What is causing props to come flying off?

[Tinmania]

I'd say a bit like checking if the wheels are bolted on to your car. checking for fuel would be equivalent checking the charge on the mavic's battery.

I'd say it is more like checking tires on a motorcycle. A car will usually still be controllable with the loss of a tire; a motorcycle will not.



Mike

 

[FrankIII]

"What is causing this to happen more often?" Simple: Lots more Mavics in the sky these days. It's not a threat if you check your props each flight and inspect them closely occasionally. I use a magnifying lens and closely look at the prop hub about once a month, looking for any signs of stress fractures. I NEVER take my props off either. That's just asking for trouble.

I personally cant see how you can closely inspect the props with a magnifier if you don't ever take them off. How about if one of the three flanges on the bottom of one has minor damage? You wont see it.

 

[FrankIII]

I take my props off after every flight, as I believe the constant pressure on the springs wears the springs out. 14 years later, my car seems to sit lower as the springs wore out. I do agree though, I double and sometimes triple check all props before a flight by holding the motor and trying to move the prop.

I concur!!!!!!!!!!!! Always remove props and closely inspect at least every few flights. I also agree about the springs eventually losing some of their springiness (for lack of a better word) by keeping them on all the time..

 

[FrankIII]

I think spring wear is a fallacy, unless there is technical evidence to the contrary.

Well is there technical evidence its not a fallacy? Might as well be cautious than not!

 

[dvarapala]

I'd say a bit like checking if the wheels are bolted on to your car.

Which nobody does.

 

[ICHOTT]

D

I personally cant see how you can closely inspect the props with a magnifier if you don't ever take them off. How about if one of the three flanges on the bottom of one has minor damage? You wont see it.

Don’t want to argue about it but you are right, you would not know, but why would it get damaged! If you’ve hit a tree or had a bump etc then sure remove and inspect.
It’s reasonable to ‘occasionally’ remove and inspect but removing every time is like jacking up your car to relieve the springs and pressure on the tyres - pointless.

 

[Classic flyer]

Do a good pre-flight that should help greatly in preventing a mishap....PRIOR PLANNING PREVENTS POOR PERFORMANCE

 

[Masa]

I have them always on, check now and then. Had one crash out of nothing when back-right propeller jumped out mid-air in about 30ft (10m). And I hadn't touched the propellers in many flights prior to crash (also not checked) so remains a mystery why it jumped out.


Guarantee covered everything, paid 0€.

 

[Howcroft22]

I've noticed that the past few threads of people having their mavic crash has been the result of a prop coming off mid flight. What is causing this to happen more often? I'll be honest, I don't check my props before every flight. But I would think you wouldn't have to unless you had a previous crash.

I realize you started this thread early in the week. But. I’ve had this issue a few times and figured out exactly what the problem is. You push down and twist. And After you twist the prop on, you need to make sure the prop pops back up. That’s where it’s locked. If it doesn’t pop up all the way, it’s not locked in. That’s when you start to run into props flying off. Sometimes it might happen on takeoff. It may happen after having flown through a couple batteries. But once I started making sure all 4 props popped back up completely, it stopped happening. You may have to pull up on some of them to get them to lock fully. Since I got my mavic I’ve noticed at least one of the springs doesn’t push the props up like it should. So it’s probably the same thing with yours.

 

[colinfowler]

My props only come off when I'm packing pro in Carry on bag.
Refit correctly and never had a problem

 

[Skeye]

I realize you started this thread early in the week. But. I’ve had this issue a few times and figured out exactly what the problem is. You push down and twist. And After you twist the prop on, you need to make sure the prop pops back up. That’s where it’s locked. If it doesn’t pop up all the way, it’s not locked in. That’s when you start to run into props flying off. Sometimes it might happen on takeoff. It may happen after having flown through a couple batteries. But once I started making sure all 4 props popped back up completely, it stopped happening. You may have to pull up on some of them to get them to lock fully. Since I got my mavic I’ve noticed at least one of the springs doesn’t push the props up like it should. So it’s probably the same thing with yours.

And one can easily check whether the props are locked on with your fingertip, where you want to feel the top of the axis just level with the surface of the prop.

 

[Pcarlsen]

Prop can fail from material defects, notches or marks turning to cracks, or by the joints. That would at least be the most likely in my mind.

Having foldable props is very practical, but it also introduced two possible points of failure per prop!

A good example; I bought two sets of props for my MP. One original set, and a set of third party props.

Aftermarket props; packaging looks very much like the original packaging (both in the picture are third party).


At a first glance they look fine.


The blades themselves are however very, very thin and extremely soft. Soft props are usually less effective (they flatten out when revved up) than stiff props - and these are so soft and thin that it's almost a joke. In the pic below I'm applying a small amount of bending on it, although it looks wild,.


..and here's the kicker. The pins do not protrude though the bottom half of the hub assembly - this is seriously problematic as all stress will be concentrated at the fit between the pin and the top part of the hub hules.. So these are going straight in the bin.

 

[raymo]

Well is there technical evidence its not a fallacy? Might as well be cautious than not!

Without getting into a lot of detail, generally, springs do not "wear out". They do, however, suffer from overload or cycle fatigue. There is one case where springs do wear out. This in in the case of stacked leaf springs, as found on older auto suspensions. The leaves actually rub against each other, oxidize and literally wear against each other becoming thinner as time goes on. They lose their strength. In the case of coil springs or torsion springs, this is not the case.

