The View Up Here

Random scribblings about kites, photography, machining, and anything else

Raptor 2000 Advance – A Maiden At Last

Posted by Tom Benedict on 05/07/2013

Despite having flown the Raptor several times, I didn’t really consider any of those a real maiden flight. The first set was hand-thrown gliding tests, just to make sure I got all the controls moving the right way, and to make sure I could land. The second set was powered flights, but the controls were so squirrelly and the plane flew so poorly, it was all I could do to bring it down in a reasonably safe manner. Even then, I wound up snapping off one of the tail feathers.

It wasn’t until yesterday that I did what I considered to be a real maiden flight: powered takeoff, long gliding flight, and a safe landing. But to get there I had to answer the remaining questions from the earlier flights: why was I rolling off to one side, and why did the plane pitch up violently under power? It turns out both had the same root cause: the removable tail.

The Raptor 2000 Advance is a V-tail motor glider. The tail is removable, and the control surfaces must be unlinked before removal. When the tail is put back on, there is nothing to indicate proper setting of the control surfaces. They have to be dialed back in every time. Yesterday and today I flew the Raptor, and each time I installed the tail to the best of my abilities. The flight characteristics were wildly different each time.

Yesterday’s flights were almost dream-like. The plane had no noticeable P-factor (the tendency for the plane to roll when power is applied), and it flew clean and level while gliding. This morning’s first flight was the exact opposite: it had a strong tendency to roll to the left, and rolled harder under power. It also pitched up, constantly trying to do loops. Under power the plane pointed straight up in the air and went ballistic at wide open throttle.

I traced the problem back to the tail. After looking at the setup, I noticed both control surfaces were angled up by about 2mm. I zeroed them to the best of my abilities, and with my heart in my throat I tossed the plane into the air a second time. That time it flew beautifully, just like yesterday.

Long-term I’d like to either make an alignment jig that lets me center the controls accurately every time, or replace the control rod ends with threaded clevises I can Loctite in place. In the short-term I’m just not removing the tail now that I have it set properly.

The one other piece I knew I needed was some form of airbrake. The field where I fly is quite small, and the Raptor loves to glide and glide and glide. I needed some way to stop it in the air and bring it down. So I added adjustable crow.

The idea with crow – or butterfly as it’s also called – is that you bring the flaps down, and at the same time you bring the ailerons up. This increases camber at the root of the wing, and reduces it at the wing tips. Overall it adds drag, which slows the plane down. But an over-cambered wing will stall before an under-cambered one, so this makes sure the wing root stalls before the wing tips. This keeps the pilot in control, and makes a stall a less violent maneuver than if the camber was reversed.

I tested the idea on my Bixler 2 first: The three position switch on my transmitter controls whether I’m using flaps, crow, or keeping the trailing edge neutral. With the switch all the way up, the flaps are centered and the ailerons work normally. One click down, and the flaps can be controlled via a knob. Two clicks down and that same knob controls the amount of crow. This lets me hit the brakes, and dial in how strong the brakes are.

And a good thing, too! On the Bixler 2, five to ten degrees of crow is enough to dump speed and bring it down in a hurry. On the Raptor 2000 Advance, I had the flaps 45 degrees down before it visibly slowed. With the plane at a nice safe altitude, I tried bringing the flaps 90 degrees down and the ailerons 30 degrees up. WHOMP! It slowed down FAST. Having the ability to dial in the brakes during approach was a must.

In the end, it worked like a charm. Every landing was smooth, and at the end of the day I went home with two undamaged airplanes, ready to fly!

Enjoy the video:

– Tom

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