Help! How Slow Are Gliders

[Inq]

Trying to find an answer on the Internet always leads me to how fast a glider can be made to go - 548 mph.
or real full scale sailplanes are most efficient around 45 - 70 mph.

What I'm looking for, is for a typical RC glider that is common on this forum, how slow (relative air speed) can they go and create enough lift to climb?

What I'm after is to make a self powered glider that can still climb with the absolute minimum power module. This involves it just barely chugging along and climbing. I'm right now taking a WAG at around 20 mph, but I'm wondering if this can be shaved even lower.

Thanks.

 

[danskis]

(14) 2018 FAI F1D World Indoor Free Flight Championship at West Baden - YouTube

Admittedly I know nothing but you may be starting with the wrong questions. My balsa, two meter glider weighs about 15oz, has an 1806 2300 kv motor, 7X4 prop, 650mah 3 cell. It can go up at about a 75 degree angle for ten seconds and without lift stay in the air for about 3 minutes. It flies well in up to a 10 knot breeze. That glider probably weighs about half of what a foamboard glider weighs or possibly about the same as a printed glider.

The glider club set up a timed course about 3 years ago to judge air speed. I'll see if I can get those numbers.

Also, if you're looking for thermals it helps if a glider flies relatively fast . Since you only stay up for so long looking for thermals it helps to be able to cover a lot of the field looking for them rather than going slow and hoping you bump into one close by.

 

[Piotrsko]

Slowest I have seen demonstrated at a contest is about 15mph (brisk run) no wind, but that was a while back. The indoor super lite guys are slower. From what I have seen, at these speeds the airfoil can be a flat sheet because you don't seem to be making much of an upper pressure drop. YMMV.
Climb can be a function of thrust, one of @sponz aircraft tail sits for takeoff

Suspect @quoreng is the expert here

 

[AIRFORGE]

Also, see @bracesport.

 

[quorneng]

Inq
"a self powered glider that can still climb with the absolute minimum power module".

Climbing involves using additional energy working against gravity so the extra power required is directly proportional to the planes total weight.
If you want the minimum power to climb then sacrifice structural strength and the aerodynamics necessary for fast flying to keep the airframe as light as possible.
A by product of this approach is that for a given size airframe and power it reduces the plane's minimum flying speed which in turn reduces the power required to maintain height thus leaving a bit more available for climbing.

A plane weighing 436g (16 oz) with a modest 70W available but can maintain height using just 12W then it has 'spare' power to climb quite readily - and it does.

 

[Inq]

Thanks all! These give me some great bracketing of the problem.

BTW - I didn't get notified anyone had replied. The forum seems to be having a lot of troubles lately.

 

[AIRFORGE]

Some major overhauls are in progress. Some features have been hit and miss for me, at times. They said it might take a while.

 

[bracesport]

I am mostly a glider guy but am in the process of building an F5K (DLG with a motor).

When I plug in the power for the motor I get some beeps but the motor does not run when I throttle up - do the initial beeps mean it is seeing power, or that it is seeing a signal (I don't get the secondary beeps), but maybe the calibration needs to be set?

When you do calibrate the throttle end points, is that info stored in the ESC or the Rx - as It was running on a previous Rx.

Regards,
Phil

 

[Mr NCT]

I am mostly a glider guy but am in the process of building an F5K (DLG with a motor).

When I plug in the power for the motor I get some beeps but the motor does not run when I throttle up - do the initial beeps mean it is seeing power, or that it is seeing a signal (I don't get the secondary beeps), but maybe the calibration needs to be set?

When you do calibrate the throttle end points, is that info stored in the ESC or the Rx - as It was running on a previous Rx.

Regards,
Phil

It's stored in the ESC. To calibrate the esc first disconnect the battery & remove prop for just in case. Then turn on the tx, move throttle to max and plug in the battery on the plane. Once all the beeping stops pull the throttle down to off and the motor should beep some more and it's calibrated.

 

[bracesport]

if I previously calibrated the ESC and the motor ran (on the bench) - would it be something else preventing it from running?

Maybe I should also use a New Model with default settings and check it can run?

It's stored in the ESC. To calibrate the esc first disconnect the battery & remove prop for just in case. Then turn on the tx, move throttle to max and plug in the battery on the plane. Once all the beeping stops pull the throttle down to off and the motor should beep some more and it's calibrated.

 

[Mr NCT]

if I previously calibrated the ESC and the motor ran (on the bench) - would it be something else preventing it from running?

Maybe I should also use a New Model with default settings and check it can run?

Did you calibrate it with the same rx or a servo tester? In the past I've tested with a servo tester and then had to recalibrate with the rx.

 

[bracesport]

it is a new Rx (same type)

Did you calibrate it with the same rx or a servo tester? In the past I've tested with a servo tester and then had to recalibrate with the rx.

 

[Mr NCT]

it is a new Rx (same type)

I'd calibrate it with the new rx and if that doesn't work then start looking at wires to make sure one hasn't pulled loose from the motor. If the esc and motor combo worked with one rx then they are probably good.

 

[bracesport]

I will report back!

I'd calibrate it with the new rx and if that doesn't work then start looking at wires to make sure one hasn't pulled loose from the motor. If the esc and motor combo worked with one rx then they are probably good.

 

[bracesport]

The answers are always more simple than you think - it occurred to me the GRRX8 might be in SBUS (no CH7 output) - and it was!

FYI - the current manual is incorrect for switching SBUS to PWM - you actually need to use the jumper on pins 1/2 and re-bind it to turn off SBUS (that took some head scratching)!