FPV cruiser wing

[Fluburtur]

Less sweep, less chord, more efficiency! Or at least that's the goal.

For about a month I've been thinking about making another 1.2 meter flying wing for fpv, the old one that we killed wasn't very good because it was slow and not efficient because the cutting of the wings was pretty bad, for the past few weeks the store didn't have foam so I had to wait until today to start building, here are the specs of the plane so far:
Airfoil: PW51
Sweep: 20°
Root: 29cm
Tip:19cm

Unlike my previous wings, this one has no washout since the the PW51 is supposed to work without (neutral pitching moment) and it has also less sweep, 20° vs 30 for my old ones. It also has a thinner chord than my old 1.2m wing, as a matter of fact it has the same as my 80cm wings.
I might build many of this model so I will probably experiment with different amounts of washout, also I will design a 3d printed pod to hold the electronics and a pan system for the fpv camera. I mentioned I want to chase a paramotor with this one so I need to be able to look around.
As for propulsion, it will use a 1400kv motor with 8x4 prop and 2200mah 3s lipo. It should give a pretty decent efficiency and flight time given it is a wing and I will try to refine the aerodynamics as much as possible.

Photos of the build so far:

 

[Morgan]

Looking forward to seeing this finished!!

 

[Fluburtur]

Proto 1 is almost finished, with some luck I will be able to maiden it today.
It doesn't have the full 3d printed pod because I was lazy but it does have a 3d printed motor mount and spinner!

I tested the spinner and it seems to hold up fine but I have no idea how it will look after several minutes of flying.

Also it doesn't have the video gear on yet so I will add some nose weight for this flight, I expected it having less sweep would mean it would be easier to get nose heavy but apparently not, but I guess the big motor mount influences that a lot. On the version with 3d printed pod it will poke out the front so it will be easier.

 

[Fluburtur]

Back from the maiden, it was mostly a success!

The plane was flexing a lot because no spar, I guess that was to be expected but at least it will be easy to fix.
The spinner worked fine for a few minutes but then it exploded, the "skirt" actually flew off so I will try to fix that.

When it broke it also made the motor vibrate a lot (but that didn't show up in the video, yay flexy wings?) and it ripped off half the mounting screws so it was left holding by only one that was almost out. If the motor completely detached from the plane it wouldn't be a big problem however because it would be held by the wires and the inside of the mount, even after breaking if flew fine.

But the flying itself was fine, didn't need much power to fly and had a very good glide slope. Once the issues are fixed it will make a very good fpv plane!

 

[Hai-Lee]

Looks nice! Pity about the motor problems but then you will fix them for the next flight I am sure.

I am posting as to you washout statements. With a flying wing if the CG is set correctly or even slightly forward of the ideal position a stall is impossible. Without a tail the aerodynamic lift balance on each wing determines the ability to "Nose up" or remain held "nose up".

When travelling too slow the airflow can become insufficient to maintain lift and then the wing will either just loose height, (sink), in a controlled manner or it will drop the nose of the wing which increases the speed and the lift which raises the nose, (a Nodding action).

Only when the CG is too far aft does the airflow actually separate from the wing causing a wing to drop and then as the craft rotates and builds up speed towards the ground it regains proper airflow and is controllable again, (in minor cases it seems that the wing is wandering all over the sky!

Washout is definitely necessary on conventional, (tailed) aircraft but on wings and even Canards it is just a section of lesser or no lift at the wing tips. Fitting washout will not adversely effect the handling of your wing but I do question is it really is necessary. Washout can even produce a somewhat variable centre of lift based upon AoA and make pitch movements less than linear.

Just a few thoughts!

Have fun!

 

[Fluburtur]

I found my wings with washout need no up trim, even some down trim in some cases. And looking at the numbers of the airfoils I use it looks like the washout angle also reduces the drag a bit, but as stated by Peter Wick himself the PW51 airfoil has a neutral pitching moment so it shouldn't need any up trim or washout to be stable.
If wings with no washout work well enough it will almost make my life simpler, I wanted to build a rotary cutter to make cutting wings easier.
I will build next one with washout and see how it compares in the handling and low speed performances.

 

[Hai-Lee]

I love simple wings and washout was long discontinued in my designs as being unnecessary as long as the CG is correct or forward. The reduction in drag is due to the less lift induced drag at the outer wing. a similar drag and lift can be obtained from wings with no washout at slightly smaller span.

Your wingtip plates/winglets are HUGE for the span and do not need to be quite as tall and are equally effective if just fitted from the 50% cord to the 100% cord points at the tip or even with a minor amount of overhang. If chasing efficiency all drag should be considered but then the drag figure is relatively small.

My next KFM design wil be of similar size and was ordered cold without any plans by someone who has a similar application in mind.

As I am building from cut slabs of FB with some paper removed, (to save weight), I will be inserting strips of balsa in slits cut into the FB to improve or should I say remove wing flex.

I truly envy your power pod arrangement!

Have fun!

 

[Fluburtur]

If you think the winglets are huge you should look at my previous wings, especially the BigS!
Those ones are tiny for my standards (also I cut them and slapped them on a few minutes before going to fly so they might not be optimal)

 

[Hai-Lee]

If I have offended you I apologize but I was trying to assist you.

Winglets are a feature that almost needs its own area of study and the BIG boys have spent Billions trying to get them right.

Apart from their function in directional stability they have a role in wing efficiency, Drag minimisation, and of course the reduction of wing tip vortices.

Have fun!

 

[Jetcrafter_2000]

Wow, this thing looks great!

 

[Fluburtur]

No offense taken, as a matter of fact I was thinking into putting the motor on a yaw vectoring mount on one of my wings for good yaw control and flat spins but it would mean that it would be unstable with no power.
I will be changing the winglets for smaller ones and see how it works anyways, I did say that I want to optimize this plane.

 

[Hai-Lee]

One method of instituting Yaw control without using a central and trailing rudder is to use a pair of "Drag" rudders.

A drag rudder is basically a winglet which is hinged on the rear portion in a similar manner as a rudder BUT to turn the trailing portion is hinged outwards on the side which is to be the side closest to the centre of the turn. (The rudder like winglet trailing Portion NEVER hinges inboard for stability reasons.

They can be fitted using a single centrally mounted servo using a pull cord from the servo to the pusher mechanism. The pusher mechanism is just a push pin, a small spring, (from a pen), and a small plate for the spring to push/anchor against. The winglet is cut with a hinge, (so that the trailing portion can pivot outwards), But extends vertically above and below the actual wing for the the end part of the wing to act as a limit on the winglet trailing portion hinging inwards. All up weight can be as little as a gram or 2.

Have fun!

 

[Fluburtur]

I have been thinking of making that and I guess I could come up with something I could 3d print but I want to keep this plane simple for now, but I will try that for sure at one point.

 

[Hai-Lee]

Sweet! If you later would like to have me rough out the design I was talking about just let me know!

have fun!

 

[Fluburtur]

I glued the spar inside and will maybe put a fpv system in the plane tomorrow, then I will be able to do some proper flight testing. I would like to get at least 30 minutes of flight time from this plane, this can I can put it on my friend's radio and do more formation fpv.