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  1. #1
    Airfield Ops newflyer17's Avatar
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    Cumulus/Large Cumulus/Cumulonimbus

    I'm aware from various sources that microlights should not be anywhere near CumuloNimbus clouds.

    I've also read from a variety of sources and understand the theory of how Cumulus clouds develop.

    However, I'm a bit stuck on a more practical level.

    How do I know if there are Cumulonimbus clouds around? Unless I am mistaken in the UK when we have thunderstorms there seems to be a thick layer of cloud and there is no way to see CNimb clouds at altitude through them. Is it simply just a case of ensuring no thunderstorms are forcast on Met Office? I dont ever recall every having seen a CumuloNimbus cloud in the UK that looks like the ones in the textbooks. I also unerstand that their effects can be felt a long way away anyway.

    I also understand that Cumulus clouds become large cumulus clouds when there height is higher than their base, which does occur fairly regularly in the UK. And that these can in theory go on to become CNimb.

    So as a microlight pilot, when do I need to worry. At what point does flying under or around cumulus clouds become a danger rather than just 'a bit rough'? Is flying under large cumulus clouds dangerous, or is it just a bumpy experience? And when do I need to worry about cloud suck?

    I keep being told it all comes with experience, but if I do something too wrong I'm not even going to gain that experience!

    Any tips/advice would be appreciated.

    Thanks in advance.


  2. #2
    Captain MadamBreakneck's Avatar
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    Hi Newflyer,
    That is one of those simple questions with a lot of potential answers - mostly complicated.

    Let's start with cloud recognition; eg at this Met Office page. Cumulus clouds are individual clouds with gaps (of varying sizes) between them. As you point out it's sometimes not possible to see the gaps because af layer cloud (stratus) filling them in. The only way on those occasions to see the gaps would be to get above the layer cloud, which we may not (and usually can't) do in microlights. It is possible though to look on the internet using published satelite and/or radar images, such as the Met Office's rain radar page. if it shows on that, then the cloud is, by definition, Nimbus of some sort - it's rain-bearing.

    Let's not get engrossed in explaining weather systems, but what your concern seems to be about is what we'd refer to as embedded Cb (cumulonimbus embedded in a bed of stratocumulus) which most often is a feature of an occluded front; ie when a cold front catches up with a warm front near the centre of a depression and they mix their weather systems up into a single area of yuk.

    Come summer, you'll be able to see Cb building up and looking something like the photos you see in the books with high tops and anvil heads and all that sort of thing. As we all know, what goes up usually comes down... look through your books or internet searches for 'microburst' or more colloqially 'cloud burst'. That will show you why you are advised to stay away from them... they can produce very powerful gusts that a microlight would find exciting up to 20 miles away.

    Will it be life threatening, scary or just a bit bumpy? Let's just say at this stage that the bigger the cloud the more 'interesting' it can get. You can gain experience by noting when your instructor says 'no' and asking them - nicely - to explain. They might offer to take you up in such conditions so that you can learn why not to

    Meanwhile, cloud suck shouldn't trouble a microlight in the UK in weather your instructor would let you up in, you can always throttle back and lower your nose. That'll get you out of most situations and if you are still going up, you can increase power a bit to pull yourself down as long as you stay below Va if the air is rough, and definitely below Vne. You can also just fly yourself out from under the sucking cloud and go around it.

    So that's the short answer - with luck someone else will come along with their thoughts.
    Last edited by MadamBreakneck; 11-03-19 at 18:34 PM.



    Back to just bimbling in the TST.

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  3. #3
    Airfield Ops newflyer17's Avatar
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    Thank you for the reply.

    You can gain experience by noting when your instructor says 'no' and asking them - nicely - to explain.
    Unfortunately (or fortunately) I've finished training now, so the decision is all mine. Hence asking the question. I possibly shouldn't have put it in the training section, but thought it seemed relevent to trainees or less experienced pilots.

