Need help with Goblin flight

[willsteffen]

Ive scratch built 12 Flite Test planes so far (so addicting). Almost all have flown great.. Maiden flight goes without issue.. Except the Goblin... This is my first plank/wing style plane.

Build info:
2205 2300KV
APC 6x4 (running 22amps WOT)
3S 2200mah battery
AUW 17oz
Throws about 15degrees with lots of expo

Day of maiden was calm.... CG was a bit nose heavy as I always setup my planes.. Gave WOT and did a poor hand launch by grabbing the end of the wing and tossing it like I see them do on the FT videos.. I didn't want to do a overhead launch for fear of prop strike.... A bit paranoid about it.... I screwed that up and launched into the ground (The FT guys make it look so easy).. My buddy offered to do the same type of hand launch and resulted in a busted-up Goblin...

After repairs and some reinforcing she is 18oz and I replaced the 6x4 with a 5x3 (thinking I was too aggressive in power)
So, questions:
How do you all hand launch the Goblin. Side wing fling, standard overhead toss? catapult??? Is the 18oz too much of a pig? Is the 5x3 too wimpy? Go back to the 6x4 and launch with 50-75% throttle???

Would love some feedback.

Will

 

[whackflyer]

Just grab it right behind where the nose slides onto the fuselage on top. I used that technique on a scaled down goblin it worked well, just watch out for the prop.

 

[Paracodespoder]

I don’t think I have much to offer in terms of help, but I gotta say that looks sweet with the carbon reinforcements!

 

[JasonK]

- some video of the launches would be helpful for figuring out the issue(s)
- what throttle were you launching with? I do basically every one of my hand launches between 50 & 75% (and the lower end are for very over powered craft)

 

[clolsonus]

This past summer I scratch built a goblin and got it to fly pretty well. I didn't spot anything obvious in you build or information, but I can share my experiences.

My first flights I had the CG slightly aft of the front of the recommended range and the result was extremely sensitive and unpredictable in pitch. (It flew ok-ish, but would sometimes tuck under and dive as my speed increased which can lead to a few need-to-change-your-pants moments.) I moved the CG to the front of the recommended range and everything got a lot more stable and predictable. My take away is you can't cheat, even a little bit on CG with this design. Put it at least at the front of the range or even a bit forward of that.

It's important to have some reflex dialed into your pitch trim at the start. I couldn't see if you had that or not, but the tips of the elevons should both be deflected up a bit, probably about the width of the material or a tad bit more. If you are launching with the elevons at true neutral, that could be why you are seeing a quick dive.

Overall it's a really quick airplane. It's a hoot with it's extremely high roll rate. It's definitely designed for an adrenaline rush, not to be a slow flyer with lots of time to think through what's going on.

For launching, I've had pretty good success with an FT style discus(?) style launch. I hold it by the wing tip, run up the throttle to maybe 1/2 (you can feel when it wants to go, you definitely don't need full throttle here on the recommended setup.) And then I just send it as straight as I can with maybe 20 degrees nose up. I was probably a bit lucky that mine flew pretty ok on the maiden so I was able to get onto the controls before anything really unfortunate happened.

There are other things that are "obvious" except I know I've screwed them up for no reason. It's possible to run the motor the wrong direction (I managed to do that on a plane some how... even after what I thought was ground testing.) It's possible to get controls reversed, or the elevons mixed wrong. Even experienced modelers can suffer brief bouts of brainus-invertus. Please don't take that wrong, I see nothing here that indicates that might be happening, I just wanted to mention it because I have to always be fighting against that for myself.

I don't know if any of that helps, but if everything is built pretty straight, and if you have the CG in the right place, and motor mounted as per the plans, and control surfaces near their ideal trim point and moving the right directions with your stick, then I think it should fly gloriously.

Edit: if it's still not behaving, it might be worth finding a hill or some long grass and trying some old school glide tests. That might help slow things down and help sort out if it's power/thrustline issue, a CG issue, a control mixing/setup/trim issue, etc. It won't glide very far, it has a L/D ratio similar to the space shuttle I think.

 

[willsteffen]

Appreciate the response...

I think my biggest issue was the hand launch... Just really screwed it up twice and busted the plane... Don't want to do that again... I'll focus on my wing tip side launch coordination

The power output with the 6x4 was impressive and I gave it about 80-90% for launch, probably too much torque.. Paired that with a poor angle of launch did her in....

I have up elevon trim as recommended in the pre-flight config... She should be air worthy, just need a solid launch...

I'll report back when I get a chance to re-maiden.... The weather in St. Louis is crappy for the next several days...

Thanks,
Will

 

[CarolineTyler]

Mine I always did an underhand launch, reflex very important to have or it will nosedive before you can get back on the control sticks.

 

[mrjdstewart]

like Caroline said, under hand launch w/left hand (you won't catch fingers if you keep arm moving up) and reflex are the keys to launching this plane. once in the air it flies on rails.

me

 

[willsteffen]

Thanks for all the input.. I got her up a few days ago with the underhand pitch.. Flies like a dream.. I added FPV gear and the antenna is kinda in the way for the underhand pitch, so now I grab the front of the wing and thrust it into the air at a 20-30 degree angle and she flies great. I so appreciate everyones help.. She's an amazing FPV platform.. I'm sure I'll smash her into a tree soon enough, but she's a super simple build...

 

[CappyAmeric]

I wing launch all pusher props (I’ve had too many prop strikes on my hand). I launch with my left hand, 75% throttle, and my right hand stays on the aileron/rudder stick.

 

[willsteffen]

Yep, thats what I'm doing now.. Seems to work just fine, once you get the process down.

 

[sprzout]

I wing launch all pusher props (I’ve had too many prop strikes on my hand). I launch with my left hand, 75% throttle, and my right hand stays on the aileron/rudder stick.

Same here. Works pretty great, except when you're maidening something that hasn't been adjusted properly. I did that this morning with a Versa Wing that had too much right aileron and up elevator in the initial configuration; it ended up doing a bit of a loop to the right and ended up pancaking flat on the runway as I tried to correct. No broken props or anything, but it wasn't a good launch. So, my suggestion, if you're having a pusher flown for the first time, have someone else throw it for you until you can get it trimmed out for good flight.

I know some guys will build in something like a 10% up elevator on a switch for a launch, so that the pushers will climb cleanly without stick input, and then just throw it back to "normal", but I tried it and it nearly backfired on me. I'll say, with regards to this, DO WHAT YOU FEEL MOST COMFORTABLE WITH!!! If you want it for launches, more power to ya.

 

[Sero]

When I hand launch I've always had my left hand on the throttle, and right hand throwing the plane. Not many people do it that way, but it has always worked for me.
Anyways, when I wing tip launch my Goblin, I hold on to the right wing with my right hand and toss it on my left side. This way I can hold on to the leading edge more than the wing tip allowing a more linear toss. I find I can toss it with less yaw movement. I found it works better than tossing it on my right side from the left wing which I can only grab the tip and the plane wants to spin.

 

[sprzout]

When I hand launch I've always had my left hand on the throttle, and right hand throwing the plane. Not many people do it that way, but it has always worked for me.
Anyways, when I wing tip launch my Goblin, I hold on to the right wing with my right hand and toss it on my left side. This way I can hold on to the leading edge more than the wing tip allowing a more linear toss. I find I can toss it with less yaw movement. I found it works better than tossing it on my right side from the left wing which I can only grab the tip and the plane wants to spin.

Pretty much exactly how I toss it, except I throw with my left hand, and right hand on the ail/ele stick. Whatever works, and you can get the plane up without hitting anyone or crashing it, I'd say it's successful.