High altitude flutter - Vne

[bildan]

Interesting subject needs new thread.

It strikes me that a glider designed to soar in weak thermals is well
off its design point when running fast in a wave XC or, for that
matter, in strong thermal conditions. Ballast helps, of course, but
the basic airframe aerodynamics are wrong for extreme conditions.
Flutter shouldn't be allowed to become the limiting condition.

There were hints that Klaus Ohlman's Nimbus 4DM was modified to
increase Va and Vne for the record flights. It was never made clear
just what those mods were. With today's records being set in
extremely strong conditions, an increase in Va and/or Vne seems like
it would be more important than any increase in the already high L/D
max.

[Eric Greenwell]

bildan wrote:
> Interesting subject needs new thread.
>
> It strikes me that a glider designed to soar in weak thermals is well
> off its design point when running fast in a wave XC or, for that
> matter, in strong thermal conditions. Ballast helps, of course, but
> the basic airframe aerodynamics are wrong for extreme conditions.
> Flutter shouldn't be allowed to become the limiting condition.
>
> There were hints that Klaus Ohlman's Nimbus 4DM was modified to
> increase Va and Vne for the record flights. It was never made clear
> just what those mods were. With today's records being set in
> extremely strong conditions, an increase in Va and/or Vne seems like
> it would be more important than any increase in the already high L/D
> max.

Time to order your DuckHawk - 200 Kt Vne, 160 knot Va, 10.75 lbs/sqft -
just what you need for those high-speed wave flights!

--
Eric Greenwell - Washington State, USA
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[Allan[_3_]]

> Time to order your DuckHawk - 200 Kt Vne, 160 knot Va, 10.75 lbs/sqft -
> just what you need for those high-speed wave flights!

But whats the L/D at 160 & 200 Knots? 10 & 5 ?

Allan

[Darryl Ramm]

On Jan 2, 10:52*pm, Allan > wrote:
> > Time to order your DuckHawk - 200 Kt Vne, 160 knot Va, 10.75 lbs/sqft -
> > just what you need for those high-speed wave flights!
>
> But whats the L/D at 160 & 200 Knots? 10 & 5 ?
>
> Allan

L/D? When the nose pushed down at 160 knots, crabbing into a 50+ knot
headwind and you've got +5 knots of up in wave you won't care...

I can't wait to see what magic Greg Cole pulls off with the Duck Hawk.

Darryl

[Eric Greenwell]

Darryl Ramm wrote:
> On Jan 2, 10:52 pm, Allan > wrote:
>>> Time to order your DuckHawk - 200 Kt Vne, 160 knot Va, 10.75 lbs/sqft -
>>> just what you need for those high-speed wave flights!
>> But whats the L/D at 160 & 200 Knots? 10 & 5 ?
>>
>> Allan
>
> L/D? When the nose pushed down at 160 knots, crabbing into a 50+ knot
> headwind and you've got +5 knots of up in wave you won't care...
>
> I can't wait to see what magic Greg Cole pulls off with the Duck Hawk.

Darryl has it right - the limit for high speed wave flights is Vne, not
L/D. But, extrapolating from an ASW 27 B polar gives ~20:1 at 160 knots.
Attempting to extrapolate to 200 knots is pointless, so we'll have to
wait for Windward Performance to publish a curve.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[Greg Arnold[_2_]]

Darryl Ramm wrote:
> On Jan 2, 10:52 pm, Allan > wrote:
>>> Time to order your DuckHawk - 200 Kt Vne, 160 knot Va, 10.75 lbs/sqft -
>>> just what you need for those high-speed wave flights!
>> But whats the L/D at 160 & 200 Knots? 10 & 5 ?
>>
>> Allan
>
> L/D? When the nose pushed down at 160 knots, crabbing into a 50+ knot
> headwind and you've got +5 knots of up in wave you won't care...
>
> I can't wait to see what magic Greg Cole pulls off with the Duck Hawk.
>
> Darryl

That would be mighty strong wave to have you consistently going up at an
airspeed of 200 knots.

