Choosing the right engine for your application

Updated as of the 18th of September 2015.

 

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. Go to the tables below by thrust segment and check the thrust-to-weight-to-price ratio.

5. Establish the following point: do I need a high quality engine to match a high quality airframe?

6. Consider the following complementary factors in decreasing priority:

·         Does this engine fit in the Airframe ?

.         What is the service interval, is service provided locally ?

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

·         Is the idle thrust low enough for my plane ?

·         What fuel/oil combination does it burn ?

7> Decide on the engine.

 

Also bear in mind that oversizing the engine for the airframe will cost you a lot more than picking up the right size. You'll 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
B500F 500 3780 10615 1.25 4.71 3.56 13.2
B300F-STG 300 2620 6860 1.67 4.37 3.82 11.5
B300F 300 2650 5910 1.92 5.08 4.48 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
B160F 160 1320 3468 3.50 4.61 3.81 12.1
B140F 140 1240 2880 3.92 4.86 4.31 11.3
B100F 120 1210 2518 3.94 4.77 4.81 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-120G (-20) 120 1280 2300 4.08 5.22 5.57 9.4
K-140G (-20) 137 1630 2450 3.43 5.59 6.65 8.4
K-180G (-20) 176 1704 2990 3.45 5.89 5.70 10.3
K210G (-20) 210 1650 3250 3.92 6.46 5.08 12.7
Jetcat P-20SX 24 362 2795 2.37 0.86 1.30 6.6
Jetcat P-60SE 62 845 1995 3.68 3.11 4.24 7.3
Jetcat P-80SE 97 1445 2195 3.06 4.42 6.58 6.7
Jetcat P-90Rxi (-80) 105 1504 2195 3.18 4.78 6.85 7.0
Jetcat P-100RX (-20) 100 1060 2395 3.94 4.18 4.43 9.4
Jetcat P-140RX (-20) 142 1570 2895 3.12 4.91 5.42 9.0
Jetcat P-180RXi (-80) 175 1565 3295 3.39 5.31 4.75 11.2
Jetcat P-200SX 230 2510 4295 2.13 5.36 5.84 9.2
Jetcat P-300RX (-20) 300 2630 6195 1.84 4.84 4.25 11.4
Jetcat P-400RX (-20) 395 3550 6195 1.80 6.38 5.73 11.1
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 VT80BL (-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 60 954 2595 2.42 2.31 3.68 6.3
JC Rabbit 100 106 1120 2795 3.39 3.79 4.01 9.5
JC Cheetah 147 1360 3195 3.38 4.60 4.26 10.8
JC Rhino 175 1970 3695 2.40 4.74 5.33 8.9
JC Mammoth 225 2400 4795 1.96 4.69 5.01 9.4
Evo 220Ex (-120 ) 220 1690 4250 3.06 5.18 3.98 13.0

 

Below is the overall ranking for all the engines listed.



Designation Thrust N Weight gr Price USD Thrust/price/weight ratio
Merlin VT80BL (-80) 80 860 1950 4.77
Merlin M100XBL (-20) 100 955 2495 4.20
K-120G (-20) 120 1280 2300 4.08
Merlin 200XBL (-20) 200 1480 3390 3.99
B100F 120 1210 2518 3.94
Jetcat P-100RX (-20) 100 1060 2395 3.94
B140F 140 1240 2880 3.92
K210G (-20) 210 1650 3250 3.92
K-60G (-20 ) 58 830 1800 3.88
Jetcat P-60SE 62 845 1995 3.68
K-100G (-20) 98 1280 2050 3.73
Merlin M140XBL (-20) 140 1285 2990 3.64
K-80G (-20) 84 1284 1825 3.58
B160F 160 1320 3468 3.50
K-180G (-20) 176 1704 2990 3.45
K-140G (-20) 137 1630 2450 3.43
JC Rabbit 100 106 1120 2795 3.39
JC Cheetah 147 1360 3195 3.38
Jetcat P-180RXi (-80) 175 1565 3295 3.39
Jetcat P-90Rxi (-80) 105 1504 2195 3.18
JB180 180 1580 3600 3.16
JB220 220 1640 4300 3.12
JB190 190 1580 3850 3.12
Jetcat P-140RX (-20) 142 1570 2895 3.12
Jetcat P-80SE 97 1445 2195 3.06
Evo 220Ex (-120 ) 220 1690 4250 3.06
JC Bee II 60 954 2595 2.42
JC Rhino 175 1970 3695 2.40
Jetcat P-20SX 24 362 2795 2.37
Jetcat P-200SX 230 2510 4295 2.13
JC Mammoth 225 2400 4795 1.96
B300F 300 2650 5910 1.92
Jetcat P-300RX (-20) 300 2630 6195 1.84
Jetcat P-400RX (-20) 395 3550 6195 1.80
B300F-STG 300 2620 6860 1.67
B500F 500 3780 10615 1.25

 

And then, the ranking by engine class.

 

Ranking for 20 to 60 N class

Designation Thrust N Weight gr Price USD Thrust/price/weight ratio
K-60G (-20 ) 58 830 1800 3.88
Jetcat P-60SE 62 845 1995 3.68
JC Bee II 60 954 2595 2.42
Jetcat P-20SX 24 362 2795 2.37

 

 

Ranking for 80 to 100 N class

Designation Thrust N Weight gr Price USD Thrust/price/weight ratio
Merlin VT80BL (-80) 80 860 1950 4.77
Merlin M100XBL (-20) 100 955 2495 4.20
B100F 120 1210 2518 3.94
Jetcat P-100RX (-20) 100 1060 2395 3.94
K-100G (-20) 98 1280 2050 3.73
K-80G (-20) 84 1284 1825 3.58
Jetcat P-90Rxi (-80) 105 1504 2195 3.18
Jetcat P-80SE 97 1445 2195 3.06

 

 

  

Ranking for 120 to 160 N class

Designation Thrust N Weight gr Price USD Thrust/price/weight ratio
K-120G (-20) 120 1280 2300 4.08
B100F 120 1210 2518 3.94
B140F 140 1240 2880 3.92
Merlin M140XBL (-20) 140 1285 2990 3.64
B160F 160 1320 3468 3.50
K-140G (-20) 137 1630 2450 3.43
JC Cheetah 147 1360 3195 3.38
Jetcat P-140RX (-20) 142 1570 2895 3.12

  

 

 

Ranking for  170 to 200 N class

Designation Thrust N Weight gr Price USD Thrust/price/weight ratio
Merlin 200XBL (-20) 200 1480 3390 3.99
K210G (-20) 210 1650 3250 3.92
K-180G (-20) 176 1704 2990 3.45
Jetcat P-180RXi (-80) 175 1565 3295 3.39
JB180 180 1580 3600 3.16
JB190 190 1580 3850 3.12
JC Rhino 175 1970 3695 2.40

 

 

Ranking for 210 N and above class.

 

Designation Thrust N Weight gr Price USD Thrust/price/weight ratio
K210G (-20) 210 1650 3250 3.92
JB220 220 1640 4300 3.12
Evo 220Ex (-120 ) 220 1690 4250 3.06
Jetcat P-200SX 230 2510 4295 2.13
JC Mammoth 225 2400 4795 1.96
B300F 300 2650 5910 1.92
Jetcat P-300RX (-20) 300 2630 6195 1.84
Jetcat P-400RX (-20) 395 3550 6195 1.80
B300F-STG 300 2620 6860 1.67
B500F 500 3780 10615 1.25

 

 

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

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