• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Help improve my crazy design

#1
I'm looking for some input, critique and suggestions on a design idea -

The plane's target weight with a GoPro Hero 4, a 3S 3,000mAh battery and supporting electronics is under 45oz

Construction will be a 3D printed frame of carbon fiber filled nylon - with two 7.5mm CF tubes through the wings - main sections will be printed in 500mm long sections. Tail surfaces are printed as single pieces.

Wing is a S1210 foil with no dihedral or control surfaces. There are small Hoerner style wing tips. Wingspan is 1.7M with a chord of 255mm - Wing will be covered with film. Projected wing weight based on partial builds is 650g. approx 4.65 sqft

The tail surfaces are NACA 0015 and all fully articulated - so little actual motion needed - maybe too much control but I want to fly s l o w l y . Think of my Bix3 as "fast".

Body tube is CF 30mm tube - servos will be fit in the front of the CF tube.

Nose pod is for all electronics and battery to try and move the CG forward enough - it can be easily moved or extended - it may be allowed to pivot to remain "down" even while the plane is banked or turning.

Motor is currently intended to be a D2836 1100KV (because I have one)

My goal is something very slow that can stay aloft for an extended time but turn well enough to do a figure eight pattern in as little as a football field - the elevator could be elevons but there seems to be some difference of opinion on elevons with a long straight wing (even w/o any dihedral)

I'm trying to build a camera platform that you can almost "take for a walk with you" but my initial goal isn't FPV - just line of sight.

This is an experiment in designing 3D printable parts (in Sketchup) and printing frames, not complete surfaced wings, to keep weight down w/o reverting to balsa.

The high mounted motor is an attempt to borrow a bush plane concept of attaching part of the flow to the top of the wing (even before you start moving).

Thanks!

Mark

SLOWFLY 3 iso.jpg SLOWFLY 3 Top.jpg SLOWFLY 3 front.jpg
 

Fluburtur

Cardboard Boy
#2
That looks like a pretty good concept and should work quite well but without ailerons you might still want some dihedral, im not sure having the weight under will be enough to balance it.

Can't wait to see it!
 

rockyboy

Skill Collector
Mentor
#3
Looks pretty good, but I'd echo the concern of going with straight wing but no ailerons. If you do want to keep it 3 channel control, and don't want to crack the wing in the middle for dihedral, consider adding an upward angled panel at the outside of the wings to help give you the stability while retaining strength across the center of the wing where the forces are greatest.
 

JimCR120

Got Lobstah?
Site Moderator
#4
Hello Mark.
You jumped in with a nicely detailed post and already getting responses.

How about a bit more about yourself. Where in the world do you fly? How long have you been in the hobby and how did you get interested?

Welcome to the forum.
—Jim
 

AkimboGlueGuns

Biplane Guy
Mentor
#5
You're definitely going to want some dihedral. The weight blow the wing will help keep you stable, but it won't keep you coordinated in rudder only turns, and it will start to slip. Ailerons will certainly help if you don't want to do dihedral, but you will still lose some stability in that flat wing.
 

JUSS10

I like Biplanes
#6
Cool idea. Do you have much experience printing with nylon? It can be very difficult to prevent warping and in my experience bed adhesion is not very good. Is there a reason to use the carbon fill? I've never understood how carbon strands that are no longer than the nozzles diameter can really add that much strength vs just using a filament with good layer bonding properties.

Very cool design though! And as all others stated, dihedral will be your friend here.

Good luck!

Justin
 
#7
I'd also suggest a wing either a bit in the style of the KfM3P wing for a blu baby (see below; without the KfM steps, naturally) or if you want something a bit more sleek looking and aerodynamic, something like a MPX Easystar wing. Both solutions compensate nicely for the lack of center dihedral, giving that little bit of roll neccesary to get a nice sort of coordinated-ish turn out of adding sideslip with the rudder, and still lets you have the simpler, stronger, straight wing on most of the span.


32_Old_Yeller_test.jpg
easy-star-ii-just-arrived.jpg
 
Last edited:
#8
All,

Thanks for the input and suggestions - I am considering all of the ideas carefully -

One thing that I am struggling to understand is what exactly constitutes a "high aspect ratio" wing - the reading I have done suggests that at some point, the length of a straight wing itself provides a "semi-coordinated" turn, as the speed differential is great enough between the two wing tips so as to result in a aileron like tip w/o any flight control - AND I can keep the elevator split as elevons if needed - I'm not afraid of channel count or servos and linkages.

