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Engine Position

Old 01-11-2009, 10:03 AM
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Default Engine Position

Is there an issue with how close the prop back-plate is to the fuse cheeks?

The instructions say 1/4" in front of the cheeks but I am trying to push the engine back as far as possible to help with CG (ST-51 in a 4*-40 ARF).

See photos...I have it about flush to the cheeks. If I push it any more back, I will have to cut the cheeks which I do not want to do. Is flush OK?
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Old 01-11-2009, 10:07 AM
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Default RE: Engine Position

As long as it doesn't hit or rub against anything, I can't see where it would matter much.

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Old 01-11-2009, 10:10 AM
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Default RE: Engine Position

Hi!
No!
The only problem you will have is with that plastic spinner ...and mounting the engine too high above the prefered tank level.
An aluminum spinner nut is more suitable...and mounting the engine on its side will render the tank more in line with the carb...which will make your engine settings more reliable.
Old 01-11-2009, 10:23 AM
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Default RE: Engine Position

The amount of movement you are able to get by moving engine back that tiny amount will be incidental, Since you feel it's a bit nose heavy don't be overly concerned. Fly it and then make any adjustments you feel are needed. If you have located your bat. pack back and find you do still need CG further rearward you can remove spinner, relocate elev, rudder servos all the way back to tail. I really doubt you will need this amount of adjustment. Fly it
Old 01-11-2009, 10:35 AM
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Default RE: Engine Position


ORIGINAL: jaka

Hi!
No!
The only problem you will have is with that plastic spinner ...and mounting the engine too high above the prefered tank level.
An aluminum spinner nut is more suitable...and mounting the engine on its side will render the tank more in line with the carb...which will make your engine settings more reliable.
Jaka: Why aluminum? What is wrong with the plastic. In terms of the tank, it is an ARF so it is where it is. The tank is a little below the center line of the carb but with a vertical mount, nothing I can do there. Yes, I could mount side-ways but then I have to completely cut out the check and it will look lop-sided unless I build a cowl or something beyond my construction abilities. I just checked my TH 40 trainer and the tank and carb at at the same height as in this 4*-40 ARF.
Old 01-11-2009, 10:39 AM
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Default RE: Engine Position


ORIGINAL: TedMo

The amount of movement you are able to get by moving engine back that tiny amount will be incidental, Since you feel it's a bit nose heavy don't be overly concerned. Fly it and then make any adjustments you feel are needed. If you have located your bat. pack back and find you do still need CG further rearward you can remove spinner, relocate elev, rudder servos all the way back to tail. I really doubt you will need this amount of adjustment. Fly it
Thanks Ted. I was just trying to set the engine mount position and used double-side tape to allow me to check CG prior to drilling out engine mount.
If a 1/4" on the engine position does not affect things too much, maybe I am just trying to push it back to far with no benefit...I had hoped that heavy engine would swing the CG depending on the location I spot it on the mount.

I am trying to figure out how to put the battery pack on the tail-end side of the servo tray instead of the front side of the servo tray (where there is a ton of room). It is hard to reach in behind and would need some sort of tray to allow the pack to be held in place. Anyone have some photos?

Old 01-11-2009, 11:44 AM
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Default RE: Engine Position


ORIGINAL: chemie
Why aluminum? What is wrong with the plastic. In terms of the tank, it is an ARF so it is where it is.
Aluminum spinners are great but there is nothing wrong with a good quality plastic one either. The only plastic spinners I have seen problems with were some of the ones that come with cheapo ARF's. If you have a good Dubro, GP, SIG, etc. you will be fine.

Your tank/engine alignment may not be "ideal" but it'll work fine. Lot's of ARF's out there with engines that run great.
Old 01-11-2009, 12:31 PM
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Default RE: Engine Position

If possible show a pic of the area you have behind servos. Perhaps upon seeing this someone could make a suggestion.
Old 01-11-2009, 01:13 PM
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Default RE: Engine Position

Your engine is in fine,,the thing about spinners is if you use a starter to start the engine it will ugly up a plastic spinner pretty quick...the only thing I can see that you need to do is,, that spot of open wood by the neeedle needs to be covered/ painted/ nail polish, anything to cover bare wood so it doesnt get oil soaked from the fuel...Rog
Old 01-11-2009, 06:10 PM
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Default RE: Engine Position

