Category: Design (Page 2 of 4)

The Tiny Cedar Flea now has a removable canopy – making it very easy to fly with an open cockpit in summer, and an enclosed cockpit when it is cooler.

(1) Basically, the canopy bolts onto the fuselage which is pre-fitted with a 6mm ID bearing.  A simple M6 bolt secures the canopy left and right.
(2) Unclip latches at the bottom of the canopy and at the windshield, and pivot the canopy up and rearwards.
(3) The canopy rests securely on the fin while the pilot enters or leaves the cockpit providing the same ease of access as when the TCF was configured for open cockpit flight.
Notice also the main gear mounts.  Simply by swapping the left and right gear legs, the TCF can be transformed from a tail-dragger as shown, or a nosewheel airplane.  Of course, one would need to fit the bolt-on nosewheel strut, either leaving the lightweight tailwheel in place, or removing it and replacing it with a spring steel tip-back guard.  The tailwheel assembly weighs a mere 1500g, so leaving it in place is not a real issue.  Standard tyres on the TCF are 21-inch (535mm) mains, and 8-inch (200mm) tailwheel – also of the soft baloon variety.

After worrying the thing to death, I finally decided to put the pilot’s seat on rails, in order to micro-adjust the CG for different weight pilots.  After all, not all pilots weigh the same, and the pilot sits quite far back from the CG.

The steel rails have holes placed at 70kg, 80kg, 90kg, 100kg, 110kg stations.  All the pilot has to do is to slide the seat back or forward to correspond with his (or her) weight, drop in the locking pins (both sides), and the CG will automatically be in the correct lateral position for safe flying.

Some other changes:
(1) The fin has been moved back 300mm, in order to increase the rudder moment arm to a very generous distance.  In fact, it now exceeds that of the very well-behaved HM293

(2) A triangular main gear leg allows one to swap them (left/right) which transforms the undercarriage from tail-gragger to tricycle.  Of course, one also has to remove the bolt-on tail or nose gear and replace it with the other flavour.  Both nose and tailwheels will be supplied as part of the kit.

(3) I have zeroed-in on the ideal powerplant:  The Aeromarine v-twin.  60kg (with prop, redrive, starter, radiator – yes, it’s water-cooled), EFI 60hp.  Actually, any powerplant with at least 35hp can be used, but then correct CG placement becomes an issue depending on weight.  One extremely interesting development with the Aeromarine v-twin is that they are currently developing a v-twin HYBRID electric motor.  No details re: weight, power or cost, but watch this space.

(4) I am in discussion with Cato Props (as well as a local prop guru) with a view to getting a custom (quiet) prop fitted.

If you are contemplating moving up a gear and building a canard-Flea, there are some caveats to be aware of.  PLEASE DO NOT PROCEED WITH YOUR CANARD-FLEA PROJECT WITHOUT READING THIS FIRST.

1. A canard-Flea does not have its ideal CG at the usual 25% of the combined chord.  It is closer to 35%
2. The NP (Neutral Point) is also much further aft (at about 41% of combined chord)

In Feb 2011, Axel Darling (Pou Renew #41) did pioneering work in his analysis of the Raymond Baudoin reverse wing Pou.  He wrote: “In the final analysis, I found that starting at 90cm/90cm [Ed: horisontal and vertical wing gaps] with any of the most used aerofoils on Pou’s that they remained in laminar flow all the way down to about 20cm/20cm”

In other words, so long as the vertical and horisontal wing gaps were identical, one could expect laminar flow over both wings.  This in itself is a huge breakthrough from an extremely well-respected aerodynamicist (and Pou advocate).

