"Educated guess" about the economy

VmaxProbe was a space age design ( and estimated to go 240 mph at 50 hp ). So was AR-5 and it does have 25% more cross section area than Max III. AR-5 was estimated to go 206 mph and did 213 mph gear out and Bearcat style open radiator on the front.

VmaxProbe also has gear out and about 3.5 feet longer than Max III with about 25% more wetted area in the fuse. Wings albeit small in area are non tapered and have about same drag as Max III with 1/3 more wing ( area ).

Max has poor mans area ruled fuse and very ( extremely ) light engine + laminar effect in cooling and retractable gear ( saving around 9% of the total drag ).

I draw an assumtion that 60 kg lighter AC with 15 % less drag would be also 15 % faster with same power. This equals 115 x 240 mph = 276 mph. This speed would be obtained at 520 g/hp/ hr SFC rate ( 1 liter gas is 0.71 kg ).


This equals 444 km/h top speed at 50 x 520 gramms of fuel around 36 liters / hour and 8.1 liters pro 100 km.

This is not yet very economical, but if you take the smaller Limbach L275E
( http://www.limflug.de/files/pdf/DS-L275E.pdf ) with 20 hp power and use 65% power 13 hp and still go 265 km/h ( cruise 165 mph ) you get 400 g / hp/ hr and 13 x 400=5,2 kg = 7.3 liters for 265 km and 2.78 liter pro 100 km.

All this of course need a new engine mount and shaft arrangement and structure ( much lighter than for the 50 hp engined version ).

All in all two separate AC:s would have to be built the other for speed record ( 276 mph ) and other for super economical flying ( also fast at about 205 mph top speed ).

But this is not all Air Power Technologies provide even better engine in respect of the consumption: http://airpowertechnologies.net/UAV_116cuin.html

At 65% power it uses only 1 oz of fuel / min. This equals 280 km/h speed at 2.37 liters used. This engine is also one kilo lighter.

This would mean 0.85 liter consumption pro 100 km thus 449 km per gallon of fuel in other words MPG of 266 !!!

I have asked APT to verify if this figure is correct ( the 65% consumtion ) and they claim their reed valve invention saves that fuel in 2-stroke engine of theirs. I find this hard to believe since it is nearly 3 times better than in well know aviation engine such as Limbach.


What would this mean in practise ?

If I took off with Max III in London and headed for Cádiz in Spain for a round of Golf at 04:00 in the morning and flew at 65% power at 280 km/h. I would arrive in Spain in 08:30 and after 4 hour round and a 1 hour at the clubhouse I would head back to London and arrive there at 18:00 in the ( six o'clock ) evening. I would have used 9 x 2.37 liters = 21.3 liters of fuel that here costs 1.2 euros per liter = 25.6 € for the whole trip. I would not even have to fill the plane is Cádic Spain ( if I landed at the par-5 course in Valderrama etc ).

Limbach L275E would have used 9+7.3 liters 65.5 liters ( worth 79 € ) of gas.

Limbach L550E at full throttle would have taken me to Cádic in 3 hours and back to London in 03:00 in the afternoon, but I would have have to have 110 liter tanks and fill her up again in Valderrama and used 260 €:s worth of fuel.


If just even ½ of this was true I would start to manufacturing MAX pushers with APT engines very soon...wouldn't you ?

Idea of using smaller L275E or APT 11.6 cu in engine came to me when I realised that L550E costs 17 000 €:s and knowing that APT and Limbach 20-22 hp engines just $ 4000 and 4500 €.

All this needed tuning MAX III into 90% size of what it was a week ago. Well worth it don't you think ? Also the landing gear wheel is 260 mm dia instead of 290 mm. All saving the weight and drag.

There is saying you have to multiply the power to the square to increase the speed..that is where I got the "65% power speeds" if you wonder. In fact 165 mph of 276 mph is 59%..and increase of that by 41 % would require...how many more hp:s ? : )

Apparently the old saying is not true is it ?

Fuse by 4 ft longer and 3-4 times more powerful engine propelled the AR-5 at 165 mph at 3 gph and 4 gph at 175 mph speed. Certainly the consumption specs of MAX III are pretty close the truth and better than in AR-5, but it needs a certainly lots of experts in the team and good selection of parts and components to make it work 100%.

What is also noteworthy is that 2-strokes deliver lotsa power ( to weight ) and are quite thirsty, but not so much at lower settings.....in fact very little at 65% power. If someone thinks MAX cannot fly with 22 hp APT I can always place 2 of them in the fuse ( running contra props ) and get the 133 mpg at 65% if that is what it needs. I recall PIK-20E motorised glider needed 38 hp for take off, but it weighed 3x Max III weight empty. Also good to remember that twin egined Cri Cri was able to fly home with one engine after other seized ...@ 9 hp power ( other engine outboard and unfeathered prop braking ! ).


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