[Roy Clark, \B6\]

On Jan 3, 9:46*am, Greg Arnold > wrote:
> Darryl Ramm wrote:
> > On Jan 2, 10:52 pm, Allan > wrote:
> >>> Time to order your DuckHawk - 200 Kt Vne, 160 knot Va, 10.75 lbs/sqft -
> >>> just what you need for those high-speed wave flights!
> >> But whats the L/D at 160 & 200 Knots? 10 & 5 ?
>
> >> Allan
>
> > L/D? When the nose pushed down at 160 knots, crabbing into a 50+ knot
> > headwind and you've got +5 knots of up in wave you won't care...
>
> > I can't wait to see what magic Greg Cole pulls off with the Duck Hawk.
>
> > Darryl
>
> That would be mighty strong wave to have you consistently going up at an
> airspeed of 200 knots.

I've listened on channel 9 while a westbound United flight crew was
surprised they were climbing in
wave near Denver with a 160 kt headwind on the nose. Net speed had to
be well over >200kt and wing
loading well over 10.75 lbs/sqft!

The big problem with high altitude and wave flight is the constriction
of your flight envelope. At Minden, I
discovered ambudant ballast in a G-102 during a wave flight pre-take-
off check. Ship had been flown
the day before by a petite pilot (I'm about 200 lbs with wave flight
gear). Calculated my flight envelope at
the ballasted weight after the flight - not much between stall and
flutter.

Made me appreciate the A12 and U2 pilots who often had +/- 3 kts or
less [Shadow Flights by Curtis Peebles, pg 96].

Also made me appreciate my insistance on going through my check-list
even tho the tow plane was ready!

[Andreas Maurer]

On Fri, 2 Jan 2009 17:10:34 -0800 (PST), bildan >
wrote:


>There were hints that Klaus Ohlman's Nimbus 4DM was modified to
>increase Va and Vne for the record flights. It was never made clear
>just what those mods were.

It's got fully balanced control surfaces.

[John Smith]

Andreas Maurer wrote:

>> There were hints that Klaus Ohlman's Nimbus 4DM was modified to
>> increase Va and Vne for the record flights. It was never made clear
>> just what those mods were.

> It's got fully balanced control surfaces.

Which you usually don't want on gliders, because it makes the controls
heavier (see DG-1000 vs. Duo).

[[email protected]]

On Jan 3, 9:00*am, Eric Greenwell > wrote:
> Darryl Ramm wrote:
> > On Jan 2, 10:52 pm, Allan > wrote:
> >>> Time to order your DuckHawk - 200 Kt Vne, 160 knot Va, 10.75 lbs/sqft -
> >>> just what you need for those high-speed wave flights!
> >> But whats the L/D at 160 & 200 Knots? 10 & 5 ?
>
> >> Allan
>
> > L/D? When the nose pushed down at 160 knots, crabbing into a 50+ knot
> > headwind and you've got +5 knots of up in wave you won't care...
>
> > I can't wait to see what magic Greg Cole pulls off with the Duck Hawk.
>
> Darryl has it right - the limit for high speed wave flights is Vne, not
> L/D. But, extrapolating from an ASW 27 B polar gives ~20:1 at 160 knots.
> Attempting to extrapolate to 200 knots is pointless, so we'll have to
> wait for Windward Performance to publish a curve.

Just to finish the thought - you only need 8 knots of lift to maintain
altitude at 20:1 and 160 kts. I've never had a Vne issue in thermal
soaring, even at 18,000', though I have been occasionally concerned
about it in strong lift approaching cloudbase. Even a great
cloudstreet is unlikely to have sustained lift that strong so if you
are keeping decent clearance from cloudbase you can usually let your
altitude vary rather than running up the airspeed. I could easily
imagine it being more of an issue in wave, particularly for those
folks running wave under IFR above 18,000'.