He then axamined the relationship between front and rear wing areas, and wrote: “One of the types of vortices on a typical wing is generated at about 89% of the semi-span as the flow from below swirls with that from the upper surface.”  He concluded: “A great deal of the interaction for an aftplane tip occurs here so the aftplane could be positioned at say 85-90% foreplane chord for good effect. ”

And building on this, he reasoned that it would be extremely beneficial to have a smaller wing up front.  Why?  Because “the smaller foreplane leaves lift bumps at about the vortex locations, which when the aeroplane yaws, allows a much greater yaw/roll force and much stronger dynamic lateral stability and much better and immediate pilotage in turns. This undoubtedly is the reason why Baudoin exclaimed that his backward Pou flew so much better than the reverse”

But he cautions designers/builders to consider the CG position in a canard-Pou:  “Consider the stability of such a planform… the N.P. is going to be much further back than in a standard Pou planform, even equal span, equal chord. For instance, with 4.4M forespan and 5.8M aft the N.P. is ~1.3M as apposed to .997M for the [standard Mignet] planform. That’s 41.3% as opposed to 31.65% of total chord”

Finally, David Isley (Pou Renew #48) hauled out his trusty sliderule, and using Axel’s analysis of the Baudoin canard-Pou, worked out a simple formula for estimating reverse-Poux CG positioning.

What I found difficult was that with the larger wing in the rear, it was extremely challenging to get things to line up.  My weights & balance estimates always placed the CG too far aft.  I had started off looking at one of the 35hp paramotors (both 4-stroke and 2-stroke) but they were simply too light.  Electric was only slightly better with similar weights, but batteries could be moved about to affect the CG.  And then there was the issue of required power.  I figure I’d need at least 35hp (continuous) to fly acceptability, even with 130ft^2 wing and 450lbs MAUW) So I looked at two smaller engines (fore & aft) in a push/pull config.  This would give me the power, but not the required CG.

Finally I ran out of options, and started plugging in numbers for a heavier engine.  I happen to have a Valley Engineering Big Twin (53kg with redrive, starter, full of oil and exhausts, 50hp).  That gets me very close.  But I keep glancing over at the Aeromarine v-twin (63kg, 60hp, EFI) but at a huge cost of over $10k USD.  I’m still not sure, but it sure looks attractive.

I wrote to OpenPPG and asked about their SP140 motor system.  This is their reply:

If your continuous cruise of 17.5kw is needed then I think the SP140 motor is a bit outside the scope of what your needs are. It is best to have your cruise power level around 25-35% of the total max output for your power system. 

For example, on the Sp140 our cruise power is 4 to 5 kilowatts and our max power is about 20 kilowatts so that would leave us around 25% usage for our cruise power you can go up a little bit from that to say 30-35% but I would not push it much past that as it’s best to not be living on the edge of what your power system can handle.

So you would want a larger power system most likely you would be looking at something around 2x as large and also probably 2x the cost.

OK – so, investigating electric power…

Forgive me if I seem naive, but surely all one needs is a motor, some batteries, a Battery Management System, some software to tell the motor how much power to draw (i.e. a throttle), some feedback so that you know what the hell is going on, and a charger to get the show on the road.

What’s the difference between this and (ho-hum) RC electric flight which is well-established and has the bugs sorted out?

If one goes with a company like Compro (https://www.mgm-compro.com/) they offer all the above which play well together.  What’s the big deal about ordering a 45kW system from them where everything talks to everything else?

45kW is 60hp.  And that’s exactly what we need.

So weight and cost is all we need to tie down.

Things evolve.
What started out as an open cockpit is busy growing a roof.  Still under 3m in length, but with a raked fin and a slightly longer nose.

This version is very similar to a design I drew a few years back – but I think it is coming of age.

Still the cedar strip construction, so it is going to look gorgeous, and the Canard-Pou wing configuration.  Power?  Still tyying to find the perfect powerplant…

First up:  the Aero 1000 by Blackhawk

This is a 4-stroke PPG engine.  From their website.  On paper, this looks like an extremely attractive package.

