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May 23, 2018, 08:41 PM
Disaster magnet
Discussion

Mystery Roll??


I have a bit of a mystery to me here. I recently finished building the Axon from Experimental Airlines, and tried flying it today. because the battery I was planning on using was only 1800Mah and I was not planning on using a camera, I opted to make the shortened fuselage option with a 52" wingspan. Unfortunately, it did not work when I tried flying it about an hour ago.

It flew fine for about three seconds, but it then quickly rolled over into a dive. The roll tendency was too strong for me to counteract with the ailerons. maybe because the propeller is so close to the tail stabilizer, the rotating airstream from the prop still had enough rotational energy to tip the plane? Or was it the torque? was it just top-heavy? I thought high wing planes were more stable?

Electronics used:

30A ESC
Emax rs2205 2300KV motor
9 gram servos
1800Mah battery

Is the motor just not strong enough? was it just a stall?

Total weight: 635 grams.

ANY ideas or thoughts are welcome. I really want to know what I did so wrongly.
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May 23, 2018, 09:21 PM
Kimbers Keeper.
BHOFM's Avatar
Check side to side balance, it really sounds like a common every day stall.
May 23, 2018, 09:32 PM
treefinder
springer's Avatar
First, along with what BHOFM said, have you done all the pre flight checks? CG at the locationrequired with all gear on board. I would guess 20-25% from LE for starters. Did a power off glide test and got a straight ahead gentle arc with no roll offs, dives or nose up into a stall. Made sure all control surfaces go the right way.

Given all that, what was the plane doing right before it rolled? Straight and level? Climb? Starting a turn? What was power setting? Knowing all this will give us help in figuring out what happened.
May 23, 2018, 09:44 PM
IMO ( In My Opinion ) →
balsa or carbon's Avatar
Are you 100% sure the ailerons are moving correctly ? Looking at the plane from the rear , when moving the transmitter's aileron stick to the right .... the right aileron should go up and the left aileron should go down .

If possible , shoot a video of your next attempt ..... that can tell us a lot more than a verbal description & photo .
May 23, 2018, 09:47 PM
Disaster magnet
BHOFM: I checked right before the flight, it was right in the center.

springer: Ed didn't ever say exactly where the CG should be in his videos, so I assumed a little in front of the leading edge. I'd say it came out at around 15%, so maybe that small amount was the problem?

I did not do a glide test. How are you supposed to do one without damaging the plane on landing?

All control surfaces were correct.

It was doing a gentle climb to gain altitude before it happened. The power setting was pretty high, I'd say about 80%. I had not yet made any attempt to bank, it initiated it on it's own.

balsa or carbon: Yes, I checked before the flight, and then just right now to make sure. They are moving as you described.
Last edited by Chelonian; May 23, 2018 at 09:52 PM.
May 23, 2018, 10:10 PM
Build straight - Fly twisty
Whiskers's Avatar
Quote: Ed didn't ever say exactly where the CG should be in his videos, so I assumed a little in front of the leading edge

A little in front of the leading edge?
I hope you mean 20% to 30% behind the leading edge.
If not it's a wonder you got as far as you did.
May 23, 2018, 10:21 PM
Disaster magnet
Quote:
Originally Posted by Whiskers
Quote: Ed didn't ever say exactly where the CG should be in his videos, so I assumed a little in front of the leading edge

A little in front of the leading edge?
I hope you mean 20% to 30% behind the leading edge.
If not it's a wonder you got as far as you did.
Yes, I am not really sure why I typed in front, I certainly meant behind. It probably was around 15% behind, so possibly it was a little too far forward?
May 23, 2018, 10:30 PM
Build straight - Fly twisty
Whiskers's Avatar
Yep! But I doubt that is the problem.
May 24, 2018, 12:52 PM
flyin' fool
goldguy's Avatar
Start with the CG at 30% back from the LE.

