Nope. This was first noticed during maiden flight when I was trying to hand launch. When I threw the model straight into the wind, it travelled (maybe due to the force of the throw) in a straight line, but then very quickly kept turning right.
So it was solved by putting about 5+ degree left rudder as this is a 3 channel setup. since then it has been flying OK, but even then has a tendency to turn quickly to right but remains sluggish while turning left

too much of down and right thrust, adjust the mount, best is the hover test, inside house hover it ever so lightly holding the aircraft on its spine and see which side it is falling,adjust it to the opposite side. little bit of variation with varying power will be there, this is because of the corkscrewing air's interaction with the fin.

I thought it was right thrust, but then the motor is in line with the horz stabilizer and the nose. At least the right/down thrust is not visible.

There are 2 things [1] Torque reaction [2] interaction of corkscrewing air with the fin

[2] will depend on the pitch of the prop, RPM and distance from prop to fin

I think i have made my self clear.

now you need to counteract this, not my adjusting Rudder trim, but by adjusting thrust line

For post # 100 - Have you checked, the fin, tailplane and wing alignment individually and in relation to each other? Then is your fuse itself straight? All these will have direct contribution on your described characterstics.

For post# 102 - To centre the engine/motor after right thrust has been built it is common practice to offset the engine mount to the left (looking from tail).

Unless your motor/engine is rotating in a clockwise manner if the model turns right, it can only mean two things, either your thrust line is way off to right or the airframe is crooked. Start looking at thrust line (as adviced by Gusty) and then go on to other probable causes

could this also be if one wing is producing more lift than the other? being a scratch build I don't think I will be able to make exact aerofoils

The image in post #1 of this thread is the plane photo

http://www.rcindia.org/beginners-zone/i-finally-got-to-build-and-fly-a-pusher-trainer/msg42632/#msg42632

Pankaj
check your fuse, is it in the centre,? i have my doubts, used gimp to measure doesn't look like may be it is very slightly out

For Control Force , Power and What Servo to use read this thread

http://www.rcindia.org/beginners-zone/how-to-calculate-the-type-of-servo-needed/msg42979/#msg42979

Sir
My scratch built blue baby is doing exactly what you explained in dutch roll.
It oscillates the same way. If i do just the glide test (without power and without giving any control), it glides very nicely, very stable but as soon as the throttle is increased, it oscillates the way you explained and crashes.

How do i make it stable?

You can see the picture of the blubaby here:

http://www.rcindia.org/electric-planes/blu-baby-33-inch-using-monobloc/msg61203/#msg61203

extremely simple, give it 3 deg anhedral [see image]

Fro Speed of Sound and its relationship with temperature and how it varies with height , read this
http://www.rcindia.org/chatter-zone/sound-density-and-temperature/

Sir,
Will the dutch roll reduce if i increase the vertical stabilizer area?

Do both give it a little anhedral as well, Vertical fin is required for directional stab too, apart from its contribution in lateral stability

anhedral vs dihedral - that should be an interesting topic...

twist in the prop RpM and Forward speed, read this
http://www.rcindia.org/rc-general-topics/behaviour-of-propellor-in-rest-and-motion/msg62055/#msg62055

Why do pylon racers have wings like this

1. It is because of the Drag, Drag depends on wing in section and in planform. In section it needs to have low Thickness to Chord ratio (See Image 1) needs to be Straight in planform (See Image 2), both these put together will give profile cleanliness to the aeroplane, and therefore low Drag consequently Higher speed for given power.

2. In fact where the fuse joins the wing , the fuse needs to be waisted, this is to achieve a ideal body of revolution. called Area Ruling, this is to reduce the interference drag. (Aeroplane Shown above is not Area Ruled)

3. You will ask me if i sweep back the drag should be less, because all high speed aeroplane is swept back, the answer is they are designed to travel at transonic and supersonic speeds, so their Critical Drag Rise mach number needs to be high. (See Image). However at low RC Speeds Swept Wing has more drag than the straight wing

Any more Doubts ? Shoot


Next Topic is Gurney Flap

Waisting or Area Ruling (See Images) Self Explanatory

First of all, these models are called F5D models and they are relatively new, 1990 onwards. The wing tip is elliptical because it will lead to lesser induced drag than square tipped planes whose effect becomes more prominent at higher speeds. Also higher aspect ratio will lead to reduced drag, but making the model more difficult to control.They use the MH airfoil whose transition is much later on the wing. Transition is the change from laminar to turbulent flow, laminar is what you want.

But all that can be achieved with an elliptical wing tip, but these planes have a very peculiar tip. PFA pic.

From what I understand, the stream of air on the lhs wing tip leaves it much later after the wing, where vortices will be formed, on the other hand the stream of air on the rhs will leave sooner leading to vortice being created very near to the wing.

Sorry for the shady drawing, but explains it. Experts correct me if im wrong.

Sweet!
Thanks a lot Augustinev and Husein. Will rep++ whenever I can

Quote from: augustinev on May 15, 2011, 07:39:39 PM
You will ask me if i sweep back the drag should be less, because all high speed aeroplane is swept back

This was bugging me for so long. I feel much better now

Quote from: SunLikeStar on May 15, 2011, 08:45:31 PM
Thanks a lot Augustinev and Husein. Will rep++ whenever I can

Good to see the reputation system being put to good use Over the coming years, this should be helpful to everyone.