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Old Jan 17, 2013, 02:22 AM
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Been looking at using drag rudders on another plane. I can see tying those drag rudders in with the elevators. When the wing is at a high angles of attack laminar flow will change and the top drag rudder will have less effect than the bottom. Elevator inputs will cause drag from both upper and lower drag rudders to be the same. How much differential you need is up to experiment.
Ive been playing with a alpha fin to detect the angle of attack for differential control for the drag rudders and a beta fin for yaw detection. This single and the transmitter input mixed and feed into a gyro for stabilization.
Still experimenting with this.

LX Model's B-2 uses drag rudders that are deployed all the time to induce drag at the tips. They only retract in turns. Simple but looks ugly.

How did Chris Gold's B-2 react to varying AoA?

Can't wait to see how your design comes out.
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Old Jan 17, 2013, 07:15 AM
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I understand you comments around the drag rudder effectiveness varying with AoA / elevator, so in effect the drag rudder is counter acting the elevator. Luckily there is a lot more elevon surface area than drag rudder, in fact as pointed out in an earlier post the drag rudders are smaller than scale.

Yes you could mix drag rudders with elevator so that the upper drag rudder opened some and the lower drag rudder close some when up elevator was input. However, that would require a seperate servo on each drag rudder surface (two on each side = four) and as currently designed with one servo for both surfaces per side I can not open upper surfaces whilst closing the lower surfaces.

No idea about the Chris Golds model other than comments that it was very stable and flew "like a trainer". There are no videos around of this flying.
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Old Jan 17, 2013, 01:00 PM
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Canada, AB, Okotoks
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PeterF,

I just found this build, beautiful work Looks amazing. Had one question, with the fans being so far into the fuselage do you need to make thrust tubes or is the outlet not to far from the fans?

Cheers
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Old Jan 17, 2013, 03:52 PM
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Quote:
Originally Posted by thedeuce View Post
PeterF,

I just found this build, beautiful work Looks amazing. Had one question, with the fans being so far into the fuselage do you need to make thrust tubes or is the outlet not to far from the fans?

Cheers
Thanks for the compliments.

There will need to be some form of inlet ductwork to smooth the down and in flow and then there will be some form of outlet ductwork as well, not yet sure what form that will take. On the original build from 1998 by Chris Golds the fans were 70mm and sat higher so a simple slightly conical thrust tube was all that was required. I may have to have an eccentric cone, keeping the outlet level with the top of the fan and brining up the bottom of the cone if you see what I mean. As this is not a fast flyer I am after more static and low speed thrust so I will not be reducing the oulet very much compared to the FSA.
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Old Jan 17, 2013, 04:04 PM
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Flying surface test.

I have completed the other drag rudder and put the model together to test all the flying surfaces. See the Youtube clip, I am prettry sure I have them all working the right sense.

The sequence is rudder right then left with one rudder opening and the other closing. Then it is elevator up and down followed by aileron left then right. Note the drag rudders are coupled to the ailerons as per plan instructions. I then show extra opening of both drag rudders either on a manual slider or when gear is down. Final action is showing rudder right and left whilst the drag rudders are open with the gear down to show it still has full range on both sides. I have reduced the fully open throw somewhat from the maximum servo travel I could achieve shown in the earleir post as they were almost both 90 open in that shot.

What next, I either need to do the gear doors or install the fans, neither of which I have plans for so I need to develop ideas as I go along. I may stall for a bit whilst I work out what to do.

Test flying surfaces Chris Golds RC B2 Stealth (0 min 42 sec)
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Old Jan 17, 2013, 05:06 PM
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So this plane flies with the drag rudders open? This will induce drag for yaw stability so you will not be on the sticks all the time.

The system I was thinking about is much more complicated as the drag rudders are closed and electronics are used to keep yaw stable. But the plane I am designing does not have the luxury of long wings with the big moment arm. Still may go with drag rudders deployed part way with electronics so servo duty cycle is reduced.

