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Old Sep 08, 2012, 04:43 AM
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Hi Stuart,

A good friend of mine in Arizona (USA) uses Solid Works and is able to show motion ... it is an expensive program though.

Jens
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Old Sep 08, 2012, 05:31 AM
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Jens,I could just pin a wing profile to the bench and get the plot that way,a bit tedious and I'm not sure how many measurements would be needed to get accurate data.
Stuart
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Old Sep 08, 2012, 09:03 AM
Just call me crash for short
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Sketchup has a plugin called Sketchyphysics. It will animate your drawings but it is brand new to me and I haven't figured it out yet. Blender (free program) also does very good animation (people make movies with it) but I find Blender to be a nightmare to do anything with, though it has some very impressive results. maybe One of the Rino users here have some animation skills. Today, I am sorry to say, just not up to that task. I figure it will be a few months before I get a good handle on the Sketchyphysics.

Mark
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Old Sep 08, 2012, 10:54 AM
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For your amusement and commenta preliminary sketch.
The dark blue lines are the top and bottom wing joiner plates.These will need to be extremely rigid.
The yellow elements are the tubes around which the wings pivot.The top and bottom plates are connected by bolts through these.
The green lines are free floating discs providing a sliding surface between the plates and-
The brown hatched areas which are the wing roots.These will need to be circular in the area between the discs,with a connection to the drive shaft inboard.
None of this is to any sort of scale;as to materials I would welcome suggestions,though I imagine some sort of composite for the plates.
Stuart
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Old Sep 09, 2012, 10:15 AM
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Additions and modifications.
The added plan view shows the wing roots at 0 and 50*
The red elements are rods bolted through the plates to give addition strength near the wing root,which,along with the discs,would need slots as shown.This is similar to the method I used on the glider.
Drafting error! As shown I have a main joiner tube placed centrally along the chord,it would be in a more usual position.This would allow the tube to extend past the centre of the disc.Rod and slot moved to suit.
The connecting arms to the drive are placed at 25* above and below the centre line to minimise the splay.
Stuart
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Old Sep 09, 2012, 10:18 AM
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This is looking pretty darn good. I'd be sure to wrap the spar caps at the hinge area.

Kent
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Old Sep 09, 2012, 10:37 AM
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Thanks for the comments Kent.So do you think I'm heading in the right direction here?
Re the wing joint,I've been wondering about making the inboard portion of the root integral to(with?) the wing.This would be stronger but would mean detaching the wing by removing four bolts and the connection to the drive(not to mention the wiring)
Regards Stuart
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Old Sep 09, 2012, 11:07 AM
Herk
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Originally Posted by Stupot46 View Post
Thanks for the comments Kent.So do you think I'm heading in the right direction here?
Re the wing joint,I've been wondering about making the inboard portion of the root integral to(with?) the wing.This would be stronger but would mean detaching the wing by removing four bolts and the connection to the drive(not to mention the wiring)
Regards Stuart
Hi Stuart, How big do you expect this model to be? I built the blue trout in one piece to save weight - 90 inch span. Just fits in the vehicle.

The F-14 had an over-sweep setup for parking and storage - reduced its parking space substantially. You might consider something similar if you expect transportation to be an issue.
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Old Sep 09, 2012, 11:28 AM
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Herks,a one piece might be a sensible option.Had a 2400x300mm piece of board in my saloon car so a 2m or so version of this with the wing in a plank type configuration should be ok.
Not sure about the folding thing.It would be more complex than dismantling
Regards Stuart
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Old Sep 09, 2012, 11:42 AM
Herk
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Originally Posted by Stupot46 View Post
Herks,a one piece might be a sensible option.Had a 2400x300mm piece of board in my saloon car so a 2m or so version of this with the wing in a plank type configuration should be ok.
Not sure about the folding thing.It would be more complex than dismantling
Regards Stuart
Stuart - sorry if I wasn't completely clear. There was no folding of the wings on the F-14 - they just swept them more than the maximum flight sweep to make the package narrower when they parked it. So your max sweep considered for flight is 50 degrees. Using this strategy one might provision the design so that it could be swept to 60 degrees or even more for transportation and storage.

The F-14 wings were limited to 68 degrees in flight but could be swept to 75 degrees for parking.
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Old Sep 09, 2012, 12:15 PM
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So do you think I'm heading in the right direction here?
It's looking good, but this hinged wing connection at the center of the wing is going to be a tough design challenge. Keep in mind that swept wings will try to flutter, so if your wing hinges have any slop in them at all, that slop will allow the harmonic flutter to start just within the "slop range", then if there is any flex in the structure, it will deflect more allowing a stronger flutter to develop. So fly slow if possible. Flutter seems to get stronger and stronger feeding off it's last oscillation. Kinda like talking to a crazy person. It just gets worse and worse.

