|Jan 12, 2007, 09:19 PM|
Active sweep flying wing
A thousand words but not worth a picture.
Post what part you do not understand and I will post a diagram.
It is ashame to have channel 4 unused.
Help design sweep control rods on Sloflys active sweep flying wing.
We'll start with a flat epp flying wing because it works.
Only the root taper cut will be extreme for major sweep (or delta for the literal)
The nose is taped to make a hinge at the nose.
another delta shape piece of EPP holds the motor at the rear and the tip is the nose of the plane.
The wings root chord tips meet at the nose of the delta piece.
Servos on the delta piece spread the wings in or out.
Designing to not break the servos deserves attention.
If the wings go between two delta plates they can have a wheel going through them at the rear. This acts like a spar since the wings are only held together at the wing tip.
To prevent the wings lifting up is a challenge.
You may need a positive attitude, google and a passion for trying different sweeps while in the air to come up with something!
Oh how fun it will be to use ch. 4 while spring loaded to control sweep while ch. 3 is used for throttle on the same stick!
|Jan 12, 2007, 10:46 PM|
Man thats a cool idea, what wingspan you thinking? I might try this after things level out, my wife is having a baby hopefully sometime this week
|Jan 12, 2007, 11:59 PM|
I can see a whole lot of problems with that, BUT HE IDEA IS AWESOME. You will somehow haver to perfectly time it so they both come out at exactlyt he same time or it will go into a frisbee like spin as there will be more drag on the wing that isn't quite as far swept back. that would mean that you would nneed to be able to do very fine small mechanical trims to the mechanism. You would also need to add a very large vertical stab to the delta shape that hold the swing mechanism as the trogue of the wings moving would want to move the center section causing huge ammounts of unwanted yaw motion from spinning the plane and throwing it into a frisbee like yaw spin. Its inherently unstable during transition, but if you work on that you should be able to do it.
just my 2 cents,
|Jan 13, 2007, 09:06 AM|
Mechanicaly, this should be no problem. As long as both wings share the same pivit point.
You could attatch a gear to each wing and sweep it like a plastic model f-14.
Even if you used one or two servos to push them apart, the sweep would always be even with a common pivot point. I could see using a dc motor and limit switches to make a stronger gearbox actuator.
The vertical stabs will need to be located on your delta plates, or you would induce drag when they are not parallel to the models motion. Or you would need linkages to keep them in line (too heavy).
The big challenge will be to shift the cg, or you will have to suffer with an over forward cg while they are spread for glide (which would kind of defeat your goal), but it would be in the right spot for sweep.
I have an idea, that would involve a sliding battery tray.
It is a good idea, and I look forward to seeing it succeed.
This has the potential to add a ton of weight, so keep it light and simple.
|Jan 14, 2007, 01:33 PM|
I too look forward to this.
I don't see how you can avoid a change in CG doing this so I surely want to see how this is overcome.
|Jan 14, 2007, 02:09 PM|
cg is reason
the change in cg is the reason for making this.
At my disposal is solidworks and flying wing formulas but I do not have them were I can add my component weights to get CG while combining square inch weight of the EPP in the calculation. Mean Aerodynamic Chord is not enough.
The leverage formula will tell you how grams at certian distances will act out from the cg but you need to layer on top of this the area formula to get weight in front and in back of the cg line.
As the wing sweeps back the cg goes back too.
My current components are a 12 gram motor putting out 8oz thrust with 7035 prop.
2 6.6 gram servos, Berg 4L rx, 1-2 gram 2 cell lipoly converter to 5v, 300mah 2 cell lipoly
If you make a wing with these components and it is tail heavy you are stuck adding nose weight or more battery weight.
My goal is to keep it light as possible so the wings need to be swept back enough so that the motor weight and nose weight is ahead enough of the MAC and CG to keep the nose down.
An active sweep wing is a great way to get an association of various sweeps to component weights. It helps in designing planes off the top of your head. While it will be at least 1/2oz heavier with an extra servo, epp and linkages the benefit from studying sweep in real time flight makes it a worthy scientific tool.
So to answer your question you get to choose the feel while you fly!
Sweep it back a bit for very sturdy pitch control.
Slow down, crank those wings forward so it is pitch sensitive and pull off a few super tight loops.
Come out of the loop in a straight line,sweep wings way back and pull off some fast axial rolls.
The plane can go from little sweep and pitch sensitive to swept back and a bit nose heavy.
On a regular wing the variables to achieve this are component weights, positions and cut angles on the epp.
With the active wing the above have a dynamic effect on flight based on sweep position versus the static effect on one sweep.
Please check out this thread for flat flying wings:
Flat flying wings are the ultimate research tool.
Databases with widths and cut angles for matching components to characteristics should be common place
|Jan 14, 2007, 02:13 PM|
It is usable through all stages of transition and the transition is actively controlled with a 4th channel.
A flat center fuselage under the flat wings holds both devices. The wings are pushed out from this part. The motor is also on the flat part.
