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AXN Excessive Climb Under Power

PostPosted: Tue Aug 13, 2013 2:38 am
by Glen J
I am a relative newbie and thoroughly enjoy flying the AXN (my second). But I am really bothered
by the fact that the plane persistently wants to climb when I add power. Being a newbie
I mostly enjoy just launching, cruising around and floating to a landing (in a grass field).

Today, I got downwind and needed a lot of power to get the plane to come back. But with around 75 %
power, I found that I had almost full nose-down trim to keep the nose down.

I am using a 3S 1800 mah battery pushed fully forward into the nose.

I tried using a mix on my DX6i to force in nose down trim when adding power. But, then,
when I chop the power the nose pitches up sharply (no surprise there) and I sometimes stall.

Strangely, regardless of the trim setting, the plane always seem to glide beautifully (often, too beautifully,
well past my intended landing spot).

I know that any plane should climb when its airspeed increases (other things remaining unchanged).
But I have not experienced this dramatic climbing tendency with a couple of other planes (RCPowers foamies and Blu-Babies)

Any suggestions?

Thanks in advance.

Re: AXN Excessive Climb Under Power

PostPosted: Tue Aug 13, 2013 3:28 am
by AshleyB32
you may need more weight in the front especially if your flying in windy conditions, i fly mine with a 2200lipol and it balances the plane correctly & sounds like you may also need to increase the throws on you elevator if your unable to correct climbing at high power going into a head wind

Re: AXN Excessive Climb Under Power

PostPosted: Tue Aug 13, 2013 5:25 am
by cynr100
Recheck your COG, from memory this is located right on the wing spar. the AXN is better suited with a 2200mAh.
The natural tendency for the AXN is to nose down when given full power until airflow is increased over the wing.
I would hold the AXN down and apply full throttle and check to make sure you have no hidden mixes applying up elevator.
Remove all sub trims and make sure you have the same up/down throw on your elevator, the natural position of any control surface is neutral with a centred stick and throws should be the same value.

Re: AXN Excessive Climb Under Power

PostPosted: Fri Aug 16, 2013 9:07 am
by Flyinbrian
Does this model have any down thrust? if so increase it, if not put some in.

Re: AXN Excessive Climb Under Power

PostPosted: Sat Aug 17, 2013 2:19 am
by Glen J
The model is a pusher with a high mounted motor aft of the CG. It is not clear to me what would represent "down thrust" Thrust line tilted down? Up?

Re: AXN Excessive Climb Under Power

PostPosted: Sun Aug 18, 2013 9:04 pm
by loopy
Is it only when power is 1st applied or as airspeed increases?

The thrust line for a pusher is high at the rear pointing down towards the front of the aircraft. In other words, putting a couple of washers under the lower motor mount will cause the nose to lift under power. (Most cloud fly's pitch down under power and increasing the thrust angle will help cancel this).

In your situation I would look a bit further and examine the angle of incidence of the elevator in relation to your main wing. This needs to be flat or as airspeed increases the nose will want to pitch up.( I have seen on other forums cases of the cloud fly having unwanted incidence causing the same problem as you have).

If incidence is ok you should be ok to put spacers under the top motor mounts which will lower the thrust angle and help cancel some of the upward pitching :)

Re: AXN Excessive Climb Under Power

PostPosted: Sun Aug 18, 2013 9:40 pm
by Glen J
The climbing tendency is highly pronounced at anything more than
50 % power.

Interesting theory about the incidence of the horizontal stabilizer to the wing. The AXN wing has a lot
of camber on top. On the bottom, it is slightly cambered back to the spar and then flat from there to
the back of the wing. The flat part of bottom of the wing is, indeed, parallel to the horizontal stabilizer.
However, if the incidence of the wing is measured through the wing chord, then the horizontal stab is
slightly angled (front edge lower than back edge). This would, of course, cause the stab to "lift"
downward, increasing the AOA of the wing. The point is, I'm not sure how to properly measure the wing angle.
Through chord? Or along the flat bottom?

I have added a few spacers at the top of the motor mount and this seems to help.

Re: AXN Excessive Climb Under Power

PostPosted: Mon Aug 19, 2013 2:40 am
by cynr100
I recently destroyed my AXN but from memory the tail plane sits in the same horizontal as the under side of the main wing. I have been through 4 AXN's in each case I made sure that the tail plane sits snuggly in it's position. A closeup pic of your tail setup back and side would help us.

Re: AXN Excessive Climb Under Power

PostPosted: Sun Oct 20, 2013 3:42 pm
by ashsz1
I destroyed my AXN Cloud recently and ordered my second. My Cloud was tail heavy, hence it was always climbing. I had to elevator down all the time to compensate the plane from pitch up. Some people recommended placing lead weights on the nose. Any idea how much weight do I have to place? Anyway I am using 1800mAH lipo. 2200mAH doesn't make much difference.


Re: AXN Excessive Climb Under Power

PostPosted: Sun Oct 27, 2013 4:31 am
by loopy
I use an 1800 on mine and it flies nice although it does pitch down when power is 1st applied then as airspeed increases starts to climb.
I have never added weight, have the battery and frsky receiver as far forward as they will go and the speed control cable tied to the back of the cockpit just forward of the motor mounting.
I figured that it was just a natural tendency for a wing, that as airspeed increases, so does lift.
Tail heavy aircraft are really nervous and squirrely but with this setup my floater isn't.

Was yours real hard to control?
Another way to tell is to fly inverted and if you have to hold up elevator to stop it climbing it is tail heavy.

A good rule of thumb is to balance at 1/3rd wing chord.