Regarding Hiram Maxim's 1894 plane:
"
The actual horse power delivered to the screws is 363 when the engines are running at 375 revolutions per minute. ... The thrust of the screws, when the machine is moored, is 2,100 lb., and when it is running it is 2,000 lb. We give these figures as they were supplied to us, omitting decimals. The total lift is something over 10,000 lb. at a speed of forty miles an hour and with the aeroplanes making an angle of about 7.25 degrees with the horizontal."
Source:
The Sydney Mail - Google News Archive Search or
The Pioneers : An Anthology : Sir Hiram Maxim (1840 - 1916)
2000 lb * 40 mph / 363 HP = 58.7% - The efficiency of the propellers is simply too high for 1894. It should have been below 50%.