    I think my concern is a more general one - recognising the conditions I should be going up in against the ones I shouldn't be.

    The cumulonimbus is obviously one where I'd not attempt if I was aware it was around, but I'm even more confused by blur between cumulus and large cumulus, and what is calm, what is uncomfortable and what is dangerous. I think I had assumed that it was cumulus=calm, large Cu = rough and uncomfortable but not dangerous, and CNimb was dangerous. But would be interesting to hear if that is a fair assessment or whether those lines blur a bit.


  4. #4
    Co-Pilot Randombloke's Avatar
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    Quote Originally Posted by newflyer17 View Post
    The cumulonimbus is obviously one where I'd not attempt if I was aware it was around, but I'm even more confused by blur between cumulus and large cumulus, and what is calm, what is uncomfortable and what is dangerous. I think I had assumed that it was cumulus=calm, large Cu = rough and uncomfortable but not dangerous, and CNimb was dangerous. But would be interesting to hear if that is a fair assessment or whether those lines blur a bit.
    Cumulus clouds are usually the result of convective activity in the lower layer, and this is usually dependent on instability in the same.

    Microlight pilots tend not to be as knowledgeable about meteorology as glider pilots, yes, I'll get slaughtered for this, but if you want to get a handle on this then I'd suggest you get a second hand book written by someone like Derek Piggott (RIP) who was a major player in this area, buy his "Understanding Flying Weather", learn it cover to cover and you are done. It will be worthwhile study, it will keep you safe and save you wasted trips to fly.

    You can also learn to use the RASP forecasting tool at http://rasp.stratus.org.uk/app/welcome.php which will allow you to get forecasts of everything from thermal strength to over development potential and Cu-Nb risks.

    Forecasting Cu-Nbs isn't hard. Post cold front with a Polar Maritime airstream is medium to high probability. They tend not to exist on the sea breeze side of things on an unstable day.
    Steve U.
    PG, HG & microlights
    "Weekend bimbler, day to day car driver & genuinely undeserving Southern oik who has never done anything of any worth"

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  6. #5
    Captain MadamBreakneck's Avatar
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    Ah! ... or from our very own Mr Cosgrove: https://www.pooleys.com/shop/crowood...ather-cosgrove Other books, and suppliers, are available.**

    NewFlyer, do you fly at a private strip in isolation from others? if so, try to benefit from their experience (that doesn't mean trying to fly whenever they do, but you can try asking these questions over a cuppa and a hobnob, or whatever the local nibble is).

    Beyond that, I've always had a simple rule that's kept me alive thus far - if in doubt, don't go (I set a limit of 30 seconds sucking through the teeth trying to decide - longer than that says there's doubt). I'm sure you'll have heard the old saying that "it's better to be on the ground wishing you were in the air, than in the air wishing you were on the ground", and my own personal experience confirms that.

    Another clue, by the way, to nastiness of summer thunder storms (in the UK) is that the really nasty ones often clear the sky around them - you get a single humungous cloud covering a lot of ground and going up very high. Intuition says there's a lot of rogue energy building up in there. I have my own rule of thumb which says if the top is more than 30 degrees above the horizon, it's probably time to put the aircraft away (or at least tie it down!).

    **the one I used years ago was: Meteorology For Glider Pilots By C E Wallington


    PS.
    Quote Originally Posted by newflyer17 View Post
    ... Unfortunately (or fortunately) I've finished training now, so the decision is all mine.
    Getting your licence doesn't ban you from seeking help and advice from your favourite instructor. if you are unsure about flying in certain types of weather, I'm sure you wouldn't be turned away for asking for a bit of further training in handling 'interesting' weather. Apart from anything else, it would count towards your 1 hour in 2 years minimum instruction for revalidation by experience.
    Last edited by MadamBreakneck; 12-03-19 at 18:02 PM. Reason: footnote, then PS



    Back to just bimbling in the TST.

    No longer instructing - just pontificating.


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