ULF-1 Discussion Archive
Anonymous static archive of the former Mailman list
Anonymous static archive of the former Mailman list
Re: [ULF-1] Ulf-1 Digest, Vol 34, Issue 4 Why is Vne 80km/hr
Dear Dieter, Thank you for your explanation of the reasons for the Vne of the ULF-1. It sounds as if not only does one have a well defined "red mark" for Vne but that the aircraft will give aproaching warning through the effects on the controls. This is comforting to know and I shall respect the Vne. At the moment I'm making the spar caps and with your explanation in mind progression through to the "D" box will be made with utmost care, once again thank you for your help and explanation. Best Regards, Richard (Dr Member 67) >________________________________ >From: "[email]" <[email]> >To: [email] >Sent: Sunday, 15 May 2011, 18:44 >Subject: Ulf-1 Digest, Vol 34, Issue 4 > >Send Ulf-1 mailing list submissions to > [email] > >To subscribe or unsubscribe via the World Wide Web, visit > http://lists.ulf-1.com/listinfo.cgi/ulf-1-ulf-1.com >or, via email, send a message with subject or body 'help' to > [email] > >You can reach the person managing the list at > [email] > >When replying, please edit your Subject line so it is more specific >than "Re: Contents of Ulf-1 digest..." > > >Today's Topics: > > 1. Re: Why is Vne 80 km/hr (Member 9) > > >---------------------------------------------------------------------- > >Message: 1 >Date: Sat, 14 May 2011 22:13:51 +0100 >From: "Member 9" <[email]> >To: <[email]> >Subject: Re: [ULF-1] Why is Vne 80 km/hr >Message-ID: <7376F4AFDB9248F48921F00E1E20CB3F@pcreich> >Content-Type: text/plain; format=flowed; charset="iso-8859-1"; > reply-type=original > > > >Dear all, > >the cambered WORTMANN high lift wing section behaves almost >like a symmetrical airfoil with a plain - down deflected - trailing edge >flap. It produces a rather high (zero lift) nose down pitching moment, which >increases with velocity squared, causing high torsion loads on the wing >D-box. > >>From about 70 km/h onwards, the airflow on the lower side of the wing >separates, which leads to considerable performance losses, simultaneously >reducing downwash angle and dynamic pressure in front of the horizontal >stabilizer. The latter can't do its (complete) job anymore and needs the >help of the (up deflected) elevator, thus resulting in further performance >losses >and rapidly climbing control stick forces. > >Both, torsion strength of D-box and stick force, limit the ULF-1 "never >to exceed speed" (VNE) to 80 km/h. This value includes a 10 percent speed >margin, and a safety factor of 1.5 against structural failure. > >Regards, > >Dieter > > > > > >----- Original Message ----- >From: <[email]> >To: <[email]> >Sent: Friday, May 06, 2011 7:51 PM >Subject: Re: [ULF-1] Why is Vne 80 km/hr > > >> >> 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? >> >> >> _______________________________________________ >> ULF-1 discussion list -- [email] >> >> Subscribe, Unsubscribe, Preferences, List information: >> http://lists.ulf-1.com/listinfo.cgi/ulf-1-ulf-1.com > > > >------------------------------ > >_______________________________________________ >Ulf-1 mailing list >[email] >http://lists.ulf-1.com/listinfo.cgi/ulf-1-ulf-1.com > > >End of Ulf-1 Digest, Vol 34, Issue 4 >************************************ > > >