Loss of spring tension can be caused by several factors. 1. Exceeding yield strength. This is when the spring is compressed or stretched beyond its designed compression or tension curve operating limit. Maybe you've taken a small coil spring and given it a good tug and deformed it or taken a "slinky" and pulled it too hard. You exceeded its yield strength. 2. Heat damage. High temperatures will permanently damage springs by resetting their atomic structure order. Auto springs can be damaged this way, although if the springs are damaged by heat, the car is probably a write-off anyway. More commonly would be guns that have been in fires. Usually the hardened gun parts are still good, but the springs in the gun are shot and need to be replaced. Have had this happen by the way. 3. Creep. This is caused by loss of strength over long periods of time, usually years or decades and is accelerated by heat. This is hardly an issue for Mavic owners at this date. 4. Fatigue. This is caused when springs are continually or intermittently, but often flexed. Flexing can introduce micro fractures into the spring material and reduce its compression or tension strength. This is where it applies to our case. Constantly compressing and relaxing the coil springs in our Mavics can (but probably not) reduce their strength or range. The way the mounting is designed in Mavics requires that the propeller mechanism be compressed, then rotated to a locking position, then released up into that locked position. As long as the prop is in that locked position, and this requires much less force than is actually exerted by the Mavic coil springs, those props will NOT "spin" off. One of the only scenarios that the props will exit completely is where the three locking tabs fail simultaneously due to stress fractures on the tabs themselves. These are probably induced by previous impacts or by imbalanced props. (The other case of prop failure can be the axle points for each blade on a Mavic prop.)

Constantly removing and replacing props is just opening up your likelihood of having a prop come off, not because of lack of spring tension, but rather because they are not getting placed back into a truly locked position. I would rather check to see if I can spin the prop at all against a held motor each time I fly, or at least each time I go out for a set of flights. Removal each time would be like removing the wheels from your car each time you go out to drive. It's just inviting trouble as you at some point will not torque up the lug nuts properly or you will cross-thread them. Likewise, full size aircraft pilots don't remove the prop each time, but they do routinely inspect them for damage. Tip strikes always initiate a further inspection.

Hope this helps.

 

[s_murphy]

My cousins daughter grabbed mine shortly after landing and before i could get to it before her. Didn't pay much attention to it because it happened so quickly but fast forward a day or two later I'm back home and just took off out of my back yard about 30 feet up and tumbling down comes my MP luckily into my tree breaking the fall... seconds later a prop all by itself comes tumbling down. I check my props all the time now!

 

[Xero]

What is causing this to happen more often?

I will say :
Wrongly fixed props.
Wrong storage who cause stress on the props.
POS non genuine props bought for cheap price (cheap=****)

 

[moonlitnite]

While the earlier Phantom props were self-tightening, occasionally one not properly secured would spin off when making an extreme maneuver (quick descent followed by sudden direction reverse). The point being, immediately after takeoff and still at a low altitude, NOW is the best time to exert your craft to a range of motions to validate various subsystems can take the stress of your mission.

 

[BJR981S]

I have found that you should not trust third party clone props. They are not manufactured and tested to the same stringent accuracy as the DJI OEM props.

Have at look at this clone prop for a spark and see if you can tell what is wrong with it.

This one is obvious, but what about the ones that aren't obvious? I only buy OEM now.

 

[dennyc39]

I leave my props on unless I have a specific need to take them off, or if I think there has been an impact. I worry more about possible wear on the locking lugs caused by repeated removal, or possibly, "just once", getting it wrong when I install the four props. My belief is that the springs are in a steady state once installed, and that wear on them is not a factor.

The chances of putting a prop on incorrectly are rather small. On the other hand, the odds of doing it correctly 200 times ( x 4! ) in a row are not as high as we'd like, particularly if one of those times we might be in a hurry. I had a prop come off on each of my first two flights, each time in a low hover.

 

[Lake_Flyer]

I leave my props on unless I have a specific need to take them off, or if I think there has been an impact. I worry more about possible wear on the locking lugs caused by repeated removal, or possibly, "just once", getting it wrong when I install the four props. My belief is that the springs are in a steady state once installed, and that wear on them is not a factor.

The chances of putting a prop on incorrectly are rather small. On the other hand, the odds of doing it correctly 200 times ( x 4! ) in a row are not as high as we'd like, particularly if one of those times we might be in a hurry. I had a prop come off on each of my first two flights, each time in a low hover.

Agreed, I have the same experience, during one of my first flights with the MP, prop coming off after being a bit hurried to get in the air. Luckily it spun off right at motor start. On my Inspire1 I replaced the quick release props with screw on (with extra snap over locks) props. Feels a lot safer to have to screw them on and know/feel they are tight.
So I leave the MP props installed and check them regularly for damage. And before every flight I check if they are still locked correctly.

 

[JohnC]

The last batch of DJI props I got are a much tighter fit on the motor axis, the springs can’t overcome this fit so will not spring up on their own.

What I do is check that the end of the motor axle is flush with the hub, so when they go on against the lock pull them up and while holding the motor rock the hub back and forth to confirm the lock is seated in the hub plate.