Keep up the great work.
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Old Jan 18, 2013, 12:50 AM
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In case anyone was wondering, on the real jet, they are called rudders or speedbrakes, since they function as both, but they are not drag rudders.
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Old Jan 18, 2013, 03:18 AM
deltas are cool
AIR SALLY's Avatar
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wow looks just like a "S" bit on the real deal. im thinking the rudders need to close up a bit more ...im sure they need some to keep the yaw in ck ,the real deal they are open a few degrees for normal flying ...im sure you can see this in any inflite pics. but with out a gyro they may need to be open more.im getting ready to build a small B-2 65" wing span ...i plan on using a gyro on the yaw axis.
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Old Jan 18, 2013, 07:02 AM
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I am going by the plan and the build notes on the plan and that is what the plan states as the settings. However, he does state that as you get more experienced that you can reduce the neutral opening of the drag rudders, but for the first flights he recomends these settings. The thing is and there are comments on the foamy B2 threads that at low speed they are much less effective, just when a maiden flight is going to go wrong, just after take off without enough yaw stability. They have also found it is easier to fly with the drag rudders open, although some poeple do say they close then once flying at speed.

As the wings are swept back there is some effect akin to dihedral on this model, the plane yaws to the left, the right wing now shows more frontal drag rudder area and the left wing less, so there is some auto correction. It might not be enough but again Chris Golds did not fly with gyros. Perhaps the drag rudder opening in flight is they key to gyro / no gyro.

I plan on keeping things like they are until I have a feel for this. As I have set them up on independent channels I can set the neutral position more closed with a mixer and not have to change the mechanical linkages.
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Old Jan 18, 2013, 10:25 AM
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United States, CA, Chino
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A R/C Grouper foamie scratch builder gpw has done a flat profile finless B-2 park jet. It had fairly good yaw stability but then in a later version it incorporated fixed partially open rudders and yaw stability was noticably improved. I don't think Hepdog ever had any on his ,and his met it's end in a landing spin where ground contact resulted in a bounce back into the air and then a bad yaw into a spin. So they do help to keep it's nose towards the front.
The spin that crashes many of the Banana Hobby models seems to be from asymetrical thrust from the fans . Yours with 4 EDFs will be interesting.

Rodger is your 65" small one gonna be balsa or foam?
4 motor fans or 2 ?
Highly detailed or a prototype model A test bed ?
I'ld really love to see you get going on it and what you come up with.
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Old Jan 18, 2013, 05:04 PM
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Quote:
Originally Posted by Jetnfast View Post
In case anyone was wondering, on the real jet, they are called rudders or speedbrakes, since they function as both, but they are not drag rudders.


Here is a great video to show the rudders, break-rudders, drag rudders how ever you want to say it.


http://video.answers.com/learn-about...tics-161780473


Cheers
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Old Jan 18, 2013, 05:43 PM
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Quote:
Originally Posted by alpea 41 View Post
The spin that crashes many of the Banana Hobby models seems to be from asymetrical thrust from the fans . Yours with 4 EDFs will be interesting.
aaaaagghh, asymmetrical thrust, something else for me to worry about. I have read posts noting the BH planes shedding rotors or loosing thrust due to ESC problems. Hopefully I will avoid this as I have gone for quality fans and motors, perhas not as quality on the ESCs, but with 4 of everything, the chance of loosing one is 4 times that in a single plane.

I took it along to our club bring a model night a few days ago, everyone was very interested, the general consensus was that my mad streak continues.
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Old Jan 18, 2013, 05:57 PM
deltas are cool
AIR SALLY's Avatar
Tehachapi ,CA.
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im sure you are right about having them open more for flying with out a gyro .cant wait to see how this is going to fly.
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Old Jan 18, 2013, 06:11 PM
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Air-Jon's Avatar
CA
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837 Posts
The aileron to ruder mixing is cool. The "dihedral effect" of swept wings is what keeps pure wings (no vert stabs) poining forward...but they do wander a bit. Nice to have the rudders to and help out. It would be nice to have a rate gyro hooked to the rudders
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Old Jan 19, 2013, 04:35 AM
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As the rudders are on two seperate channels then I either need to put in two gyros or Y lead the rudders together and forego the easiness of opening or closing them both together. I am not averse to gyros, I use them in my twin scale planes such as the Mossie in my avatar, something I will keep in ming as they are relatively cheap now, two of them would not be such a problem.
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