RE: Minimum Power Requirement  
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RE: Minimum Power Requirement - 3/7/2008 2:44:24 PM   
kerklein2


 

Posts: 84
Joined: 7/30/2003
From: Austin, TX, USA
Status: offline 		Thank you for the reply,

How is the stall speed irrelevant? Wouldn't minimum power be what is needed to overcome drag to achieve the stall speed? If you are below the stall speed, you crash, and above it, you fly (assuming all else equal).

Right.

< Message edited by da Rock -- 3/8/2008 12:08:55 AM >

(in reply to HighPlains)
       Post #: 26

RE: Minimum Power Requirement - 3/8/2008 2:26:39 AM   
pimmnz


 

Posts: 522
Joined: 11/9/2005
From: Auckland, NEW ZEALAND
Status: offline 		The stall speed is irrelevant because it is weight dependent. Stall angle is always the same, probably around 8~10 degrees positive. Weight will determine how soon you get there, thats all. The power required to fly depends on the drag of the airframe only. If you solve the drag equation for all 'normal' angles of attack at the expected flying speeds then you will know how much thrust your engine will be required to meet. You will find that at one particular AOA there will be a minimum drag, this will determine the minimum power to fly, at the weight (L) used for the equation. This is best L/D. At any higher AOA more power will be needed to fly, at any less AOA you will need to fly faster, or come down. Maximum power required will be at the slowest speed needed to sustain flight at the maximum AOA which you can fly at without actually stalling.
Evan.

(in reply to kerklein2)
       Post #: 27

RE: Minimum Power Requirement - 3/8/2008 4:20:40 PM   
Jim Thomerson



Posts: 2824
Joined: 10/9/2002
From: Austin, TX, USA
Status: offline 		Most any sport 40 size glow engine will run in the horsepower range you listed in your first post.

(in reply to pimmnz)
       Post #: 28

RE: Minimum Power Requirement - 3/8/2008 6:06:27 PM   
Red B.


 

Posts: 1022
Joined: 8/29/2002
From: Jonkoping, SWEDEN
Status: offline
quote:

ORIGINAL: pimmnz

... You will find that at one particular AOA there will be a minimum drag, this will determine the minimum power to fly, at the weight (L) used for the equation. This is best L/D. At any higher AOA more power will be needed to fly, at any less AOA you will need to fly faster, or come down. ...


Actually, for minimum power flight the aircraft should fly at the speed where L^1.5/D is at its maximum. This usually occurs at a speed that is slightly slower than the speed where L/D is at its maximum.


_____________________________

/Red B.

(in reply to pimmnz)
       Post #: 29

RE: Minimum Power Requirement - 3/22/2008 8:42:40 PM   
kerklein2


 

Posts: 84
Joined: 7/30/2003
From: Austin, TX, USA
Status: offline 		So I don't have any updated information on the actual airfoil, but the plane did fly today at 9lbs with a Saito .91 and a hand launch. The hand launch was not a problem. The final engine will end up being smaller than that, but we are encouraged by the ability to hand launch easily.

(in reply to HighPlains)
       Post #: 30

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