I think that the body tube is torsionally stiff enough to muscle the wing over from the tail - although the long wing could result in the same issue as elevons with a dihedral in the main wing - where supposedly, the nose and tail are trying to do opposite things and fight each other.

The wing tips are also printed - they can be easily modified and replaced - so adding a winglet for stability or efficiency is very much a part of the experimental plan.

The Hoerner tips seem to be well liked for slow and high angle of attack - so I thought I would start there.

I specifically chose not to explore slats or slotted flaps, as I want slow to be the full time "mode" not a landing and take off function - although flaps/spoilers/airbrakes might become a necessary "wind evasion" requirement to actually get the plane to sink when necessary.

Remember that my target flight speed is just north of a stall - but in a big enough plane to carry a GoPro but act more like an indoor flyer.


My RC past started with a short lived 0.49 string control plane at about age 12 - with no experience or any connection to others in the sport - just the instruction in the box from Cox -

I didn't lose any fingers, I didn't destroy any property, I discovered that the wing wanted to fly at bicycle speeds while riding to a parking lot big enough to fly. I learned that brittle plastic isn't an ideal trainer material, written instructions are a little less than comprehensive and keeping a plane attached with a string or two has some advantages - including keeping most of the parts in an easily gathered circle.

I returned to kites and stunt kites to lick my wounds and contemplate how and why anyone would want to invest ten times more money in a plane that wasn't attached to you, took weeks or months to build and wasn't likely going to survive a crash much better.

I continued to bike out to Pratt Wayne Woods and watch the flying field there (Chicago Suburbs), where some clearly more experienced pilots flew some significant planes but they all drove to the field - and had motors to start their engines - and more than one plane each - my overall take away was two-fold - this required disposable cash in larger sums than lawn mowing AND everything flew really fast -

Somewhere around age 24-25, I built a Drifter II and learned to fly it - hi-start took a little time to understand but the plane flew for extended amounts of time and with proportional switched off just before landing, I could stall it in the air and just reach out and grab it at the end of a flight - but alas, that plane was very light and couldn't penetrate a headwind very well - it met its match and got blown down range until it met an Oak - but I was hooked on slower flight and longer time aloft.

Major gap - my uncle sent me a Bix3 and some extra parts - at age 53, I was doing RC again... and I had the most fun flying the Bix in nearly stalled conditions, not usually more than 50 feet off the ground and it didn't always respond quite promptly enough for the space at hand.

THIS TIME, I had the web and Google and could query everything running through my head and try to understand exactly what was happening and how to correct, fix or modify to suit my style.

Watching bush planes, I decided I wanted to have an RC bush plane - specifically a STOL style capable of ridiculously odd behavior and if a real people carrying "aircraft" could land with a 10'6" roll out (the current record) I needed to study what they were doing.

This is an attempt at a very low speed/high lift airfoil, flying control surfaces and an "easy" build - I already had the 3D printer -

I have a build volume on my printer of 300mm x 300mm x 600mm - so more than average. Skinned wings are really easy and fascinating to print - like the 3DLabs planes and I started the design there - but I just couldn't get the wing loading and total weight down - they were going to fly too fast. It was difficult to get a wing down to 1kg/meter and even then the area was too small to result in low loading.

These parts are printed with one shell and NO fill - so the structure is like little hollow box beams and the angles allow them to be printed vertically without any supports at all - so very clean. The carbon filled nylon material is remarkably tough and light. Balsa is 0.1-0.2g/cc and this plastic is 1.1g/cc - so it has to be used sparingly and the DF spars are 19g each. A 500mm section of wing prints in about 16 hours.
 
#9
CF Nylon

Justin,

I have some experience with printing Nylon and have tried several products - the best I have found so far is CF Nylon from 3DXtech.

Adhesion is troublesome at times - a Kapton bed surface at 105C is working well for me and is obviously VERY important when you are printing something as tall and thin as these wing sections, but its working so far.

Layer adhesion with Nylon seems to be significantly better than anything else I have printed with so far and having an enclosed printer I'm sure helps - I have a Raise3D N2plus -

CF filled seems to be a very controversial topic - and I understand the points on all sides - I seriously considered a MarkForged machine with the continuous fiber capability until I fully understood the limitations of placing the fiber - not to mention the cost of materials.

