Hello fellow Travellers,
the first thing I tried to do after getting FF&S was building a light
Helicopter. Browsing to the book, I found a special Lt MTR assembly, for
Helis with less than 2 tons. And so I start to build one using this
rotor assembly. I checked a source for actual (1994) Helicopter designs,
to find a base for a start.
Here is a list of the IC-Powered helicopters available on the market today:
Power un/loaded weight speed range Weight/
(in KW) (in kg) (in km/h) (in km) Thrust ratio
Robinson R22 Beta 119 379/621 180 592 5.22
Rotorway Exec 90 113 420/646 153 290 5.72
Brantly B-2B 134 463/757 145 400 5.65
Schweizer 300C 142 474/930 153 360 6.55
(source: Flug Revue,January 1994, p.75; ISSN 0015-4547)
For my design, I take the following data:
loaded weight: 720 kg; range: about 500 km...so I get a performance between
the R22 and the B-2B.
I start using the Lt MTR construction, which provides a Thrust/Power-Ratio
of 4. Using 720 kg as base, we need a 180 KW engine...very big in comparison
to the numbers above. Next step is the engine weight: The improved
Internal combustion engine weights 450 kg...ups...only 270 kg left
for those necessities named Frame, Pilot Seat and Fuel. And because the
engine needs 112.5 kg of fuel per hour, I would get an endurance of
less than 1 hour if I would like to load at least two pilots (75 kg each).
Obviously this figures do not work.
The obvious problem is the weight of the engine and the Thrust-to-Power ratio
of the Light Main-Tail-Rotor assembly. To get the things running, I used
a Thrust-to-Power ratio of 6 instead of 4. The following design is the result:
projected weight: 720 kg; TL: 6
Power Plant (120KW) 300.00 kg 600 Cr (!) imp.IC
Lt MTR Assembly 54.00 kg 5400 Cr
Airframe (Simple) 7.20 kg 7200 Cr
Basic Mech. Controls 0.00 kg 200 Cr
2 Cramped Seats 40.00 kg 2000 Cr
TL-5 Flight Avionics 1.00 kg 10000 Cr used, because no power req.
Radio (30km) TL 8! 10.00 kg 250 Cr requires 1 KW! ridiculous!
Fuel (2h) 150.00 kg
----------- --------
562.20 kg 25650 Cr
=> 157.80 payload, pilot and passenger.
Thrust: 120*6*0.1 = 72 tons => G-Rating: 72/720 *0.85= 0.085
Max Speed: 3500 * 0.085 = 297.5 kph => Cruising Speed = 220 kph
NOE Speed = 40 kph => range: 440 km.
Note that the TL-8 Radio is required, because it is small enough to fit in
the Helicopter. The power consumption of the Radio is - as mentioned -
ridiculous. My RC-sender uses 0.5 Watt (!) for a range of about 1 km.
And a CB uses between 1 and 4 Watts for ranges up to the horizon. Why
do I need 1 KW for a range of only 30 km ?
The sheet of this Helicopter looks like this:
TL: 6(8 for Radio)
Price: 25650 Cr (compare to $113850 fly away price of a Robinson R22)
Size: 43.2 kl = 3.1 tons (Mc)
Mass: unloaded: 562.2 kg, loaded: 720kg max.
Power: Improved IC=120 KW, Lt MTR assembly creating 720 kg of thrust
Maint: how do I calculate this ?
Controls: Basic Mechanical, TL-5 Flight Avionics
Commo: Radio (39km) TL-8(!)
Sensors: None
Life Support: None
Cargo: 157.8 kg, pilot and passengers included !
Crew: 1
Passenger: 1
Speeds: Max: 297.5, cruising: 220, NOE:40
Travel Move: 880, Combat Move: 41 ...what ever this will mean in such a case
Fuel Capacity: 156 liters = 156 kg
Agility: 4
I did not bother to calculate any other combat factors, because this thing
is likly to come down if hit by something more serious than a pistol bullet.
The problem of this Helicopter is the fact, that it is much too fast for
its power, but according to the rules, we have no choice.
Any comments are strictly encouraged!
Juergen Kirsch
[email removed]
P.S.: I will check the design of heavier Helicopters too. They have
turbine engines as power plants. Perhaps those have a better
weight to power ratio than the poor Improved Internal Combustion
engines. Note that a 100 KW imp.IC engine weights 250kg. A bit too
much if you ask me.