Positives:

1. 4-stroke
2. EFI
3. 35hp
4. Water cooled
5. 4.3 litre/hr
6. 38kg

Some potential issues:

• Vibration: it’s a single-cylinder design
• Cost is higher than some other contenders ($9450)

Next:  The Vitorazi 185
Yes, I know.  It’s a 2-stroke.  But in its favour:

1. It’s quiet – honestly…
2. It’s light (17kg – half the weight of the Aero 1000)
3. It has very low fuel consumption (3.5l/hr – even lower than the 4-stroke Aero 1000)
4. Fully EFI
5. It’s cheap ($3200)
6. Can be fitted with the exciting auto pitch compensating Variomatic prop (https://youtu.be/_S45iiXN2XM)

Some issues, however:

• Relatively low HP (26hp)
• Single cylinder (potential vibration)

3rd on the list:  The Hummel v-twin

Based on the Predator 670cc .  This from Laurie at Hummel Sales:
The base engine we use is the Predator 670. We basically strip everything off of it. The only thing left is the cylinders, crank and pistons. Everything else is high performance or custom.

What I like is that this is a two-cylinger engine, built on a base engine of which probably thousands have been made, and many of them are mounted in fixed wing airplanes.

What I DON’T like is the fact that this is a converted industrial engine, which while it might be extremely reliable, is nevertheless a generation (or two) behind the latest engines above.  Fuel consumption is actually double that of the Aero 1000))

Some specs and issues:

• $7184
• 39kg ready to fly (same as Aero 1000)
• 8 litre/hr (almost double both the Aero 1000 and the Vitorazi 2-stroke)
• 38hp (same as the Aero 1000)

Based on this quick run-down of specs, it seems that the race is between the Aero 1000 4-stroke and the Vitorazi 185.  The deciding factor for me is the rather piddly 26hp of the 2-stroke.

Out of left-field is the OpenPPG SP140 – an electric powerplant.

Specs:

• Cheaper than the competitors ($6759 vs $9450 – Aero 1000 and $7,184 for the Hummel v-twin).  HOWEVER, the Vitorazi 185 costs a mere $3200.  You can buy TWO Vitorazz motors for the price of the others.  But also significantly less power.
• 33hp equivalent, (30hp continuous)
• 36kg with the large battery pack
• Flight endurance (on a PPG which is extremely draggy): 70 minutes.  With a second battery (about $2k) connected in serial), flight endurance is over 2 hours
• Cost per flight hour: 60 cents vs almost $8 at today’s gasoline prices in Australia.

So when it comes to powering your TCF, the choices are many and varied.  Depending on what powerplant you decide on, extreme care will need to be taken in ensuring the CG falls where is MUST.  The CG location is a non-negotiable.

The big question is – can the TCF fly acceptably on 30hp?  Currently investigation is underway to answer this question.

The universally quoted reason why electric planes aren’t more prevalent, is that battery capacity is insufficient.

NOT TRUE.

How long do YOU fly for in a typical sortie?  My average is about 45 minutes.  That’s enough to get airborn, do some circuits, some stalls, and generally have a good time.  Or enough time to enjoy that early morning or after work spin, some low flying over farmland, and a circuit or two.  Or even to go on a scenic flight around the neighborhood, follow some rivers or streams at low altitude and pretend to be a WWI ace.

The OpenPPG electric power system (which costs the same as an ICE) gives you up to 80 minutes of absolutely secure never-fear-the-dreaded-engine-failure flight.  80 minutes.  That is enough for a short cross-countrty hop.  Plan your route well, and you can cover as much distance as you wish if you’re able to drop into an airfield after an hour or so and change batteries.  And that’s the secret.  Carry a spare fully charged battery.

So – let’s talk numbers.  How much does a spare battery cost, and what does it weigh?

Cost (according to OpenPPG) is $2,200 and weight is 22.5kg.  If you can afford either the 22kg weight penalty or the $2.2k price tag, get a second battery, (and use it to help arrange your CG.  Batteries don’t lose weight as they lose power…)

I’m sold on this idea of an electric Pou.  The question remains – can a 33hp-equivalent powerplant fly the Tiny Cedar Flea?

With just on 87m^2 (about 100 sq ft) of wing area, and an empty weight of 92kg (203 lbs), the OpenPPG electric motor will be MORE than sufficient to make this bird fly like a Valkierie for over 60 minutes.