The filled material warps less and is MUCH stiffer than the same nylon w/o fill - I've printed sample parts out of both materials from the same manufacturer just to compare and its quite remarkable how much lighter and stiffer the filled nylon is - I wouldn't have remained skeptical part from having both parts in hand.

As for tough - its amazingly tough. I can stand on these sections without crushing them.

_DSC9501.JPG

These were all developmental steps before determining I needed to skin the wing with film for this plane - these samples were all printable but the 3DLabs style fill was the lightest but also has the most surface roughness on the flight surface. With a design for two shells, it could be perfectly smooth.

They have a very "magic" process - I believe that you can't actually get there without editing and controlling the g-code in more detail than most slicing software can - their stuff is really amazing.
 
#10
looks a lot like a Bix...

The lower plane - the EasyStar? - looks a lot like the Bix 3 (which I do have and like).

I agree that I may need some dihedral or some form of false dihedral from winglets to get a "neat" turn and (unfortunately) I don't really care a lot about the appearance but smooth is good for flow - which hopefully yields lift at low speeds...

I want to fly much slower than the Bix3...
 
#11
Just for tickles and grins, have you given any thought to the very early aircraft, such as the 1909 Antoinette or the Bleriot? Granted they were very draggy birds with all the wires and struts, but their top speed was probably slower than a Cessna 150's stall speed. Just a thought.
 
#12
One thing that I am struggling to understand is what exactly constitutes a "high aspect ratio" wing
Aspect ratio is simple enough to explain, it is simply the wingspan divided by the mean chord. So a short and wide wing has a low aspect ratio, and a long and narrow one has a high aspect ratio. In general, and given the same basic airfoil, a high aspect ratio wing will usually have less drag per amount of lift generated, i.e. be more efficient, than a low aspect one.
In itself aspect ratio generally has absolutely nothing to do with Lateral (=Roll) stability, however.

The lower plane - the EasyStar? - looks a lot like the Bix 3 (which I do have and like).
The Multiplex Easystar is basically the (closing on 20 year old) plane all Bixlers and other similar ARF planes are (Chinese?) clones of:
http://diydrones.com/profiles/blogs/roundupreview-of-all-the

.....not saying that some of the clones didn't add any new ideas or improvements. The original one came with a brushed speed 400 with a rubbery Günther 6x4 prop and was flown on a rediculously heavy NiCd battery pack. The Easystar II did add a brushless driveline and I think also an improvement in the foam strength. Ailerons is a generally a clone thing on these though.

This wing can be fairly easily be made to fly much slower than your Bixxler typically does - You just have to keep the wing loading very low. Be aware though, that with low speeds, your control surface authority will fall considerably (It's basically proportional to the speed squared at low speeds.) You may need to increase your control surface area, dependent on just how slow you want to go.
 
Last edited:
#13
Just for tickles and grins, have you given any thought to the very early aircraft, such as the 1909 Antoinette or the Bleriot? Granted they were very draggy birds with all the wires and struts, but their top speed was probably slower than a Cessna 150's stall speed. Just a thought.
Take that to the extreme and you will most likely end up somewhere near this:
 
#14
DKchris,

Thanks for the input on aspect ratio - I was specifically looking for the point at which a straight wing of "high aspect ratio" starts to provide a coordinated turn on its own w/o ailerons (or elevons) just because of the differential in flight speed - seems like a "soft" definition and probably somewhat dependent on the linearity of lift vs speed for a specific airfoil - also wouldn't help with stability under any conditions - but it also seems like you could build a wing with a terminal tip stall brought on by any turn - which wouldn't make my design very effective!

I love watching the slow indoor flyers - I wonder how many of those flying in formation would be required to carry a GoPro?

and yes - I have seen the RC helium blimps - apart from their susceptibility to wind, that would be perfect for me - no stalls, spins or sloppy turns - just mushing through the gaseous air slush.

Interesting to hear more background on the Easystar - I was curious if there was a "root" to the whole series of planes that seem to share some of the same features.