Wouldn't the 200 kt Vne be from sea level up to some limited altitude?
If so, you probably don't need to figure the L/D at 200 kts IAS for
wave flying - you'll be flying no faster than Va in wave above the
upper teens to low twenties (depending on how high the 200 kts is good
for), so 8 kts of up will be the strongest lift in which you'll be
able to hold altitude (versus 6-7 kts for, say, an ASW-27).

I will need to get used to the idea of flying that fast in a glider
that weighs 300 lbs empty.

9B

[Greg Arnold[_2_]]

wrote:
> On Jan 3, 9:00 am, Eric Greenwell > wrote:
>> Darryl Ramm wrote:
>>> On Jan 2, 10:52 pm, Allan > wrote:
>>>>> Time to order your DuckHawk - 200 Kt Vne, 160 knot Va, 10.75 lbs/sqft -
>>>>> just what you need for those high-speed wave flights!
>>>> But whats the L/D at 160 & 200 Knots? 10 & 5 ?
>>>> Allan
>>> L/D? When the nose pushed down at 160 knots, crabbing into a 50+ knot
>>> headwind and you've got +5 knots of up in wave you won't care...
>>> I can't wait to see what magic Greg Cole pulls off with the Duck Hawk.
>> Darryl has it right - the limit for high speed wave flights is Vne, not
>> L/D. But, extrapolating from an ASW 27 B polar gives ~20:1 at 160 knots.
>> Attempting to extrapolate to 200 knots is pointless, so we'll have to
>> wait for Windward Performance to publish a curve.
>
> Just to finish the thought - you only need 8 knots of lift to maintain
> altitude at 20:1 and 160 kts.

I am skeptical about 20:1 at 160 knots. I think the best Dick Johnson
flight test was the ASH-26 at 9 pounds wing loading, and it was below
20:1 at 120 knots. A more realistic figure might be 10:1 at 160 knots,
which would require 16 knots of lift to maintain altitude.



I've never had a Vne issue in thermal
> soaring, even at 18,000', though I have been occasionally concerned
> about it in strong lift approaching cloudbase. Even a great
> cloudstreet is unlikely to have sustained lift that strong so if you
> are keeping decent clearance from cloudbase you can usually let your
> altitude vary rather than running up the airspeed. I could easily
> imagine it being more of an issue in wave, particularly for those
> folks running wave under IFR above 18,000'.
>
> Wouldn't the 200 kt Vne be from sea level up to some limited altitude?
> If so, you probably don't need to figure the L/D at 200 kts IAS for
> wave flying - you'll be flying no faster than Va in wave above the
> upper teens to low twenties (depending on how high the 200 kts is good
> for), so 8 kts of up will be the strongest lift in which you'll be
> able to hold altitude (versus 6-7 kts for, say, an ASW-27).
>
> I will need to get used to the idea of flying that fast in a glider
> that weighs 300 lbs empty.
>
> 9B

[[email protected]]

On Jan 3, 4:34*pm, Greg Arnold > wrote:
> wrote:
> > On Jan 3, 9:00 am, Eric Greenwell > wrote:
> >> Darryl Ramm wrote:
> >>> On Jan 2, 10:52 pm, Allan > wrote:
> >>>>> Time to order your DuckHawk - 200 Kt Vne, 160 knot Va, 10.75 lbs/sqft -
> >>>>> just what you need for those high-speed wave flights!
> >>>> But whats the L/D at 160 & 200 Knots? 10 & 5 ?
> >>>> Allan
> >>> L/D? When the nose pushed down at 160 knots, crabbing into a 50+ knot
> >>> headwind and you've got +5 knots of up in wave you won't care...
> >>> I can't wait to see what magic Greg Cole pulls off with the Duck Hawk..
> >> Darryl has it right - the limit for high speed wave flights is Vne, not
> >> L/D. But, extrapolating from an ASW 27 B polar gives ~20:1 at 160 knots.
> >> Attempting to extrapolate to 200 knots is pointless, so we'll have to
> >> wait for Windward Performance to publish a curve.
>
> > Just to finish the thought - you only need 8 knots of lift to maintain
> > altitude at 20:1 and 160 kts.
>
> I am skeptical about 20:1 at 160 knots. *I think the best Dick Johnson
> flight test was the ASH-26 at 9 pounds wing loading, and it was below
> 20:1 at 120 knots. *A more realistic figure might be 10:1 at 160 knots,
> which would require 16 knots of lift to maintain altitude.

