Thread Tools
Apr 12, 2019, 01:20 PM
Registered User
Thread OP
Discussion

trimming for thermaling-how you do it?


how you trim your sailplane for thermaling?
that is, if you want it to sail into a thermal, how it glides?
just flat?
straight?
turning at certain radius?
if so, what radius for a given wingspan?
why?
thanks
please, just answers to the questions.
Last edited by phil alvirez; Apr 12, 2019 at 03:43 PM.
Sign up now
to remove ads between posts
Apr 12, 2019, 03:43 PM
Registered User
Thread OP

what i do


perhaps if i tell what i do and why, may bring comments based on others experiences.
i trim my sailplanes to turn on the smallest circle without diving or getting into a spin; at their minimum sinking speed.
and near the edge of a stall. this means that the plane is going into oscillations, like waves, pointing slightly up for a few moments, and when is about to stall, it changes attitude and moves its nose a little bit down .
this way, when detecting the slightest 'up' air, when at the moment of having its nose up, instead of changing to slight nose down, it continues going up with the thermal.

i learned this at the days when i flew free flight.

so once finding a thermal, there is little that i need to do. it is a free flight plane going on its own, and i only need to do something if it is drifting too far.

so, how you do yours?
Apr 12, 2019, 10:34 PM
Registered User
how you trim your sailplane for thermaling? - trim for slower speed with camber and a bit of up elevator
that is, if you want it to sail into a thermal, how it glides? - not applicable (see above)
just flat? - not applicable (see above)
straight? - not applicable (see above)
turning at certain radius? - not applicable (see above)

* I might have expanded more on this, but the OP requested to only answer these questions....
Apr 13, 2019, 12:27 AM
Registered User
If you want to FIND a thermal, best to fly at moderate speed, smoothly, in long straight lines that don't go through the same air twice. (Keeping in mind that the thermals will drift with the wind.) Go faster if you're in sink. When flying into a thermal the model will seem more lively. Either it will fly faster without sinking faster, or it will rise without slowing down.

If the model is pitching up and down much, you're losing energy. In a thermal, you should fly fairly slowly, but not so slowly that the model stalls or oscillates very much. AIrspeed control is quite important, though of course unless you're using telemetry you'll have to infer the airspeed from the behavior of the model. Another thing to keep in mind is that thermals come in different sizes. In a narrow thermal, tight turns will be rewarded if it's strong enough. In a wide thermal, it's more efficient to fly in a wider, gentler turn*. Thermals tend to get wider as they go up. On different days, the average thermal is of different sizes. Sometimes the thermals are so wide that you can fly all over for 10 or 20 minutes and stay up. The secret of staying up then is to launch when the thermal is around, and then find excuses not to fly for a while when the sink comes in. This sort of thing is more prevalent later in the day, say after noon or 1, but of course depends on the weather and local conditions.



*Up to a point. I doubt if there's all that much difference in sink rate when turning with a 3 degree bank instead of a 6 degree bank.
Apr 13, 2019, 01:54 AM
Registered User
mhodgson's Avatar
Surely if the model is oscillating up and down, without control input, then it is stalling. Each stall is a loss of lift and surely an inefficient way to fly.
Even the most inefficient flying model will go up if the air around it is climbing faster than the model is descending.
I was taught, by much better pilots than I, that the smoother you flew the less height you would loose and that includes when turning in thermals. Keep the wing as flat as possible to maximise the lift produced but turn as tightly as possible to keep in the centre of the thermal where the lift is strongest. It's a compromise and balance that you need to modify for different thermals and lift types.
I'll never forget the chap who spotted for me in a competition and as I bounced around a thermal he told me "put 2 notches of down trim in now". I did and suddenly my model flew more smoothly and went up more quickly. Why did it work? He said I was flying too slowly and the model was stalling, the extra downtrim added just that little extra speed to stop the stalling. I flew much better after that, and made my first flyoff at that competition.
Apr 13, 2019, 07:16 AM
Registered User
R.M. Gellart's Avatar
I trim for conditions, that is it. I have thermal mode, the TE setting and some difference in aileron throw and expo, but my stab trim is native to my cruise setting. As Mr Hidgsin said, down trim is usually my choice once I have ascertained conditions, especially in strong air. Reason for down trim is, in strong air, I am pulling hard since the energy is there to use but when I let off the stab I want the ship to stay efficient not suck all the energy out with nose up trim.

In light air, yes, near the minimum sink trim and keep the turns very efficient. You do not have energy to burn so to speak, use it wisely. As Dave Thacker said, zero sink is lift, and to use it you cannot being mixing paint with the sticks.

Finally, do not think there is a given trim for “lift”, there is trim for energy available.

