Doodles with numbers - Brainstorming 'Nano Cub' details

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Floydr92

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Hi all. I've been doodling a while, my first doodles many years ago were overly complicated, different for the sake of being different and wholy impractical, but i think my latest doodle has some merit to be explored. I'd like to build it, but time will tell. life has a habit of getting in the way of these things.

Here's my doodle:
NanoCub - DRAFT.jpg
NanoCub v1.jpg

This thread is intended to be a discussion on the details. How things might work, and be constructed. Ironing out details, suggesting alterations etc. Please don't be that guy who says 'just build X, Y or Z' - they're pretty much the same.

Here are the intended categories:
FAR 103 - (Empty weight - 254lbs/115kg Stall - 24kts Max cruise - 55kts)
SSDR (UK) - (MTOW - 661lbs/300kg Stall - 35kts)
Sub 70kg (UK) - (Empty weight - 154lbs/70kg Stall - 20kts)


The wing is sized for the Sub 70kg category which allows it to meet all the above regulations with a MTOW of 170kg, however MTOW will be set at 300kg for the purposes of structures. (Even though you'd need to be a rather large pilot) because i can see this being on floats in the SSDR and possibly 103 category ;-)

Features i want:
Keep it in my garage or an enclosed trailer (Limits length to 16' wings folded)
wings fold for the purposes of above. Simple as possible rigging.
off airport fun - STOL - low and slow (big tyres, forgiving suspension, stable at low speeds)

Construction:
I'm going to concentrate on the smaller parts before the bigger parts. Weights of big things can be easily estimated or googled (Wings, fuselage, powerplant, fuel tank, tyres etc). It's the little bits that will add up which is why nothing is getting built until every component is modelled. The fuselage will be vacuum infused carbon sandwich. My weight estimation is based on 2x200gsm/6mm pvc foam/2x200gsm as the layup which comes to 12.06kg for the basic 'tub' excluding local reinforcements.
The wing i had intended to make rutan style with solid xps foam core due to the short chord/low volume/high AR. using the same layup schedule of 2x200gsm at +-45 on 32kg/m2 XPS core.

Wing (Left): Main wing: (Foam 9.35kg - skins 2.86kg - total 12.21kg) Slat: (Foam 0.72kg - skins 0.74kg - total 1.46kg) Flap: (Foam 0.42kg - skins 0.63kg - total 1.05kg) TOTAL 14.72Kg
Wing (Right): As Above (14.72kg)
Fuselage Tub: Internal skins 4.75kg - external skins 4.75kg - PVC core 2.56kg TOTAL 12.06kg

so with the big bits out the way we have a total of 41.5kg

Powerplant: I've been looking at the Bailey v5 Paramotor engine:

Engine weight 15.2kg (complete with all ancillaries)
Capacity 210cc
Power 20.5hp
Static Thrust (1.3m propeller) 60kg
Fuel consumption 2-3l/hr cruse
4 stroke, 2 valve, overhead camshaft.
Unique Bailey 'easy start' System.
Oil Capacity 500cc
Forced Air Cooling
CDI ignition

Add 10L of fuel (3hrs endurance) that's 7.7kg plus a tank, call it 8kg

That's us up to 64.7kg!

Still left we have landing gear, control system, struts, folding mechanisms, rudder and horizontal stab, cushion, windscreen, minimal avionics. Fair to say it's not going to meet 70kg empty weight at that, so can anything be changed? I could increase the flaperon chord and reduce the main wing chord to eat volume out the foam, as an example. reduce internal fuselage skin thickness, use less pvc foam (calculated for a solid layer but it would be smaller pieces on flat areas). But if its not going to be sub 70kg, then it would be interesting to see how close it could get.

I was dabbling around with landing gear geometry and construction ideas lastnight. I watched a video about 'forged' carbon fiber. basically compression moulded chopped fibers in 3d printed moulds. would need to do some testing first but i'll post a screenshot of my idea. uses carbon tubes (stock sizes) with the joints being this solid forged carbon. any hinge points are basically a brass tube wrapped in FG, squeezed into the bigger hole in the carbon part, then nylon washers either side so everything is electrically insulated and low friction. I might just go back to bungee cord but this one was to have 270mm shock springs to add dampening. 300mm travel and 4.2deg camber change over the full range. Maybe a sub 70kg version would need a solid gear with little wheels but that kind of defeats the goal.
NanoCub v3.jpg
NanoCub v3LG detail.jpg

So, let's throw some ideas around :)
 
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Floydr92

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I could increase the flaperon chord and reduce the main wing chord to eat volume out the foam, as an example.
Increasing the flaperon to approximately 20% chord reduces overall wing weight by 1.49kg per side (due to core volume).
reducing endurance to 2hrs saves 3.08kg in fuel. We're potentially down to 58.64kg for the 'big bits'
 

jedi

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I like the concept with the exception of flaperons. I think of it as a modern,single seat, Aeronca C-2. A great design goal.

