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4.5:1 ASH-25

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Pete Marsden
Posts: 29
Joined: 17 Mar 2018, 08:45
Location: Southampton

4.5:1 ASH-25

Post by Pete Marsden »

Dug my 1986 ASH-25 fuz out and have started working it (yes, I know, supposed to be completing the 1/4 Jantar but I'm at the rubbing down/priming stage on the wings and I don't like rushing it).
This ASH fuz came from Popenhausen below the Wassekruppe. The surface is a bit porous due to the weight of glass cloth used (quite coarse) so in the photo it has a generous layer of 2k high build primer on it.
I've made the tail and rudder but am scratching my head over the wings. The drawing shows zero degrees of washout but using the same basic section throughout, albeit slightly thicker at the tip.
When I've designed wings I've often substituted washout for and different tip section - usually more under-cambered - and this has worked well.
if sticking to the sections on the plan I'm inclined to build in 2 to 3' of washout - any thoughts out there?
Cheers
Pete.
Attachments
Model Fuz.jpg

John Vella
Posts: 241
Joined: 20 Mar 2017, 22:09
Location: UK

Re: 4.5:1 ASH-25

Post by John Vella »

Hi Pete on the ASH25 I would be very wary of putting extra washout on those wings which will "unload" the tips and bend them downwards on approach , especially using "crow". The reduced tip clearance increasing the chance of ground looping. I know from full size how tricky the handling of these high AR wings can be. The ASH is a very pretty sailplane.
Regards John.

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terry white
Posts: 573
Joined: 18 Mar 2015, 21:08
Location: wareham,dorset.england

Re: 4.5:1 ASH-25

Post by terry white »

Peter, can you tell us why you would choose 'more' under camber at the tips when you are trying to keep the stall away from the tips. It is usual to make the tips stay flying and let the center of wing to stall first by giving them less lift to do,hence when in crow mode the ailerons go 'up' to stay off that stall. :roll:

Also with such a high degree of washout as you are proposing on a fast flight such as a fly-past etc when the center part of the wing may be at 0 degree angle of attack the tip would be at a minus 3 degrees. This would have the effect of twisting the wings downward. Not a pretty sight.

On fast modern glass ships I favor the section change method. From center section of the wing, to a less lifting section at the tip, with no washout built in.

roo Hawkins
Posts: 831
Joined: 18 Mar 2015, 20:12
Location: Northamptonshire

Re: 4.5:1 ASH-25

Post by roo Hawkins »

hi peter what terry says is right . the first glass/foam wing glider I scratched built was a jantar 1 when I built it a put washout in. it flys great until I stick the nose down on a fast run and what happens ? the wings bend down not good. a good section I use is a hq 2.5/12 ant the root and a hq2.5/10 or faster section at the tip. with NO WASHOUT. ROO :D http://airfoiltools.com/airfoil/details ... =hq2512-il http://airfoiltools.com/airfoil/details ... =hq2510-il

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Antonia
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Joined: 17 Mar 2015, 22:30
Location: Oxfordshire

Re: 4.5:1 ASH-25

Post by Antonia »

Yay another ASH 25 !.. :D

My.... in need of a bit of TLC 1/5 scale ASH 25 from Rosenthal which has a span of 5 metres originally, but 5.3 with my tips had/has no washout nor much of a section change, it was not suseptical to dropping a tip unless pushed. When I get round to repairing it, most probably with a new wing I'll be coping the original platform and sections, I've attached a photo as reference.

Please keep posting the build, "the world needs more '25 's..."
Attachments
image.jpeg

Pete Marsden
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Joined: 17 Mar 2018, 08:45
Location: Southampton

Re: 4.5:1 ASH-25

Post by Pete Marsden »

Hi Guys,
Many thanks for the feed back.
Re: My rationale for Section changes:
Many years ago having had this conversation with a renowned model designer, I ran an experiment with a 1/4 HP-18 that I had. I built 3 wings; one with what looked like a modified Clark-Y (typical Wanitscheck) with 3' washout (as per plan), one set with E-207 root to tip with 3' wash out (as per the Wanitscheck 1/5 Jantar 2) and one set with original Clark-Y type root changing to E-207 at the tip with zero wash out.
Guess which one will fly slowest and thermal turn without dropping a wing!
A: In order of flying qualities the 3rd wing is the best followed by the 1st and finally the 2nd - although to be fair the 2nd (E-207) wing does climb better in light airs. (and to be strictly accurate - I hate the HP-18's flying qualities in general!)
All my subsequent gliders, and there have been a few, have more under-camber at the tip (+ the usual sharper root LE) and I've experienced no problems (admittedly not 39:1 AR!).
I'm not a speed merchant; it's only my Jantar standard that I aerobat and that wing is so stiff the wash out (again 3') wouldn't bend it!
Regarding negative flex; my SB-10 (5m60 - not scale) has washout and at speed does tuck its tips down a bit (I've seen full size gliders on racing finals doing exactly the same thing) but even that flexes up on the flair as the AOA increases.
Having said all that, I'll stick to the plan and try it, and if I'm not happy I'll try a different set-up. Probably one of the reason I've so many unfinished projects (they fly but have never been cosmetically completed) is because I keep experimenting!
Thanks again
Pete.

