RE: Re: Treger and Schramm

From: hermann andresen <hermanna_at_hotmail.com>
Date: Fri, 17 Aug 2012 08:24:21 +0000

What's really scary is that Schramm has rounded tips. Jim Richmond claimed 2 min (5%) improvement on his CatWalker by squaring off the rear tip to the TE.
Some 60yr ago (while in grammer school) a span limit was imposed on low ceiling gliders. My scaled down model fell short. In desperation, the scissors removed 20% of the span including the rounded tips. Result: 10% more time! Since then removing rounded tips has produced 5-10% more duration.
Lower AR, higher wing loading, better performance, made no sense. FLUID-DYNAMIC LIFT by Hoerner shows that even full sized planes have the tip vortices pull inboard of the tips, for more induced drag. This is agrevated by the thick (on order of 1/2") wake in the models. Thick wake results in high profile drag. Another problem with the rounded tip is that the wake only drops as the sq root of the chord, so if a 5cm chord near the tip will have 1/2 the wake as the 20cm root chord. 1/4 the lift, 1/2 the drag, not a great tradeoff.

So what's bottom line? An additional 2 minute advantage next time?

To: Indoor_Construction_at_yahoogroups.com
From: ykleetx_at_gmail.com
Date: Tue, 14 Aug 2012 20:26:43 +0000
Subject: [Indoor_Construction] Re: Treger and Schramm
















 



  


    
      
      
      It sure would be great if we could invite Treger and Schramm to fly at Lakehurst. Does anyone know how it would be possible to invite a German and Slovakian citizen to gain access to a U.S. military base?



About why Treger and Schramm are ahead of the pack, I have absolutely no clue. Not even an inkling.



--- In Indoor_Construction_at_yahoogroups.com, Jake Palmer <82.jake_at_...> wrote:

>

> What are Treger and Schramm doing that makes their models perform so well

> in Belgrade? They're the only two people that are flying in the 37 to 39

> minute range with everyone else in the 33 to 35 minute range. They fly

> very different models, but I have to believe they've both figured out

> something that everyone else has not. After this year's champs it seems

> that thermals have been pretty well eliminated as the primary candidate.

>

> I think one place to start is the propeller. On the plan for Treger's 2010

> model he specifies a unique pitch distribution. The main section of his

> blades are 26" and the tips drop down to 20.5". Is this allowing his prop

> tips to be more efficient in high pitch? Perhaps this enables him to leave

> the prop in high pitch longer which drops his average RPM? Anyone else

> have thoughts on this subject?

>





    
     

    
    






                                                 
Received on Fri Aug 17 2012 - 01:25:17 CEST