Prop Lock Slop - Could Be Cause of Some Crashes

[Skyhawk]

This is worth checking to avoid losing a prop, and your flybaby!

As part of preflight check I have a routine that "may" have averted a near future crash.
Without going over my entire preflight checklist, I'll cut to it and share what I found.

One step, of just one of the Prop prechecks prior to turning the MP for flight is;

• I hold each motor one at a time with one hand, and twist the prop center or hub gently left and right with the other hand. I am checking that the prop hub is securely locked into the motor
• At the same time I am also checking for "wear travel" (or slop) while gently twisting left and right.

My threshold for slop is zero, as there has never been travel on any prop once correctly locked in.

TODAY
This morning, during preflight check, I found one of the props had noticeable slop (or travel) when locked in.
I checked all the others again and found the other three were completely secure and zero left-right travel. The one with left right slop was determined to be about 1/16 of an inch. I changed the one out and flew for an hour and a half. I then returned to the hanger (aka - my home office). Here I checked again to see that the initial concern was still there. It was, and to eliminate the motor lock connection as the issue, I tried the prop in other motors and the lock had the same amount of slop.

PROGNOSIS - this prop lock connection was headed for failure
Now this may seem a little picky, but we hear about crashes and post crash analysis concluding the aircraft lost a prop. My current props all have about 120 flights and 900k feet of flight, over about 18 hours total time.

ACTION TAKEN
It's not good risk management to put your MP (and others on the ground) at risk for a $3 prop, when finding any signs of wear. My answer is change it out.

Hope this saves one of your flybabies.

Smooth air!
Craig

 

[Dave A]

Interesting and seems like sound advise. thanks.

 

[Former Member]

This is worth checking to avoid losing a prop, and your flybaby!

As part of preflight check I have a routine that "may" have averted a near future crash.
Without going over my entire preflight checklist, I'll cut to it and share what I found.

One step, of just one of the Prop prechecks prior to turning the MP for flight is;

• I hold each motor one at a time with one hand, and twist the prop center or hub gently left and right with the other hand. I am checking that the prop hub is securely locked into the motor
• At the same time I am also checking for "wear travel" (or slop) while gently twisting left and right.

My threshold for slop is zero, as there has never been travel on any prop once correctly locked in.

TODAY
This morning, during preflight check, I found one of the props had noticeable slop (or travel) when locked in.
I checked all the others again and found the other three were completely secure and zero left-right travel. The one with left right slop was determined to be about 1/16 of an inch. I changed the one out and flew for an hour and a half. I then returned to the hanger (aka - my home office). Here I checked again to see that the initial concern was still there. It was, and to eliminate the motor lock connection as the issue, I tried the prop in other motors and the lock had the same amount of slop.

PROGNOSIS - this prop lock connection was headed for failure
Now this may seem a little picky, but we hear about crashes and post crash analysis concluding the aircraft lost a prop. My current props all have about 120 flights and 900k feet of flight, over about 18 hours total time.

ACTION TAKEN
It's not good risk management to put your MP (and others on the ground) at risk for a $3 prop, when finding any signs of wear. My answer is change it out.

Hope this saves one of your flybabies.

Smooth air!
Craig

I agree. Some people never check them, and they go fly. I check every time.

 

[Marko9219]

I grab each prop, check it before each flight. Always have, always will. Also I NEVER remove my props. To me, frequently removing props is inviting disaster. Not checking props each flight is also inviting disaster.

 

[Robert Mitchell]

Good post, and I always do the same.

 

[Mad Mavic]

This is worth checking to avoid losing a prop, and your flybaby!

As part of preflight check I have a routine that "may" have averted a near future crash.
Without going over my entire preflight checklist, I'll cut to it and share what I found.

One step, of just one of the Prop prechecks prior to turning the MP for flight is;

• I hold each motor one at a time with one hand, and twist the prop center or hub gently left and right with the other hand. I am checking that the prop hub is securely locked into the motor
• At the same time I am also checking for "wear travel" (or slop) while gently twisting left and right.

