Horse Power help!

Discussion in 'General Experimental Aviation Questions' started by Ar2hur, Oct 10, 2012.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Feb 13, 2020 at 8:57 PM #41

    BBerson

    BBerson

    BBerson

    Well-Known Member HBA Supporter

    Joined:
    Dec 16, 2007
    Messages:
    12,631
    Likes Received:
    2,577
    Location:
    Port Townsend WA
    Certainly. It is much more work to pedal an airplane than a bicycle or walking.
    But you could build an airplane that flies on a 1/4hp. It would not be very strong for typical conditions.
     
  2. Feb 13, 2020 at 9:46 PM #42

    lr27

    lr27

    lr27

    Well-Known Member

    Joined:
    Nov 3, 2007
    Messages:
    3,518
    Likes Received:
    522
    Airplanes aren't NECESSARILY less "efficient" than cars. Some airplanes, in cruise, get better mileage than a small car. I wonder what mileage the DA-11 gets cruising at 125 mph with a 20 hp engine?

    80 percent efficiency is pretty good, but I doubt very many airplanes see that at any time during their takeoff run. NONE get that at the moment of brake release on a calm day. A variable pitch prop can only help with part of the problem. At low speeds, you need a large diameter to be efficient. The famous Daedalus human powered airplane used an 11.3 foot prop to absorb a fraction of a horsepower at something like 15 mph, at low rpm.

    If wheel bearing drag was significant, hubs would be smoking hot after landing. 1 hp is equal to 746 watts, or as much power as an ordinary microwave.
     
  3. Feb 13, 2020 at 9:50 PM #43

    proppastie

    proppastie

    proppastie

    Well-Known Member

    Joined:
    Feb 19, 2012
    Messages:
    4,035
    Likes Received:
    1,186
    Location:
    NJ
    which brings up another issue. ....I thought humans could only generate about 3/4 hp.
     
  4. Feb 13, 2020 at 9:57 PM #44

    proppastie

    proppastie

    proppastie

    Well-Known Member

    Joined:
    Feb 19, 2012
    Messages:
    4,035
    Likes Received:
    1,186
    Location:
    NJ
    Probably just mental masterbation.....we can account for the loss and do accurate calculations.....that it is not intuitive should not be an issue.
     
  5. Feb 13, 2020 at 10:40 PM #45

    pictsidhe

    pictsidhe

    pictsidhe

    Well-Known Member

    Joined:
    Jul 15, 2014
    Messages:
    7,323
    Likes Received:
    2,106
    Location:
    North Carolina
    For how many seconds? 100W is the sustained output per day of a average healthy person. Athletes can double that. Peak hp from a horse is around 15. But if you want it to work for 10 hours, it is 1 horsepower. From a fit human, the peak is over 1. At the age of 18, I somehow got into a pissing contest with someone. It involved running up 3 flights of stairs, carrying sacks of flour. I won. I manged to do it with 220lb of flour on my shoulders. I was quite glad when he admitted defeat...

    The English Electric Wren flew on 8hp, and managed 50mph 87.5mpg. It was not very spritely, however.
     
  6. Feb 13, 2020 at 10:53 PM #46

    Dana

    Dana

    Dana

    Super Moderator Staff Member

    Joined:
    Apr 4, 2007
    Messages:
    8,829
    Likes Received:
    3,173
    Location:
    CT, USA
    No, you're confusing torque with work. Torque and work have the same units, which makes it confusing, so we usually refer to torque as ft-lb (or newton-meters or whatever), that is the length of a lever times a force applied perpendicular to the end of the lever. You can have torque without motion if there is an equal opposing torque. Work is force applied over a movement in the same direction as the force; we usually say lb-ft to make the distinction. In metric units, one joule is one newton-meter of work.

