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RTH descend 4m/s. Warning to FC40 and P1 users with 9443 or 9450 props.

Discussion in 'Phantom FC40 Discussion' started by lake_flyer, May 2, 2015.

  1. lake_flyer

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    I found out, since I have FPV-OSD now, that the FC40 comes down with 4m/s while in RTH/FS, and there's nothing we can do about it. This is TWICE the maximum safe descend speed for 9450's or 9443's.
    I switched it out of RTH immediately when I noticed it, realising that 9" props are in fact posing a hazard, every time I fly. I rely heavily on RTH. Use it every flight to come home.

    I must add that only recently I started to use 9443's (from my P2) because the old 8"s where a bit scuffed and still fly great but vibrate a little too much.

    Food for thought. Why does DJI allow us, P1 and FC40 users, to fly our birds into pieces and doesn't do anything to warn us, while at the same time, all P2(V3+ whatever) users are restricted to 2m/s and patronised like school kids with their Naza/Phantom mode.
    Why wouldn't we be able to change the max descend rate in Naza-M to 2m/s?

    Right! According to DJI, the 9" props are not standard for a FC40 but they are for a P2. Now why don't they advise P2 users to use 8"s?
    Because that would shave off 2 minutes flying time (although very safe) and that's not cool in this business. Flying time is the magic word.
    Simple really.

    I guess I'll order a couple of 8" sets. Don't want to see the bird tumble from the sky just because of props. Besides, new undamaged 8" props are extremely smooth anyhow.

    What do you think about this matter?
     
  2. IflyinWY

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    Dude, awesome title and great find.

    Here's your first answer.
    The FC40 and P1 have too small of a brain for them to program. Thank goodness. So they built in a slow, but sure self destruct mechanism and it's called VRS.
    Now we can't actually blame this on DJI though. DJI does not endorse the use of 9 inch props on our birds, as far as I know. That's the end of my "conspiracy" answer.

    Answer number two.
    With the 8 inch props, 4 M/s is safe?
    They aren't even thinking of looking back at our birds. They are lunging forward at break-neck speed trying to keep up and/or out do the other guys in the industry.
    I believe that's why those of us with the P1 and FC40 have to solve our own issues. Thank goodness we don't have the "So called" smart battery. LOL

    I would appreciate not getting slammed for my thoughts. The brain is old and tired. Typically it takes me 2 to 4 days to process this type of info.
    Who's next?
     
  3. lake_flyer

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    I have used 8" on the FC40 for a year and never had VRS, no matter how fast I came down. Sure, it's always a bumpy ride down but never a problem.
    If you look at a similar Blades or Walkeras, they shoot down like meteors at >5m/s in a RTH. Never heard those users complain about VRS.

    I don't really want to get into the conspiracy thing. I just want people to know that their bird isn't safe in fail safe or RTH, using 9" props.
    I always assumed, in RTH, it would always come down in a safe speed, although it always felt and looked much faster than the P2, after upgrading to Phantom Assistant version 3.x.

    Maybe together we find a solution that makes flying our birds safer.
    We could ask DJI to consider to add an option to change the max descend speed in Naza-M (V3?). Not that I expect them to honour that request though. But if they are aware that we know about this problem and hand them a suggested solution, they might be afraid for future law suits.

    Suppose you use the RTH function, and straight above the heads of you AND bystanders (in the park, on the beach, sometimes coming like flies on a birthday cake), and while your FC40/P1 is coming down, unattended, it gets into VRS and plummets like a mad lawn mower on peoples heads. You could prevent that by switching out of RTH as soon as you saw VRS starting and if it would be still high enough
    ...and experienced enough.

    Suppose you didn't invoke RTH yourself but Naza did, because your radio stopped working. You wouldn't even be able to switch out of FS. So who would be to blame?

    You know who.
    You are. Because now you all know that using 9" props is a hazard in RTH/FS. The 9450's are a slight improvement OK, but I still noticed the VRS tendency on my P2, even with 2m/s. And while test flying them on my FC40 for the first time yesterday I noticed it with the first fast descend as well.

    To me, and a lot, if not most, of P2 users, the 2m/s max descend speed limit for the P2 already is kind of rediculous, and generally not fast enough when you have to change altitude suddenly, for safety reasons.

    However, if DJI knows about it but clearly chooses not to educate their P1/FC40 users, because it would lay bare the problem with their entire Phantom 2 series descend behaviour, which they only circumvented by crippling the P2 software, never calling out or addressing the root cause, they would be liable I believe.

    Hmmm, I didn't want to make it sound like a conspiracy, but honestly, the only way to address this is by abductive reasoning, which is the default way for humans to explain the unexplainable, until DJI comes clear.

    And by abductive reasoning, we now all know that:

    Hitler escaped to the moon,
    George Bush is an illuminati,
    Hitler also was an illuminati
    And is still alive as a clone in Brazil
    Bin Laden was a close friend of GWB,
    And GB ordered the 911 strike
    Kennedy was murdered by the FBI,
    as was Marilyn Monroe,
    The moon landing never happened,
    UFO's are secret US weapons
    We get sprayed upon constantly by US jetliners
    There are aliens working at the Pentagon


    Need I go on?
    I hate conspiracy theories actually.
     
    #3 lake_flyer, May 3, 2015
    Last edited: May 3, 2015
  4. lake_flyer

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    I actually meant it would lay bare the problems with the design of their props.
    They adapted the Phantom 2 to the props, which they desperately needed to gain market share with longer fly times than the competition. [abductive reasoning, here we go]
    The wrong way around.
    The Phantom itself is not the problem.
     
  5. N017RW

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    Wow...
    It's just a toy.

    Conspiracies???
     
