do you think it's tail heavy?

[martinpineyro]

Hi, I am new to this forum and I would like to share a video of one of the first flight of my new simple cub:

https://vimeo.com/226794591?utm_source=email&utm_medium=vimeo-cliptranscode-201504&utm_campaign=28749

Do you think it is tail heavy? Any suggestion (apart from launching into the wind next time )

Thanks!
Martín

 

[TazRC]

If it is tail heavy it can't be by much. I always maiden a little nose heavy until I see how it flies and get it trimmed out. You may try reducing aileron and elevator throws slightly and add expo if you don't already have it, or increase it. It can't hurt to move the battery forward a few millimeters to see if that helps. Here's a model of mine that was tail heavy on maiden:

I had all I could do to get it back down in one piece!

 

[jack10525]

When you first launch the nose tips up which does make it look tail heavy. If you can try flying straight with minimal control input. Does it go up, down or sideways. May just need a trim. Also how windy was it that day? I agree with TazRC (and Josh's recomendations) slightly nose heavy is the way to go.

 

[Paden501]

I'm definitely not an expert, but my maiden flight looked a lot like that also. Like Taz mentioned above, I moved the battery and the RX forward and it made it a little nose heavy. That helped a lot... I found that with a little nose bias you just need to keep the power on a bit more to keep the nose up when you want to hold altitude.

Mine was also twitchy like that on the roll axis. I set my expo to 30% on all axis and dialed back my dual rates on aileron by 40%. That smoothed things out a lot and made it easier to fly straight.

 

[Hai-Lee]

I would also check the wing/tail incidence angles because poorly set or mismatched incidences can cause a plane to be extremely difficult to trim and fly properly and even appear to be extremely nose or tail heavy even if the CG is correct.

Have fun

 

[cranialrectosis]

I would also check the wing/tail incidence angles because poorly set or mismatched incidences can cause a plane to be extremely difficult to trim and fly properly and even appear to be extremely nose or tail heavy even if the CG is correct.

Have fun

Define "incidence angle" please.

 

[Grifflyer]

the angle of incidence is the angle between the chord line of the wing, where the wing is mounted to the fuselage, and a reference axis along the fuselage.

The term can also be applied to horizontal surfaces in general (such as canards or horizontal stabilizers) for the angle they make relative the longitudinal axis of the fuselage.

 

[PsyBorg]

That to me looked like the main wing was either pitched up a tad as it wanted to balloon on throttle inputs or he needs to set a little more down thrust angle on the motor mount. There were several passes directly in front of the camera that were nice and level at a steady throttle

 

[Hai-Lee]

Grifflyer is correct with his simple explanation but I will elaborate a little further.

As in the post above the incidence is measured as the angle with respect to something and the 2 common points of reference are the fuselage centre line and the airflow. For my explanation I will use the airflow direction as my reference.

As the incidence angle of a wing increases to the airflow the lift also increases upto about 15 degrees and of course if the incidence angle is negative to the airflow direction then the wing generates negative lift, a lift in the opposite direction. Now here is the problem the lift generated is not directly proportional to wing incidence so that means that each degree of incidence change does not equal to an equal amount of change in lift.

If the tail and wing have different angles to each other with respect to the airflow direction you can see that the lift generated can be significantly different on each surface, wing and tail. With a mismatch of incidences the lift generated by each surface does not maintain the proportional distribution of lift and effectively the Lift centre of the aircraft can vary with speed and with a fixed CG it means forever trimming the plane to keep it in level flight at varying speeds.

In the extreme of a positive main wing incidence and a negative tail incidence it can be seen obviously that as the speed increases the main wing will generate greater positive lift and the negative wing incidence will generate increasingly more negative lift or down force. Whilst it can be managed to a degree by elevator trim or settings it will definitely appear that the plane is wanting to drop its tail, (normally considered as a definite sign of the plane being tail heavy).

On a conventional design the tail loading is very light to zero depending upon its speed range and role. Some designs, (slow fly fliers of heavy lifters use a little deliberate main wing positive incidence. But the angle is minor and often the speed range of the craft is not huge.

Simplified it means that you need to make sure that the wing ans tail are on the same level or according to the plan before worrying about fine tuning the CG position.

Have fun!
,

 

[martinpineyro]

If it is tail heavy it can't be by much. I always maiden a little nose heavy until I see how it flies and get it trimmed out. You may try reducing aileron and elevator throws slightly and add expo if you don't already have it, or increase it. It can't hurt to move the battery forward a few millimeters to see if that helps. Here's a model of mine that was tail heavy on maiden:

I had all I could do to get it back down in one piece!

@TazRC thanks for your reply, and good job bringing that one down in one piece!

 

[martinpineyro]

When you first launch the nose tips up which does make it look tail heavy. If you can try flying straight with minimal control input. Does it go up, down or sideways. May just need a trim. Also how windy was it that day? I agree with TazRC (and Josh's recomendations) slightly nose heavy is the way to go.

There was little to no wind, and that's why I didn't care much about launching in one specific direction. Watching the video it seems that a weak gust hit during launch and made things a little difficult. I will definitely try moving the battery slightly forward and also configuring expo.

Thanks!!

 

[martinpineyro]

I'll try that, thanks a lot!

 

[SlingShot]

Looked pretty good except for the launch. It was flying good at speed.

Que tal? Por donde se encuentran Uds?

 

[martinpineyro]

Looked pretty good except for the launch. It was flying good at speed.

Que tal? Por donde se encuentran Uds?

Gracias! Esto en Uruguay. Saludos

 

[danbob]

Great first post, for some people English is there second language