Horse Power help!

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

Help Support HomeBuiltAirplanes Forum by donating:

  1. Oct 10, 2012 #1

    Ar2hur

    Ar2hur

    Ar2hur

    Member

    Joined:
    Oct 10, 2012
    Messages:
    8
    Likes Received:
    1
    Location:
    Wateford, Ireland
    Does anyone know how much weight ( of an aircraft, in this case) can a 20 hp engine lift? Approximately how much hp is required to lift up to 200kg. Will be very gratefull. thanks
     
    Riggerrob likes this.
  2. Oct 10, 2012 #2

    StarJar

    StarJar

    StarJar

    Well-Known Member

    Joined:
    Sep 6, 2011
    Messages:
    1,723
    Likes Received:
    405
    Location:
    El Centro, California, USA
    As pilots, we first are tempted to correct you on the word "lift". The engine does not lift, but rather causes forward speed, so that the WINGS can lift. But to give you a general answer, 20 hp is sometimes used on planes with a total loaded (gross) weight of about 400-500 lbs. 180-250 of which is the aircraft, and the rest is pilot and fuel.
     
    Riggerrob likes this.
  3. Oct 10, 2012 #3

    autoreply

    autoreply

    autoreply

    Moderator

    Joined:
    Jul 8, 2009
    Messages:
    10,732
    Likes Received:
    2,553
    Location:
    Rotterdam, Netherlands
    Depends on the gearing. An elevator on an aircraft carrier runs on something like 20 HP and can lift a 60,000 lbs fighter.

    Raymers "Simplified aircraft design" is a great starter to get some insight into this type of questions, as is "The Simple Science of Flight" by Henk Tennekes.
     
    Riggerrob and bmcj like this.
  4. Oct 11, 2012 #4

    Dana

    Dana

    Dana

    Super Moderator Staff Member

    Joined:
    Apr 4, 2007
    Messages:
    8,852
    Likes Received:
    3,196
    Location:
    CT, USA
    As StarJar said, the engine provides thrust, not lift. The thrust overcomes drag, both parasitic and also drag produced by the wing as a by-product of creating lift. Now, power is thrust times velocity, so while 20HP might be enough to get a 200kg airborne, it will fly very slowly. Or you might power a relatively fast aircraft with 20HP, but it will have very poor takeoff and climb performance. Aircraft in the 200kg range usually have engines more in the 40-60HP range.

    -Dana

    It's only premarital sex if you're going to get married.
     
    Riggerrob likes this.
  5. Oct 11, 2012 #5

    SVSUSteve

    SVSUSteve

    SVSUSteve

    Well-Known Member

    Joined:
    Aug 21, 2007
    Messages:
    3,890
    Likes Received:
    940
    Location:
    Evansville, Indiana
    To be brutally honest, it's one of those "You can, but it doesn't mean you should" scenarios. 40 hp is about the minimum just because of those days where you're behind the curve (marginal DA, etc) that little margin of a few extra horsepower might give you the extra airspeed to make the difference between safety and biting it into the trees off the end of the runway. Then again, this is my own mileage and I don't feel any need to try to see how light or low-powered I can make something that will leave the ground. Yours may vary.
     
    Riggerrob likes this.
  6. Oct 11, 2012 #6

    BBerson

    BBerson

    BBerson

    Well-Known Member HBA Supporter

    Joined:
    Dec 16, 2007
    Messages:
    12,669
    Likes Received:
    2,591
    Location:
    Port Townsend WA
    X-Plane simulator is a good tutorial for these questions. The data is shown in real time as you fly your digital design.
    BB
     
  7. Oct 11, 2012 #7

    timberwolf8199

    timberwolf8199

    timberwolf8199

    Well-Known Member

    Joined:
    Sep 3, 2011
    Messages:
    278
    Likes Received:
    68
    Location:
    Grand Rapids area, MI, USA
    Autoreply's response demonstrates exactly what I was thinking. To answer your question you will need to define what is your intended method for lifting this weight? With gears and mechanisms (Autoreply) it could be a lot, with a propeller/rotor it will be less, with wings and thrust (starjar/Dana) it will be something else. The question needs specifics.
     
