Spoiler Drag link

[Konrad]

I hate spoiler! With that out of the way here is how I like to actuate spoilers. This set up is known as a drag link.
It maintains a possitive connection with the spoiler and servo. Does not need or use any springs or magnets. Adjustments are easily controled by the radio's end point and /or servo control curve.

 

[jvaliensi]

That looks like one of them fancy F3-RES planes.
I have a wooden sailplane project coming up and I think I'll use your system.

 

[Konrad]

Fancy!? The whole idea of F3-RES was to bring sailplanes back to the simple basics.

But yes this is a DJ Aerotech Chrysalis lite (F3RES). I'm just starting the flight test portion of the build.
You can read about it in excruciating detail here:
http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=22619.0

I'm ashamed to say I'm not the father of this system of actuation.

One other thing I like about this system over the popular free floating spoiler is that it is far less likely to allow the spoiler to peal off in an abrupt landing. I know this is a extreme case but see how the free floating spoiler pealed off the wing.

All the best,
Konrad

 

[Wayne]

What I really liked about this setup is that when the spoiler is down, it can not be sucked up like some of the other methods. It is locked down really well, so the suction on the top of the wing will not be able to suck open the spoiler. Something you do not want to happen when looking for lift.

 

[Konrad]

Have I said I hate spoilers?

So true about spoiler lift up! I recall flying my Airtronics Cumulus and Sagitta 900 at “high" speeds between thermals and seeing the spoiler pop up. In those dark days I was using torsion bar springs, dental rubber bands or small magnets to hold down the spoilers. Combined with draw strings to pull open the spoilers. These were horrible setups to keep adjusted.

When I was last at Aloft looking for programing help, Wayne was a bit surprised that I was using a 7 point curve for my spoiler to elevator compensation curve. Normally the instructions given with spoilers is to add "up" as they are deployed. Nominally this is correct. But once I started to use positive control set ups for the spoilers I noticed that the airplane does not respond in a linear fashion to their deployment. I found that at low Cl numbers (like dropping into the landing pattern) the aircraft will actually balloon as the spoilers are first starting to be deployed. I think this is because the spoiler is lifting the air that is still attached. This results in the air acting like it is working against a thicker airfoil (A+ in the drawing) with more camber. With the lift from the "added" camber the plane will pitch up needing a bit of down compensation to the elevator spoiler comp curve (-2 in the drawing).
As the lift and drag of the wing are changing rather abruptly early on in the deployment I find that the overall shape of the comp curve is asymptotic. The elevator comp reaches its full value rather early. Then as the spoiler reaches its full height, the disruption to the lift is rather constant but the drag keeps going up. So to keep from stalling I take out some of the up compensation add earlier.

 

[Wayne]

Interesting.. I can honestly say that I am no expert with this kind of spoiler. The only plane I have with spoilers is my ASW with the blade style and I have no compensation for them as they do not seem to change pitch at all. I only use them for adjusting glide slope with that plane. She is no thermal ship!

 

[Konrad]

I hate spoilers.
"Very interesting but stupid" - Arte Johnson, Laugh In

Yep, aircraft often respond weird to spoilers. That is why when setting up my radios I start with a multipoint curve. I never know how the plane will react. I take an iterative approach to setting up controls. I test fly and let the results dictate the correct action.

Now articulated trailing edges (crow) are a far better way to control the glide slope.

But spoilers are ever so slightly better than nothing as far as glide slope control. They do have a cost as far as airfoil (wing) performance from the discontinuity of their installation and the pressure bleed through*.

*Often times the higher air pressure in the fuselage will bleed over the wings unless the spoiler pocket is sealed.

Have I said I hate Spoilers?

All the best,
Konrad

 

[Wayne]

On that ASW, it has very small flaps and they are top hinged, so they don't move very far. If that was not bad enough, the plane is heavy and likes to tip stall if you get it too slow on the final approach. So, I try and land with some speed, but not so much as to damage the plane. Did I mention she is heavy? Dang she is fun in the air though!