One of the overall propulsion concepts that I like and I believe affords
much greater design flexibility amongst other benefits for VTVL's is a high
power to weight ratio rotary engine and electric motors in the following
configuration.

The rotary say 200 Hp plus electric turbo compound (see further below) and
direct drive electric generator motor. At + - 7000 rpm or so the direct dive
electric motor will weigh 40 lbs. Present state of the art electric pancake
motors are now coming available with 5:1 power to weight ratios at 8400 rpm
for 7 hp and 1.4 lbs, 6 inch dia. by about 1.25 inches thick (you can stack
for more hp). This is sustainable power without liquid cooling at that P/W
ratio and 95% plus efficiency, not pushing the temperature limits. Note
there is a new offering with breakthrough P/W about every 6 months or so.

Place 2 more pancake motors of 115 hp each in your counter rotating blades
or whatever design you favour and you're almost complete. Blade twist (many
methods) for altitude adjustment or possibly through motor speed control as
eclectic motors are able to adjust speed very fast and with great accuracy
given the right components. Lower rpm is possible by increasing the diameter
of the pancake motor. Presently 97% Eff. 18 inch dia = 150 hp at 3500 rpm at
33 lbs or 100 hp at 2700 rpm.

For greater power and lower effective fuel consumption do a turbo compound
electric.

Hook up an appropriately large as in slowest rotating for a given output you
can find off the shelf turbo charger to the exhaust and have it direct drive
a second electric motor. 200 hp base plus 40 hp turbo compound = 240 hp
gross or 228 net hp output at 95% Eff.

Weights and overall efficiency come in something like this:

- rotary engine 350 lbs installed
- main 200 hp generator 40 lbs at 95% Eff.
- shoot for 20% boost of rotary through turbo compounding uses 40 hp
electric motor at 10 lbs plus turbo charger 25 lbs? at 95% Eff.

Gross Hp 240 - net hp output to rotor motors at 95% = 228 hp

- 2 x rotor motor each 114 hp at about 37.5 lbs = 75 lbs at 97% Eff. (note
you would likely favour larger diameter, low rpm direct drive rather than
gear reduction - your call).
- misc. electronic controllers 25 lbs

Total 240 hp gross minus electric Eff. losses 240 x .95 x .97 = approx. 221
hp output for 500 lbs

Fuel consumption rotary at 0.47 sfc at 200 hp = 94 lbs per hour.

At actual 221 Hp output = .43 sfc or so.

Do rotary directly hooked to rotors through transmission and reduction drive
etc with say 350 lb engine plus 75 lbs for reduction and transmission but
with higher fuel consumption and lower hp output. Yes you can turbo compound
the engine mechanically for higher output, lower (better sfc) for probably
another 25 lbs or so.

On paper the latter (older) still appears to be the winner, however one can
develop some interesting design and power packaging concepts in terms of
getting that power to one or more rotors that would otherwise need much
added complexity for a single power source (or simply not doable).

A 2 minute battery supply can do wonders for a primary power loss for
landing.



Cheers,

Brian Feeney
alaia design


The problem with TC generators and electric motors is efficiency.
Lets say the generator is 80% and the motor is 80%. The overall efficiency
becomes 80% times 80% or 64% overall. The weight of course is out of sight.

A pure mechanical system can be 98% efficient.

Paul Lamar

Hi Brian

Do you have a link to these pancake motors and generators described above ?

Regards
Bill Mc Donald