Plane behaves differently between flying sessions

[LundiThembi]

I'm flying (novice) a Simple Cub and get the plane trimmed and flying perfectly. Two days later I'll go for another session (same location) and it flies very erratically, diving to the left, difficult to control. I don't get it? Thanks.

 

[Flyingshark]

I'm flying (novice) a Simple Cub and get the plane trimmed and flying perfectly. Two days later I'll go for another session (same location) and it flies very erratically, diving to the left, difficult to control. I don't get it? Thanks.

You might have put the battery in differently the second day, affecting the center of gravity. That could cause the diving, but probably not the left-turning part.

Another possibility is the weather -- was there maybe a lot of wind the second time you flew?

There could also be an issue with the thrust angle of your motor, if you, for example, crashed your plane into a fence or something similarly violent happened to it in between flights.

Some pictures might help us help you more accurately.

 

[LundiThembi]

Thanks for the reply. There was no crash, only a gently landing into a forgiving bush. I'm pretty careful about battery placement and checking CoG. I stand in the middle of the road, hills to the left, right and I'm at the foot of one directly behind me. Last session there was zero wind, had 4 - 5 good flights. Today, maybe 2 mph of wind and it was a disaster, plane was all over the place. Could that little wind have that much of an affect...keeping in mind that I am a novice? Thanks

 

[JasonK]

Simple cub has a detachable wing, if you remount it slightly differently then the last flight, you will need to re-trim your plane. Depending on the weather and what not, you can sometimes get a bit of shifting in the 'warp' of the foam also.

Another possibility is that if your trimmed positions are fairly far from neutral and if you were getting micro fail safes (lost of signal just long enough to trigger the receiver's fail safe for a split second - which will typically center your servos and cut the motor, the servo twitches might be noticable, but the motor doesn't spin down supper fast) - not saying I think this is the situation, but something that could explain odd flying behavior.

Do you have the 3 channel setup or 4 channel setup? If you have the 4 channel setup, are you using a y cable for the servos or 2 different ports on your receiver and mixing? (in the 2 separate receiver channels situation - if the cables got swapped, the needed servo centering/etc would be off but the control surfaces might still move correctly)

 

[LundiThembi]

Yes, I was concerned about removing the wing, battery, receiver for each time..I'm pretty careful....but....

It is set up for 4 channel, I'll look into loss of signal. I'm pretty remote and flying close to me, I don't know if that reduces the chances of loss of signal. This is the second time it has happened, I thought I had it totally dialed in.

The ailerons are on a y-cable but I wasn't paying attention to which aileron cable got plugged into which cable on the y-cable. I had both servos centered before trimming. I'm going to see what happens when I swap the connections into the y-cable.

Thank you.

 

[JasonK]

Yes, I was concerned about removing the wing, battery, receiver for each time..I'm pretty careful....but....

It is set up for 4 channel, I'll look into loss of signal. I'm pretty remote and flying close to me, I don't know if that reduces the chances of loss of signal. This is the second time it has happened, I thought I had it totally dialed in.

The ailerons are on a y-cable but I wasn't paying attention to which aileron cable got plugged into which cable on the y-cable. I had both servos centered before trimming. I'm going to see what happens when I swap the connections into the y-cable.

Thank you.

no, don't swap them then, that would only be a thing if you were connecting and disconnecting them from the receiver when you take off the wing, but your not in this case, so the concern there isn't an issue.

 

[JasonK]

why are you removing the receiver? that shouldn't need to be taken out.

 

[LundiThembi]

I was removing the receiver to get the battery in place, I should have put in a battery hatch on the bottom of the plane so I wouldn't have to keep moving things around...next build.

Swapping the aileron connectors to the y-connector didn't make a difference.

 

[PsyBorg]

Yes, I was concerned about removing the wing, battery, receiver for each time..I'm pretty careful....but....

It is set up for 4 channel, I'll look into loss of signal. I'm pretty remote and flying close to me, I don't know if that reduces the chances of loss of signal. This is the second time it has happened, I thought I had it totally dialed in.

The ailerons are on a y-cable but I wasn't paying attention to which aileron cable got plugged into which cable on the y-cable. I had both servos centered before trimming. I'm going to see what happens when I swap the connections into the y-cable.

