Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site hou4b.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxj!houxm!hogpc!houti!ariel!hou4b!mat From: mat@hou4b.UUCP Newsgroups: net.aviation Subject: Re: New Engine Unveiled Message-ID: <1177@hou4b.UUCP> Date: Wed, 3-Oct-84 17:24:37 EDT Article-I.D.: hou4b.1177 Posted: Wed Oct 3 17:24:37 1984 Date-Received: Thu, 4-Oct-84 03:47:56 EDT References: <12388@sri-arpa.UUCP> Organization: AT&T Information Systems Laboratories, Holmdel, NJ Lines: 33 With regards to the counter-rotating unducted fan ... Yes, the two fans interact. No, they don't interfere. The fans are not supposed to pull the air around and around ... they are supposed to push it BACK (cuz thats what makes the plane go forward ...) The counter-rotating fans reduce torque effects, which apparently are more severe with the unducted fan than with conventional ducted fans. The whole point of the ducts is to avoid all the interesting effects that occur around the tips of prop blades, while still getting as much momentum into the airstream as possible. [Back to Freshman Physics] Note momentum, not energy. Energy goes as the square of velocity, and momentum as the first power. Conservation of momentum holds -- so that going moving twice as much air at half the speed will take half as much power. The speed in question is the difference between the speed (relative to the aircraft) that the gasses come in at and the speed they leave at; when talking about the energy, it is the differences in the squares of the speeds. (NB Power is energy/unit time...) If instead of pushing exhaust gasses and propwash, you are pushing against something that is (almost) infinitely massive (like the earth) all of your energy goes into the thing that is moving. It follows that as the mass of what you are pushing against (or ejecting) goes down, the amount of energy you lose in it goes up. This is one advantage that fans have over straight jets ... they move a greater mass, and so have to speed it up less to get a given momentum out of it. -- from Mole End Mark Terribile (scrape .. dig ) hou4b!mat ,.. .,, ,,, ..,***_*.