The lighter the better in weak lift ?  
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The lighter the better in weak lift ? - 2/8/2003 3:01:16 PM   
yclui


 

Posts: 43
Joined: 10/13/2002
From: Hongkong,
Status: offline 		I am not too sure. . . . .

It was rather foggy ( soˇK NO thermal for sure ) off the slope today and the wind was really weak so I flew my Highlight HLG ( I believe it's the equivalent of Omega in the US. info at http://www.euro-sailplanes.co.uk/uk/html/sport-hlg/highlight.htm ) thinking that my model is probably the only one that can stay aloft. Much to my amazement, my friendˇ¦s all-mold mini NYX ( http://www.euro-sailplanes.co.uk/uk/html/sport-hlg/mini-nyx.htm ) did equally well, may be even slightly better.

Both models are 1.5m in span and have similar wing area but my friendˇ¦s moldy is twice as heavy as my HLG. The fact that both models can stay aloft equally well makes me wonder whether weight is such a dominating factor in determining how floaty a glider is under weak-lift condition.

I know the information given here is too rough and incomplete for any systematic analysis but if someone can suggest what MIGHT have counteracted the weight penalty of my friendˇ¦s moldy, I will appreciate it.

I have came across the theory that up to a certain point, increasing the weight helps to increase the speed and hence the ˇ§Reynoldˇ¦s numberˇ¨ which is supposed to make the airfoil more efficient. To be honest, I have not done sufficient reading on aerodynamics to understand that theory well but I did try it out today by putting 10% more weight into my HLG but there was not any perceivable improvement. Having said that, the test was very rough so it really didnˇ¦t prove or disprove anything. If anyone has any ˇ§thumbs-onˇ¨ experience in this regard, I would like to hear about it.

Thanks,

Y C Lui
       Post #: 1

The lighter the better in weak lift ? - 2/8/2003 3:58:06 PM   
Cactus.



Posts: 6138
Joined: 12/19/2001
From: CamborneCornwall, UNITED KINGDOM
Status: offline 		i've found when on the slope if the lift drops most pilots pull up to try and get every inch of height and end up sinking down, i put my nose down and fly faster, this keeps me going longer.
your friends plane is much cleaner looking than yours also

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My half dead website www.philsrcworld.fsnet.co.uk new site coming soon.
Redruth & District model flying club www.rcflye

(in reply to yclui)
       Post #: 2

The lighter the better in weak lift ? - 2/8/2003 6:37:13 PM   
Al Stein



Posts: 968
Joined: 1/7/2002
From: Johnstown, PA, USA
Status: offline 		The deal with the Reynolds number is that there's a speed range (which happens at low speed) in which the airflow separates from the rear part of the wing surface for most of our airfoils, leaving a low pressure rotor btween the wing and the airflow. While that condition is in effect, there's a lot more drag generated than under normal conditions. You can test whether that's happening by experimenting with trips or turbulators... the game there is to get the boundary layer air agitated enough to stick to the wing rathe than have it separate and allow that big, draggy bubble to form.[QUOTE]Originally posted by phillybaby
...your friends plane is much cleaner looking than yours also[/QUOTE]You really think so? I thought the both had good looking planforms and clean fuselages, with the highlight having a potentially better form with its pod and boom type setup. It looked to me like how well the wings and tails were (or were not) faired in could easily make either of these the slicker plane... and, in fact, the Nyx looked to me like it was more likely to have a nasty acute angle between wing and fuselage. I dunno.

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. . . Aim High!

(in reply to yclui)
       Post #: 3

The lighter the better in weak lift ? - 2/8/2003 10:59:22 PM   
Tall Paul



Posts: 4662
Joined: 6/23/2002
From: Palmdale, CA, USA
Status: online 		Ollie has posted -the- answer to this very question on E-zone, Modeling Science..

(in reply to yclui)
       Post #: 4

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