Good catch. My curve fit to the factory polar of my ASW-27 shows 20:1
at 150 kts and max gross, but that seems wildly optimistic. Looking at
a couple of final glides in relatively smooth air show less than 20:1
at 120 kts.

So the summary point would be that it would have to be one heck of a
wave day or you'd have to have an IFR flight plan to fly higher to
really need much above 150 kts of Vne on a cross country flight - at
least from a performance perspective.

9B

[Eric Greenwell]

wrote:

> Just to finish the thought - you only need 8 knots of lift to maintain
> altitude at 20:1 and 160 kts.

At 160 knots indicated at 18,000', the TAS would be 216 knots. You'd
need ~11 knots of lift (216/20). I don't know how common that is along
the Sierras. We don't get it in Washington State, but possibly along the
Oregon Cascades.

> Wouldn't the 200 kt Vne be from sea level up to some limited altitude?

I don't know how Greg sets the Vne, but my ASH 26 E uses the IAS for
Vne(IAS=146) from sea level to 10,000', and then uses TAS for
Vne(TAS=170) from point on. So, at 18,000', the Vne is down to ~120
knots IAS, but still ~170 knots TAS.
--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

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[Eric Greenwell]

Greg Arnold wrote:

>>>> L/D? When the nose pushed down at 160 knots, crabbing into a 50+ knot
>>>> headwind and you've got +5 knots of up in wave you won't care...
>>>> I can't wait to see what magic Greg Cole pulls off with the Duck Hawk.
>
>>> Darryl has it right - the limit for high speed wave flights is Vne, not
>>> L/D. But, extrapolating from an ASW 27 B polar gives ~20:1 at 160 knots.
>>> Attempting to extrapolate to 200 knots is pointless, so we'll have to
>>> wait for Windward Performance to publish a curve.
>>
>> Just to finish the thought - you only need 8 knots of lift to maintain
>> altitude at 20:1 and 160 kts.
>
> I am skeptical about 20:1 at 160 knots. I think the best Dick Johnson
> flight test was the ASH-26 at 9 pounds wing loading, and it was below
> 20:1 at 120 knots. A more realistic figure might be 10:1 at 160 knots,
> which would require 16 knots of lift to maintain altitude.

You can get the ASW 27 B curve from Schleicher's site and draw your own
line. It's guess, because the curve only goes to 210 kph, but the curve
I drew "looks right", using the 55.6 kg/m2 line as the starting point.
I'm sure it's not 10:1, but certainly between than 15:1 and 20:1. The
ASH 26 is not a good choice for comparison because it has the same
aspect ratio as the 27, and only goes to 45 kg/m2 (the 9 pounds you
mentioned).

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[Eric Greenwell]

wrote:

>
> Wouldn't the 200 kt Vne be from sea level up to some limited altitude?
> If so, you probably don't need to figure the L/D at 200 kts IAS for
> wave flying - you'll be flying no faster than Va in wave above the
> upper teens to low twenties (depending on how high the 200 kts is good
> for), so 8 kts of up will be the strongest lift in which you'll be
> able to hold altitude (versus 6-7 kts for, say, an ASW-27).
>
> I will need to get used to the idea of flying that fast in a glider
> that weighs 300 lbs empty.