OK TedMo: First two are of the rear portion where I want to put it. It is hard to access. It needs to be far enough back not to interfere with the aileron torque rods.
Last out is the front bay which has tons of space...
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Old 01-11-2009, 08:31 PM
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Default RE: Engine Position

Maybe mount your battery securely on a dowel or stick then slide it down the fuse to a point where it balances good then screw the stick down to the servo tray? I've also pulled covering off from lightening holes in the fuse and made battery mounts inside.
Old 01-11-2009, 10:15 PM
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Default RE: Engine Position

For What It Is Worth...if you move the engine to far back, you may end up against the fuel lines and brass tubing. Won't take long for the lines to develop leaks.

Happy Landings!
Old 01-12-2009, 06:57 AM
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Default RE: Engine Position

Once I set the mounting position, is there anything wrong with cutting off the excess engine mount plastic pillars beyond the engine mount flange?
Old 01-12-2009, 08:53 AM
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Default RE: Engine Position

No problem
Old 01-12-2009, 12:32 PM
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Default RE: Engine Position

chemie:

I would leave the engine alone, follow ChuckW's idea, wrapping the battery with foam as much as possible, and test flight.
If still tail heavy, just add led to the tail.
Overpowered models are seldom light anyway.

Regards!
Old 01-12-2009, 06:11 PM
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Default RE: Engine Position

I am worried about the battery bouncing around in the rear section and was thinking how to fit a "platform" given there is effectively no access....but I suppose I could wrap a TON of foam (floor to ceiling) which would just wedge the sucker in there....
The only problem is the access hole size is smaller than the floor to ceiling height but I might be able to pack it in and around after inserting the battery. Worth a try.
Thanks. I knew to wrap in a little foam for vibration but never extended that to wrapping to prevent movement. I can use packaging foam.

And Yes. I know I can fly it to check. Actually, the CG is "not too bad" with battery forward but I am thinking ahead to when it needs to get moved back a bit. I wanted to locate the on/off switch with any battery position (forward/back) in mind. Also, wanted to make sure it was "close" because of heavy engine upfront. No point drilling out the engine mount BEFORE checking the CG only to find the engine was too heavy and the thing is nose heavy. I guess I am more a planner than a "try and see" type. Work out everything from 6 angles before making anything permanent .
Old 01-12-2009, 08:40 PM
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Default RE: Engine Position


ORIGINAL: lnewqban

chemie:

I would leave the engine alone, follow ChuckW's idea, wrapping the battery with foam as much as possible, and test flight.
If still tail heavy, just add led to the tail.
Overpowered models are seldom light anyway.

Regards!
If it's tail heavy, add more lead?[sm=50_50.gif]

I'm sure that was just a typo, but anyway chemie I wedged my battery pack in the back of my extra with a bug chunk of seat cushion foam rubberbanded around it. It works fine. Give it a good shaking to see if it will hold, you don't want it coming loose and unplugging on a rough landing.[sm=thumbup.gif]
Old 01-12-2009, 09:53 PM
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Default RE: Engine Position

As shown in your pix the usual location for the battery pack is right behind tank where there's loads of room. Generally balance comes out quite well with it there. What size and type batteries? Generally 800- 1100 Ma. 4.8 or 6.0 v. ni cds are suitable. Since you appear from what you have said to be a bit nose heavy I would as said previously test fly it. Nose heavy is not a big problem as tail heavy can be. Of course the manner in which you check for balance could be questionable but will assume you know what your doing there. Off hand I would expect that if you were to move the bat. back behind servo tray you would definitly become tail heavy,N.G. By the way wrap bat. pack in foam I often use that which is used as underlayment of carpet, about 1/2 "or so thick.
Old 01-13-2009, 12:46 AM
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Default RE: Engine Position

First thing I can see is to get rid of that heavy ACP prop and either get a Master Airscrew or Evolution if you want to stay with a plastic prop, or a Top Flite Power Point wooden prop. That will make a world of difference with the CG.

ACP will not help you until you get to the higher performance planes, and if that is a trainer, will have a better chance of damageing the engine on a hard landing. Master Airscrew is more flexable and more forgiving on hard landings.
Old 01-13-2009, 05:45 PM
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Default RE: Engine Position

It will start with a master screw 11x6. Again, put in the APC to see worst-case balance issues.

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