Mount was built out of balsa, 28mm pipe clips and gorilla glue. My only concern is that it has raised the motor by about 10mm and it isn't very aero dynamic, hopefully it won't effect flight.
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Each clip is bolted through the balsa with a bolt pushed down through the clip, on the underside there is a large washer (to stop the balsa stressing) and a nut to hold it all together however it does not stop here, the forward bolt extends down into the foam by about an inch and the rear bolt less than this otherwise it would emerge out of the foam. The channels for the bolts to drop into the foam were cut before the fuselage was glued together. I used gorilla glue to glue the balsa flat onto the foam, but in addition to this I also filled the channels for the bolts with the glue as well. Gorilla glue foams up before it hardens and bonds well to foam and my theory here is (I hope) the glue will have foamed up to fill the channel and will have hardened and bonded around the bolt threads effectively anchoring the mount well into the fuselage. Additionally where the balsa meets the foam at the front I cut a slot into the foam for the balsa to slide into when putting it together this securely holds the balsa to the fuselage at the front.
In reality the balsa doesn't add much to the structure it is just there to cap off the top of the foam the majority of the load is taken up by the bolts directly anchored into the fuselage. The snap down lock on top of the clip is rated at 100lb pull so I would think the bolt mounting on the clip will be in excess of this. The only reason I ran a seam of glue along the edge of the clip was because when I had the motor out if you knock the clips they move out of alignment as they only have one central bolt so I added the glue to stop them rotating, I realised when I put the motor back in that it didn’t matter anyway because the motor body makes the correct alignment between the clips.
I think as long as I don’t glide into the ground upside down at high speed it should hold up. I guess you may look at the motor mount and decide it was over the top and that I could have just thrown the motor into the stock mount but it was a fun little project, took about 2 hours and cost a piece of balsa, 2 plastic clips, some bolts and glue.
As for the thrust angle, I read the link posted by automatik above (and assuming that this is the correct explanation of the thing, although for airframes with the prop at the front) my impression of it is this. I must say to start with that I am new to most of this and did not consider thrust angle at all. All I thought is that if I mounted the motor at the same angles as the original mount then that would be all I would need to do. I understand from reading the linked post that this can affect variables however...
If we take the stock motor and prop as supplied with the easystar you would think that the frame had been designed to work correctly with it on this basis in other words it is tuned by default for the configuration. If you upgrade to a more powerful motor and larger prop this will affect side thrust, right thrust and down thrust (I would assume) right there in the standard mount and in the standard mount how do you compensate for this anyway.
On all our runner modifications I have seen the out runner and prop are mounted a fair bit further back and in some cases slightly higher than the standard config again this must effect the thrust variables but I haven't seen any cause for concern by anyone who has an out runner mounted. So with my mount the prop is positioned in the same location front to back as the standard mount it's just a little higher. I think what I understand from this is that the easystar airframe is fairly forgiving in changes to many variables around the CG and maybe if it were a more edgy airframe or you were drastically moving the motor position or angles you would probably want to worry about this more.
All this said I am not discounting the point you made, I still have a lot to learn, thank you for raising the point it has definitely opened my interest in this and it would be something I would consider in the future, although with the easystar even if I had considered it first I don't think I could have done much more than just build it and see if it works and then make changes as required to get it right.
As you say the proof is in the flying and the crashing, haven’t had chance to fly it yet as I am going to fit a larger rudder first.
Mark
I don't mean to be rude, but... why did you go through all that work again? The new version looks a lot less structurally supported. It seems like if you got enough force from your prop (unlikely) or if you crashed nose first (more likely, no offense), the clamps would be ripped off, starting with the back edge that's parallel to your little glue fillet. And that's neglecting to mention the increased normal distance from your thrust to your CG.
But I mean... if it flies OK then who cares? Does it?
David - nice work on that mount, I would have done something similar however the motor I had available was an in runner.
TC - I plan on increasing the rudder size, I will get some practice in first before modding for ailerons.
I suggest that you increase the size of the rudder for better control turning since you now have a more powerful motor installed in place of the stock one. Also, you might want to consider adding ailersons as they will allow you to roll into a turn instead of the flat nose down rudder turn.
Just a thought.
Regards,
TCIII
see this thread on RC Groups, especially 4th post...better to take care of things before the flight...
http://www.rcgroups.com/forums/showthread.php?t=42944
looks nice ! Did you take into account thrust angle when installing new motor?