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, updated as of June 2014, including the latest 200 N class engines announced.

 

I also included a new column in the table below, showing the thrust to weight ratio for each engine. Fuel efficiency, or TFSC is available on the RCJI table.

 

 

Designation Thrust N Weight gr Price USD Thrust/price/weight ratio Thrust/price ratio Weight/price ratio Thrust/weight ratio
B300F 300 2650 6150 1.84 4.88 4.31 11.3
JB220 220 1640 4300 3.12 5.12 3.81 13.4
JB190 190 1580 3850 3.12 4.94 4.10 12.0
JB180 180 1580 3600 3.16 5.00 4.39 11.4
B100F 120 1210 2630 3.77 4.56 4.60 9.9
K-60G (-20 ) 58 830 1800 3.88 3.22 4.61 7.0
K-80G (-20) 84 1284 1825 3.58 4.60 7.04 6.5
K-100G (-20) 98 1280 2050 3.73 4.78 6.24 7.7
K-140G (-20) 137 1630 2450 3.43 5.59 6.65 8.4
K-170G (-20) 164 1630 3050 3.30 5.38 5.34 10.1
K-180G (-20) 176 1704 3250 3.18 5.42 5.24 10.3
K210G (-20) 210 1630 3850 3.35 5.45 4.23 12.9
Jetcat P-20SX 24 362 2995 2.21 0.80 1.21 6.6
Jetcat P-60SE 62 845 2395 3.06 2.59 3.53 7.3
Jetcat P-80SE 97 1445 2195 3.06 4.42 6.58 6.7
Jetcat P-90Rxi (-80) 105 1504 2455 2.84 4.28 6.13 7.0
Jetcat P-100RX (-20) 100 1060 2895 3.26 3.45 3.66 9.4
Jetcat P-140RX (-20) 142 1570 3495 2.59 4.06 4.49 9.0
Jetcat P-180RXi (-80) 175 1565 4195 2.67 4.17 3.73 11.2
Jetcat P-200SX 230 2510 5495 1.67 4.19 4.57 9.2
Jetcat P-300RX (-20) 300 2630 6195 1.84 4.84 4.25 11.4
Merlin 200XBL (-20) 200 1480 3390 3.99 5.90 4.37 13.5
Merlin M100XBL (-20) 100 955 2495 4.20 4.01 3.83 10.5
Merlin VT80 (-80) 80 860 1950 4.77 4.10 4.41 9.3
Merlin M140XBL (-20) 140 1285 2990 3.64 4.68 4.30 10.9
JC Bee II 60 964 2595 2.40 2.31 3.71 6.2
JC Rabbit 100 100 1130 2795 3.17 3.58 4.04 8.8
JC Cheetah 140 1370 3195 3.20 4.38 4.29 10.2
JC Rhino 160 1980 3695 2.19 4.33 5.36 8.1
JC Mammoth 220 2160 4795 2.12 4.59 4.50 10.2
Evo 220Ex (-120 ) 220 1690 4250 3.06 5.18 3.98 13.0

 

Below is the overall ranking for all the engines listed.



Merlin VT80
Merlin 100XBL
Merlin M200XBL
K-60G
B100F
K-100G
Merlin M140XBL
K-140G
K-210G
K-170G
Jetcat P-100RX
JC Cheetah
K-180G
JB220
JB190
JB180
Evo 220Ex
Jetcat P-60SE
Jetcat P-80SE
Jetcat P-90RXi
Jetcat P-180RX
Jetcat P-140RX
JC Bee II
Jetcat P-20SX
JC Rhino
B300F
Jetcat P-300RX
Jetcat P-200SX

 

And then, the ranking by engine class.

 

Ranking for 20 to 60 N class

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

 

 

Ranking for 80 to 100 N class

Merlin M100XBL
K-100G
K-800G
Jetcat P-100RX
JC Rabbit 100
Jetcat P-80SE
Jetcat P-90Rxi

 

 

  

Ranking for 120 to 160 N class

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

  

 

 

Ranking for  170 to 180 N class

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

 

 

Ranking for 200 to 300 N class.

 

Merlin 200 XBL
K-210G
JB220

JB-190

Evo 220Ex

JC Mammoth
B300F
Jetcat P-300SX
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.