Another Thermal Issue

[Guest davidvoogd]

I've noticed that some of the thermals can be rather strong, stronger than I've experienced in any real flying. I realize around mountains you can get some really strong verticle air currents, but just normal thermals aren't quite so strong I thought, especially the downdrafts. Yet flying in North Dakota today - with not even a hill to be seen to produce anything resembling a mountain wave I hit a downdraft so strong the 172 couldn't even keep level in it. The ground temperature was 21C, skies were clear.My real flying experience is somewhat limited (40 hours) but I've never experienced this or heard of it anywhere but when it was a downdraft associated with mountain waves. Is this realistic? If not is it possible to tone down the thermal effects while keeping the mountain verticle air currents strong? Also I've found the area affected to be a bit big, from my experience they seem usually a bit smaller in diameter too. What about allowing users to set max / min and diameter values for thermals and mountain air currents?Overall I love the verticle air currents - makes things much more realistic, though I just find the effect is a bit exaggerated, especially flying general aviation aircraft.

[JSkorna 137]

Hi David,Of course, thanks for the feedback. This was a VAS generated point correct? Right now there is no way to adjust these but by the % of their generation. I wonder though if real world pilots experience thermals while crossing areas of flat, farmland. I know there is a lot of uneven heating and cooling going on, and maybe this is what ASV is trying to re-create? Hope this helps,JimActiveSky Sales and Supporthttp://www.hifisim.com/images/asv_dev_team.jpg http://www.hifisim.com/images/asv_proud_supporter.jpg

[Guest NorthPilot]

>Hi David,>>Of course, thanks for the feedback. This was a VAS generated>point correct? Right now there is no way to adjust these but>by the % of their generation. I wonder though if real world>pilots experience thermals while crossing areas of flat,>farmland. I know there is a lot of uneven heating and cooling>going on, and maybe this is what ASV is trying to re-create?> >Hope this helps,>Jim>ActiveSky Sales and Support>http://www.hifisim.com/images/asv_dev_team.jpg>http://www.hifisim.com/images/asv_proud_supporter.jpgWe regularly hit thermals on flat areas. Especially when it is hot and clear skies somewhere after 10am. They differ in strength depending on "colour" and "texture" of the flat area (e.g. forest, river, etc.).When we were flying in african country (wet leased) we hated midday flights due to massive turbulence caused by thermals.I hope this gives some answer.Have a nice flight!Aleksandar

[Guest davidvoogd]

The thermals aren't that big of an issue - there certainly should have been some in the area I was flying, it was realistic that way - what I felt was a bit off was the very strong downdrafts. I had the 172 at the best rate of climb speed with full power and was still sinking - I'd only expect that from a mountain wave, thunderstorm or a microburst.

[JSkorna 137]

Hi All,But isn't a downdraft a mass of colder air and can occur in flat areas?Hope this helps,JimActiveSky Sales and Supporthttp://www.hifisim.com/images/asv_dev_team.jpg http://www.hifisim.com/images/asv_proud_supporter.jpg

[Guest NorthPilot]

>The thermals aren't that big of an issue - there certainly>should have been some in the area I was flying, it was>realistic that way - what I felt was a bit off was the very>strong downdrafts. I had the 172 at the best rate of climb>speed with full power and was still sinking - I'd only expect>that from a mountain wave, thunderstorm or a microburst.Hi,Sorry for misunderstanding you.As far as my experience goes I am yet to see the flat area to produce such a downdraft as you describe it and that there is no presence of CBs to generate microburst or lee side of the mountain with winds favouring generation of downforce and eddies. Flat areas like forest, marshland, etc. do contain more "cold" air. So after you hit e.g. thermal they feel like pitholes, however I have not seen that they have effect like typical downdraft. This is more pronounced in gliders. I will check with glider pilots I know how they feel them. In our engined planes we just see some loss of climb speed/increase of descend but nothing dramatical.Of course CUs have good thermals underneath them and if you are to enter the CU or worse, CB then you may experience downdraft due to unstable mass of air circulating up and down inside it. Also the downdraft can extend beneath it. Of course, CUs are generated as hot air from thermal rises into cold air mass, expands and cools. The moisture it carried upwards turns into visible mass - cumulus. If you have temp inversion thermals will dissipate once they are no longer buyoant compared to surroundings.I might have missed again, but I hope this explains a bit more. Have a nice flight!Aleksandar

[ls25 0]

Just to repeat what has been said, I regularly (to say almost daily) get severe turbulance even in clear skies & clear weather coming into my home airport of MQY in my katana, and that is over very flat, or very lightly rolling hills. I have had it rough, and while it is a very light aircraft, I have had back aches after experiencing it on occasion.the turbulance is probably not nearly as severe for an aircraft over 7000-1000lbs mark, but for my little 1720lbs Katana, it is ROUGH.