I agree, but I saw the spar stub mockups when I was at Windward
Performance in June. It's comforting that they are massive. Part of the
reason for the light weight is the wing is only 80 square feet, compared
to 99 on the ASW 27. High temperature cured pre-preg allows
significantly lighter weight than wet layups done by hand, too.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[Greg Arnold[_2_]]

Eric Greenwell wrote:
> Greg Arnold wrote:
>
>>>>> L/D? When the nose pushed down at 160 knots, crabbing into a 50+ knot
>>>>> headwind and you've got +5 knots of up in wave you won't care...
>>>>> I can't wait to see what magic Greg Cole pulls off with the Duck Hawk.
> >
>>>> Darryl has it right - the limit for high speed wave flights is Vne, not
>>>> L/D. But, extrapolating from an ASW 27 B polar gives ~20:1 at 160
>>>> knots.
>>>> Attempting to extrapolate to 200 knots is pointless, so we'll have to
>>>> wait for Windward Performance to publish a curve.
>>>
>>> Just to finish the thought - you only need 8 knots of lift to maintain
>>> altitude at 20:1 and 160 kts.
>>
>> I am skeptical about 20:1 at 160 knots. I think the best Dick Johnson
>> flight test was the ASH-26 at 9 pounds wing loading, and it was below
>> 20:1 at 120 knots. A more realistic figure might be 10:1 at 160
>> knots, which would require 16 knots of lift to maintain altitude.
>
> You can get the ASW 27 B curve from Schleicher's site and draw your own
> line.


I am skeptical about the accuracy of that curve! Didn't they claim best
L/D of 48?




>It's guess, because the curve only goes to 210 kph, but the curve
>I drew "looks right", using the 55.6 kg/m2 line as the starting point.


Can you extrapolate that way? Just as unflapped ships suffer a
noticeable fall off in performance above 80 to 85 knots, flapped ships
must have a similar speed at which their wings aren't working very well
(120 knots?).


> I'm sure it's not 10:1, but certainly between than 15:1 and 20:1.


When the Duckhawk comes out, we will put you 15 to 20 nm out over the
ocean at 6,000', and see if you want to fly at 160 knots towards the coast!


The
> ASH 26 is not a good choice for comparison because it has the same
> aspect ratio as the 27, and only goes to 45 kg/m2 (the 9 pounds you
> mentioned).
>

It is the best data point we have, I believe.

[[email protected]]

On Jan 3, 7:36*pm, Eric Greenwell > wrote:
>
> You can get the ASW 27 B curve from Schleicher's site and draw your own
> line. It's guess, because the curve only goes to 210 kph, but the curve
> I drew "looks right", using the 55.6 kg/m2 line as the starting point.
> I'm sure it's not 10:1, but certainly between than 15:1 and 20:1.

Based on a look at some actual flight logs I'd guess that at redline
(151 kts) the ASW-27 would get something like 16:1. A quadratic curve
fit to the factory polar shows 20:1. If you extrapolate out to the
aforementioned 160kts (above redline for the -27) the quadratic curve
off the factory polar yields 18:1, My guess at reality would be more
like 14:1 at that speed (and 11.5 lbs/sqft). We'll see, but I doubt
the Duckhawk will have the same performance as the -27 at equivalent
wing loadings and I also doubt it'll be able to get to much above 10
lbs/sq ft wing loading because it starts out 230 lbs lighter empty and
the wing is too small to carry enough water ballast to get above 10
lbs. Soooo, if I had to bet I'd guess an L/D below 15:1 rather than
above 15:1 at max gross and 160 kts.

Even 20:1 is enough to cruise in strong lift without gaining altitude,
so I think the main point has been established - that you probably
don't gain much by trying to optimize a design for wave XC in the 15
meter class.

