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Old Feb 08, 2012, 01:30 PM
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Joe How deep is you shroud I have a 11.5 prop and I want it to be proportional to that. I am thinking about 4 1/2 to 5 inches deep.
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Old Feb 08, 2012, 02:05 PM
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Bill
3 1/2 inches
Joe
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Old Feb 08, 2012, 04:39 PM
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Thanks Joe that's about what I thought so I cut the shade down to 4-1/2" added a wire on the inside and I will sheet this with 1/16 Bass, make up some stand-offs to mount it and I'll be back to shaping the the front fuselage.With this design I was able to lower the motor almost 4" Wow that puts the thrust line close to the center of the fuselage.Hope it's not too low but what I have been able to gather is the lower the better, will see.

Bill
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Old Feb 09, 2012, 03:04 AM
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Looking good Bill how are you fitting the rudder?
Yours looks nice and light I am having to add a lot of material behind the mast to support my shroud I'm concerned it will be tail heavy as you say will see
Joe
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Old Feb 09, 2012, 03:52 AM
What could possibly go wrong!!
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Quote:
Originally Posted by Mud Duck Bill View Post
Thanks Joe that's about what I thought so I cut the shade down to 4-1/2" added a wire on the inside and I will sheet this with 1/16 Bass, make up some stand-offs to mount it and I'll be back to shaping the the front fuselage.With this design I was able to lower the motor almost 4" Wow that puts the thrust line close to the center of the fuselage.Hope it's not too low but what I have been able to gather is the lower the better, will see.

Bill
Hi Bill,
I hope you have had permission to use the best lamp shade in the house, has it been missed yet ?.
Just my experience but on my RPG SE I lowered the motor to get the thrust line as low as possible and it ended up half an inch below the C of G. I found it unflyable as it would pitch its nose very high on the take off run and when I fed in down the rotors slowed and the nose was back on the ground, a vicious circle. I guess you might call it pitch sensitive. I then moved the motor thrust line up which ended at 3/8 inch above the C/G and it transformed it..it now takes off without any problem.
My two cents pence for what its worth. Good luck with the build and Joes. Watching with interest.


Chas
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Old Feb 09, 2012, 09:15 AM
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Glued balsa onto the foam edges to give me a cut line
Made the engine covers and pulled a test piece from thin plastic and found I need to add more balsa to the bottom to give me more plastic to cut to shape
Going to experiment on small pieces to get window frame outlines
Joe
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Old Feb 09, 2012, 09:26 AM
AND FOR MY NEXT TRICK....!
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That's pretty slick man! That will be nice and light!
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Old Feb 09, 2012, 02:11 PM
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Chas: I am concerned about that very fact and the mounting of the shroud is in direct relationship to the motor placement. I will have to finish the rest of the fuselage add the battery and radio and see if I can determine where in blue blazes the C/G will end up. And I thought this was going to be easy
Thanks for telling me about your experience. Better now than after it's all done


Joe: I found an old old servo arm with a square mounting hole not spline like most and some square hollow carbon rod that a 4-40 pushrod fits oh so nice inside of and I thought I would sandwich some thin balsa either side of that for a rudder. and mount it like you and Dave.

P.S. She was mad that I spent money on the shade only to cut it up,would have looked nice in the living room.

Bill There I go hi- jacking some one else Thread again
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Old Feb 10, 2012, 12:25 AM
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Bill
Looking good I hope you get a good thrust and cg test result
Joe
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Old Feb 11, 2012, 11:00 AM
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Daves Avian Update

Dave sent me the latest info and photos of his Avian and it looks great

Weight Auw ( without rotor blades fitted )

2200mah batt installed = 3lb 4oz

4000mah batt installed = 3lb 11oz

all the gear to install final position...... all the little jobs that add up !

Read the concerns about Cof G / Thrust line checked it this morning , used Richards RPG method ( hang from mast.hang front UC leg ...two lines cross etc )
motor is about 2" BELOW that point ?? hmmmmmn

however with 4000mah int nose , hanged model from mast with string an powered her up -

fuz remained level , but with 2200mah batt int fuz pitched slightly nose up

so ?? what do yer think to do ? angle the motor/ shroud or fit clear acetate horizontal vane int duct angled down ...

or wait till eventually try a test hop first ( wonder how full size flies sooo well ?)

For now , not going to make all the ducts for the model till successfully flown
Dave
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Old Feb 11, 2012, 12:22 PM
It was a GLITCH! Honestly!
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There are so many!..looking great everyone.

Bill,
If it were me I wouldn't worry about your motor position, just make provision so that the whole lot can be moved up and down. Really no point guessing at this stage, you need to virtually complete it so that it is almost flight ready. This will give you a far more accurate CG position with everything fitted (rotors electrics and batteries etc) Once this has been found it will all depend on whether you are going with a tailplane or not (and its area and length behind the prop).

Joe,
What's the length of David's blades (there's a reason), with a thrust line that low it will just balloon up and probably crash, I certainly wouldn't try a hop like that. It is going to have to be a really accurate set up with such a short moment arm.
I have tried thrust offset in a duct on a para motor and it just didn't work well. With a vertical fin in the prop wash it was better but still a little unpredictable. I then added some trim to the vertical fin and this worked through the whole power range. Maybe making the fin a clarke Y section may work?, but I have never tried it.

RC ParaMotor, Motor offset test (1 min 5 sec)


Regards

Rich
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Old Feb 11, 2012, 12:41 PM
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Rich
Asked Dave what blades and length he has will let you know ASAP
Joe
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Old Feb 11, 2012, 01:32 PM
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What about adding some washers under the bottom motor mount screws to aim the thrust up a little and maybe push the nose down a little
Bill
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Old Feb 11, 2012, 04:12 PM
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Joe,
What's the length of David's blades (there's a reason), with a thrust line that low it will just balloon up and probably crash, I certainly wouldn't try a hop like that. It is going to have to be a really accurate set up with such a short moment arm.
I have tried thrust offset in a duct on a para motor and it just didn't work well. With a vertical fin in the prop wash it was better but still a little unpredictable. I then added some trim to the vertical fin and this worked through the whole power range. Maybe making the fin a clarke Y section may work?, but I have never tried it.
Regards
Rich[/QUOTE]

Dave got back to me with this info

Rotor blade options :-

A. aerobalsa 23 1/2" x 2 1/4" 49g ( ,lots of lift, an drag)

B. homemade 24" x 2 1/2" 61g ( moderate lift ,lots posi head angle req,d , high head spd.)

C. homemade 25 1/4" x 3" 78g ( lots of lift, slow head speed )

i had C . blades fitted when doing the C o G hang test !
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Old Feb 12, 2012, 12:33 AM
AND FOR MY NEXT TRICK....!
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Rich...that is a cool video! Amazing what that center fin does!

Bill, I think your idea would possibly help, but I think you would want to put the washers on the top of the mount to make the motor point upwards, to keep the nose down. Correct?

I remember reading that the longer the mast, you get more stability and even though this thing is 80 percent fuse, it doesn't have that long of a mast. Quite the dilemma you have there Joe!

Well, I watch with interest!
Joe
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