Strong Low Thermals

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Kevin87

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Kevin87
Hi Guys,

I have a question for you weather guys out there. I flew on Saturday around noon and there were some strong thermals around 200ft AGL. It made the approach very uncomfortable and was really tossing the plane around. If I would have known the conditions were going to be like that, I would have not brought a passenger. Especially one who has never flown in a small airplane.

My questions is, what is the best way to check for conditions like this?

Anyone have any advice?

Kevin
 
Mainly anytime you have a bright, sunny day and it's later than 9AM, if it's thermals. Also, dissimilar surfaces contribute because the air heats unevenly. I fly out of KORL (Orlando, FL) and it's surrounded by city. Think parking lots, buildings, with trees and small lakes interspersed. When I get out to Lake Apopka, the thermals generally calm down.

It can also be other kinds of turbulence of there is wind with obstructions (mountains, tall buildings, etc.). This turbulence can reach higher than the obstructions.

(Calling for someone versed in mountain flying... the the white courtesy phone.)

Fly early (1st hour or two after sunrise) and you'll avoid the worst of it.

John
 
Yup. Main tip: don't fly at noon in the summertime.

Even in San Diego with our relatively mild summers, flying at noon through 5pm can be pretty bumpy. I am about to begin taking friends on their first plane rides, and I am scheduling them for 8:00AM and 9:00AM flights.
 
Thanks Guys. This time out it just seemed way bumpier then I remember. I guess I am just not used to it.
 
I flew into DFW class B yesterday about 1300 and I held out at 8500 till 15 miles out then dropped in. That last 12 miles at 4k and down felt like a washing machine. and if that wasn't enough, it was 21gusting 28.

Like he said....fly early or accept the challenge of flying in the chop.
 
Summer flying is challenging after early morning. Before ten and after five seems to work.
 
Would said thermals make it difficult to get an aircraft trimmed out at around 2500 agl?

I had this problem on my last flight and became frustrated and ended my flight early because of it.
 
cowman said:
Would said thermals make it difficult to get an aircraft trimmed out at around 2500 agl?

I had this problem on my last flight and became frustrated and ended my flight early because of it.
Click to expand...

Absolutely.... :yes:
 
In the summer, either go early in the morning (earlier the better), or in the evening after dinner. It will usually be smoother at those times.
 
Kevin87 said:
My questions is, what is the best way to check for conditions like this?

Anyone have any advice?
Click to expand...

Go up in a glider? ;)

Get used to it? :)

You're piloting a light craft, not a heavy one. Small boats move more on the water in even light chop, than ocean liners.
 
Fly in morning and evening or over water
 
I flew a lot last summer and don't ever remember getting strong thermals that low on final before.

Oh well. It makes it a little more of a challenge and keeps me on my game.

I guess I will take new passengers in the morning.
 
I flew in tuesday evening to around Corpus and during my final I was getting tossed around like a volley ball at a concert. Interesting, but I just forced the plane to stay where I wanted it with input. No big deal.
 
Was there a crosswind and a treeline or buildings on the side of the runway?

Normally from 200' on down what you're feeling is from wind, not mechanical turbulence.
 
Most of the airports I frequent have their low altitude quirks. Some have dips in the terrain that cause a dip in the airflow right above it (on short final), some have an asphalt road nearby that causes a local heating and thermal (on short final), some have hangars in such a way that it causes turbulence when the wind is from just the right direction.

As many a CFI has said, every landing is different.

Summer daytime heating can make for some unpleasant bumps - unless you are in a glider and that's actually what you WANT to find.
 
No different than boating. Some days you get tossed around.
Just remember the old sailors had no choice but to trim the sails and keep on.

Same in your bug smasher, slow down, add a notch of flaps if you need to be really slow, and realize it is all part of the art of flying :D
Trim is over rated, and sometimes impossible. Just fly the plane.
 
As a hang glider pilot as well as ASEL pilot, I'm familiar with this. Fly your airplane before 9:30am and be ready to launch your hang glider by 10am to catch the first thermals lifting off. This assumes clear skies. If cloudy, the thermals don't start until closer to noon.


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Or better yet just get used to it. Summer afternoon thermals are going to beat you up close to the ground, and over terrain. Avoiding them is.... limiting.
 
Autopilot helps a bunch too. I only have single access, but it's pretty responsive.
 
They don't bother me anymore from a comfort aspect but when one is trying to overcome difficulty maintaining altitude +-100 it's not ideal.

I did manage to get out late in the afternoon in smooth air recently though and proved to myself I really can fly the airplane well enough to pass a checkride.
 
dell30rb said:
Was there a crosswind and a treeline or buildings on the side of the runway?

Normally from 200' on down what you're feeling is from wind, not mechanical turbulence.
Click to expand...

This is what I was thinking as well, but the wind was right down the pipe of 18. Open field in front of it.

I flew this weekend with a bright hot sun beating down at 3PM. There were just the normal bumps coming in on final.

I'm still trying to figure out what was going on.
 
Kevin87 said:
Hi Guys,

I have a question for you weather guys out there. I flew on Saturday around noon and there were some strong thermals around 200ft AGL. It made the approach very uncomfortable and was really tossing the plane around. If I would have known the conditions were going to be like that, I would have not brought a passenger. Especially one who has never flown in a small airplane.

My questions is, what is the best way to check for conditions like this?

Anyone have any advice?

Kevin
Click to expand...
Other than the rules-of-thumb mentioned above, you can do what we glider pilots do: add a skew-T check to your wx briefing. In a nutshell, a skew-T graph will show you what you most want to know: at what altitude you can expect strong lift. They're also handy for predicting cloud base altitudes... because (unfortunately for VFR pilots) where lift peters out is usually where the clouds start to form.

Here is a good source, although there are many:

http://www.drjack.info/BLIP/RUC/

...and here's one of the clearer explanations I've seen on how to read and use them. Tailored for pilots seeking lift, but just replace "good" with "bad" wherever mentioned, and it will work for you. :lol:

https://www.ssa.org/myhome.asp?mbr=3981940746&show=blog&id=141

... these diagrams can yield a ton of varied info, but for your flight planning purposes, you just need the trigger temp (surface temp at which the conditions aloft will most likely occur) and the altitude where lift (unstable air) will be less energetic. Hint: that altitude is usually where the two most important lines on the graph intersect.

Because these graphs are only based on twice-a-day balloon soundings , and covering a fairly limited area, you should always keep the thumbnail rules in mind and pay attention to what the sky is doing as you fly along.
Best thumbnail-rule advice I can give you is that if you see flat or concave-bottom cumulus clouds with "crisp"-looking tops, the air is going to be bumpy below them, possibly all the way down to the surface. They don't have to be very big clouds... in fact, once you start looking for these visual signs, you will learn how to spot "newborn" Cus, and they often can indicate a very strong thermal that has just pushed a moist parcel of air up to where it's cold enough for the cloud to become visible. And if there is wind present, the cloud itself might be downwind a ways from the surface "hotspot" that is warming the air... thermals "lean" downwind to some extent.
 
Thanks Beaky. I will look into this.
 
Best advice I could give is to become more comfortable/confident in lower altitude turbulence. It's a reality at anytime and anywhere. If necessary, deliberately fly in those conditions with an instructor to gain confidence. Once you have the skills and confidence, it's mostly a nuisance.
 
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