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Old Jun 30, 2014, 08:09 PM
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richard9999's Avatar
Sydney, Australia
Joined Jan 2007
1,655 Posts
I just had a feel of the wing of my (unbuilt) Spit. It looks to me as though you could cut three sides of a larger rectangle out of the Orocover around the hole for the servo - maybe 3 cm x 10 cm (or less) with the uncut part at the front (so the wind can't get under the flap), always cutting onto wood. This would give some room for mounting the servos on their sides, using what ever method seems best. The actual small slot for the servo arm would then be cut and the Orocover flap reattached. This flap has just black and white colours, so any small gap could be hidden with some paint. That's how I'll do mine, anyway.
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Old Jul 05, 2014, 08:20 AM
An unexpected error occurred
Phaedra's Avatar
Belgium, Flemish Region, Duffel
Joined Apr 2012
615 Posts
I think I tackled the aileron servos problem; I will post the pics soon.
Now I'm turing my attention towards the motor mount. Everyone seems to agree that it needs strengthening, but in which way? Just glassing, or structural improvements too?
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Old Jul 05, 2014, 06:10 PM
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richard9999's Avatar
Sydney, Australia
Joined Jan 2007
1,655 Posts
I am planning to make a completely new, shorter one so I can mount my C3548 900kV motor on its alloy base. I will probably reinforce that with glass fibre.
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Old Jul 06, 2014, 10:51 AM
An unexpected error occurred
Phaedra's Avatar
Belgium, Flemish Region, Duffel
Joined Apr 2012
615 Posts
Today I have been glassing the motor mount, and while that was hardening I finished fitting connectors on the extension wires for the ailerons, and installing servo arms and control horns stuff.
Yesterday I went to my LHS to get a better propeller hub, because the one I had didn't really fit well. So today I mounted that one and put everything on the test stand again, only to find that I still have some vibrations at a small rpm range, about 3/4 of WOT. When I push the throttle further, it goes away. I tried it with and without the spinner, and it is a bit less without the spinner, but it's still there.
I checked the balance of the propeller, and it seems ok (I'm not really sure I checked it the right way), and I checked that the hub is straight when running without propeller, so that can't be it.
One thing I noticed is that the motor can move a bit up and down, because I can only use two of the four bolts to attach it to the test stand mount. Maybe that's the source of the vibration? It clearly is some sort of resonance, so this might explain it.
Maybe it's best that I repeat the test on the model itself, with all bolts installed. If I'm right, the vibrations should be gone.

I added some pictures of the retracts mounting. In the end, I used the standard gear legs, because shortening the struts that came with the HK retracts proved too difficult with the limited tools I have available.
Aileron servo problem was solved by glueing a piece of ply at the inside of the wing skin, maximizing the contact surface between wing skin and ply piece. It feels solid enough, so I keep my fingers crossed that it will stand the test.

I also bought a piece of gray covering to put over the wrong cut I made for the retracts. I figured it is better to have a different color on the bottom and the top of the wing, to avoid orientation problems (which I have been experiencing increasingly with other models lately, my eyesight having degraded these last few months).
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Old Jul 06, 2014, 02:21 PM
An unexpected error occurred
Phaedra's Avatar
Belgium, Flemish Region, Duffel
Joined Apr 2012
615 Posts
Mounted the motor on the model for further testing. I needn't have worried: it runs smooth as silk!
My theory proved right, it was all a matter of play and damping and resonance.
What a relief.... I remember the trouble I had with the same motor on my funcub, where it was mounted on a foam fuselage, allowing it to vibrate to the point of almost coming loose. Troubleshooting that problem taught me a lot about this.

Soooo.....with the model almost complete, it weighs in at 1,6 kg. So with the measured thrust of about 2kg, this should fly well

This is motivating enough to finish this one soon....
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Old Jul 07, 2014, 12:41 AM
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capteasy's Avatar
USA, Texas Hill Country
Joined May 2008
1,777 Posts
Good work Phaedra, you should be pleased with this plane and I'll be looking forward to the maiden and your impressions.
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Old Jul 07, 2014, 03:23 AM
I'll always be an amateaur
BryceVR's Avatar
Australia, NSW, Blayney
Joined Jan 2009
99 Posts
Quote:
Originally Posted by Phaedra View Post
I'm a bit stuck with the aileron servos.
I ordered some Turnigy 2kg torque servos for the flight controls, but they don't fit the openings that are provided in the model, i.e. the servos are too small.
I had some Hitec ones lying around too, and they fit, but when I mount them, they sit very high up the wing, which is not a very pretty sight, and they are extremely prone to damage in case of a belly landing.
I would rather have them installed neatly inside the wing profile, only the servo arm sticking out, but that would mean removing the covering to allow me to glue in some plywood support frames.
If I go with the Turnigy servos, I will have to glue in some extra plywood braces on the inside of the wing (intrados), which is not that straightforward.

Did everyone put in the servos like that, sticking out of the wing like that?
These are GREAT and so cheap.

http://www.hobbyking.com/hobbyking/s...8kg_0_14s.html




Fast, strong and a great fit.
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Old Jul 08, 2014, 02:24 PM
An unexpected error occurred
Phaedra's Avatar
Belgium, Flemish Region, Duffel
Joined Apr 2012
615 Posts
Had a little bit of time to continue on the Spit today.
I decided to add a bit of down and right thrust angle to the motor, which proved to be a bit of a nightmare, because it's pretty hard to position the motor inside the motor mount while the motor wires pull it to the left.
I did this because I have some experience with this motor on two different models, where I also needed quite a bit of thrust angle modification.
I also wasn't happy about the prop hub being buried a bit too deep inside the cowl. Without the thrust angle modification, the spinner was already touching the cowl, and I didn't want to move it more forward on the motor shaft, risking too much play and the vibrations it might cause. So I rounded the front of the motor mount, so the engine cowl can now move more aft, and the prop hub is protruding again at the front.
Started on the transmitter programming, getting the basics in to get the direction of movement right.
So, only things left to do is:
- attach the canopy
- attach the landing gear doors
- adjust throws and expo
- affix receiver and antennae (frSky 8XR), and do a range test.
I have added a UniSens sensor, and I'm very curious to the experience...one sensor, giving me current, power, used capacity, rmp, altitude and vario.
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Old Jul 09, 2014, 03:04 PM
Addicted to RC
YarSmythe's Avatar
USA, TX, Houston
Joined Nov 2003
2,720 Posts
Club member had one of these NIB. Picked it up today. I'll send more build photos when I get the time to work on it.

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