Ultimate-Jets

Choosing the right engine for your application

Choosing the right engine for your model might seem straightforward, but is not always as simple as peaking the cheapest offer on the web.

Jet models are meant to be flown and usually feature a fairly high wing loading ratio. The powerplant choice will significantly affect this ratio and might render a plane tricky to fly if not done properly. Consideration like price is also very important and must be integrated into the equation.

The usual workflow I use for this choice is the following:

1. Check the weight of the aircraft

2. Check the wing loading vs intended type of flying

3. Define a class of thrust from these considerations taking into account kit manufacturer recommendations

4. Pick up the highest thrust-to-weight-to-price ratio in this class

5. Consider the following complementary factors in decreasing priority:

·         Does this engine fit in the Airframe?

·         What is the build quality/ reliability of the engine?

·         Is the idle thrust low enough for my plane?

·         What about warranty conditions?

·         What is the cost of the bearing change and at what interval?

·         What fuel/oil combination does it burn?

 

Also bear in mind that oversizing the engine for the airframe will cost you a lot more than picking up the right size. You see increased airframe an landing wear due to faster touchdown speeds and high impact energy as well as higher airframe stress in flight.

 

I have included a table listing the power to weight to price ratio for some engines available on the market. This is using web published manufacturer data, including price offered in the USA.

 

 

Designation Thrust N Weight gr Price USD Thrust/price/weight ratio
B300F 300 2650 6150 1.84
JB220 220 1640 4300 3.12
JB190 190 1580 3850 3.12
JB180 180 1580 3600 3.16
B100F 120 1210 2630 3.77
K-60G (-20 ) 58 830 1800 3.88
K-80G (-20) 84 1284 1825 3.58
K-100G (-20) 98 1280 2050 3.73
K-140G (-20) 137 1630 2450 3.43
K-170G (-20) 164 1630 3050 3.30
K-180G (-20) 176 1704 3250 3.18
Jetcat P-20SX 24 362 2795 2.37
Jetcat P-60SE 62 845 2395 3.06
Jetcat P-80SE 97 1445 2195 3.06
Jetcat P-90Rxi (-80) 105 1504 2455 2.84
Jetcat P-100RX (-20) 100 1060 2595 3.64
Jetcat P-140RX (-20) 142 1570 3295 2.74
Jetcat P-180RX (-20) 175 1575 3995 2.78
Jetcat P-200SX 230 2510 5195 1.76
Jetcat P-300RX (-20) 300 2610 5800 1.98
Merlin M100XBL (-20) 100 955 2495 4.20
Merlin VT80 (-80) 80 860 2000 4.65
Merlin M140XBL (-20) 140 1285 2995 3.64
Merlin 160 170 1870 3695 2.46
JC Bee II 60 954 2595 2.42
JC Rabbit 100 100 1120 2795 3.19
JC Cheetah 140 1360 3195 3.22
JC Rhino 160 1970 3695 2.20
JC Mammoth 220 2150 4795 2.13

 

 

 

Below is the overall ranking for all the engines listed.



Ranking by Thrust/price/weight
Merlin VT80
Merlin 100XBL
K-60G
K-100G
B100F
Merlin M140XBL
Jetcat P-100RX
K-140G
K-170G
JC Cheetah
JC Rabbit100
K-180G
JB220
JB190
JB180
Jetcat P-60SE
Jetcat P-80SE
Jetcat P-180RX
Jetcat P-140RX
Jetcat P-90Rxi
Merlin 160
JC BeeII
Jetcat P-20SX
JC Rhino
JC Mammoth
B300F
Jetcat P-200SX

 

 

 

Ranking for 20 to 60 class

K-60G
Jetcat P-60SE
JC Bee II
Jetcat P-20SX

 

 

Ranking for 80 to 100 class

Merlin M100XBL
K-100G
Jetcat P-100RX
K-80G 
JC Rabbit 100
Jetcat P-80SE
Jetcat P-90Rxi

 

 

  

Ranking for 120 to 160 class

B100F (120N)
Merlin M140XBL
K-140G
JC Cheetah
Jetcat P-140RX
JC Rhino

  

 

 

Ranking for  170 to 180 class

Ranking 170-180 class
K-170G
K-180G
JB-180
Jetcat P-180RX
Merlin 160

 

 

Ranking for 200 to 300 class

Ranking 200-300 class
JB-220
JB-190
JC Mammoth
B300F
Jetcat P-200SX

 

 

 

Using the procedure described above and the tables will result in a wise and appropriate choice.

Written by Olivier Nicolas — April 17, 2013

Welcome

We are proud to introducing this web site that has been carefully designed to match your needs and desires. Ultimate jets offers some of the best engines, kits, and accessories to the jet modeller. We are exclusive distributors in the USA for Behotec and BF-Turbines and provide inhouse support and service for these engines. We also are dealer for the following brands: Aviation Design, Jets-Munt, T-Motor, Weatronic, Ultratool, Cotronics, and many other aerospace industry suppliers. So you'll discover some unique items while browsing through these pages. Enjoy... Barry, Woody and Oli.