My threshold for slop is zero, as there has never been travel on any prop once correctly locked in.

TODAY
This morning, during preflight check, I found one of the props had noticeable slop (or travel) when locked in.
I checked all the others again and found the other three were completely secure and zero left-right travel. The one with left right slop was determined to be about 1/16 of an inch. I changed the one out and flew for an hour and a half. I then returned to the hanger (aka - my home office). Here I checked again to see that the initial concern was still there. It was, and to eliminate the motor lock connection as the issue, I tried the prop in other motors and the lock had the same amount of slop.

PROGNOSIS - this prop lock connection was headed for failure
Now this may seem a little picky, but we hear about crashes and post crash analysis concluding the aircraft lost a prop. My current props all have about 120 flights and 900k feet of flight, over about 18 hours total time.

ACTION TAKEN
It's not good risk management to put your MP (and others on the ground) at risk for a $3 prop, when finding any signs of wear. My answer is change it out.

Hope this saves one of your flybabies.

Smooth air!
Craig

Good advice Skyhawk. I’ve had a few prop strikes in the past. Something interesting developed during strikes involving carbon fiber props. On each event, only one of the hooks securing the blades to the locking hub broke off, allowing me to recover and land.

Reading your post resurrected an idea. I’m curious now if the failure of one hook is perhaps a design intent. I have several prop sets lying around so maybe I’ll take them into the quality lab at my work to see if the hooks are evenly spaced.

I suspect the spacing of one of the hooks may be offset a few microns, so in the event of a strike, that one hook is sacrificed as the weak link, thus saving more valuable components in the assemble down stream. And also avoiding catastrophic failure. Catching the prop when one hook is broken or worn is key.

The offset idea is probably not the case, but I would like to know. A more robust attachment would be nice, even if it required fasteners.

I’ll post my findings.

 

[Skyhawk]

Thanks Mad Man... your theory is sound. Built in points of failure under x-conditions, for the purpose of saving the overall aircraft are well known on aircraft (ex. fixed wing landing gear collapsing under severe landing conditions)... I look forward to the results of your measurements and tests.

Thanks for sharing the the Lab environment you can check this out in. I designed and opened a Cyber Practice Range Lab over a year ago for our cyber security students. There they can test theories, scripts and identify new vulnerability inside a secure lab. This has proven a huge success for new offensive and defense protection strategies.

 

[Skyhawk]

I grab each prop, check it before each flight. Always have, always will. Also I NEVER remove my props. To me, frequently removing props is inviting disaster. Not checking props each flight is also inviting disaster.

Do you remove the props to clean motors. I remove them every 4 hours of fight (about every 10-12 flights) and blow out each motor (thru cooling vents in top of each motor) with canned compressed air. I expect there is some super fine grit collecting in the motors which will create wear. Just an item on my regular scheduled maintenance. Thoughts?

 

[black_magic100]

This is worth checking to avoid losing a prop, and your flybaby!

As part of preflight check I have a routine that "may" have averted a near future crash.
Without going over my entire preflight checklist, I'll cut to it and share what I found.

One step, of just one of the Prop prechecks prior to turning the MP for flight is;

• I hold each motor one at a time with one hand, and twist the prop center or hub gently left and right with the other hand. I am checking that the prop hub is securely locked into the motor
• At the same time I am also checking for "wear travel" (or slop) while gently twisting left and right.

My threshold for slop is zero, as there has never been travel on any prop once correctly locked in.

TODAY
This morning, during preflight check, I found one of the props had noticeable slop (or travel) when locked in.
I checked all the others again and found the other three were completely secure and zero left-right travel. The one with left right slop was determined to be about 1/16 of an inch. I changed the one out and flew for an hour and a half. I then returned to the hanger (aka - my home office). Here I checked again to see that the initial concern was still there. It was, and to eliminate the motor lock connection as the issue, I tried the prop in other motors and the lock had the same amount of slop.