I’m sold.  Are you?

in 2024, recreational aviation is in sharp decline.  Fewer and fewer younger people are joining aero clubs, signing up to Facebook aero groups, and certainly very few are spending money to buy aeroplanes.  Arguably, financial times are tough, and disposable incomes are being eroded by the rising cost of living.  Yet go along to the waterways on any given weekend, and you will see young folks whizzing by on jetskis…

Not an insignificant investment – yet this seems to be no impediment to younger enthusiasts.  And why is this?  Quite apart from the financial investment – consider the very much easier pathway into the sport.  No 40 hours of flight training, and numerous theory exams to pass.  Just about any waterway can be your playground (no trailering your new toy to one of a declining number of out-of-the-way airfields).

Foilboarding is another sport to which younger people are flocking.

Again, they’re not cheap (if one ignores those on offer at Ali Express).  But they’re exciting, there are no restrictive training or licensing requirements, and you can just slide them into the back of your car and go play.

My point is that personal aviation, once the exciting, cutting-edge passion of young men and women has given way to other more accessible sports.  And cost of entry doesn’t seem to be a significant barrier.

Closer to home, however, is the exponential growth of the Radio Controlled planes and drones.  You can buy a drone for under $100, but hundreds of new drones are sold daily around the world for $1500 plus, as people flock to the sport.
Why?  They are relatively cheap, come with all manner of flight stabilisation, onboard telemetry, cameras, navigation – you name it.  It’s exciting.

My local RC field in Brisbane is crowded to capacity every Saturday (and most evenings also) with drones and fixed wing RC planes buzzing around.  Interest in flying, per se, hasn’t diminished.  It’s alive and well.  It’s just the over-regulated, expensive and red-tape bound “recreational flying” secor which is dying on the vine.

And as interest in recreational aviation dwindles, the pace of innovation slows down, and the torch is being taken up by those sectors of aviation which currently attract high numbers.

Take the PPG world for example.  A good Powered Paraglider will set you back just short of $20k.  There are cheaper options, like the excellent Parajet for about half that price.

My point is that both the cheaper RC/drone sectors and the more expensice PPG sectors niches are booming, with hundreds, and in some cases thousands of new participants each year, even as the ranks of fixed wing rectreational aviation thin, leaving by and large old men dreaming of yesteryear.

And nowhere is this withering away more true than in the sub-genre of the Pou du Ciel.  It’s glory days are over, and increasingly, Facebook groups dedicated to this wonderful little airplane are peppered with photos of old planes, comments and photos of old designs newly built by aging builders, and a hardening of opinion ranged against anything which emerges which might not be strictly according to the “Formula”.

But this is NOT the case at rtfm-aero.

We’re not interested in strapping a parachute to our backs.  We love the quirky little Pou du Ciel (or “Flying Flea), and all our efforts are devoted on a daily basis to advancing the design.  I strongly doubt that we will ever relive the glory days of personal fixed-wing aviation, because history has moved on.  But we can aspire to attracting a whole new generation of would-be aviators to an aircraft which is:

• Cheap to build (under $15k)
• Safe and easy to fly
• Full of modern technology
• Able to spark the imagination again.

As a 2-axis plane, the Tiny Cedar Flea uses a single control stick to fly.  No ailerons, no hand/foot coordination in turns, and it is impossible to stall.  Wings which can fold in under a minute for transportation.  Easy trailerability.  Tundra tyres for rough field landings.  Very short take-off and landing.  In fact, everything which would make the TCF a delight to own.

Add in a digital screen showing all pertinent engine readouts, altimiter, airspeed, and full moving map navigation.  We’re looking at different wing configurations, different construction methods and a thorough investigation of alternative powerplants.  I’ve already written about our new construction method (drawing on the rich experience and expertise of cedar strip canoe/kayak building), and I’ve written about better wing configurations (Nanadovic, Axel Darling and Jean de la Farge have all influenced our design choices.