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Old Sep 21, 2009, 08:12 PM
GJ60 is offline
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Stinson Reliant 18" Span 1/28 Scale Rubber Conversion ( ready for another trial)


Stinson Reliant 1/28 Scale Rubber Conversion (Completed )

Hi guys, i wil be mounting a 7mm motor w/ gws 4" prop on my 18" span reliant...can anyone advise on proper downthrust and rightthrust...at least approximately?... dont know much about degrees but i can run a tape measure ...thanks for any help... George
Last edited by GJ60; Oct 24, 2009 at 12:59 AM.
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Old Sep 21, 2009, 11:24 PM
WTFLYR is offline
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3hrs and no answer
Whether they tell you or not, most folks just eyeball. We'll see how that goes over. Once you get one answer, then usually a whole slew come next, when there is something to debate.


I would not necessarily add downthrust, unless there is a known reason to do so. Finding previous builds for reference is not always easy, with some of these small planes.
The small 4"-5" props are a good idea for these small planes, in that they help reduce torque effects. I've changed from a 5" to a 4.5", and had much better results with torque reduction on a Guillows Cessna 150.

As long as you have a slightly noticable right thrust angle, it will suffice. If a rudder flyer, a combination of slightly greater right wing panel washout and right thrust is a better solution than right thrust alone. Going just slightly too far with right thrust with these small planes will give you a plane that right turns only, and maybe straight at full left rudder.
Old Sep 22, 2009, 12:44 AM
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Thanks for your advice... I'll take it...

I just completed the nose block and drill out fitting for the gearbox and motor...adding the small hinges on ruddder and stab..and reinforcemnt w/ carbon on the control surfaces.

this will be rudder and elevator plane.

thanks for the inspiring pick of the guillow cessna, very nice bird
Old Sep 22, 2009, 12:53 AM
E-Challenged is offline
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With an cross or X type radial mount, I start with two small washers on the upper right, one on upper left, one on lower right and none on lower left. With a Reliant, with ailerons, I'd position both ailerons up about 1/16" to act as washout. If no ailerons are used, twist wing trailing edge near tips upward about 1/8". You will need to mount battery pack and everything else as far forward as possible and add weight to front of cowl to get cg right, a litte nose heavy is best for maiden flight, a little right aileron and a little down elevator trim may also help. My 42" w/s SR-7 has the 1300 3S battery pack protruding through a hole in the firewall and next to the Esskay 400XT outrunner to achieve proper cg. Mine likes to ground loop, needs gradual throttle to get it rolling, then punch it to get air blast over the rudder and elevator to control take off path. Has some tendency to tip stall so land like a fighter with partial throttle. Good luck with it.
Old Sep 22, 2009, 01:14 AM
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"Whether they tell you or not, most folks just eyeball. We'll see how that goes over. Once you get one answer, then usually a whole slew come next, when there is something to debate."
Sounds like you're looking for an argument You wont get one from me Most plans say about 2 degrees right and down and I usually just 'eyeball' it. As suggested, a couple of washers under the motor mount. There seems to be no scientific way to calculate what it should be - it's all magic and mirrors stuff! When I'm mounting a small motor on a little ply disc, I just taper the disc from about 1/8" down to nothing and put it behind the mount at 45 degrees - gives about 2 deg each way.
If using a X type mount, and install it NS and EW then only two ends need washers under them.
Do any real aircraft have this offset? From what I read, most warbird pilots had huge forces to counteract when applying power - maybe they needed their thrust angles changing
Pat (FWIW)
Last edited by Pat Lynch; Sep 22, 2009 at 01:20 AM.
Old Sep 22, 2009, 04:59 AM
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'X' mount and a 1/32" washer (or bit of 1/32" ply)under the top right 'leg' for the usual 2 degrees right/down. Never had a plane complain yet

Steve
Old Sep 22, 2009, 09:28 AM
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Thanks Guys for all your input...this is my first rc build and very time consuming because its a rubber conversion... the hinges are a pain in the ..... because the wood is so thin, I had to glue them to one side, cut them down, and then reinforce the hinges with carbon rod. I hope I dont get too heavy.

E challenged I appreciate the washout tip, and was wondering where is the normal balance point on a scale reliant ??? would appreciate the help.. this plane needs a LOT of reinforcement because of the thin build... also I dont know what happened but my fuse formers are way off...somehow I,ll deviate from the plan and get it to look somewhat normal.. ill post more pics when i finish the rudder and stab.
Old Sep 22, 2009, 10:24 AM
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That's a VERY difficult project for a first time build. Good luck with it and continue to ask questions.

When you say a lot of reinforcement please be very careful with it. You need to keep it as light as you can. 5oz would be my upper limit and target 3oz.

For hinges use tape. I use the glossy clear packing tape. Apply after covering.

Is the FF balance point listed? I'd start there or maybe 1/4" forward of that. If not shown then 25-30% of the chord (from the LE).

Have you flown a lot of small models? They are a bit 'quirky' and this one will probably be more than most. Keep the speed up until you can determine how it responds at slow flight.

charlie
Old Sep 22, 2009, 10:44 AM
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thanks... I used a nylon hinge because im using cheap PZ minium servos so i dont want a lot of stress on them. I know I picked a tough build for a first time rc/ however..im so deep into it theres no turning back... thanks for your thoughts. the only small model I have flown is the PZ Cessna Centurion
Old Sep 22, 2009, 11:21 AM
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Don't worry too much. Just ask questions as you go.

charlie

PS there is always turning back You can build it and if it turns out too heavy then just hang it from the ceiling.
Old Sep 22, 2009, 12:46 PM
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Nice build! Im inspired to start an 18 inch bird dog.

I use tape for hinges, the plastic hinges seemed to require extra thickness at the leading edges of control surfaces.

The motor gear box is an interesting one to mount huh? It uses two rods for mounting. I ran two carbon fiber rods from the motor / gear box into two small balsa sheets, which I then moved around over cross member braces to get the correct thrust angles and then glued it in place. Only one balsa plate was really needed.
Old Sep 22, 2009, 03:36 PM
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Is that a Megow plan? Doesn't look like the Comet kit of similar size.

Pete G.
Old Sep 22, 2009, 03:54 PM
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Its Actually an easybuilt models rubber scale 1/28.
yes paul thanks for your help...the motor block is so thick i can probably pin it right on w/ some angled thrust.

Now I have a problem and need a solution.
as You can see on my quick mockup, the rudder and motor block are fine, but

I have a FAT FUSE...EGG SHAPE...because I somehow messed up the side formers( didnt run the stringers in tight enough, although I was sure I was following the plan taper) So now I can cut into it....or try to make a nose Cowl. The plan calls for the mounting blocks(shown in black) to be the cowl withsmall balsa pieces glued around it for the cowl bumps after its covered. Any Ideas?...on making a cowl?...or should I cut out the first 2 side formers (A)on the front and taper back from there w/ stringers?...

thanks Guys for your advice and encouragement, George
Last edited by GJ60; Sep 22, 2009 at 04:09 PM.
Old Sep 22, 2009, 07:58 PM
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maybe you can just cut another smaller former for the front. is that what happened your foremost former is too large for the cowl?
Old Sep 22, 2009, 07:59 PM
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so far it looks very light though. i bet you hit 2.5 ozs.


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