trimming a flying wing.

Do you have some reflex in the elevons? You should have some, how much depends on what the kit maker recommends as a starting point. Also, you shouldn't need too much control throw, maybe 1/2" max with more up than down..

How do you have the mixing set up on the transmitter?

Flying wings normally need the ailerons kicked up in a "reflex" attitude. No idea how much to tell you on that plane, sorry. Experiment... Dr.1 Driver "There's a Hun in the sun!"

Ok,

I have approx 1" up and 1" down of control throws, I am flying with approx

3/4 up ALL the time to maintain level flight.

I am thinking that there is some sort of balance problem. I was hoping someone may have experienced a similar problem, and help with determining if it is a balance either being too far f/w or back to how it actually performs.

I guess that I will take some small weights with me and go and try and find out what the problems are!

Bob in Aus

standard Elevon mixing, (JR652 Tx)

Normally it need a max of 1/32" up to maintain altitude. So you hav to move your COG backwards. If it is 3/4" up then put it back about 1/2 ". Then in smaller steps. Do not try to turn yet in this trimming round. Just straight lines trying to keep altitude. Next to this you need speed to maintain altitude.Go full power and when launching it make sure that it has enough speed (do not thow it upwards but in a straight horizontal line.)

Bob, The "reflex" is normally seen as the elevons being viewed as UP when in the center of their travel.

Here is a way you should be able to begin to fix your problem. With the Tx and Rx ON (and motor disconnected!), move the elevator stick to the location you need to hold to get it straight and level with the plane on a table. Then while holding that elevator, turn off the RX. That should leave the elevons in the UP mode you need. Measure the distance from the table to the top edge of each elevon with the wing secured to the table by heavy (5 pound) weights. Then turn the RX and TX on for a moment making sure the elevator trim is in the center. Unscrew the servo wheels and move them until the top edge of the elevon is at the same distance above the table you measured earlier. Reinstall the screws and turn on the RX and TX to check that you still have equal travel in both directions on both surfaces because you may need to make an engineering change or two to the entire control system - that is no fun, but it should not be a stopper.Go test fly it and see if it is better or worse.

I have just managed to find someone else who has a couple of these wings and recommended a similar thing.

I will take a few small weights with me and do some experiments and see how it flies....

Thanks for the advice, I will let you know how it goes...

Bob in Aus

determining

Bob,

Your CG should be at 15% - 19% of MAC. I fly my wings at 17% of MAC.

To calculate where 17% MAC is on your wing, go here:

Where it says, "Enter %MAC Balance Point:" type in "17". This calculator will tell you how far back from the tip of the leading edge at the root your CG should be.

Feel free to email me direct to ask questions.

Jeff

Most "wings" will set up nicely if the aiklerons follow the bottom airfoil rather so as the wing takes on a "S" shape when viewed along the top of the wing. i.e. 1 to 2% reflex. For in depth info on thrust lines etc refer to =

scroll down to =

"Flying Wings (inc Delta), Flapping Wings or Ornithopter. [see also Gliders below.]"

Flying wings

Advanced Propulsion Home Page - JLN Labs Airfoil Design for Tailless Airplanes 1 Andy MacDonalds Flying Wing page. Airfoils for Flying Wings and Tailless Airplanes *** Correx Deltas - good plans & video. Flying Wings - Trimming Flying Wing Models - Basic design Foam Wing Construction Mugi Correx Combat Flying Wing Theoretical Flying wings TWITT- The Wing is the Thing Flying Wings : An Anthology Birdworks - inc the RC Gull

Flapping Wings - Ornithopter

Bionics and Evolutiontechnique CyBird (- with movies etc) Flapping Flight Links Flapping Flight - Ornithopters Multiwinglets_Rueckstromtaschen Ornithopters ParkHawk Robofalcon - Intercept technology Truefly - Flying by flapping wings The Flutterby

1900 Clark BiWing Ornithopter

Advanced Propulsion - JLN Labs

See aklso =

"Foam Wings, Warbirds, Foam Cutting Bows, Coroplast, PVC & SPAD. [see also Gliders below.]"

regards Alan T.

Alan's Hobby, Model & RC Links

I have found that at least on the flying wings I design, build and fly that in a pusher prop configuration, about 4 degrees of downthrust works great for me.

Flying wings sold on the market today require around 5 to 10 degrees of reflex in the elevons to fly properly. That is if the CG is around

17% MAC.

Jeff

I ran the numbers thru the calculator on the web page and they came up surprisingly at 135mm from the Le at chord.

The instructions come at 155mm, and from what others are saying, I am NOSE heavy.

I am thinking something is not right somewhere..... I have added some weight to the motor, and moved the COG back approx 10-15 mm but yet, have not had a chance to test fly and see if this is going in the right direction.

Below URL is the actual model, and the image showing instructions on the page is almost readable.

I even asked people at the shop about this, and they are saying MOVE COG BACK!. I just wanna get it to fly! Once I get it flying, It means 3 minutes to the park to have a fly rather than 30 minutes to the flying field, or 2 hours to my 10Acre property to fly!

I will put together a summary when I get this thing sorted out and actually flying!

Bob in Aus.

Bob,

I check the website with the instructions for your wing. Keep the CG as the instructions say...155 mm.

If the wing is stalling in the turns, if it requires significant elevon deflection just to fly level and the CG is set according to the instructions, it sounds like it is flying very slow. My wings require almost 3/4 of full deflection just before stall speed.

I wonder if your battery is delievering enough power to the motor. I wonder if the wing is so slow that it is flying just above stall speed.

Jeff

I have just been out and had a play.

The wind was a bit on the strong side, it was over 5 knots.

But I am pleased to say that for the most part I had some semblance of control.

I finally moved the Balance point back to approx 175mm - 5/8" behind recommended, and threw it into the air, It responded well to elevator controls, VERY twitchy on aileron control, but that may in fact have been in part to the wind today.

To launch, I was going to full throttle, then throwing almost vertical, then pushing the nose down to gain speed. Once I gained a bit of speed, then it seemed to fly reasonably ok in the conditions.

At the moment, I have approx 1/2 Oz of extra weight attached next to the motor. I will do some more test flights when there is no wind and work on removing this unnecessary burden.

Surprisingly, it is a rather quick plane! it seems to want to fly at around

15-20 mph!

This being the first wing I have flown, I just need to get some stick time on it, but at least I am 1 step in the right direction.

Thanks to all those who helped get this far.

Bob in Aus

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Glad to hear the wing flew better with a rearward CG. Flying wings and tailless models are kinda strange as far as CGs go. I think a lot of designers may suggest a slightly nose heavy CG just to ensure the thing will be stable in the air. I remember building a tailless model once that was an absolute beast to land unless it was landed "hot" (read flown in to touch down at flying speed) until I cut about 1 1/2" off the nose and brought the CG back. Don't worry -- you'll know when the CG gets too far back. They'll become very "interesting" to fly! :-)

Morris

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