Gezellig
June 11th 08, 11:15 PM
On Tue, 10 Jun 2008 18:14:41 GMT, Tauno Voipio wrote:
> Tina wrote:
>> On Jun 10, 1:09 pm, Tauno Voipio > wrote:
>>
>>>Tina wrote:
>>>
>>>>One point about the lift fairy sitting on the tail I'd like to
>>>>understand is this -- actually a serious question. As I understand
>>>>it, nearly aways the tail is exerting a downward force, since the
>>>>center of lift is aft of the center of gravity on general aviation
>>>>airplanes (that is true, isn't it -- that the cg is forward of the
>>>>center of lift?). If so the tail really is imposing an increased load
>>>>on the airplane, adding to its effective weight. The question I have
>>>>is, how many pounds of weight is imposed aerodynamically for an
>>>>airplane that might be loaded with its CG at the forward limit? I
>>>>don't know where the center of lift is on ga airplanes -- a third of
>>>>the way aft of the leading edge of the wing is an ok approximation,
>>>>but a few inches error on an airplane weighing what ours does at max
>>>>could make a huge change in the required force to overcome the nose
>>>>heavy moment.
>>>
>>>A rule of thumb is that the force on the horizontal tail
>>>is 5 to 10 per cent of the wing lift. This translates
>>>to a loss of 10 to 20 per cent of the raw gross lift
>>>availbale from the horizontal airfoils.
>>>
>>>
>>>>I'm obviously thinking about increased efficiency -- extra weight
>>>>added because of either fat people, full fuel, or aerodynamically
>>>>imposed, all cost horsepower (OK, watts for you purists) to move
>>>>around.
>>>
>>>This is the reason why modern military aircraft are designed
>>>aerodynamically unstable, and the electronic gnomes of the
>>>flight control system have to work all they can do.
>>>
>>>The loss of gross lift is the proce to pay for simple and
>>>safe longitudinal stability.
>>>
>>>--
>>>
>>>Tauno Voipio
>>>tauno voipio (at) iki fi
>>
>> Thanks for the rule of thumb, Tauno. I have watched how busy the
>> flippers are on fighters when they are in the flare -- no human pilot
>> is working that hard for control. I knew the fighters are designed to
>> be aerodynamically unstable.
>>
>> So the aerodynamic longitudinal stability the tail provides might
>> cost us 5 to 10%, The obvious question is, do canards buy back that
>> fraction? They would be offering positive lift, and if they stall
>> first would provide the same sort of longitudinal stability, wouldn't
>> they?
>
> Yes - they do bring back some, and this is the reasoning behind
> e.g. Rutan's Voyager,
>
> The price is that the canard (front wing) has to stall first
> unless you want to fall to ground in reverse when the thing
> stalls. The rumours are that the canards are a PITA to land
> nicely.
Apparently only to those who don't know how to fly one.
> Tina wrote:
>> On Jun 10, 1:09 pm, Tauno Voipio > wrote:
>>
>>>Tina wrote:
>>>
>>>>One point about the lift fairy sitting on the tail I'd like to
>>>>understand is this -- actually a serious question. As I understand
>>>>it, nearly aways the tail is exerting a downward force, since the
>>>>center of lift is aft of the center of gravity on general aviation
>>>>airplanes (that is true, isn't it -- that the cg is forward of the
>>>>center of lift?). If so the tail really is imposing an increased load
>>>>on the airplane, adding to its effective weight. The question I have
>>>>is, how many pounds of weight is imposed aerodynamically for an
>>>>airplane that might be loaded with its CG at the forward limit? I
>>>>don't know where the center of lift is on ga airplanes -- a third of
>>>>the way aft of the leading edge of the wing is an ok approximation,
>>>>but a few inches error on an airplane weighing what ours does at max
>>>>could make a huge change in the required force to overcome the nose
>>>>heavy moment.
>>>
>>>A rule of thumb is that the force on the horizontal tail
>>>is 5 to 10 per cent of the wing lift. This translates
>>>to a loss of 10 to 20 per cent of the raw gross lift
>>>availbale from the horizontal airfoils.
>>>
>>>
>>>>I'm obviously thinking about increased efficiency -- extra weight
>>>>added because of either fat people, full fuel, or aerodynamically
>>>>imposed, all cost horsepower (OK, watts for you purists) to move
>>>>around.
>>>
>>>This is the reason why modern military aircraft are designed
>>>aerodynamically unstable, and the electronic gnomes of the
>>>flight control system have to work all they can do.
>>>
>>>The loss of gross lift is the proce to pay for simple and
>>>safe longitudinal stability.
>>>
>>>--
>>>
>>>Tauno Voipio
>>>tauno voipio (at) iki fi
>>
>> Thanks for the rule of thumb, Tauno. I have watched how busy the
>> flippers are on fighters when they are in the flare -- no human pilot
>> is working that hard for control. I knew the fighters are designed to
>> be aerodynamically unstable.
>>
>> So the aerodynamic longitudinal stability the tail provides might
>> cost us 5 to 10%, The obvious question is, do canards buy back that
>> fraction? They would be offering positive lift, and if they stall
>> first would provide the same sort of longitudinal stability, wouldn't
>> they?
>
> Yes - they do bring back some, and this is the reasoning behind
> e.g. Rutan's Voyager,
>
> The price is that the canard (front wing) has to stall first
> unless you want to fall to ground in reverse when the thing
> stalls. The rumours are that the canards are a PITA to land
> nicely.
Apparently only to those who don't know how to fly one.