IMHO - Low hanging fruit for weight savings is getting away from the solid core wing. Perhaps more of a conventional spar and rib of bonded foam with a foam cover to overlay the composite on. Aim to cut the core weight in half to 1/3 or more. There are some good techniques that have been used for that type of construction. How much would that help?

I have never been on board with the more or less profile fuselage designs. A triangular (vertex on top, flat on the bottom) can be much better strength to weight and not that much more to build.
 

AeroER

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After Floydr92's last thread, I made a crude weight estimate in an attempt to understand whether a 70kg 3 axis control airplane is possible.

The 20 knot stall speed is a considerable obstacle due to the wing area required. An airplane this light simply cannot tolerate anything but simplicity, and that partly means stripping away every part and detail that can't earn its way on to the airplane. Every feature past a full span slotted aileron for raising lift coefficient clobbers weight.

Then, there is the idea of drawing an airplane to weigh 70 kg, then sizing it as if it weighs 115 kg or 300 kg eliminates the possibility of hitting 70 kg before sharpening the first pencil.

I allocated 40 pounds for the engine and propeller in my estimate in order to get ~ 30 to 35 HP on the airplane to accommodate the high drag.

I allocated 1.5 gallons of fuel.

A 70 kg airplane might be possible, but the wing area will be huge compared to part 103 machines. Reducing Nz and placarding operation to near still air will likely be required.
 

Floydr92

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I like the concept with the exception of flaperons. I think of it as a modern,single seat, Aeronca C-2. A great design goal.

IMHO - Low hanging fruit for weight savings is getting away from the solid core wing. Perhaps more of a conventional spar and rib of bonded foam with a foam cover to overlay the composite on. Aim to cut the core weight in half to 1/3 or more. There are some good techniques that have been used for that type of construction. How much would that help?

I have never been on board with the more or less profile fuselage designs. A triangular (vertex on top, flat on the bottom) can be much better strength to weight and not that much more to build.

The idea of getting rid of the foam keeps coming back, i have no problems going for a moulded composite wing and that was actually what was putting me off the foam core was the ability to make two halves in female moulds leaving me a nice skin finish, but i kept coming back to the conclusion that it would be heavier after reading many arguments for and against foam core on small high aspect ratio wings. Without going and modelling all the ribs, drag braces, gussets etc i would know for sure. i also wonder if drag braces would be necessary with a stressed skin with 6mm foam core panels laminated in between ribs.

the fuselage does taper towards the top but i agree there would be benefits to increasing that taper. I'll think about it. i do still have to leave enough on the top that the two halves can be overlapped and glued together. i know i can do that with any taper angle really but it would change that glue joint from shear to tension, so it may not be quite as beneficial on a composite tub built this way.

flaperons... i hear you! i need the stall speed with smallest possible wing so that says to me full span slotted flaperons are the best bet - the slow handling and flaperons are probably not best suited though, so i'm going to split it into two flaperons with a simple mechanism to reduce the angle of the outboard one proportionally so it's always at a lower aoa especially at higher deflection. At cruise, wings level, they'll be in line with each other.
 

Floydr92

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After Floydr92's last thread, I made a crude weight estimate in an attempt to understand whether a 70kg 3 axis control airplane is possible.

The 20 knot stall speed is a considerable obstacle due to the wing area required. An airplane this light simply cannot tolerate anything but simplicity, and that partly means stripping away every part and detail that can't earn its way on to the airplane. Every feature past a full span slotted aileron for raising lift coefficient clobbers weight.

Then, there is the idea of drawing an airplane to weigh 70 kg, then sizing it as if it weighs 115 kg or 300 kg eliminates the possibility of hitting 70 kg before sharpening the first pencil.

I allocated 40 pounds for the engine and propeller in my estimate in order to get ~ 30 to 35 HP on the airplane to accommodate the high drag.

I allocated 1.5 gallons of fuel.

A 70 kg airplane might be possible, but the wing area will be huge compared to part 103 machines. Reducing Nz and placarding operation to near still air will likely be required.


70kg and 115kg are empty weights, 300kg is a MTOW. The sub 70kg 20kt limit is the hardest category, if that can be done (from a flight surfaces and sizing perspective) then it will automatically qualify for the other two categories. I'm not sizing flying surfaces for 300kg MTOW and 20kt stall. I'm making sure that the wings aren't going to fall off, or the gear wont collapse at 300kg plus a safety factor - I see that as good practice at a minimum.

VG's and fixed slats do a good job for their weight. The slat also reduces the volume of the main wing while maintaining overall camber and chord length, reducing overall weight. Just to prove it i done the numbers again - new wing with no fixed slat (maintaining the same overall chord) weighs 16.06kg and CLmax drops due to lower separation AOA so the wing needs to be bigger. overall a bad idea.

