I am looking for the approximate thrust of a C-130J Hercules under ISA sea level conditions. Also the efficiency of its propeller would be of help.

An answer to this question would really help my calculations for an assignment, so I don't have to guess values. If you could direct me to your sources as well, that would be highly appreciated.

The C-130J is equipped with Rolls Royce AE-2100 D3 engines and the propellers would be the 6-bladed Dowty R391.


1 Answer 1


Okay guys, so I found some data from an old service publication from Lockheed. It says that the new C-130J propulsion system under standard conditions and flying 80 kts is rated "4,637 SHP, but produces 10,200 lbs". So using the equation for thrust available for a propeller aircraft I get:

$T_a = \frac{\eta \cdot P_s }{V}$


$T_a = $Thrust available
$\eta =$propeller efficiency
$P_s =$shaft power
$V=$air speed

$\eta = \frac{T_a \cdot V}{P_s}$

$\eta = \frac{10200 \textrm{lbf} \cdot 80 \textrm{kts}[ \textrm{aka. }135 \textrm{ ft/s}]}{4637 \textrm{shp} [\cdot 550 \textrm{ conversion}]}$

$\eta = 0.54$

This seems quite low but its what I got for anyone wondering. The service publication I got the info from is this: https://www.sikorskyaerospace.com/content/dam/lockheed-martin/aero/documents/sustainment/csc/service-news/sn-mag-v21-v30/V25N03.pdf

  • $\begingroup$ Since the propeller is optimized for higher speeds, this result looks about right. $\endgroup$ Mar 25, 2021 at 20:26
  • $\begingroup$ Right! I was stuck on that! That would explain why its so low compared to my estimations. I was expecting something closer to 0.9, 80 kts is approximately its minimum velocity. $\endgroup$
    – Bill Shao
    Mar 25, 2021 at 20:59
  • $\begingroup$ No, 90% is impossible with such a high disk loading. I would expect 82% to be the maximum at the design point. $\endgroup$ Mar 26, 2021 at 5:29
  • $\begingroup$ Sir, if you have the time, could you briefly explain how you came to expect 82%? That seems like a relatively specific value. I assumed I could expect a high efficiency so that's why I guessed 90%. How do you know its not something like 75% or why didn't you round down to 80% for a more generalized answer? $\endgroup$
    – Bill Shao
    Mar 26, 2021 at 6:03
  • $\begingroup$ It's only a guess. In the past I played around with Hamprop and would expect to get that number as a result. This would be without installation losses, e.g. from the higher friction on the surfaces in the prop slipstream. $\endgroup$ Mar 26, 2021 at 7:21

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