The wings always come out the same rate (even with a servo for each wing)
A carbon rod comes off the bottom plate on each side of the motor to make two yaw stabilizers.
|Jan 14, 2007, 02:54 PM|
Here is an example with one center plate.
The wings can hinge elsewhere. They do not need to hinge at the center. Many designs are possible.
If they pivot at 50% root chord and are space apart a servo can control them too.
You may notice that the wings are only held on at the hinge.
A method using two plates with a wheel embedded in each wing addresses this. It would be a close call with the spars, wheel area etc... and would not make for agressive flight but for a park study tool this thing would rock.
If handed one that stayed in a nice CG range during sweep I'm sure we'd all enjoy trying to fly one at least for a bit.
Whether anyone actually wants to try and input designs and make one I'm not sure.
It could be a quick build if kept to flat sheets, simple cuts and control rods.
|Jan 14, 2007, 03:02 PM|
Rear view with wheels in wings to extend wing spar leverage to cetner plate.
Since the nose is hinged and the wing is in between a plate which is on top and bottom the plane will have support.
I'd like much better ideas but getting a idea posted can sure help get things started.
|Jan 14, 2007, 03:09 PM|
Yes Rich the F14 wings sound great. Nice battery idea.
It is a flat plate with outrunner- no glide issues. Just acrobatics/loop/roll comparisons at different sweeps.
Variable delta/sweep is an old idea but not found in foamies?
I hope my sharing this motivation is enjoyable for everybody.
|Jan 14, 2007, 08:45 PM|
Steve I do not have the visual abilities you do to illustrate my thoughts but I have been thinking on my favorite and probably the best known swing winger, the F-14 Tomcat.
This design while it could never be called a glider except as a joke, does not seem to suffer from the problem of CG change and yet it certainly benifits from the effect of the position change. This seems to be due to the fact that the part of the wing that moves is behind the CG and yet close to the CG.
My thoughts are that the closer to the CG that the swing takes place the less critical this movement would be to the CG.
Another factor is the amount of swing involved. Steve, the little GIF you have provided has made me realise that the wing not need to swing a full 90 degrees for such a design to be effective.
In other words the smaller the total swing, the less critical the CG would be. Another plus towards keeping this idea less complicated.
I believe also that the wings can be dynamically balanced ( I am not sure I am using the right term here) individually so that as the swing takes place the CG does not change at all.
one other way is to have an actual ballast weight that moves with the swinging motion so as to not allow the CG to change as the wing moves. This would not be hard but certainly would be more complicated. The balancing of the wing panel idea to me is pretty much the same thing here but less complicated for there are less moving parts.
Actually the wing balancing thing seems to be the best all around answer the more I think about this.
This and keeping the balanced swing motion on or close to the CG.
On a different aspect of the changing CG location is this:
Make the CG change "work" for you. Example:
Slope gliders are a different breed of glider than a thermal glider. One of the biggest differences is the wing loading. The slopers ( hiya Steve!) have a higher wing loading for better wind penetration and for the most part fly at much faster speeds than thermal gliders.
Gone to think some more, Robert
|Jan 14, 2007, 11:33 PM|
Joined Oct 2006
You might consider teflon rub strips instead of wheels. The strips may be easier to install. Can you try unpowered gliders to test the variable sweep idea? A quick flying glider can answer a lot of questions quickly. The test glider does not even have to have frictionless wing motion. You just fly it at a variety of sweeps.
|Jan 15, 2007, 02:13 PM|
What if you mixed the throttle setting with the swing angle? A bit like on a Heli, ie the throttle rises to a set point, then as the plane accelerates, you could then use the last 30% of the throttle stick to adjust the sweep of the wings........
Just a though as I read through this thread
|Jan 15, 2007, 04:53 PM|
Joined Oct 2006
Interesting sweep info about F14 Tomcat can be found with a Google
Wing sweepback variable from 20° leading-edge to 68°; oversweep of 75° used for carrier storage without wing fold; wing point 2.72 m from aircraft centerline; fixed glove has dihedral to minimise cross-sectional area and reduce wave drag; small canards on F-14A known as glove vanes extend forward progressively to 15° from inboard leading-edge to balance supersonic trim change and unload tail surfaces.
Lateral control by long-span spoilers, ahead of flaps, and tailerons; automatic leading-edge slats assist manoeuvring; strakes emerge from wing glove leading-edge at high airspeeds; automatic wing sweep has manual override; automatic scheduling of control with airspeed; autostabilisation and angle of attack protection; autopilot and automatic carrier landing system (ALCS). Airbrake panel above and below tail, between fins. Twin fins and rudders.
|Jan 15, 2007, 04:59 PM|
Joined Oct 2006
And from Wikepedia: http://en.wikipedia.org/wiki/Swing-wing
One problem discovered while testing the Bell X-5 was that as the wing pivoted rearward, the center of lift also moved to the rear, pushing the nose down. A system to compensate for this basic effect had to be added for any such design to be viable.
How about a canard that extends as the wings change angle in an effort to provide the correct center of lift.
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