PROGNOSIS - this prop lock connection was headed for failure
Now this may seem a little picky, but we hear about crashes and post crash analysis concluding the aircraft lost a prop. My current props all have about 120 flights and 900k feet of flight, over about 18 hours total time.

ACTION TAKEN
It's not good risk management to put your MP (and others on the ground) at risk for a $3 prop, when finding any signs of wear. My answer is change it out.

Hope this saves one of your flybabies.

Smooth air!
Craig

Can you PM me your pre-flight checklist? I would love to see it.

Also, just so I am understanding this correctly...
you are holding the motor/mavic in one hand and your other hand is gripping the prop and you are gently (applying very little force) trying to move the prop left and right to see if there is any give? I don't have my mavic on hand atm so it is a bit hard to visualize.

 

[Skyhawk]

Can you PM me your pre-flight checklist? I would love to see it.

Also, just so I am understanding this correctly...
you are holding the motor/mavic in one hand and your other hand is gripping the prop and you are gently (applying very little force) trying to move the prop left and right to see if there is any give? I don't have my mavic on hand atm so it is a bit hard to visualize.

Hey Magic Man! Thanks for the request for the pre-flight checklist. Happy to PM it to you, once I return to the hanger this eve.

Roger that issue with visualizing. Here you go;
I have the MP sitting on the ground or the hood of my car.
For each motor - with my left hand I hold the outer edge of motor from turning, with my right hand I grip the prop hub (without pushing down of course), and I gently attempt to move the prop hub left and right.
One, this checks that it's locked.
Two, this also determines if the prop has any play or travel. Again, any travel is time for me to replace that prop.

Hope that's a bit more clear.

 

[black_magic100]

How were you able to notice 1/16 of an inch movement? I just tested it and it moved a little, but that's because it's impossible to hold the motor 100% still as you try to move the props.

 

[Mossiback]

...It's not good risk management to put your MP (and others on the ground) at risk for a $3 prop...

Thanks for the information. I never check for prop slop but now I will.

It may be a typo, but $3 for a prop?

 

[Mad Mavic]

Thanks Mad Man... your theory is sound. Built in points of failure under x-conditions, for the purpose of saving the overall aircraft are well known on aircraft (ex. fixed wing landing gear collapsing under severe landing conditions)... I look forward to the results of your measurements and tests.

Thanks for sharing the the Lab environment you can check this out in. I designed and opened a Cyber Practice Range Lab over a year ago for our cyber security students. There they can test theories, scripts and identify new vulnerability inside a secure lab. This has proven a huge success for new offensive and defense protection strategies.

Sorry for the delayed response on the lab results conducted on but it seems that the attachment points are equally spaced,

Thanks Mad Man... your theory is sound. Built in points of failure under x-conditions, for the purpose of saving the overall aircraft are well known on aircraft (ex. fixed wing landing gear collapsing under severe landing conditions)... I look forward to the results of your measurements and tests.

Thanks for sharing the the Lab environment you can check this out in. I designed and opened a Cyber Practice Range Lab over a year ago for our cyber security students. There they can test theories, scripts and identify new vulnerability inside a secure lab. This has proven a huge success for new offensive and defense protection strategies.

Good Morning Skyhawk. I apologize for the long delay in getting back with the prop test results. However I was able to gain access to our lab and conducted measurements using out CMM to establish the latching mechanism gemoetry. As it turns out, aside for the common variations inherent to injected molded plastic parts, the hooks that attach prop to motor are equally spaced.

The following are some sound and acceleration/distance tests I conducted with three props different props. Tests were conducted in to outdoors.

