The thrust above wing theory makes sense. Let say im punching full throttle banking high, to setup a dive into a low full throttle fly by. I would be pulling back on elevator though out the approach, but once in the flat section of the pass I'm possibly allowing the stick to center, and the above wing thrust is causing a scary dip in my flight under power. If I kill power at the start of the dive and cruise by its uneventful with the same stick input. So I guess I will put it down to pilot error and adjust my input. It helps a lot understanding why things happen. Thx guys for your input

Mick

Originally Posted by Bravo47

The thrust above wing theory makes sense. Let say im punching full throttle banking high, to setup a dive into a low full throttle fly by. I would be pulling back on elevator though out the approach, but once in the flat section of the pass I'm possibly allowing the stick to center, and the above wing thrust is causing a scary dip in my flight under power. If I kill power at the start of the dive and cruise by its uneventful with the same stick input. So I guess I will put it down to pilot error and adjust my input. It helps a lot understanding why things happen. Thx guys for your input

Mick

Hi. guys

I'd say this was a Thrust line issue

To compensate for this. add "Up thrust" to the fan mounting
just enough to stop the nose being pushed down under full power.

Originally Posted by Bravo47

If the CG was too far aft would not the nose rise? My CG is actually a little aft at the moment behind the recommended 80mm. It seems to glide nice and flat when I kill the throttle though.
Mick

It might depend on the model. EG, my Vampire did that when the CG was as described in the manual. On throttle up, the thing would head for dirt and on throttle down, it would balloon. Putting the battery more forward and moving the CG 10mm to 20mm forward has corrected this. The V-70 is whole other breed, so who knows if that's what causes it.

Non-centerline thrust line obviously causes pitch down with full power if the thrust line is above the centerline. And in Zephyr it is. It is not very severely high thrust line because the diameter of the EDF is smaller than a prop would be in a similar plane (like Multiplex Easystar) so the pitch down is less prominent. Prop planes (full size also) with high thrust line (like amphibians) require a lots of trimming with power changes (which is not desired, it is a control deficiency).

Centerline thrust is the only way to avoid all thrust-line related control deficiencies in the design. The deficiency that the high thrust line causes to the control harmony of the Zephyr is not very severe especially when you know to expect it.

Hmm I never noticed much down pitch in the zephyr. I fly mine a little tail heavy and haven't noticed any issues. I like how sensitive it is to pitch.

I'll have another look at it next weekend and perhaps tinker with CG. What are your thoughts guys on a vectoring tube on this aircraft, to be used for trimming the thrust angle?

Link- http://www.hobbyking.com/hobbyking/s...dProduct=21152

Originally Posted by ty_horn

.. is hobbyking the only place to get one of these?

... thanks dunster :-)

H.K. is the only place, "DURAFLY" is their "house brand".

Originally Posted by Bravo47

I'll have another look at it next weekend and perhaps tinker with CG. What are your thoughts guys on a vectoring tube on this aircraft, to be used for trimming the thrust angle?

Link- http://www.hobbyking.com/hobbyking/s...dProduct=21152

It's really not needed
1 - 3 degrees should be enough to cure it.
Packing washers under the fan mounting will do.

A rearward CG will make the aircraft more pitch (elevator) sensitive
and accentuate any thrust line problems.

Your Glide is good, so I'd leave the CG alone and work on the Thrust Line
to correct Power On problems.

BTW with China "quality control" it's unlikely all zephyr aircraft have
exactly the same Thrust Lines , so it's worth experimenting

Just got mine in, and will be putting it together this weekend. Glad I read this thread from about page 40 on for the glue tips, etc. Hope to get some footage soon!

Originally Posted by Reflex1

It's really not needed
1 - 3 degrees should be enough to cure it.
Packing washers under the fan mounting will do.

A rearward CG will make the aircraft more pitch (elevator) sensitive
and accentuate any thrust line problems.

Your Glide is good, so I'd leave the CG alone and work on the Thrust Line
to correct Power On problems.

BTW with China "quality control" it's unlikely all zephyr aircraft have
exactly the same Thrust Lines , so it's worth experimenting

Ok thanks Reflex1. I will experiment with the thrust line as you suggested.

Mick

So how many out there are flying the Zephyr with a 4s pack ?
Flying 4S all the time ?

Originally Posted by jnoel

So how many out there are flying the Zephyr with a 4s pack ?
Flying 4S all the time ?

This has been discussed quite a bit already. You can fly it on 4S but the extra punch takes the plane just beyond the speed where the wings begin to flutter. Do so at your own risk. I'm quite happy with mine on 3S.

Originally Posted by jnoel

So how many out there are flying the Zephyr with a 4s pack ?
Flying 4S all the time ?

If you are looking for that little extra punch, you might instead look towards running 3S with a thrust tube. No higher top end..but quicker acceleration when you need it.

A few people have already tried this in this thread..

Either that or run 4S at your own risk...and start strengthening all the flight control surfaces.

-mike-

Originally Posted by Reflex1

BTW with China "quality control" it's unlikely all zephyr aircraft have
exactly the same Thrust Lines , so it's worth experimenting

Just a follow up on this comment. This afternoon I removed my EDF to fit a couple of washers under the front mounts but noticed during the process that the EDF does not fit flat on the mount. There are some raised locating pieces on the mounting plates. These locators are actually larger than the recess in the EDF assembly making the lock down process and position a little random depending on your how hard you screw down your EDF. So I've just finished with dremelling out the EDF recesses so they fit over the locators, and my EDF housing now mounts flush on the mount base. So I'm looking forward to a test flight to see if a flush mount reduces my nose down under power issues, or agrivates it

Mick

You need to put the washers under the Rear mounts
for your original problem.

But first. try it, now you have the fan mount corrected.