9B

[Greg Arnold[_2_]]

wrote:
> On Jan 3, 7:36 pm, Eric Greenwell > wrote:
>> You can get the ASW 27 B curve from Schleicher's site and draw your own
>> line. It's guess, because the curve only goes to 210 kph, but the curve
>> I drew "looks right", using the 55.6 kg/m2 line as the starting point.
>> I'm sure it's not 10:1, but certainly between than 15:1 and 20:1.
>
> Based on a look at some actual flight logs I'd guess that at redline
> (151 kts) the ASW-27 would get something like 16:1. A quadratic curve
> fit to the factory polar shows 20:1. If you extrapolate out to the
> aforementioned 160kts (above redline for the -27) the quadratic curve
> off the factory polar yields 18:1, My guess at reality would be more
> like 14:1 at that speed (and 11.5 lbs/sqft). We'll see, but I doubt
> the Duckhawk will have the same performance as the -27 at equivalent
> wing loadings and I also doubt it'll be able to get to much above 10
> lbs/sq ft wing loading because it starts out 230 lbs lighter empty and
> the wing is too small to carry enough water ballast to get above 10
> lbs. Soooo, if I had to bet I'd guess an L/D below 15:1 rather than
> above 15:1 at max gross and 160 kts.
>
> Even 20:1 is enough to cruise in strong lift without gaining altitude,
> so I think the main point has been established - that you probably
> don't gain much by trying to optimize a design for wave XC in the 15
> meter class.
>
> 9B


But a 200 knot redline would sure make for an impressive flyby!

[Eric Greenwell]

Greg Arnold wrote:
>>
>> You can get the ASW 27 B curve from Schleicher's site and draw your
>> own line.
>
> I am skeptical about the accuracy of that curve! Didn't they claim best
> L/D of 48?

Maybe we don't have the same curve? The one I got from their download
page has a line labeled E=48.

http://www.alexander-schleicher.de/service/prospekte/27E.pdf

>
>> It's guess, because the curve only goes to 210 kph, but the curve I
>> drew "looks right", using the 55.6 kg/m2 line as the starting point.
>
>
> Can you extrapolate that way? Just as unflapped ships suffer a
> noticeable fall off in performance above 80 to 85 knots, flapped ships
> must have a similar speed at which their wings aren't working very well
> (120 knots?).

That's certainly part of the problem trying to extrapolate. A bigger
problem is I put my dot on the graph paper in the wrong place when I
calculated from the 36.6 kg/m2 curve, so now the curve looks like a 14:1
glide at 160 knots IAS.
>
>> I'm sure it's not 10:1, but certainly between than 15:1 and 20:1.

14:1 is the new 15:1!

> When the Duckhawk comes out, we will put you 15 to 20 nm out over the
> ocean at 6,000', and see if you want to fly at 160 knots towards the coast!

Apparently, I would slow down a bit sooner than I first anticipated,
doing the last nm in ground (water?) effect :)

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[Greg Arnold[_2_]]

Eric Greenwell wrote:
> Greg Arnold wrote:
>>>
>>> You can get the ASW 27 B curve from Schleicher's site and draw your
>>> own line.
>>
>> I am skeptical about the accuracy of that curve! Didn't they claim
>> best L/D of 48?
>
> Maybe we don't have the same curve? The one I got from their download
> page has a line labeled E=48.


The point I was trying to make, maybe not very well, is that their claim
of 48 probably is unreasonably optimistic (it was measured at 45.6 by
the Akaflieg). Thus, the rest of their polar curve probably also is too
optimistic.


>
> http://www.alexander-schleicher.de/service/prospekte/27E.pdf
>
>>
>>> It's guess, because the curve only goes to 210 kph, but the curve I
>>> drew "looks right", using the 55.6 kg/m2 line as the starting point.
>>
>>
>> Can you extrapolate that way? Just as unflapped ships suffer a
>> noticeable fall off in performance above 80 to 85 knots, flapped ships
>> must have a similar speed at which their wings aren't working very
>> well (120 knots?).
>
> That's certainly part of the problem trying to extrapolate. A bigger
> problem is I put my dot on the graph paper in the wrong place when I
> calculated from the 36.6 kg/m2 curve, so now the curve looks like a 14:1
> glide at 160 knots IAS.
>>
>>> I'm sure it's not 10:1, but certainly between than 15:1 and 20:1.
>
> 14:1 is the new 15:1!


And if their polar curve has some "salesmanship" in it, and allowing for
a possible drastic dropoff in performance at high speeds, even 14:1 is
too high.