    Power is the rate of doing work, e.g. lb-ft per second or joules/sec. 550 lb-ft/sec is one horsepower; in metric, one Watt equals one joule/sec.
     
    wsimpso1, pictsidhe and proppastie like this.
  7. Feb 14, 2020 at 12:17 AM #47

    Jay Kempf

    Jay Kempf

    Jay Kempf

    Well-Known Member Lifetime Supporter

    Joined:
    Apr 13, 2009
    Messages:
    3,771
    Likes Received:
    1,029
    Location:
    Warren, VT USA
    Yeah, the old torque vs. HP debate that goes on in most motorsports forums and garages/hangars around the planet. Been lobbying for years that we should call that Torque that is graphed on an engine dynamometer power curve "Dynamic Torque." as it is unfolding at some RPM. The more classic Newtonian or Archemedian one we can call "Static Torque." Whaddyathink?
     
  8. Feb 14, 2020 at 3:08 AM #48

    mcrae0104

    mcrae0104

    mcrae0104

    Armchair Mafia Conspirator HBA Supporter

    Joined:
    Oct 27, 2009
    Messages:
    3,096
    Likes Received:
    2,131
    Location:
    BDU, BJC
    There is a paper entitled What Price Speed? that deals with this topic. It is interesting to see that some aircraft can be more efficient--relative to their speed--than some wheeled vehicles. Pages from EPPaper080229E.jpg
     
    wsimpso1 likes this.
  9. Feb 14, 2020 at 3:27 AM #49

    lr27

    lr27

    lr27

    Well-Known Member

    Joined:
    Nov 3, 2007
    Messages:
    3,518
    Likes Received:
    522
    As I recall, the right version of a fully loaded 747 can get the equivalent of over 110 seat miles per gallon on a medium long trip. I don't remember just how long, but I think it was more than 1,000 miles.
     
  10. Feb 14, 2020 at 3:45 AM #50

    Aesquire

    Aesquire

    Aesquire

    Well-Known Member

    Joined:
    Jul 29, 2014
    Messages:
    2,382
    Likes Received:
    973
    Location:
    Rochester, NY, USA
    Human powered planes figure on 1/3 hp. And they pick skinny little guys with big legs and thin arms. G loading designed for 1.x so the Gossamer Condor never banked more than about 30 degrees.
     
  11. Feb 14, 2020 at 4:19 AM #51

    lr27

    lr27

    lr27

    Well-Known Member

    Joined:
    Nov 3, 2007
    Messages:
    3,518
    Likes Received:
    522
    The Daedalus airplane broke up in the air while, I think, setting up for landing. Fortunately from low altitude over water.
     
  12. Feb 14, 2020 at 5:20 AM #52

    BBerson

    BBerson

    BBerson

    Well-Known Member HBA Supporter

    Joined:
    Dec 16, 2007
    Messages:
    12,631
    Likes Received:
    2,577
    Location:
    Port Townsend WA
    Last edited: Feb 14, 2020 at 5:42 AM
  13. Feb 14, 2020 at 1:39 PM #53

    Swampyankee

    Swampyankee

    Swampyankee

    Well-Known Member

    Joined:
    Dec 25, 2015
    Messages:
    1,411
    Likes Received:
    367
    Location:
    Earth USA East Coast
    James Watt concluded that a horse could produce about 33,000 ft-lbf/second of power (he was wrong. Horses can routinely produce and sustain more than a horsepower, and there is significant feeling in the engineering and communities that he chose 33,000 ft-lbf/min knowing that this was significantly less than a horse could produce as he wanted to sell steam engines to replace those horses ;))
     
    proppastie and wsimpso1 like this.
  14. Feb 14, 2020 at 2:04 PM #54

    wsimpso1

    wsimpso1

    wsimpso1

    Super Moderator Staff Member

    Joined:
    Oct 19, 2003
    Messages:
    6,150
    Likes Received:
    3,459
    Location:
    Saline Michigan
    The reason most props are not more than 80% efficient on takeoff is because most props are designed for best efficiency in cruise. If you wanted a prop to be 80% efficient at low speeds and low power, you could do that. You could even design it for that efficiency at zero speed, if you were measuring change in air energy in the thrust direction per unit power input. On the other hand, total propulsive efficiency is always zero when you are not moving- that is called "trivial case".

