Re: [ULF-1] Why is Vne 80 km/hr

From: Member 62
Date: 2011-05-06 19:51 UTC+01:00
Message: #0266

Hi Richard,

I think you may have misunderstood the polar curve.  It 
shows the sink rate through the speed range, rather than absolute 
values for lift.  This enables glide angle to be determined at various 
speeds (and head/tailwind components too by shifting the origin) and is 
useful for speed-to-fly and so forth.  Forgive me if I'm patronising 
you here - but maybe I misinterpreted your meaning.

Flying fast, the 
wing will generate a lot of lift, causing a tendency to raise the 
nose.  This needs to be countered by lots of down elevator.  So with 
increased speeds come increased loads on the wings and tail (and hence 
the bit that holds them together too).  I would guess that the tail may 
be the weakest link here.  There is also the danger of flutter, which 
would not go well on a light, stiff structure.

As to the specific 
value, then yes - Dieter will have a far better answer.

Member 62

P.S.  
Hope your build is going well.  I'm just waiting for my next Member 60 order 
to be delivered ...



I think that this may be a question for Deiter, 
can anyone please explain what limits the VNE to 80 km/hr? The aircrapt 
is well stressed to stand +6g -4g.
The very slow airfoill section 
begins to lose lift above about 40km/hr, does this indicate the 
possibility of a high speed stall at some speed well above the 80 km/hr 
Vne? In other words what is the Vne safety margin and what determines 
Vne for the ulf-1?