  6. lake_flyer

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    That's why I say that I hate conspiracy theories, read the lines, or rather, between them even.
    But to say it's just a toy....the FAA doesn't seem to think so.
    To you it's just a toy. For DJI it is a crown juwel, like the iPhone for Apple. Extremely serious business for them.

    Saying you're just sending a toy in the skies, invading the airspace of the bigger birds, is a bit ignorant in my opinion (I mean generally speaking, not to bash you). But maybe I'm biased (not bi-assed :)) because of my professional aspirations for UAV operating (going to get certified) and my background of 45 years of RC flying and private pilot training.

    I think it is this thinking of "just a toy", that keeps officials awake. Too many people are playing with toys in dangerous places. Anything that weighs over a kilogram and hurls through the skies, capable of going anything up to 2000 high or away, far beyond LOS, at 60Km/hr, controlled by some idiot trying to get a lot of hits on youtube, is serious, like it or not!

    If I would use a Phantom P1 or FC40 for my certification (it's possible), I would have to explain in the official flight manual what the safe descend speed is and why. I also have to explain the safety features, like RTH and Failsafe. If I would have to explain (if I use 9" props), why I wouldn't use RTH or Failsafe because of risk of VRS, our NLR would not approve the manual, and the quad itself would not be certified. But I would of course use the stock 8" props (now I know all this), so the issue wouldn't come up.

    Unless I would have a fatal crash during a professional job, and it would turn out I used different props (9443 or 9450) than 8"s mentioned in the flight manual. I would be sued and lose the licence for sure.
     
    #6 lake_flyer, May 3, 2015
    Last edited: May 3, 2015
  7. SimonH78

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    Never had any issues decending fast using these props EVER on my FC40 infact they are a far better prop for flight times.

    As you can see my avatar pic
     
  8. lake_flyer

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    VRS is a combination of factors that only sometimes occur, not always. Some people are lucky and never experience it. Probably, IF you never experienced it, you don't know how to recognise it when/if it occurs.
     
  9. lake_flyer

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    Thanks for reacting anyway :)

    I see in your signature your bird is very sleek in spite of the rich config. Well done.
    My FC40 (2 batteries) and P2 both are around 1380 grams.
    Definitely has something to do with it. Your power to weight ratio is a LOT better than a P2 with the same stuff. Your flight time will be limited but less chance to VRS.

    20150503_172036.jpg
     
  10. IflyinWY

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    Please stay focused Ladies... the subject is rate of descent and 9 inch props.

    Did anyone read this part of the second post?
    "I would appreciate not getting slammed for my thoughts. The brain is old and tired. Typically it takes me 2 to 4 days to process this type of info."

    I don't see where I said SHOOT HERE because I used the word "conspiracy". Ok, I'm through whining.
     
    #10 IflyinWY, May 3, 2015
    Last edited: May 3, 2015
  11. dtitus6297

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    Just some info about the 9450 props....if you go forward while descending, the vrs almost completely goes away. I always fly around in circles over me while descending from up high. Not sure if anyone else knows about this or not but it works with 9443 as well
     
    IflyinWY likes this.
  12. Beario

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    I think weight is a factor in this issue. I no longer have a dual battery setup, prop guards, or a gimbal on my setup and this has not been an issue again. The quad seems more balanced when the battery and weight is in the center and not on the outsides. That has been my experience so far. On the old setup the quad dropped 4 times when I was coming down. It's scary especially when it starts that weird side to side bounce coming down:eek:
     
  13. varangian

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    I fly a FC40 with the 9" props and when I want to descend quickly I'll max the throttle and bring her down in a straight line at abaout a 45 degree angle and level off 10-20' off the deck. It's stable with no hint of VRS.
     
    dtitus6297 likes this.
  14. lake_flyer

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    the problem with RTH is that it decends in a straight line with 4m/sec, thus invoking VRS. I never mentioned that VRS would occur when flying in a glide slope.
     
  15. Clive

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    I did a controlled flight trial today testing RTH. FC40, Lightweight Prop Guards, Walkera G 2-D and gopro, Black magic 3000mAh. AUW of 1186g. Sure enough, where I have never experienced VRS in RTH before with 8in Stock props, with 9in 9450s entered a very unpleasant VRS state oscillating violently and then falling... I deselected RTH slowed descent and powered forward to recover but the whole manoeuvre cost me around 60ft. Same config. with stock 8in props some slight oscillation but safe landing. I have some 9in 3xblades which are well balanced. Will try them tomorrow and report. Will try without prop guards as well as they do make VRS more likely.
     
    IflyinWY likes this.
  16. Clive

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    ...oh, and I get that descending on a glide slope avoid VRS... I am specifically concerned, very concerned, about lake flyer's original report re RTH descents.
     
  17. Clive

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    Tested in same config but with 9443s... Nasty VRS in auto RTH as with 9450s above. 3 bladed props no problem, although it flew a stepped descent. Bottom line, if I need 9in props for the load I will use the 3 bladed ones.
     
  18. Clive

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    I may check without the prop guards... I fly almost exclusively with them as I operate from a restricted site surrounded by tall trees and obstacles but... In the interests of science!
     
  19. PTCX

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    I fly with 9050 triples and there has been no sign of VRS when self landing on the rare occasion I let it self land.
    If I use RTH/FS I usually take control for the landing as I have seen 4 or 5 meters inaccuracy in the home point before and that is enough to potentially land me in the water or swamp at most of my regular flight zones.
    In any case I will mostly decend in a gentle sloping path or if restricted for space I'll come down in spirals to avoid any wobbly issues.
     
  20. Clive

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    PTCX... Agreed on all of that... The wobbles started very quickly after the descent started with the 9443s so I won't use them again. You never know when your radio might crap out and RTH/FS will initiate. I think the triples are much quieter too.