Sound recordings were taken at 1 meter AGL and 10 feet away from detection device (I phone 7 plus dB Meter app)

Altitude tests were conducted with drone placed at idle and clock started when full up throttle was initiated. Total time, 10 seconds in Sport mode

weather conditions at time of test:
51 degrees
winds 4 from 200 degrees
Humidity 85%
ASL 1200 FT

base dB 49


1A) Stock MPP "quiet " props - 69 dB
1B) 124 feet
1C) 167 feet

2A) Carbon fiber with same shape as stock MPP "quiet " props - 71 dB
2B) 125 feet
2C) 168 feet

3A) generic Carbon fiber props - 74
3B) 124 feet
3C) 167 feet

Conclusion:

With the exception of dB range, each prop showed only slight differences in performance.

There is a considerable advantage using carbon props in windy conditions. For example, a 15 mph headwind with gusts has actually caused my drone to lose forward motion, actually moving it backwards at full forward throttle. Changing to carbon. I was able to move forward with ease in the same conditions. Unfortunately I didn't record data during that flight. My estimate was 15 mph winds with gusts at 25

 

[Mad Mavic]

Update on carbon fiber props ( props shaped like the Mavic ProPlatinum quiet props) sold by RCGeeks on eBay

These props are a disaster waiting to happen. Each blade is held together with threaded fasteners, all of which have right hand threads.

Threaded fasteners are IMHO, the worst possible fastener for several reasons. Aside from the high probability of them becoming lose, they are likely to come out all together. Counter rotating devices such as bicycle peddles for example, implement both left and right hand threads to prevent the peddle from becoming un-threaded during peddling.

Also there could be an issue of the threads grinding away at the plastic should the fastener be threaded along the full length of the tiny bolt. In other words, if the bolt and the plastic blades rotate any at all, the resulting friction in conjuction with increased inertia, the mounting hole is subject to deform.

After about 5 hours flight time the propellor blades are very loose. The fasteners holding the assembly together are lose. Bottom line, not worth the risk

Their are good quality props out there. I have had three sets of the carbon fiber props sold by Droneworld that have performed well after countless hours of use. They too, as any prop, will eventually need to be changed out as a maintenance precaution.

 

[dewster]

I’ll have to check mine for prop slop. It’s a sickening feeling watching your bird just drop out of the sky. I had one weigh almost seven pounds drop after a prop break. I swear I squeezed out a diamond.

 

[Skyhawk]

Sorry for the delayed response on the lab results conducted on but it seems that the attachment points are equally spaced,



Good Morning Skyhawk. I apologize for the long delay in getting back with the prop test results. However I was able to gain access to our lab and conducted measurements using out CMM to establish the latching mechanism gemoetry. As it turns out, aside for the common variations inherent to injected molded plastic parts, the hooks that attach prop to motor are equally spaced.

The following are some sound and acceleration/distance tests I conducted with three props different props. Tests were conducted in to outdoors.

Sound recordings were taken at 1 meter AGL and 10 feet away from detection device (I phone 7 plus dB Meter app)

Altitude tests were conducted with drone placed at idle and clock started when full up throttle was initiated. Total time, 10 seconds in Sport mode

weather conditions at time of test:
51 degrees
winds 4 from 200 degrees
Humidity 85%
ASL 1200 FT

base dB 49


1A) Stock MPP "quiet " props - 69 dB
1B) 124 feet
1C) 167 feet

2A) Carbon fiber with same shape as stock MPP "quiet " props - 71 dB
2B) 125 feet
2C) 168 feet

3A) generic Carbon fiber props - 74
3B) 124 feet
3C) 167 feet

Conclusion:

With the exception of dB range, each prop showed only slight differences in performance.

There is a considerable advantage using carbon props in windy conditions. For example, a 15 mph headwind with gusts has actually caused my drone to lose forward motion, actually moving it backwards at full forward throttle. Changing to carbon. I was able to move forward with ease in the same conditions. Unfortunately I didn't record data during that flight. My estimate was 15 mph winds with gusts at 25

Great info on noise levels for different prop materials. Thanks so much for sharing.

 

[Skyhawk]

Thanks for the information. I never check for prop slop but now I will.

It may be a typo, but $3 for a prop?

Yep, they are $9 a set, that's $4.50. My $3 per pro was a SWAG.