As for control authority at low speeds - the Bix3 will without a doubt fly slower than tail surface "authority speed" ;-o

I did think about just increasing the control areas enough to give it good control much closer to stall speed but some radioactive bug must have bit me and made me think I could just design a purpose built plane -

So far, I think I am abandoning ALL of the wind structure designs I have tested so far - they just don't yield the strength/weight compromise I want .

The next experiment is CF Nylon ribs, leading edge and trailing edge all spaced out on CF tubes - still the same aggressive airfoil and straight wing but much more conventional looking in structure - I would love to have a non-balsa 1.7M wing with a weight around 400g - aiming for "less than EPO but more than balsa" range and the very thin trailing edge seems like it would be very vulnerable in foam.

Mark
 
#15
........I was specifically looking for the point at which a straight wing of "high aspect ratio" starts to provide a coordinated turn on its own w/o ailerons (or elevons) just because of the differential in flight speed - seems like a "soft" definition and probably somewhat dependent on the linearity of lift vs speed for a specific airfoil - also wouldn't help with stability under any conditions - but it also seems like you could build a wing with a terminal tip stall brought on by any turn - which wouldn't make my design very effective!
Ahem......as far i've been taught, if a wing is perfectly straight, doesn't have any dihedral or any aerodynamic sort of built in arrow shape or sweep effect, regardless of the aspect ratio it should not generate roll if you input sideslip. It should just stay in the sideslip, which just reduces lift equally on both wings. If the airfoil is constant along the wing, it's effect is evened out. The wing halves are both moving at the same speed, and both are at the same angle to their path through the air, which is now just not othorgonal.
(Note however that arrowshape and sweep effect induces both longtitudinal and lateral stability, and will also induce the desired roll in the sideslipped wing. Pure di-/polyhedral without arrowshape or sweep only induces lateral stability, but does generate the same desired roll effect in sideslip... and more of it per degree of deviation from straight wing, compared to sweep or arrowshape effect)

Perfectly aerodynamically straight Wings are however near impossible to build, and if one would try you would in reality end up with a wing with either a slight amount of positive or negative dihedral effect, and some sort of sweep effect, either positive or negative. Impossible to predict which it will be.
If the majority of the added effects are negative, adding sideslip will put the plane in a situation where it will likely slowly roll in the wrong direction and do so in a self-amplifying manner, ending in an out of control spin. Not desirable.

Which is why modelers and fullsize plane builders alike tend to add a few degrees of dihedral and, if it makes sense, also an amount of sweep and/or arrowshape, just to be on the "long end" of the lever with regard to securing positive stability.

On the other hand, if you'd want to make an aircraft very agile, making it borderline unstable would theoretically help a lot with that......given you build in other means of keeping it within control, like effective ailerons, electronic regulation, gyros etc. .....which is how they made the F-16 and many other fighter planes so great. For us RC'ers , having ailerons does most of the job though. Moving just a tad back from the stability limit again usually brings the rest.

PS: There IS an effect that could cause a slight degree of roll in sideslip, even with this theoretical perfectly straight wing: If the part of a given fuse forward of the wing obstructs the airflow over the wing in sideslip, the obstructed side should loose a bit of lift. Your design won't do this, as the forward fuse section is out of the wings airflow. And the effect also wears off as the wingspan to forward fuse section length ratio increases (the influenced percentage of the entire wing reduces), which usually is what tends to happen if one chooses to take a given plane construction to higher aspect ratios (If area stays constant for unchanged wing loading, chord must drop and span increase.)
 
Last edited:
#16
DKchris -

you get all the bonus points and thank you's for the day - THAT explanation makes sense to me -

I had been reading about various bush planes and run across the dubious statement from a seemingly serious source - but, especially taking the Fuse into consideration - it makes sense of the comment - it would have been true for their design but probably not for mine.

As I am printing parts, I can introduce a little dihedral and a little sweep with as little as a few mouse clicks - so it seems "responsible" to add a little of both and not rely entirely on a gyro -

I was aware that some of the "best" military designs are completely dependent on "assistance" to be pilot friendly and it doesn't come as a standard switch on any of the RC radio's Ive seen - although the gyros are awfully close.

All attempts to print a full structure or a skinned structure are failing to meet my wing weight goals and I am now working on what looks like a more traditional balsa wing but with printed ribs and edges - I can't imagine a way to build the very fine trailing edge of this airfoil directly out of balsa - it would be too thin and too vulnerable -

Thanks!