    Riggerrob likes this.
  8. Oct 11, 2012 #8
    If you mean "lift at cruise", with 20 Hp could lift a pretty heavy motor glider, say 1000 kg.
    The Solar Impulse would probably fly with 20 HP, and it weights 1600 kg.

    To lift 200 kg with a high performance wing you would probably need more power to counter skin drag et c. than lift-induced one, theorically even 5 HP could suffice.

    In practice, you don't design a sport aircraft for lift at cruise, but for the required climb ratio and/or speed (and a lot of other project parameters !).
     
    Riggerrob likes this.
  9. Oct 11, 2012 #9

    bmcj

    bmcj

    bmcj

    Well-Known Member HBA Supporter

    Joined:
    Apr 10, 2007
    Messages:
    13,176
    Likes Received:
    5,084
    Location:
    Fresno, California
    AR2HUR... are you asking about lifting a plane on an elevator or the lift of a plane in flight? You are getting good answers for both here, but the answers might seem confusing until you tell us which you mean.

    As for climb rate in flight, I'd like to add that climb rate is determined by "excess power". Excess power is basically what you have available to you after subtracting out the power that is required for level flight at the given altitude and airspeed. Once you know the excess power, it is basic mathematics to determine climb rate. Remember, one horsepower is 550 foot-pounds per second.
     
    Last edited: Oct 12, 2012
    Riggerrob likes this.
  10. Oct 11, 2012 #10

    Ar2hur

    Ar2hur

    Ar2hur

    Member

    Joined:
    Oct 10, 2012
    Messages:
    8
    Likes Received:
    1
    Location:
    Wateford, Ireland
    Sorry for my incorrect wording, but I meant if an aircraft has a 20 hp engine, what is the max weight of the aircraft for it to lift off.... Thanks for your answers!
     
  11. Oct 11, 2012 #11

    Ar2hur

    Ar2hur

    Ar2hur

    Member

    Joined:
    Oct 10, 2012
    Messages:
    8
    Likes Received:
    1
    Location:
    Wateford, Ireland
    I meant about lifting a plane with elevator.
     
  12. Oct 11, 2012 #12

    Ar2hur

    Ar2hur

    Ar2hur

    Member

    Joined:
    Oct 10, 2012
    Messages:
    8
    Likes Received:
    1
    Location:
    Wateford, Ireland
    with a propeller.
     
  13. Oct 11, 2012 #13

    Topaz

    Topaz

    Topaz

    Super Moderator Staff Member

    Joined:
    Jul 30, 2005
    Messages:
    13,964
    Likes Received:
    5,589
    Location:
    Orange County, California
    Ar2hur, the problem here is that the answer depends upon a lot more than the engine power. It's more than "lifting" the aircraft. An underpowered aircraft can usually become airborne, but might not be able to climb more than a few feet above the ground - with obvious bad consequences. So what you really want to ask here is, "Can I get an adequate climb rate with 'x' horsepower in 'y' airframe, at 'z' takeoff weight?" The second part of that question is, "What is an adequate climb rate?" People's opinions vary on that, but you'll usually see "adequate" values falling in the "500fpm or more" range.

    Getting an answer to the first question takes a little bit of work, but nothing hugely difficult. Wing loading, wing aspect ratio, overall drag of the airframe, plus several other factors go into determining how much climb you can get out of a given horsepower and airframe weight. The books in our "Recommended Reading" section can get you there. If you just want the "quick and dirty" first-pass design knowledge, then Raymer's Aircraft Design for Homebuilders is a good value at about $32 on Amazon.
     
    Riggerrob likes this.
  14. Oct 11, 2012 #14

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    6,640
    Likes Received:
    2,532
    Location:
    Rocky Mountains
    These two clarifications still leave me a bit confused. :ponder: Here in the US "elevator" is used to describe both a mechanical lifting platform and a pitch control device on a plane.

    Making the assumption that you are using elevator to mean the pitch control device then bmcj's info in post #9 is the most relevant.

