Well I went out this morning to try and fly my Bixler for the first time. I have quite a bit of multirotor flying experience, but no fixed wing outside of a simulator. I guess predictably it ended in failure.
I'm guessing my first two hand launches weren't powerful enough, as the plane flew straight at the ground even with full up elevator. Damage was suffered both times, but nothing that couldn't be fixed on the spot with some duct tape.
Third launch was a success (I gave it a bit of a run up and a push) and it took to the air. However I could tell it was in trouble as it wallowed about, banked right and hit the ground wingtip first. This broke the wing spar so it was game over.
So I'm guessing my COG wasn't correctly placed. I'd placed the battery so that the plane balanced when held under its wing spar, but given todays performance perhaps this is too far forward. Perhaps I should pull out the washers that came glued in the nose?
If anyone has any other general advice I'd appreciate it greatly.
Thanks,
Chris
Replies
Third attempt was a charm! I made sure I'd correctly placed the COG, launched on half throttle with a hard throw and we were off.
I made sure to stay at least "two mistakes" high, and kept repeating the mantra "small corrections" to myself. I ended up with around 20 minutes of incident free flying. Even my landings didn't do any damage! I'm impressed with how this thing glides with no throttle.
Anyway, just wanted to share. This made my week!
was the cog the biggest culprit?
I had a bit more success yesterday. I pulled out the washers and relocated the battery so that the plane balanced on the wing spar. Checked that it glided ok by chucking it into some long grass.
I had two perfect launches, and two less than perfect landings. I really need to work on not over-compensating with the controls. I ended up upside down at one point!
All in all it was quite a thrill, and no damage done that can't be fixed with a bit of epoxy.
I was in your exact same shoes a couple months ago - trying my first fixed wing - a Bixler - all alone. My first 4 or 5 launches were failures, luckily I was trying it in very tall grass and there was minimal damage.
Things I changed to make it work better - throw REALLY hard, you've got to get enough airspeed for it to climb. Like CC says - 50% throttle is plenty, more makes it harder actually. I launch with all controls in the neutral position; I thought I should launch with a bit of elevator up, but that seemed to make things worse. Lettering on the prop should always be forward and you should be able to feel it pulling forward.
Be very careful about your battery moving around and changing your COG. The COG needs to be right under the carbon wing spar, but if your battery isn't firmly affixed (I use a lot of velcro) it will slide and you will most likely crash. I had that happen and in the crashit ended up shorting out the ESC and setting it on fire. I barely saved my plane and burned my fingers getting it out.
Hello,
I am also learning on a Bixler. I was hoping you could tell me if 1/2 throttle on take off is for a fully laden FPV plane like my own. Or is that for a plane that is a lot lighter?
Thanks, for the help.
It all depends on how heavy it is, what motor you're running, what ESC you have, what propellers you've mounted and if you have any headwind.
Since I wrote the post above, I've really gotten in the habit of doing a glide test before my first powered launch. I now always toss the Bixler, fully loaded but with the motor off, whenever I change a battery or change the weight distribution in any way.
Assuming that you've got the COG right (absolutely essential) the plane will glide very nicely. If you want, you can use your elevator a bit to flare out as it lands, but you really won't need to if everything is right. If you need to you can adjust trims to make it glide better.
Once you've got it gliding nicely, it doesn't really matter if 50% is too low, you know that worst case if you don't have the time to adjust the throttle up it will just glide a bit further. No harm done and next time you can adjust the throttle up a bit.
I would say to start with the throttle lower rather than higher. It can be very tricky to get an overpowered Bix in the air.
The Bixler is a great flying plane, it will help you out a lot. Have fun!
They are some good tips. I will try and glide it to get it right.
I had this problem where it would nosedive on hand launch, i think i may not have been throwing it enough - does this sound right? I thought it may have been CG wrong, but it would balance from the correct CG points. When it is correctly balanced with the CoG should the plane be perfectly horizontal?
Thanks
If the CG was right, it sounds like your trims may have been off. It definitely should not nosedive - it should glide down on a fairly gentle slope. If I give a nice throw on mine, I easily get a 40' to 50' (15 m) glide. And when it touches down, it's a nice landing, not nose down.
Are the trailing edges of your elevator and ailerons in line with the edges of the wing and horizontal stabilizer when your servos are at their middle positions? If they are, maybe a wee bit (1-2mm) of up elevator would help a bit.
Yes, if you put one finger under each wing, directly under the carbon spar, the plane should balance horizontally level.
Some people give a little up elevator when taking off, starting before the throw. I add the elevator once the bird is out of my hands and my hands are back on the transmitter. It takes no more than 20% up elevator to get this puppy to climb nicely.
Thanks,
Im thinking it must be because i launched it with full throttle.
It has a 1400kv with a 7x4 prop - just changed it to a 7x5.
So i think mabye on full throttle - with the downward thrust of the Bixler motor mount it was pushing it into the ground.
I will be out and flying again in a couple of days - so i will try it all out.
On a side note - i am putting in a side access hatch into the bixler under the wings, in the fueselage. Just not sure how big will structurally weaken it. I only need to access the bottom of the fueselage to put in APM and a stabilizer when not APM. Any thoughts fellow Bixler flyer!
Thanks
Yeah, full throttle is too much, that will cause you problems. You most likely want 1/3 to 1/2 throttle in my experience. Gentle works better than forceful.
Why a stabilizer and an APM? The APM is fun - I have one in one of my planes and it makes for nice and easy FPV. Plus RTH is nice insurance. But it does a great job stabilizing, so do you really need a second stabilizer? Be careful with the APM's automated landing - not always the best!
If you can, to compensate for the weakening, I'd epoxy some carbon fiber tow around the inside of your new opening. Or if you can't find tow, a couple of strips cut to frame the new hole, ends matching so they have some torsional strength.
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