    As to size for efficiency, you are now confusing Efficiency with Effectiveness. EffIciency is the ratio of work made good vs work input. In props that has to do with how much air moved by how much change in velocity is made on the air. Small props can have high efficiency, but will still be lower static thrust than a larger prop at same efficiency. Helicopters use large rotors for this reason - larger props mean more static thrust from any given amount of power. Daedalus needed a large lightly loaded slow turning prop to make enough thrust from one human to drag a large lightly loaded airframe into the air.

    Billski
     
    Last edited: Feb 14, 2020 at 8:04 PM
    delta likes this.
  15. Feb 14, 2020 at 2:47 PM #55

    lr27

    lr27

    lr27

    Well-Known Member

    Joined:
    Nov 3, 2007
    Messages:
    3,518
    Likes Received:
    522
    I think your version of efficiency may be good for fans, but for airplanes I think the correct unit of measure is thrust times airspeed divided by shaft power. If it doesn't show up as thrust, the airplane can't really use it, even if you knock over that guy standing 100 feet back, directly in line with the prop's axis.

    You could put 100 hp into a teensy prop that transferred 80 percent of the shaft horsepower into the kinetic energy of a Mach 0.5 stream of air. However, it wouldn't fly a cub as well as a 40 hp engine turning 2,000 rpm with a large prop.
    It's possible to define efficiency in useful ways and in less than useful ways. I once participated in a wave energy project with a device which we calculated as 140 percent efficient. If that had been true with an appropriate definition of efficiency, we would have had the trickier half of a perpetual motion machine. Alas, it was not to be.
     
  16. Feb 14, 2020 at 3:10 PM #56

    BBerson

    BBerson

    BBerson

    Well-Known Member HBA Supporter

    Joined:
    Dec 16, 2007
    Messages:
    12,631
    Likes Received:
    2,577
    Location:
    Port Townsend WA
  17. Feb 14, 2020 at 3:47 PM #57

    Dan Thomas

    Dan Thomas

    Dan Thomas

    Well-Known Member

    Joined:
    Sep 18, 2008
    Messages:
    5,003
    Likes Received:
    2,157
    I think a Greyhound bus could do better than that. 4 MPG (guessing here) times 45 pax is 180 seat-miles per gallon.
     
  18. Feb 14, 2020 at 10:17 PM #58

    lr27

    lr27

    lr27

    Well-Known Member

    Joined:
    Nov 3, 2007
    Messages:
    3,518
    Likes Received:
    522
    Obviously, no airborne vehicle will beat a well faired bicycle with a teensy motor or a truly lightweight, streamlined rail vehicle, or a sailing ship At least on seat miles per gallon.
     
  19. Feb 14, 2020 at 10:37 PM #59

    proppastie

    proppastie

    proppastie

    Well-Known Member

    Joined:
    Feb 19, 2012
    Messages:
    4,035
    Likes Received:
    1,186
    Location:
    NJ
    Hill launch or winch launch glider.
     
  20. Feb 15, 2020 at 1:18 AM #60

    wsimpso1

    wsimpso1

    wsimpso1

    Super Moderator Staff Member

    Joined:
    Oct 19, 2003
    Messages:
    6,150
    Likes Received:
    3,459
    Location:
    Saline Michigan
    Hmm, OK, let's do data.

    Adult humans have about 100W of waste heat just sitting in a chair. That is 0% efficiency, but without it, that human is DEAD, so that poor efficiency is acceptable.

    Couch potatoes may only be up to generating 100 W of motive power, either moving themselves around or walking on a drum windlass to run a crane on an ongoing basis, but professional cyclists can make 400 W continuously for several hours a day, every day. It is just a matter of how well trained the human in question is at processing oxygen and how many calories they consume.

    And the point of my observation on my personal peak horsepower? When someone says something has horsepower, some folks see a galloping race horse. This 63 year old man can make a couple HP for a few seconds. When somebody says two to three horsepower, this 63 year old man does not see a galloping horse, he sees a critter with six to ten times his muscle mass at a modest walk turning a windlass all day long and hardly get worked up. One horsepower is a pretty anemic horse, but it does lift 550 pounds one foot per second. It is just a unit of work per unit time that Watt came up with to market his steam engines, and most students of the topic know that he underestimated how much a horse could do to his benefit.

    Billski
     
    dog likes this.

Share This Page

Group Builder
arrow_white