Author Topic: Zen 90  (Read 293 times)

Offline Adam broomhead

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Zen 90
« on: 14, February 2019, 08:30:03 AM »
hello I have reacantly got a zen 90 and I’m putting a120 fs super custom in it how do you work out the thrust angle and a good prop size ?
Thank you

Offline SimonC

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Re: Zen 90
« Reply #1 on: 14, February 2019, 11:07:17 PM »
Hello Adam,
I have neither flown a Zen 90 nor used an SC120FS, so there will be others more suited to give you advice. However, I have experimented with quite a lot of planes over the years and would offer the following advice (others may disagree!):

1. Prop choice is always a matter of trial and error - it will depend to some extent on your personal flying style as well as the model AND the flying conditions. I have always started with the prop recommended by the engine manufacturer (or somewhere in the range) and then experimented over time. I don't know what SC recommend, but I would think that something like a 14x10 or 15x8 would be about right. If you use the recommended prop then you will have a good staring point, but be prepared to spend a bit of time and money on others if you really want to optimise.

2. Regarding thrust lines, I would just go with that already built into the kit. If after flying you find that it is not perfect, then it is quite easy to trim it out using simple throttle to rudder and throttle to elevator mixes. I am convinced that this is perfectly alright for all but the very top competition fliers

3. Whatever you do, get the c of g right to your liking  before doing too much adjustment as this will affect all other trims and mixes.

Good luck
Simon

Offline Peter Jenkins

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Re: Zen 90
« Reply #2 on: 14, February 2019, 11:27:24 PM »
Adam, I agree with points 1 and 3 by Simon but I would always fix thrust line problems at the source.  Mixes are fine for a quick fix but are only good at one speed and if your speed control is not perfect then you will find the engine thrust line problem has not gone away and may indeed have reversed!


If your engine thrust line runs mid way between the tailplane and wing then the chances are that setting up/down thrust to 0 deg is a good bet.  If the engine bulkhead is angled to the right i.e. the right thrust is built in, use that as Simon has suggested.  A useful thing to have is some shimming material.  This is available in a variety of thicknesses from your local tool shop.  Unfortunately, it tends to come in long rolls so if someone you know has some shimming material beg/borrow some off them.  I have shim material that is 8 thousands of an inch thick.  This allows quite fine adjustment to the thrust line.  If you cut an oval shaped section, drill through with the size used for your engine bolts and then cut away the material on one side so that you can slide the shim behind any existing washers and around the bolt.  As I say, getting very thin material gives you great control over the amount of change you can make.



I'm assuming that you are using the GBRCAA trim chart to help you through your trimming process. Simon is quite right to say that any change in CG position will affect every other setup. 

Offline Mike Wood

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Re: Zen 90
« Reply #3 on: 15, February 2019, 12:55:33 AM »
One thing I'd throw in about adjusting right thrust is, establish a vertical line first and then see what it does.

By this I mean don't pull from level flight and observe as it may veer off one way or the other due to many other reasons,
one wing heavier than the other, a warp, unequal elevator movement on each half ...

So pull to vertical, correct it so that it is going vertical, release any correction, keep the power on, then see what it does from there.

Mike
« Last Edit: 15, February 2019, 12:58:07 AM by Mike Wood »

Offline Mike Wood

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Re: Zen 90
« Reply #4 on: 15, February 2019, 01:18:29 AM »
Just in case you haven't got the manual:  https://www.theworldmodels.com/store/upload/manuals/html/A101/

Mike

Offline Ashley Hoyland

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Re: Zen 90
« Reply #5 on: 15, February 2019, 08:23:32 AM »

Hi Adam


Welcome to the forum of the GBRCAA.


A copy of the 'Trim Chart' referred to above is attached.




Offline Adam broomhead

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Re: Zen 90
« Reply #6 on: 15, February 2019, 05:09:54 PM »
Thank you all for your advice and pointers I shall have a look at the model when all my parts have arrived from America