Whatever scheme that you come up with for the structure, I'd suggest making a quick mock up of just the structural parts and test them to destruction. This way you can know which approach performs the best.

Kent
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Old Sep 10, 2012, 05:23 AM
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This cog thing has been bugging me since I posed the question earlier.So a rig to maybe get some sort of answer.
A 600mm radius circle,circumference divided into 5*segments.Set the dividers to this and marked off,checking with the protractor.
The balsa "wing" is 102mm wide,I've marked the length at 970mm.
I'll put the measurements at each 5* position into the cog calc.later today.
A graph plotted sweep angle against cog position should show if the cog movement is linear(I think)
Stuart
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Old Sep 10, 2012, 06:53 AM
Herk
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A question for our cad designers.First a disclaimer in case what follows is nonsense.I have no idea what your programmes are capable of.
Would it be possible to lay out a planform of a swing wing,and move the wings through the full sweep?I'm thinking if so by taking measurements at points along the sweep we can calculate exactly what the cog is doing.
If the wing movement will to some extent self correct the balance,could this and(Kents?)idea of weight in the wing be be sufficient?
The rough and ready three position measurements I took from the chuck glider would suggest that a weight could be tuned to move the same distance as the cog to balance the wing.The only drawback with the wing weighting is that it would move in an arc.
The above was prompted by the fact that the belt and pulley drive could have been used to move a weight,not so the latest version.
We will need to determine if cog shift needs to be built into the drive- this could be done using the linear belt drive I sketched out in a earlier post,the underside of the belt moving the weight.
Stuart
Hi Stuart, The problem with this issue is very intimately related to the specific layout of this intended model. I think that's why it is a bit of a muddle now.

Here is the situation. When the wings sweep aft, the MAC moves aft with the wing. The effective MAC also gets longer because of the increased length of the apparent chord. Just for reference this theoretical thing we call MAC divides a straight taper wing panel into equal areas - so it is somewhat inboard of the spanwise center of the panel. If the wing panel's lateral balance point is near the MAC that means the weight of the wing moves aft with the MAC - or the MAC moves aft with the wing. Thus as the CG needs to move aft because of the sweep, it will move aft because of the movement of the weight of the wing panels.

The wing panels will likely be somewhat heavy with the need for stiffness (Kent and I have both mentioned the flutter issue) and the fact that the servos must be mounted out in the structure.

Of course the thing that doesn't move is the center pod with the sweep mechanism. So, as the wings move aft their weight will compensate, but the plane will get somewhat more nose heavy because of the fixed weight of the pod. How much depends on the relative weight of the wing panels and the weight of the pod bit. Until there are specifics spans and weights to work with the answers will remain elusive.

That said, there is then the actual dynamic of flying. With the wing forward one probably wants to soar - hence the desirability of a more forward CG. (relatively speaking of course). When one has the wings fully aft, one will likely be going for higher speed and penetration - hence the desirability of a more forward CG.

So, to some extent the whole process is likely to be self adjusting and the need for in-flight CG control may be small or it may evaporate all together. I do believe you may get some feel for this by the experience you can get with your test glider. Bottom line - it will be more of a concern when you have the flying hardware laid out - but at that point you will be able to develop a clear picture of whether it's a concern at all -- and the magnitude of it will be a relatively simple calculation.
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Old Sep 10, 2012, 08:07 AM
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Herk, great post. I just read it twice to make sure I didn't miss something. Very good points and I for one say thanks for sharing.

Stuart, think thrust bearings out in the edge of the radius. That would stiffen things right up.

Mark
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Old Sep 10, 2012, 01:32 PM
I don't like your altitude
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Herks as Mark says,thanks a lot for that.Well explained.
What led me to do this was mostly curiosity,just to see what the relationship was between cog and sweep.
As you say in the last paragraph,any adjustment may be small,but I would like to be able to build the drive parts to allow such an adjusting device to be easily retro fitted if needed.

Mark,the thrust race idea has been on the table from early on.Hence the turntable bearings in the two drive mock ups.After a lot of searching commercially produced bearing of a suitable diameter(£275 each!)I'm thinking about having a go at making one.
Should be possible-a disc of say 5mm thick nylon,mounted on a spindle the correct distance away from the stand drill,milling cutter in the chuck.Glass/plastic balls are readily available,spacers from sections of thermoplastic rod bent to suit.
Once cut the inner portion removed leaving a ring 10/15mm wide.
Now if I had a lathe-------
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