Centre of Gravity (6 min 23 sec)
May 24, 2018, 02:36 PM
treefinder
springer's Avatar
Chelonian: CG at 15% aft of LE is generally more forward than optimal, though I personally would feel more comfortable with that than the 30% Goldguy suggested. Every time I got CG that far aft on a conventional configuration like yours, the plane was too twitchy for me. Not at all good for a first flight. You can shift Lipo aft some to get CG to 20%, but I wouldn't go that far (30%) until you are successful in flying it.

I studied your motor specs, and note that the recommended prop is a 5x4.5. A high speed motor with a small dia. Prop is probably not best for a 52" span plane. Generally that motor/Prop setup generates good thrust, but doesn't push enough air to give good low speed performance. If you just use a larger prop, you will "over prop" the motor and not be able to develop the rated prop speed and thrust, but put all the amps into generating heat (and maybe burning up the motor). A 50"+ span plane will need a 50 gram 1000kv motor spinning a 9x6 or so prop to push enough air to stay flying.

In this light, what may have happened was the plane was hand launched ok, but not with enough thrust, so in the nose up climb, slowed, stalled and rolled off.
May 24, 2018, 03:17 PM
An itch?. Scratch build.
eflightray's Avatar

Mystery roll ?


Some thread titles will always get my interest.

But then you read them and .......

The only mystery should be what flavor --




Ray
May 24, 2018, 04:56 PM
Disaster magnet
Quote:
Originally Posted by springer
Chelonian: CG at 15% aft of LE is generally more forward than optimal, though I personally would feel more comfortable with that than the 30% Goldguy suggested. Every time I got CG that far aft on a conventional configuration like yours, the plane was too twitchy for me. Not at all good for a first flight. You can shift Lipo aft some to get CG to 20%, but I wouldn't go that far (30%) until you are successful in flying it.

I studied your motor specs, and note that the recommended prop is a 5x4.5. A high speed motor with a small dia. Prop is probably not best for a 52" span plane. Generally that motor/Prop setup generates good thrust, but doesn't push enough air to give good low speed performance. If you just use a larger prop, you will "over prop" the motor and not be able to develop the rated prop speed and thrust, but put all the amps into generating heat (and maybe burning up the motor). A 50"+ span plane will need a 50 gram 1000kv motor spinning a 9x6 or so prop to push enough air to stay flying.

In this light, what may have happened was the plane was hand launched ok, but not with enough thrust, so in the nose up climb, slowed, stalled and rolled off.
I think I came to a similar conclusion as you about the small prop and fast motor not really being suitable. So I converted it into a Noob Tube, which was a surprisingly easy conversion. All I did was shorten the wing, remove the "power pod", move the motor to the front, add 6" to the nose (to make it 30" long), and changed a few other minor things.

I'm hoping that the smaller wing will work better with my power setup, but I guess we will find out when I test fly it. I did all the checking that I could possibly think of, the CG is exactly 10" from the nose, and it balances side to side just right when hanging it from a piece of string at the nose and the tail of the plane. It came out weighing 520 grams.

If there is anything else I should check before I fly it, please chime in.

Here's a photo of it: (the green thing on top is to protect the receiver in case of an upside-down landing)
May 24, 2018, 05:21 PM
gpw
gpw
“There’s no place like Foam”
gpw's Avatar
Tail feathers look a little small too … just saying …
Latest blog entry: Lost plans
May 24, 2018, 05:30 PM
Disaster magnet
Quote:
Originally Posted by gpw
Tail feathers look a little small too … just saying …
It's the exact dimensions that Ed calls for in the video, so I'm hoping that will be okay?
May 24, 2018, 08:18 PM
Registered User
Transmitter flaking out at a distance? The exact same behavior happened to my neighbor's plane. It was at mid/high speed in trimmed level flight when it suddenly rolled over and crashed. At first I thought it was him, but then he showed me that it did the same thing again with hands off the sticks. Sure enough we did a range check and it would intermittently move surfaces drastically even when not touching the sticks...


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