Thank you.

How you hold your radio when you fly can cause weirdness ... specially if you keep your craft close giving a high chance of flying in the dead zone where the radiated signal is weakest. Picture a giant doughnut surrounding your radio with a giant hole straight out of the top of your radio. If you cross into that dead zone you could have weak or no signal to the receiver for a very short period. It will / could brown out or even fail safe for a split second.

 

[Hai-Lee]

CG, wing position and even wing incidence angle can make a great deal of difference. Other things that can produce weird effects are related to the FB used and how the FB is finished or sealed. High humidity in the storage area can soften any unsealed fb paper and it can even stretch not only making the wing more flexible but also change the wing geometry slightly.
On my cub I increased the wing incudence angle ot recuse its flying speed and to make it more suitable for my students to learn on. I stored it in a constant temperature in the place I live and eventually gifted it to one of my students as he wanted one and I was effectively finished it.

Another point to be aware of is that the tail is not braced and can alter its geometry in storage or through hangar or transport damage so be aware.

Have fun!

 

[LundiThembi]

Thank you everyone for comments and suggestions. The voltage on the transmitter was 4.6 volts, is it all or nothing in terms of signal or does it vary by the level of charge?

Thank you

 

[JasonK]

Thank you everyone for comments and suggestions. The voltage on the transmitter was 4.6 volts, is it all or nothing in terms of signal or does it vary by the level of charge?

Thank you

the signal strength isn't driven by your battery voltage (outside of that being to low for the TX to work) but antenna alignments, RF noise in the area, things like that.

 

[bisco]

wind? it can be difficult to judge on the ground

 

[LundiThembi]

I know there is often turbulence around hills, I'm launching at thee base of 3 hills. Thought it might be contributing a bit, but the wind (at ground level) was only very slight but changing directions...I'm sure it would be nothing for someone with more experience.

Interesting comment about humidity, I brought my planes from sea level to 6700 feet.

 

[bisco]

i have that problem sometimes even with bnf's from horizon. sometimes they fly amazingly, other times they feel twitchy. i attribute it to the wind, but maybe i'm wrong.

 

[Tench745]

I know there is often turbulence around hills, I'm launching at thee base of 3 hills. Thought it might be contributing a bit, but the wind (at ground level) was only very slight but changing directions...I'm sure it would be nothing for someone with more experience.

Interesting comment about humidity, I brought my planes from sea level to 6700 feet.

Here's the thing about wind at ground level... That's not where planes is fly.
In all seriousness though, as you go up in elevation you can have significant changes in wind speed or direction. And any obstacles; houses, trees, hills, cars, etc, that the wind has to travel around will cause some amount of turbulence. Flying between the hills like you were, you were probably standing in, essentially, a puddle of calm air. Picture a puddle of water, and some wind blowing over the surface. What do you get? Waves.
If the wind was blowing faster above that puddle of calm air you were standing in you would get waves where the faster and slower air intersect, ie, turbulence.
Without being there to experience it, it's hard to say what effect the wind/weather conditions had on your flying, but I would not be surprised if you went out on another no-wind day and the plane would fly normally again.

 

[bisco]

i usually speed up if it is behaving strangely. if it is wind, performance improves. if not, i crash

 

[LundiThembi]

Here's the thing about wind at ground level... That's not where planes is fly.
In all seriousness though, as you go up in elevation you can have significant changes in wind speed or direction. And any obstacles; houses, trees, hills, cars, etc, that the wind has to travel around will cause some amount of turbulence. Flying between the hills like you were, you were probably standing in, essentially, a puddle of calm air. Picture a puddle of water, and some wind blowing over the surface. What do you get? Waves.
If the wind was blowing faster above that puddle of calm air you were standing in you would get waves where the faster and slower air intersect, ie, turbulence.
Without being there to experience it, it's hard to say what effect the wind/weather conditions had on your flying, but I would not be surprised if you went out on another no-wind day and the plane would fly normally again.

Thanks for your thoughts, I know I shouldn't shy away from flying in the wind, haven't quite got over the fear of crashing. I know the sooner I let that go, I think I will become a better flyer

 

[bisco]

a lot of expert pilots would say you should shy away from the wind

 

[Piotrsko]

If you fly slope, you prefer wind, the more the better.