The removalists arrive on Monday to cart our stuff to New Zealand. I will have limited access to CAD, so here is a summary of the major design features now locked into the Tiny Cedar Flea.
MAUW: 237kg (520lbs) Estimated
Month: July 2024 (Page 1 of 3)
With the (optional) removable canopy which when fitted can hinge rearwards, there is a slight issue in that if it were allowed to swing back all the way, it would place quite destructive stress on both the canopy itself, and on the hinges. So the TCF now has a fixed camera mount/external aerial mount/canopy stop. Check it out.
The circled bit is the fixture in question. It protrudes from the fin with a rubber tip to stop the canopy from tilting back too far. But it ALSO acts as a very convenient mount for a Go Pro (or similar) giving a near-pilot view of the flight (see the dotted line of sight). And finally, it can house an external antenna for your radio or nav.
Also, notice the way the (optional) side windows fold down to allow easy entry and exit from the cockpit. Heat shaped, the windows attach to the fuselage, and can be dropped (as shown in the graphic above. One can fly:
(1) without either a canopy or side windows
(2) with a canopy but no side windows
(3) with both the canopy and the side windows fitted
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.
- A canard-Flea does not have its ideal CG at the usual 25% of the combined chord. It is closer to 35%
- 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.
This is direct from the manufacturer, and forms a reliable baseline. So I wrote to MGM Compro asking about their complete 45kW package. As soon as I hear back, I’ll update you.
https://www.mgm-compro.com/propulsion-system-units/45-kw-propulsion-system/
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:
- 4-stroke
- EFI
- 35hp
- Water cooled
- 4.3 litre/hr
- 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:
- It’s quiet – honestly…
- It’s light (17kg – half the weight of the Aero 1000)
- It has very low fuel consumption (3.5l/hr – even lower than the 4-stroke Aero 1000)
- Fully EFI
- It’s cheap ($3200)
- 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.
I’m in that wonderful honeymoon design stage where everything is possible and even major changes can be completed in half an hour.
I’m referring to the Tiny Cedar Flea, of course. I currently have two candidates…
My first design candidate was the open cockpit version. Which has been joined by a closed-cockpit contender. Different airframe shapes, but wings and powerplants identical.
Oh – and the current preferred powerplant is the OpenPPG 33hp equivalent electric motor. With a second battery – over 2 hours of flight time.
Your preference?
Both designs have their merits:For example, the open cockpit version is simple and easier to build. It will be constructed in two parts: Both top and bottom halves are basically the two halves of a normal cedar strip kayak. But it is also (being an open cockpit) quite draggy, and I’d expect a poor glide ratio because of this.
On the other hand, the closed version is more “racy”, far cleaner aerodynamically, will glide much better. But because of the closed-in cockpit with a hinged canopy, much more difficult to build. It is also a bit more cramped, and probably won’t accommodate larger pilots (although a “XXL” version is quite easy to design).
Both have identical wings: front: 4.4m, rear: 5.8m, with a combined wing area of 12.25 m^2. In the old language, this equates to: 131.8 ft^2 And that’s a lot of area for a plane with an empty weight of about 120kg (265lbs)
As for power, the OpenPPG electric motor (33hp equivalent) is advertised to give 70 minutes of flight (in a PPG – which are notoriously draggy machines – after all, they are dragging a huge parachute behind them). An amply-winged airplane should do far better than this. Even so, 70 minutes isn’t bad. But if one hooks up a second battery pack (20kg) and switches to the second pack in mid-flight, one gets 140 minutes (minimum). That’s 2hrs 20min. Not at all a bad endurance. I’m very comfortable with this.
So it comes down to preferences: sleeker profile or cheerful and open? Ease of build. Glide ratio. And the comfort of a closed cockpit for those less than balmy days.
I’d be very interested to hear your thoughts on this.