Brings me on to your next point. flying in perfect conditions with near still air - you're quite right there, which is why CL has a higher importance than just stall speed, and why high lift devices (be it as simple as possible) are necessary. It may be possible to build a massive wing with a really low wing loading and have it get off the ground at 20kts, but it will be unflyable. In summary increased CL leads to reduced wing area for same stall speed which results in higher wing loading which results in being blown around less.

feel free to share your calculations, i'd be interested to see your breakdown.
 

Victor Bravo

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If weight is a priority, then removing the wing slats will save worthwhile weight. When you are down into the "nano" speed range, you may well run out of pitch/yaw control, making the last little bit of AoA (from the slats) not worth their weight.

Also, one ounce of VG's has been shown to give you 90%+ of the STOL capability of your proposed 3KG of slats. That's about a gallon of fuel.

I very much like the Nano Cub concept overall.
 

TFF

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I don’t think you can dictate a look and make weight. It has to be shaped for 100% function. Beauty is in pulling it off. A powered Archaeopteryx is barely doable but you still pretty much have to step off a cliff to get into the air. It’s hard enough making a Cub shape fly at 115kg.

Struts are doing what with this style of construction? They are too far in for strut braced and should not be there for the cantilevered style wing you are making.

While narrow, I like your fuselage over the Affordaplanenothing to keep wagging fuselage.

Wheels and landing gear are weight. Designing at 70 kg, but you have landing gear that contributes nothing to strength. You have to subtract the engine weight, not contributing to strength. The Archaeopteryx claims 55 kg airframe so that is really about the target weight the airframe needs to be to add the other stuff.
 

Floydr92

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Struts are doing what with this style of construction? They are too far in for strut braced and should not be there for the cantilevered style wing you are making.

The wings fold on the struts, so yes they are strut braced. Creates a bit of a bending moment in the inboard portion due the outboard portion being larger, but the struts do still help significantly with structure and serve that second purpose of supporting the wing when folded
NanoCub wing fold2.jpg
 

Floydr92

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If weight is a priority, then removing the wing slats will save worthwhile weight. When you are down into the "nano" speed range, you may well run out of pitch/yaw control, making the last little bit of AoA (from the slats) not worth their weight.

Also, one ounce of VG's has been shown to give you 90%+ of the STOL capability of your proposed 3KG of slats. That's about a gallon of fuel.

I very much like the Nano Cub concept overall.

Think of it as 'foam core lightening'...

noslats.png

granted i haven't yet worked out the weight of the brackets for joining the slat to the main wing, but excluding those, blue outline wing with foam core and skins weighs more than the original outline with slat by about 1.34kg per side. a little more skin weight and a little less foam weight. Just taking the slat off the front reduces effective wing area by about 9%
 

TFF

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But are you giving up free strength? Ground handling items for wing folding can stay on the ground. As stiff as the outboard portion of the wing already is, it’s overkill between the struts, which means it weighs too much there. The strength of the struts built into the wing with this type of construction makes more sense. An open structure makes more sense with struts. What G loading are you designing to? Size of spar caps and web?
 

Floydr92

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But are you giving up free strength? Ground handling items for wing folding can stay on the ground. As stiff as the outboard portion of the wing already is, it’s overkill between the struts, which means it weighs too much there. The strength of the struts built into the wing with this type of construction makes more sense. An open structure makes more sense with struts. What G loading are you designing to? Size of spar caps and web?
spar caps and web are TLAR for now until i've confirmed build method. spending a bit more time on the smaller components at the moment. my concern with cantilevered attaching to a 200mm wide fuselage is just that. the wing would have to carry through to the other wing which seems to me to add complexity that could be achieved with 2 pin joints at the wing root to fuselage and a strut, pin jointed at both ends. I will look into this though and calculate exactly what would be required. It might be a case of weighing up a hollow strut braced wing structure versus a cantilevered solid foam structure making the assumption these pairs match up better. Maybe I like triangles too much 😂
I think +4 -2 is probably a good design load factor with a margin in there for actual values vs data sheet values.
 

AeroER

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70kg and 115kg are empty weights, 300kg is a MTOW. The sub 70kg 20kt limit is the hardest category, if that can be done (from a flight surfaces and sizing perspective) then it will automatically qualify for the other two categories. I'm not sizing flying surfaces for 300kg MTOW and 20kt stall. I'm making sure that the wings aren't going to fall off, or the gear wont collapse at 300kg plus a safety factor - I see that as good practice at a minimum.

