Trying to figure out why my aircraft nosedived.

[Ducky84]

So I had a pretty gnarly crash today that took my Explorer out of commission. Normally when I crash I have a pretty good idea of what went wrong, and I have an idea on what might have gone wrong with this flight, but I'm still a bit stumped. (More on that down below)

So I have a scratch built Explorer that I have many hours on. I went out today to do some flying and it was a very low\no wind kind of day which is rare here.

I did all my preflight checks

• Check balance (Slightly nose heavy)
• Check throw direction
• Check throw range
• Check FC calibration

Everything looked fine, so I launched.

Right as I launched I could tell something wasn't right. I was having to pull back on the stick almost completely to keep the thing level. When I let go of the stick, the nose would dive. I do run a flight controller (iNAV) and I have a switch to toggle manual mode where the FC offers no assistance. I toggled that just to make sure it wasn't an FC calibration issue, but still the nose would dive (Even harder)

So I brought it in for a somewhat controlled crash landing. I went through all the flight checks again, make sure nothing seemed off, or out of whack. Really gave everything a close inspection, and launched again.

The flight characteristics were the same. I was struggling to keep the nose up. This time though I wasn't able to bring it in for a controlled crash landing. I just crashed hard and had to do the walk of shame. (Which sucked because the field actually had people at it today which was one of my first times flying with others)

The wing snapped, the nose was jacked. The thing was toast other than the tail section.

Here's the kicker

I made a modification to my plane before this flight. See, with the Explorer, the wings are typically held together with 2 sticks and rubber bands. I'm not really a fan of that because the wings tend to shift around in flight, and after having the rubberbands on for a long time (As this aircraft has seen many flights) they tend to warp and wear away at sections of the aircraft. It also looks kinda lame...

So I decided to remove the rubberbands, and apply a small amount of hotglue to attach the wings to the fuselage. I paid careful attention to make sure the wings lined up perfectly, and also made sure that the wings sat as far forward as they normally do with the bands. I marked everything to make sure it fit just the same.

My guess is this had to have something to do with it, but I don't understand why. The angle of attack was still the same as the wings sit flush with the fuselage. The balance of the airplane was also the same as I made sure to measure front\back and side\side balance.

I just don't know what went wrong here. Maybe it was something else?

 

[PsyBorg]

Did the elevator servo peel the paper from the foam and can flex in and out as pressure is applied?

 

[Ducky84]

Did the elevator servo peel the paper from the foam and can flex in and out as pressure is applied?

I went and checked, and the elevator section still looks fine. No paper or anything pulling off. While I don't have it hooked up at the moment to check the server throws, I did verify during my preflight that the elevators moved in both direction with good distance.

I'm going to be rebuilding the plane maybe this week or next, so if it's an issue with the tail section I'll know for sure since I'm reusing it.

 

[quorneng]

A servo control check should include "Is the surface in the correct position when the sticks are at neutral".
It is possible for a servo arm to 'jump a spline' if the surface has been forced by an accidental impact or a crash.
The surface still moves fine but the previously trimmed 'neutral' position is wrong.

 

[PsyBorg]

I went and checked, and the elevator section still looks fine. No paper or anything pulling off. While I don't have it hooked up at the moment to check the server throws, I did verify during my preflight that the elevators moved in both direction with good distance.

I'm going to be rebuilding the plane maybe this week or next, so if it's an issue with the tail section I'll know for sure since I'm reusing it.

Yes moving on the ground may look like all is good. Its when you get the wind resisting movement in flight where things get complicated. Now saying that.. how much does your control wire / rod flex under resistance? Try holding the control surface while moving the sticks see how much they flex. you may have to glue or heat shrink BBQ skewers to them to make them stiffer.

 

[Tench745]

It's a long shot, but I wonder if your rubber bands were weak and let the leading edge of the wing lift a little as it gained airspeed. With the wing glued solidly, it would hold a lower angle of attack and not lift the nose so much. Again, wild guessing based on the one change you know occurred.

 

[Ducky84]

It's a long shot, but I wonder if your rubber bands were weak and let the leading edge of the wing lift a little as it gained airspeed. With the wing glued solidly, it would hold a lower angle of attack and not lift the nose so much. Again, wild guessing based on the one change you know occurred.

Yeah, I actually had started considering that last night. I imagine there has to be a large amount of air flowing underneath to lift the wing like that, but I suppose it's possible?

I did go back and hook up the tail section again since it's in good shape. The centering and throw range for the elevator was where I would expect it to be.

I'm starting to wonder if it really was the angle of the wing without the rubberbands.

 

[Bricks]

Make sure your elevator servo works when you put pressure against the flying surface while operating the radio, you may have a stripped servo. Is there a chance that the servos are not plugged tight into the receiver? Did you check to make sure your flight controller is actually being turned off by the transmitter switch? Just a few other things to check. If you were using at least 6 rubber bands I do not think hot gluing the wing permanent would cause this huge change. unless you were using less rubber bands....but I have been wrong before.

 

[Ducky84]

Make sure your elevator servo works when you put pressure against the flying surface while operating the radio, you may have a stripped servo. Is there a chance that the servos are not plugged tight into the receiver? Did you check to make sure your flight controller is actually being turned off by the transmitter switch? Just a few other things to check. If you were using at least 6 rubber bands I do not think hot gluing the wing permanent would cause this huge change. unless you were using less rubber bands....but I have been wrong before.

I used 4 before. They were going crossways.

I'm still rebuilding but once it's all together I'm going to test the tail section again and check on the things you listed.

 

[Hai-Lee]

Do yourself a favour and build yourself an incidence gauge.

A wing increasing in incidence can be problematic as can be a tail boom that is loose or moving in flight.

Have fun!

 

[Bricks]

Do yourself a favour and build yourself an incidence gauge.

A wing increasing in incidence can be problematic as can be a tail boom that is loose or moving in flight.

Have fun!

AAAAhhh come on what fun is it if foam is not in constant flux.

 

[boogieloo]

Are you sure you want an explanation? You're doing a pretty darn good job covering up a mishap already known. Wrong mode.

 

[boogieloo]

Is this airplane broken? Don't let go of the control sticks. For fixing it or getting a new one? Why don't you just make a new one? Where is this location? California? Is this your first flight? Have you had any practice runs before. Like no connection, then connection. Well I kind have years experience in Atari and joysticks. So this probably made it easier. Already know how to set it and move the sticks. Just put it on full
throttle.

Okay. It broke. Take it apart and set it away. I mean the airplane set up. It's not working any more. See what you can salvage. What works and what doesn't. There is a way to test the parts if its working. What kind of airplane was this? Spitfire? This small airplane is really popular among younger ones. It flies really fast.

I tested my TATTU BATTERY at 1300 mAmp/hours. With a multimeter. There is still a reading at 200 miliAmps. But I would need to make few calculations from there to come up with the correct reading. Test all parts like this. If any resistance still exist or some continuity.

 

[mikedkelly]

I took an EPP wing to work and left it in the car for a few hours. I didn't realize the warm temps in the car had caused the wing to warp slightly. It didn't go well with the bungee launch.

 

[Quinnyperks]

Are you sure you want an explanation? You're doing a pretty darn good job covering up a mishap already known. Wrong mode.

there is no reason to be rude to them, only asked a simple question about an issue experienced.