Marc
Apr 13, 2019, 07:30 AM
Registered User
Thread OP

great


terrific input, thank you guys. everybodyelse: keep bringing it.

and, kablair, its ok if you tell us more, as others do.
no problem.
Apr 13, 2019, 11:45 AM
Registered User
First, I balance my planes to give me a moderate (yes, very subjective) forward glide when my surfaces are at 0-0 using my battery position for adjustments. For me, this is part of trimming.

Efficient elevator trim is key for me. I only use a small amount of camber on two of my planes, but I feel there is little added performance especially since I do not have full trailing edges. I like my airfoil to do the work so I normally fly in what many consider a "cruise" mode so I work a lot with my elevator trim to maintain an AOA that conserves energy while allowing my planes to turn well.

I minimize control surface deflections as much as I can so I am not introducing more drag. I fly with dual rates and expo for both elevator and aileron functions. When thermalling, I go to low rates to give me a softer touch.

Dave
Apr 15, 2019, 04:26 PM
Phil.T-tailer
Phil.Taylor's Avatar
Quote:
Originally Posted by phil alvirez
how you trim your sailplane for thermaling?
just answers to the questions.
how you trim your sailplane for thermaling? - I don't - I trim it for straight flight, hands off
that is, if you want it to sail into a thermal, how it glides? - I start a turn & add a bit of up elevator to maintain the turn (or a lot for steep turns)
just flat? - yes
straight? - yes
turning at certain radius? - no - I trim it for straight flight, hands off - then turn - see above
if so, what radius for a given wingspan? - irrelevant - the turn radius depends on how big (or small) the thermal is

Phil - its ok for you to "trim" your RC sailplane like a free-flight - so it flies hands off circling in a thermal - as you have described. But - the moment you try flying straight ahead with that "trim" - the plane will stall because of the up "trim" to keep it circling. i.e. You will need to re-trim with some down trim to fly straight and level.
Meanwhile - most RC sailplane pilots do it the other way around - trim for straight flight, then when in a thermal manually input up elevator and/or aileron & rudder to keep it circling nicely. But - its ok to be different !
Apr 15, 2019, 05:33 PM
Registered User
Thread OP

either way


in free flight you trim for thermals, as you cant do nothing, but with r/c there is the option of trimming for thermal or for flying straight.
if done as you do, you dont need to do nothing when searching; if done as i do, i dont need to do nothing once in a thermal.
and, as i expect to stay longer in thermal than searching, i will spend less time sending commands.
either way, you cant have the cake and eat it.
but depending how the weather is, 1 will need less commands
Apr 16, 2019, 05:31 AM
Phil.T-tailer
Phil.Taylor's Avatar
Quote:
Originally Posted by phil alvirez
either way, you cant have the cake and eat it.
Of course you can - thats what Tx flight modes are for
Cake 1 - free-flight thermal turns - hands off
Cake 2 - straight & level cruise - hands off
Enjoy eating cakes while flying by just switching the mode switch.
While the rest of us are enjoying the thrill of RC soaring by stick twiddling - searching out lift - avoiding sink - shifting turns to core thermals...
Phil.
Apr 16, 2019, 05:44 AM
Registered User
Thread OP
then you have to have a radio that has the capability to program that-and the knowledge to do so
which brings us to another subject that could be worth exploring-but not here.
and then, where you left this that you said?:
"Meanwhile - most RC sailplane pilots do it the other way around - trim for straight flight, then when in a thermal manually input up elevator and/or aileron & rudder to keep it circling nicely. "
Apr 16, 2019, 09:48 PM
Registered User
tewatson's Avatar
Is there a facepalm flight mode?

Tom
Apr 16, 2019, 10:32 PM
Detail Freak
target's Avatar
How do you not start a sentence with a capital letter?
Apr 17, 2019, 01:59 AM
Registered User
Thread OP
Quote:
Originally Posted by target
How do you not start a sentence with a capital letter?
k. i. s. s.?


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Trimming for a climbing turn -- a simple question for those w/ free-flight experience aeronaut999 Modeling Science 3 Jan 19, 2019 11:43 PM
Discussion Cheap/compact thermal imaging for smartphones, someone should mod this for FPV londez FPV Equipment 9 Jan 26, 2016 04:05 AM
Help! Trim issue: ZMR250 wants to flip with centered trim? Glitch5618 Multirotor Drone Electronics 7 Nov 04, 2015 02:18 AM
Discussion Setting Trim/Sub-Trim for 450Quad on KK board CADQuad Multirotor Drone Talk 4 Nov 18, 2014 01:17 PM
Question Thermal Turn Trim Settings David McNeill Thermal 14 Sep 28, 2005 08:42 AM