    A quick way to estimate the minimum Hp needed for level flight is to use the lift to drag ratio of the plane if it is available. For example a 1000 pound plane with a L/D ratio of 12 to 1 would generate around 80 pounds of drag thus needing 80 pounds of thrust to remain in level flight at the best L/D speed. There are formulas to estimate the Hp needed to produce thrust. Flying faster or slower than the best L/D speed will require more Hp. For a quick reality check I generally use 4 pounds of thrust for each Hp, but that number can vary considerably depending on the situation.

    To answer your original question more directly with a couple of examples: A Quickie with a gross weight of 500 pounds, and a L/D ratio of 12/1, will fly and climb adequately with 20 Hp giving a cruise speed of around 110 MPH. A Monerai motor glider with about the same weight and Hp, but with a higher L/D ratio of around 22/1, can remain in level flight with less hp but will climb faster than the Quickie on the same power.

    If you could overload the Monerai to around 830 pounds it would have the same climb rate as the Quickie, but at a much lower speed because it's best L/D is at a lower speed.

    So there is no one simple answer. It depends on several variables. With most conventional configurations it would be hard to design a practical plane that could operate safely on 20 Hp that weighs more than 1000 pounds. Half that much, or 500 pounds, is more realistic as the 2 examples would indicate.

    Edit: To add to Topaz's book recommendation, if you are just starting down this path I'd recommend Model Aircraft Aerodynamics by Martin Simons ISBN#1-85486-5. All the theory applies to full size airplanes, it's an easier read for the beginner, and it's cheaper!
     
    Last edited: Oct 11, 2012
    Riggerrob likes this.
  15. Oct 11, 2012 #15

    Dana

    Dana

    Dana

    Super Moderator Staff Member

    Joined:
    Apr 4, 2007
    Messages:
    8,852
    Likes Received:
    3,196
    Location:
    CT, USA
    Ar2hur, rather than asking "how much can I lift with 20HP", why don't you tell us what you're trying to do, so we can know how to answer?

    -Dana

    I'm not saying let's go kill all the stupid people... I'm just saying let's remove all the warning labels and let the problem sort itself out.
     
    Topaz likes this.
  16. Oct 11, 2012 #16

    clanon

    clanon

    clanon

    Well-Known Member

    Joined:
    Jun 6, 2007
    Messages:
    1,101
    Likes Received:
    217
    I think he means "To fly"
    with 20hp...:ponder:

    PS:Sarcastic are we becoming , young padawans...?
     
    Topaz likes this.
  17. Oct 11, 2012 #17

    Jan Carlsson

    Jan Carlsson

    Jan Carlsson

    Well-Known Member

    Joined:
    Jan 11, 2009
    Messages:
    1,860
    Likes Received:
    387
    Location:
    Sweden
    20 hp can lift 1500 kg one meter in one sec.
    you should not lift the aeroplane in the elevator.
    20 HP can lift 200 kg 7,5 meter in one sec.
    minus drag, and efficiency losses.
    it also depends on the temp and air pressure.
    Troll don't fly.
     
  18. Oct 11, 2012 #18

    clanon

    clanon

    clanon

    Well-Known Member

    Joined:
    Jun 6, 2007
    Messages:
    1,101
    Likes Received:
    217
    The guys who said invented the Air-plane (a flying machine) used ~ 12 Hp...

    PS: i wonder what kind of answer would they get on this forums...:ponder:
     
  19. Oct 11, 2012 #19

    Topaz

    Topaz

    Topaz

    Super Moderator Staff Member

    Joined:
    Jul 30, 2005
    Messages:
    13,964
    Likes Received:
    5,589
    Location:
    Orange County, California
    Let's try to turn this into a learning opportunity, folks. The OP came here to learn. Let's help him do so.
     
  20. Oct 11, 2012 #20

    clanon

    clanon

    clanon

    Well-Known Member

    Joined:
    Jun 6, 2007
    Messages:
    1,101
    Likes Received:
    217
    Already did !
    Sent him 5 or 6 ebooks this morning.
     
    Topaz likes this.

Share This Page

Group Builder
arrow_white