow, but rather turbulent as the air from each prop intermixes with that from the other props. Airflow off props has a circular component. Light airplane vertical fins have an angular offset due to this twisting flow. The downwash angle is going to vary with the speed. Hovering it is straight down, when moving it's a combination of the downwash and the forward motion, which varies with speed. You would have to do a lot of research to figure what's best, and it would be different for a photo task than an long range task. Then any fairing adds weight and you have to trade the drag reduction against the increased weight. More weight requires the props to turn faster to get more lift. If you added fairings to change the shape as described you could easily make it worse in some or all situations. I seriously doubt you could find much benefit and you could easily make it worse.

You all should read what John Shaw wrote in a previous post. He is spot on. Also, smoothing the props is fine, as long as you don't OVERDO it. You run the risk of modifying the shape too much and messing things up. They may (probably will) run quieter, but it's already so much quieter than any Phantom. Any improvement in lift is likely to be negligible. If you want to see some information that might convince you that any difference you might make is trivial, read up on the difference between early Piper Cherokee "Hershey Bar" wings and more current "Taper" wings. There's really not much difference between the performance of the two, and you would sure think there would be looking at them. However, as John stated, airflow is a completely different animal on a quad vs. fixed wing flight. I'm personally glad I learned to fly in an oldish Cherokee with Hershey Bar wings--you get some decent skills.

 

[Attex]

Honestly I didnt read through all these post so forgive me if a later one stated this but I believe Aerodynamics of this would be more of the downward flow of air the props are producing. Let the wind blow down easier and hovering would be more energy efficient. Not head on aerodynamics.