VG's and fixed slats do a good job for their weight. The slat also reduces the volume of the main wing while maintaining overall camber and chord length, reducing overall weight. Just to prove it i done the numbers again - new wing with no fixed slat (maintaining the same overall chord) weighs 16.06kg and CLmax drops due to lower separation AOA so the wing needs to be bigger. overall a bad idea.

Brings me on to your next point. flying in perfect conditions with near still air - you're quite right there, which is why CL has a higher importance than just stall speed, and why high lift devices (be it as simple as possible) are necessary. It may be possible to build a massive wing with a really low wing loading and have it get off the ground at 20kts, but it will be unflyable. In summary increased CL leads to reduced wing area for same stall speed which results in higher wing loading which results in being blown around less.

feel free to share your calculations, i'd be interested to see your breakdown.

They're simplistic, I assumed a weight fraction for the wing and the weight allotments above to find what was left over for everything else.

I think that weight is so critical that preliminary sizing is required to get usable numbers. And I don't believe that the structure can be too simple, for example constant thickness spar webs or tube spars.

I don't believe a 70 kg 3 axis airplane is impossible to build, or easy to build.
 
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rotax618

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I originally had slats on my ICP Savannah, I removed then and replaced them with VGs, the stall went up 2 knots and the cruise by 12knots. Slats are completely unnecessary on a very light aircraft, it is dubious that you will be able to attain the AOA on landing with the short UC to make them worthwhile, if you can afford to add that weight, increase the chord and add VGs it will be a greater gain in lowering Stall and landing speeds.
I agree with AeroER, it will be nigh impossible to build your proposed airplane at 70kg. Your design has merit and my comments are in no way critical of the overall idea. As Henry Mignet said about building materials, “if you throw it up and it falls down - it is too heavy”
 

Floydr92

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And I don't believe that the structure can be too simple, for example constant thickness spar webs or tube spars.

I totally agree with you from an intuitive standpoint, but you'll know as well as me the number of people who are smarter than me who say foam core is lighter than internal structure for anything below X chord (i think 4ft was the ballpark). I'm open to drafting out a new internal structure, doing away with the foam and working out bit by bit what it's going to weigh. at a minimum though it will add an extra skin of carbon before any ribs are added. I do wonder if the Peter scripol hollowed out foam core has merit in this application. I'd need to do FEA at a minimum.
 

AeroER

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I totally agree with you from an intuitive standpoint, but you'll know as well as me the number of people who are smarter than me who say foam core is lighter than internal structure for anything below X chord (i think 4ft was the ballpark). I'm open to drafting out a new internal structure, doing away with the foam and working out bit by bit what it's going to weigh. at a minimum though it will add an extra skin of carbon before any ribs are added. I do wonder if the Peter scripol hollowed out foam core has merit in this application. I'd need to do FEA at a minimum.

The first details to understand in Sripol's hollowed cores are the shear load, the adherend (foam) shear strength, and the bond line strength at the location of the greatest shear stress across the section.

I like the idea. I can't get around the weight of covering the outer moldline of the wing, except I can guarantee I would never use Monokote.

I also believe the maximum Nz will need to be reduced. Maybe to 3g's with the bank angle placarded to 60 degrees. That gives a 10 degree cushion plus the factor of safety, along with the placard to flying in low to no turbulence.

The landing gear problem has already been pointed out. Put the lightest wheel and tire on the centerline and take off with a wing runner or tiny wing tip wheels, it's really not a big deal, the wings will level up almost instantly.

Are you considering an optimistic maximum lift coefficient?

The Sandlin Bloop idea is a good place to start, with two thirds of the weight carved out. Maybe not so attractive with that complication.
 

WonderousMountain

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I agree with post #15, this current wing build is hard to get behind,
it would be good to see a few stiffening members here in there so
unless you are determined to be a shell structures shifu.
 

rotax618

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What you don’t get at 70kg is an airplane that is durable enough to withstand normal handling ie. taxyiing and flight in “normal conditions” with a standard weight pilot. Here in Australia we have a category for single seat amateur designed and built aircraft known as 95.10, it allows up to 300kg T.O.W. I have built a number of aircraft that were registered in that category over the years, nearly all of them were durable enough to be still flying, originally the rules required an empty weight of not more than 150kg and not greater than 30kg/sqmetre wing loading at gross TOW, I can tell you it was not easy to build a useful sport single seater at that weight - it may be possible using exotic materials, but if you are talking aluminium, wood and foam its going to be difficult to get down to 70kg.
 

AeroER

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So someone help me understand what specific benefit, or major breakthrough, happens when you get down to 70 KG that you don't get with SSDR ???

No licensing required in the UK.

I believe the vehicle is subject to approval by the government or a proxy.

I answered my question about the maximum lift coefficient. In order to meet the 20 knot stall speed at 365 pounds gross weight (70 kg + my clothed weight) the lift coefficient required is 5 for the geometry in the sketch.

Please show us your source.
 
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