Wot 4 foamie

[Diamond Geezer]

Hi All

repaired front of fus new motor mount and motor does this look right measures 253mm from table top to centre of motor shaft really appreciate it if someone could measure theirs.

[Diamond Geezer]

[GrumpyGnome]

To my naked eye, that looks to have upthrust - is there a 'correct' way to put the motor mount on?

[john davidson 1]

I would think some downthrust

 

[Diamond Geezer]

18 hours ago, GrumpyGnome said:

To my naked eye, that looks to have upthrust - is there a 'correct' way to put the motor mount on?

Not as far as I know it’s the same reversed

[Diamond Geezer]

17 hours ago, john davidson 1 said:

I would think some downthrust

 

Any idea how much

[Mike T]

The motor centreline needs to be parallel to the top of the rear fuselage (i.e. //el to the tailplane).  Although in the pic shown it appears to require downthrust, it doesn't.  Can you put up a pic showing the entire fuselage side - as square-on as you can get it?

 

 

PS. - preferably with your back to the window...

Edited June 17, 2023 by Mike T
sp.

[paul devereux]

@Diamond Geezer- I had to epoxy my motor mount as I faceplanted it after using the wrong memory. It flies well on this- which is as close to the original way it was fixed- which didn't have down-thrust that I could see. My personal thought is, since you have already repaired it- it'll probably fly fine, and you can judge from the first flight how much trim you might need.

[Andy Stephenson]

It's looks the same with the standard wooden Wot 4, it seems like it's got upthrust but when checked on an incidence meter it's slightly down.

[Diamond Geezer]

Mike 

side view 

[Diamond Geezer]

[Mike T]

OK - I was hoping for something a little more square on, but I stick with my original judgement that your thrustline is OK:

 

 

PS - if that break in the rear fus. was severe, you might want to check that the carbon boom hasn't splintered.  If your rear fus. is excessively bendy, it might have.  If so, run some thin cyano down it from the wing seat end and hope that it binds the fibres together.  (If it doesn't, then limit your 'G' accordingly!!)

Edited June 18, 2023 by Mike T
extras

[Diamond Geezer]

1 hour ago, Mike T said:

OK - I was hoping for something a little more square on, but I stick with my original judgement that your thrustline is OK:

 

 

PS - if that break in the rear fus. was severe, you might want to check that the carbon boom hasn't splintered.  If your rear fus. is excessively bendy, it might have.  If so, run some thin cyano down it from the wing seat end and hope that it binds the fibres together.  (If it doesn't, then limit your 'G' accordingly!!)

Ok thanks Mike

[Geoff S]

There was a discussion about incidence meters last week.  Here's an occasion when one might be useful.  Failing that, if you have a smartphone, download an angle program (which the uncouth call an 'app' 😞 )  and use that to check the angles.  A couple of degrees of down thrust is quite common and about the same right thrust but often there's none.

 

Set the model up with the tail plane horizontal (I usually use a small spirit level) and then check that the motor mount is at 90 degrees and go from there.

[Mike T]

If you do as Geoff suggests, make sure you reference the front face of the removable part of the engine mount, as this has downthrust bent in.  TBH, it's easier to fit a prop and make sure that a line through it (vertically) is square to the fus. top/tailplane using your Mk I eyeball.  Side thrust is already built into the mount.  Note that newer versions of the kit have the lower mounting screws at the rear packed out with washers to effectively remove the downthrust bent in at the front!