When using spoilers it seemed to just push the plane down, not really SLOW it down... is there a specific technique. ...

From : Don Stackhouse

Spoilers don't slow an airplane down, they just make the glide path at a given airspeed steeper.

To fly slower, you need to make more lift. Spoilers DESTROY (i.e.:"spoil") lift. That's what they do, and that's how they get their name. The stall speed actually increases when you put up the spoilers.

Glide slope is approximately equivalent to the ratio of lift to drag ("L/D", pronounced "ell over dee"), at least for L/D's greater (i.e.: flatter glide angles) than about 5:1 (i.e.: the airplane goes 5 feet forward for each foot that it loses in altitude). For a steeper glide without increasing airspeed, we can either increase drag or decrease lift. Spoilers do both, but their effect on lift is probably the most pronounced of the two.

Flaps both increase lift and increase drag, although at large flap deflections the increase in drag is proportionately much greater. The increase in lift allows a slower stall speed (and therefore a slower landing speed), while the disproportionately larger increase in drag also results in a steeper glide angle. This results in better possible landing performance, but it can also be a trap for inexperienced fliers. If you find yourself too low, you can't just retract the flaps to stretch your glide. Since the airplane is flying slower than normal due to the lift increase from the flaps, if you retract the flaps too much without also diving to get your airspeed back above to the no-flaps stall speed, the airplane is likely to stall. Since you are trying to retract the flaps because you're already too low, you probably also don't have any spare altitude to use for a speed increase.

The lift increase from the flaps occurs mainly in the first 20 degrees or so of deflection, so you can retract the flaps safely up to that 20 degree point, but if that's not enough of an improvement, you're essentially out of options.

OTOH, since spoilers increase the stall speed, you can retract them completely without risking a stall. In fact, the higher stall speed with the spoilers open could mean that you might have a little excess speed after you retract them, allowing you to stretch the glide a bit more. This is a much safer situation for an inexperienced flyer, which is why we designed our 2-meter Chrysalis sailplane with spoilers, not with flaps. We also designed those spoilers so that they interact with the tail to create a very slight nose-down trim change when open, to automatically account for the slight increase in stall speed caused by the open spoilers.

Don Stackhouse
DJ Aerotech