Thermal mode

[mikey100]

I know this is probably a stupid question, but as I am new to this thermal flying.....

...when I put my Pike Superior into thermal camber (1.5mm down flap and ailerons) it slows, climbs initially, but seems to have a higher sink rate than when on cruise mode. I have added a little bit of down-elevator compensation to keep speed up, but am getting better flights (longer) in cruise. What am I doing wrong? Same problem with my Jaro Muller Escape.

Am I wrong in assuming that Thermal mode should be the best 'minimum sink' mode. Cheers , mike.

[recep]

Not if you are in sink; here is an info to the bottom of the linked page starting with the glider polar curve till the speed to fly.
http://www.jdburch.com/glidercd/AERODYN.HTM#AER1
If you are in the thermal core it is good to use the advantage of the high lift of thermal mode camber but if you come across a sink area you will stay in that downdraft longer because you are flying slow with thermal mode on.

[Neil Stainton]

Am I wrong in assuming that Thermal mode should be the best 'minimum sink' mode.

Yes, you are wrong. Thermal camber increases max Cl, allowing slower tighter circles in the core of the lift. This increases the rate of climb, despite the very slightly increased drag (and still air sink) of the glider.

Neil.

[mikey100]

So, just use THERMAL mode when you are definately in lift and circling in it...CRUISE in neutral air...and SPEED when in sink to get out of there fast?

[mikey100]

Neil....'max cl'...what is 'cl' ?

[jkettu]

....'max cl'...what is 'cl' ?
http://en.wikipedia.org/wiki/Lift_coefficient

[Neil Stainton]

So, just use THERMAL mode when you are definately in lift and circling in it...CRUISE in neutral air...and SPEED when in sink to get out of there fast?

Correct.

Neil.

[Neil Stainton]

Neil....'max cl'...what is 'cl' ?

What jkettu linked to. (Thanks jkettu.)

Cl = lift coefficient. Max cl (or cl max) is the maximum value of cl before the section stalls. Applying flap increases cl max, but also increases cd, the drag coefficient. Generally cl/cd will decrease, meaning the drag increases more than the lift, meaning the plane will sink a bit faster, despite the fact it is flying slower.

Neil.

[mikey100]

So...., just use THERMAL mode when you are definately in lift and circling in it...CRUISE in neutral air...and SPEED when in sink to get out of there fast?

[Neil Stainton]

So...., just use THERMAL mode when you are definately in lift and circling in it...CRUISE in neutral air...and SPEED when in sink to get out of there fast?

YES!

Neil.

[target]

Also, try NOT to turn around in sink, if possible. After you fly a while longer, you will know why.

Target

[mikey100]

Thanks all. Am trying to work this 'thermal flying' thing out....so..........
- just use THERMAL mode when you are definately in lift and circling in it...CRUISE in neutral air... SPEED when in sink to get out of there fast...and don't turn in sink.
...Any other basic tips?

[target]

...Any other basic tips?


Never drag a wingtip landing if at all possible. The molded TD planes are made to handle decently harsh nose first landings, but if you side-load the tail boom by hitting wingtip first, and then nose, you will be asking for the tailboom to break behind the wing TE....
So try to land wings level always, and try to get your flaps up right at landing.

On your other post of the tipstall problem, a fwd CG may actually make your problem worse, by requiring more up elevator (too much) to get the pitch response you desire. DONT FORGET to turn the elevator down a touch as you move the CG back....
Also, differential and rudder mixing can be overdone. Sometimes when a little is good, more is not better.
Make one change at a time, and see what works.

G/L!

[ACooper]

Never drag a wingtip landing if at all possible. The molded TD planes are made to handle decently harsh nose first landings, but of you side-load the tail boom by hitting wingtip first, and then nose, you will be asking for the tailboom to break behind the wing TE....
So try to land wings level always, and try to get your flaps up right at landing.


Amen! Top shelf advice! :p

Speaking of tail booms...anyone beef up theirs with some spray foam?

[Radian]

Amen! Top shelf advice! :p

Speaking of tail booms...anyone beef up theirs with some spray foam?


I did on a DLG...

Added 4 grams of "tail weight" but made the boom noticeably stiffer.

Radian
www.phflyers.com

[FrogChief]

Amen! Top shelf advice! :p

Speaking of tail booms...anyone beef up theirs with some spray foam?

Run away from spray foam like the plague. ;)

[GDbot]

Run away from spray foam like the plague. ;)

Why? I haven't tried it anywhere yet but it sounds like a useful building technique.

[jkettu]

Messy, heavy, will expand and break/deform every structure around it, will never cure in enclosed spaces.. try it yourself and fill out the rest of the list.

[lesterpk]

Did it on a Supra to hold the internal pushrods secure, done carefully and allowing for the expansion, no problem at all.

[ACooper]

Glad that I asked. I was worried about expansion back into the elevator linkage area.

[tomcat5109]

Mikey,

I have a cross tail Superior flying at 75 oz. In the beginning I experienced the same mush behavior when cambering the trailing edge in thermal mode. With help from a few local experts, the Superior came alive for me after I moved the cg back from 106 mm to 109 mm from LE AND flew the plane a bit faster. Now the Superior really performs great in the flatland TD soaring that I do. Just keep the speed up a little more when thermal camber is deployed.

Also, the amount of thermal camber is controlled by a slider switch on my transmitter. I don't just use the recommended set amount as all or nothing. Depending on the air, the Superior requires different amounts of camber. You should experiment with it.

Of course, this works for me. YMMV

Tommy

[mikey100]

Thanks Tomcat...I am finding that keeping the speed up and only using camber in strong lift is helping. Will try a more rearwood cg.