[Guest CaptainSensible]

I have a weird problem when I use ASV which "may" be related to the VAS generation..I am having great difficulty landing any of my usual aircraft when using ASV. I get to the threshold no problem but even at the correct landing speed the aircraft (I used the SF-260 to test this) just floats for ages! Even with the throttle closed (on flight yoke and keyboard) it floats and floats for ever...Without ASV switched on I dont get this problem.Very odd indeed?RegardsAdam

[Guest davidvoogd]

Adam that happens when you get a strong thermal generated by ASV right over the destination, I had it myself and posted it in another thread, even someone in a 767 reported it.Jim to my understanding with convective turbulance the thermals / updrafts are strong and cover a small relative area, while the downdrafts are weak and cover a much larger area, I just re checked that up in the FAA Aviation Weather book and this is how it explains it. So while there will be a general sink to the air, as Alexsandar mentioned there shouldn't be any such intense downdrafts, outside of a thunderstorm or microburst. Lower to the ground over certain terrain such as forest and rivers there can be somewhat stronger downdrafts, but not anything a 172 can't outclimb.Here is a pic from the FAA Aviation Weather book..http://ca.geocities.com/davidvoogd@rogers.com/thermals.jpgOf course it's not possible to fully simulate real convective current in FS, and ASV is a great improvement from the default weather which has no verticle air currents, but the downdrafts away from mountains seem excessively strong, the only time I'd expect to experience such an intense downdraft would be related to a microburst, mature thunderstorm, or a mountain wave.On the product page it indicates that vertical air currents are generated from different triggers - including mountains, so would it be possible to tone down the convection downdrafts while keeping mountain related downdrafts strong?

[mnmon 0]

Just to give a little more feedback on the original post on this thread: I also would like to see the vertical shear turned down just a bit (or perhpas a user adjustable slider). My case was on final to KBDL (Hartford) with the PMDG737. On the approach to Rwy 6 about 8 miles out there is a small ridge in the town of Simsbury. While crossing the ridge I hit a very large vertical shear such that the AP could not longer track the glide slope and began large oscillations. I've flown into KBDL many times in airliners in real life and never experienced anything like this even under some tough weather. I imagine there is such shear about this ridge that would probably affect small planes, but to send an airliner into such oscillations seems too much. I really do like the inclusion of such vertical shear! Just maybe needs some fine tuning for the next upgrade. BTW, I learned to fly in C172's around the Ft. Collins, CO area. On clear summer days we would go bouncing along as we passed over planted fields then transitioned over a field that was bare ground. The difference in updrafts were amazing. We often tried to steer over the planted fields due to the much smaller updrafts generated. All this on land flat as a pancake. Mike

[3atcos 1]

Hi AdamI've had the exact same problem. As I was about to flare with the default Cessna, the aircraft just floated for ever. I managed to fly 2 circuits at idle power, flying all the way down the runway before turning - without landing. I stayed at about 150 feet AGL.it doesn't happen to me every time, I guess only when ASV has put a thermal over the runway.RegardsAsbjorn

[Guest CaptainSensible]

Just got back from flying my "real" aeroplane at Denham. Bit blustery and very hot but no problems with the landing on 24.Jumped in my FS2004 PA-28 and did some circuits with ASV. Excellent replication of the "actual" weather but yet again all fine until I reach the threshold and then with power OFF (notice OFF!) it just floats forever - impossible to land - had to go around and "place" it on the runway;)Would it be possible for the ASV guys to remove thermal effects over the airfields? Or at least let me switch them OFF. Otherwise I can take off, cruise, approach but not land lol!RegardsAdam

[Guest davidvoogd]

I think avoiding airports may be impossible, just "toning down" the effect would probably do the trick.

[Guest CaptainSensible]

Flew some more circuits at Denham earlier.With "Auto Generate VAS points" switched OFF (but ENABLE VERTICAL AIR SIMULATION switched ON) there were no problems.As soon as I tried with both "Auto Generate VAS points" and ENABLE VERTICAL AIR SIMULATION switched ON everything went very weird.The aircraft started speeding up (in level flight with no throttle input) and I couldn't reduce speed at all on the downwind or approach segments. I eventually bled off some excess speed to 80 knots (still way too fast for the flare) and floated down the runway. No throttle, full flap, level flight the aircraft refused to slow down. I went around and tried again but it still floats along the runway maintaining height even at 60 knots full flap no throttle.Sounds like some sort of weird bug to me but luckily it is avoidable if you switch OFF "Auto Generate VAS points".It's strange that more people haven't noticed this. I have tried with 10 different aircraft at 10 different airfields. Always the same effect with "Auto Generate VAS" points switched on.Hope this helpsRegardsAdam

[Guest davidvoogd]

It's definately the VAS points doing it - just that they are too strong I guess.