A really (too?) small & light micro-bipe STOL project (hybrid maybe)

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Xanadrone

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Nov 24, 2011
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Bucharest Romania
Yes, the latest LiFePo4 technology already allows a good "energetic density" at more abordable prices than the Li-Ion ones and without the risk of firecrackers - ex:
https://www.ev-power.eu/LiFePO4-special-cells/Lithium-Iron-LiFePO4-Battery-Cell-LFP-3-2V-72AH.html

That means 0,230 kWh for 1.75 kg weight and 90 USD (without taxes) - say 4 lbs per unit including connectors.
Practically speaking, for an [ultra]light E-experimental plane, a pack of 15 would assure 3,5 kWh at 48V (13S for RC-freaks ;) ) and a max. discharge rate of 360 amps (5C), weighting 27 kgs (60 lbs) and for "just" about 1.5K USD.

Two such packs (7 kWh, 54kgs/120lbs) methinks would be just fine for a small one place E-bimotor to fly one hour at 50-60% power - and even double for a glider-style aircraft with good L/D.
An unlimited number of other combinations would certainly be possible for those unhappy with just 14-15 kW onboard (18-20 HP), such as the use of only one pack for take-off E-power boost and/or emergency use, along with a small IC engine for the level flight. Or other hybrid/small generator solutions etc. etc.

Btw, the favourable evolution of battery tech seems to be accelerating, and this made me not only sketch, but also calculate a few versions of some viable, simple and most of all affordable E-microlight. One without cross-country attributes for sure (for the time being at least), but perfect for cheapo leisure flights because the +2,000 recharge cycles of the new LiFePo4's would compensate rapidly the batteries cost.

So, I'll be back soon with the final version (3-views + performance estimations) for your precious aid - meaning constructive criticism, with or without 437 posts about some wrong angle of the winglets - luckilly it doesn't have any. :gig:
Just a few words for now: I tried to imagine an even smaller Cri-Cri, in biplane form (Mitja would say... topspeedish-small at just 9 ft. 6 in. long), but also less complex, expensive and time-consuming to build.

...Woud it fly though, despite its span of 16 ft.? And how good? - This would be the major point of debate, being a real theoretical nightmare at a first glance (prone position of the pilot, sesquiplane, inverted V-tail... or sort of, electric and/or IC-propulsion etc. etc.)

P.S: The pilot in the scale-image is... sort of me also, being 30 years younger and - more important - 30 lbs lighter :gig: than the actual Me.

DSCF1353.jpg
 

cluttonfred

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It's a neat concept, but you are right that it's a lot more complex than it needs to be. At first glance I'd say the wingtip "feathers" are unnecessary and the "reverse tricycle" landing gear would be very short-coupled and twitchy on the ground. You might want to check out the Hovey Whing Ding, not as an actual project tackle since it has a reputation as a fairly complex build despite the size, but for some idea that are proven to work. A simpler design inspired by the Hovey Wing ding with a modern paramotor engine and your twin tails might work well.

hovey-wing-ding.jpg
 

Xanadrone

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Nov 24, 2011
Messages
195
Location
Bucharest Romania
First of all thanks for your input! I was initially tempted to post this idea in the Motorcycle Of The Air thread, or Flying With 14 HP (only in level flight though), or, or..., but I thought finally that it deserved a separate topic, because it includes some new and combined solutions serving the main interest of it - and the point of start for me: to maximize the... minimalising simplicity and affordability of the flight for a single guy (it can be married also, but some would say not.) :grin:
More seriously speaking, this micro-bipe is intended to be a ludic (and cheap to build) object and not an utilitarian flying device - baptizable as an air-toy methinks, so I am waiting also for some possible name proposals from you, my already imaginated names being a bit too laughable for now - thats why I do not mention them.

Anyway, until refining the other 2 views of my micro-bipe Ride-And-Glide project (it might take a couple of weeks), it is necessary to clarify some basic details to correct a few explainable confusions:

- The landing gear would be a classic tail-dragger and not inverted, with two fully shock-absorbed 25 cm (10 inches) main wheels fixed on the lower wing (1 foot 4 inches chord, 10 feet span); just the little bit advanced position of the lamellar spring suspended tailwheel is somehow peculiar, because...
- ...the ampenage IS an inverted V-tail, but a non-classic one whilst supported by two small oblique pseudo-stabilizers - a more draggy solution for sure, but the only feasible keeping in mind the... 2D fuselage (with a saddle - do not forget the prone position) and its original (I guess) and very simple command by feet, without any mixer.
- Those strakes of the upper wing (2 feet chord, 16 feet span) seem to be a good solution for STOL-style flight, since a number of old and not so well-known studies claim to reduce the L/D at high AoAs and also increase the stall limit; claims that I’ve got to verify on a 1/2 scale model though - yes, 1/2 whilst the real airplane would be tiny enough to allow such a good scale-ability.

Oh, and that hook of the scale-pilot in the drawing is just a graphic joke ...with the secondary purpose of a readers’ attention check - congrats for discoverig it!

Many other details must be revealed anyway (including the type of materials intended to be used - it would be mainly wood/ply for the sake of affordability - some better suggestions?), so I will deliver them to you in some other not-too-long-to-be-boring posts.
 

Xanadrone

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Joined
Nov 24, 2011
Messages
195
Location
Bucharest Romania
A simple (and just preliminary) napkin-sketch would be more clarifying than words about its inverted V-tail and landing gear:
DSCF1374.jpg

A few other details: this hybrid version with permanent IC-engines propulsion and e-motors used only for climb / take off is only one of three possible variants, that could be also:
- either pure electric -- maybe with a more glider-style span and A/R, lets say 19-20 ft for the 2 ft chord
- or only IC-motorized; this one could be lighter without the batteries and with greater... but riskier autonomy, implying also another position of the wings (further backwards). The STOL-favorising effect of the four small e-motors placed ahead the upper wing would dissapear too.
A Screamer Veloce ;) 50 HP two-stroker could be tempting though.

The hybrid and/or electric versions have the implicit advantage of an advanced CG/CP by positioning the relatively heavy batteries upfront, thus resulting a not so short-coupled geometry for such a tiny air-toy.
Second advantage: the possibility to optimise the permanent functioning IC-propellers for cruise (level flight) and those folding e-props for climb (lower pitch.)

Please correct me if I am wrong - even like a friend of mine (he IS funny, albeit being an aerospace engineer) that asked me if I did not choose these micro-dimensions by lacking A3-format millimetric paper. :gig:
 
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