Pete Marsden
Posts: 29
Joined: 17 Mar 2018, 08:45
Location: Southampton

Re: 4.5:1 ASH-25 - Correction!

Post by Pete Marsden »

I don't know what's happened to the 'little grey cells' since I retired but I'm glad my former work colleagues won't see these scribblings elst they'd be reviewing all my work over the last several decades!
Correction: My wings increase in under camber at the tip BUT do have 2 - 3' washout as well - why?
My conclusion from testing is that as the AOA is increased for slow flying or landing the inboard wing starts to 'sag' (approaching stall) first, but the tips keep flying.
The wash out is intended to ensure that at high speed the tips do not deflect upwards too much - I'm trying to get the whole wing to share the load.
As to 'crow' braking, I wasn't aware the full size gliders employed this - certainly the ASW-17 didn't - the last true scale model I built (well before computer radios) and fitted with mechanical full length flaps with the outboard section doubling as ailerons (and lots of slop!).
I've not had the advantage of owning any advanced ARTFs or high-end kits so suspect I'm way behind the times! However, since my moulds are adjustable, i.e. I can twist them during the laying up of the skins, I'll be able to run some more tests on the ASH.
I've already got the bin liner ready!
Cheers
Pete.

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RobbieB
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Joined: 07 Mar 2015, 22:22
Location: North West

Re: 4.5:1 ASH-25 - Correction!

Post by RobbieB »

Pete Marsden wrote:
12 Jul 2018, 08:45

'..................Correction: My wings increase in under camber at the tip BUT do have 2 - 3' washout as well - why?
My conclusion from testing is that as the AOA is increased for slow flying or landing the inboard wing starts to 'sag' (approaching stall) first, but the tips keep flying........................'
Pete, this strategy has been the mantra in the full size gliding world for many years (not sure if it still is today) and the thinking behind it is, the increase in camber at the tip is offset by the washout which is set at the difference between the zero lift angles of the root and tip sections - or a touch more. Doing it this way both the root and tip reach their respective stall angles at the same time so you don't get a tip stall and the tips don't bend down at speed.

Being doing this for a while now on my my models and it works well for me.

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terry white
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Joined: 18 Mar 2015, 21:08
Location: wareham,dorset.england

Re: 4.5:1 ASH-25

Post by terry white »

Hi Robbie and Peter,
I don't understand that following at all,unless you are only talking of aircraft of yester year when wind tunnels and computer programs were not available and trial and error was the way. In relation to today's modern glass the wings of these aircraft were short low aspect ratio with a thick under cambered section which is far removed from today's modern quick semi aerobatic sections. We not only try to make the whole wing to stall at the same time while flying straight and level but when we are circling as in a thermal. Considering that a tip on the inside of a circle will be flying at a greatly slower air speed than the outside tip, we could expect that tip to stall first especially if a down going aileron is initiated. Therefore a change in the tip section which will cope with the slower speed should be selected if wash out is not to be employed. Also we have a great deal of turbulence going on at and around the tip.increasing more as the AOA increases but also with aileron movement. This not only makes the tip lift less effective but increases the drag which all goes to help induce the dreaded stall, Again that is why we carefully select either the correct sections layed out by NASA or RG or HQ all who have done extensive wind tunnel tests for our befit.
These test results are readily available easy to understand and most designers would not think of straying too far away from them.Why would we the work of the designers is already done for us .You will read from these reports that on modern glass ships such as the high aspect ratio of the ASH-25 that wash out should not be the preferred choice.However if it should be employed no more than 1-1.5 degrees nose down.
You will also find many discussions on this very subject on YouTube. Ter

Pete Marsden
Posts: 29
Joined: 17 Mar 2018, 08:45
Location: Southampton

Re: 4.5:1 ASH-25

Post by Pete Marsden »

Hi Terry,
Not bumped into you this year as yet. Trust all's well.
As an interesting reference for this topic I like the Glider Handbook - (https://www.faa.gov/regulations_policie ... h_ch03.pdf) - which gives some interesting comments on washout - see 'tapered wings'.
Just looked at my DG 800 'part kit', 1/3rd scale with epoxy fuz and foam cores that I bought in Germany in the late '80s (never built it but probably will in the near future).
Anyway, this employs both the change in section and 2' washout in the wing.
As I say, I have a bin liner on standby!
Cheers
Pete.

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