[John Smith]

> But a 200 knot redline would sure make for an impressive flyby!

Older aerobatic savvy gliders had redlines of 350 km/h (SZD Kobuz,
Lo-100), 380 km/h (Mü-28) and even 450 km/h (DFS Habicht). Somehow
sometimes somebody decided that in 99.9% of the flights this was not
necessairy and that for 99.9% of the pilots a better L/D at lower speed
was more disirable because it fits better the requirements for average
weather conditions.

[Eric Greenwell]

Greg Arnold wrote:

>>> I am skeptical about the accuracy of that curve! Didn't they claim
>>> best L/D of 48?
>>
>> Maybe we don't have the same curve? The one I got from their download
>> page has a line labeled E=48.
>
>
> The point I was trying to make, maybe not very well, is that their claim
> of 48 probably is unreasonably optimistic (it was measured at 45.6 by
> the Akaflieg). Thus, the rest of their polar curve probably also is too
> optimistic.

A curve with 5% error is plenty good enough for our wild guessing about
the likely performance of a nominally similar glider, for which we don't
even have the calculated curve and is designed for speeds way beyond the
curve we are using :)

Greg Cole hasn't shared any secrets with me, but it's possible he's
chosen to use airfoils and flap settings that favor very high speed
flight more than Waibel chose to do when he designed the ASW 27. And, it
is a higher aspect ratio wing (30:1 versus 25:1). Also, he's not using
winglets, which are generally considered a drag at high speeds.

Someone mentioned the wing won't hold enough water to get to max wing
loading, which is true. I believe Greg is planning a fuselage tank to
make up the difference, like the early ASW 27s had to use.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[Gary Boggs]

I sure wish he'd change the name from Duck Hawk to something a little
more pleasent sounding,
It sounds a little too much like Duck Fart.

Gary Boggs

www.nwskysports.com

[[email protected]]

On Jan 4, 8:00*am, Eric Greenwell > wrote:
>
> Someone mentioned the wing won't hold enough water to get to max wing
> loading, which is true. I believe Greg is planning a fuselage tank to
> make up the difference, like the early ASW 27s had to use.

A fuselage tank would help, but...

The max gross weight is listed as 860 lbs, which gets you to only 10.7
lbs/sq ft - more than pound per sq ft lower than the -27. I estimate a
wing that size can carry about 25 gallons of water. If you add a 5
gallon tank in the fuselage and a 165 lb pilot, chute, instruments, O2
tank, etc. you only get to 9.7 lbs/sq ft. To get to max gross you'd
either need a 245 lb pilot (might be a tight squeeze in that cockpit)
or a 15 gallon fuselage tank. I'd be surprised if you could put that
much water in a fuselage that size - unless it goes in the pilot's lap
- ;-)

If the empty weight is more like 400 lbs than the listed 300 lbs you
could get to max gross more easily - but the minimum wing loading
would be 7.8 lbs which could be high (the three-view doesn't show
flaps - or ailerons). With flaps it would be like thw -27. But missing
the target empty weight by more than 30% might have other
consequences.

Alternatively, we can all go on a Krispy-Kreme diet.

Eric, you mentioned using the 55.6 kg/m^2 curve in one post and the
36.6 kg/m^ in another, which is a big difference. The right number for
trying to get to an expected loading for the Duckhawk is more like 50,
but as you correctly pointed out extrapolating has inherent
inaccuracies and the assumption that one glider will perform about
like another at the same wing loading includes a fair amount of
heroism too.

It's mostly nit-picking now as I think where we got to is any glider
that can get to ~150 kts ought to be fine for making the most out of
all but the most extreme lift conditions (sustained wave/streeting >10
kts) and/or altitudes above 18,000'.

9B

P.S. Irrrespective of any of the above - the use of pre-preg
construction is a great innovation for sailplanes and it's fantastic
to see a US manufacturer taking full advantage of it.

[DRN]

Guys - Using a quadratic to estimate high-speed polar is
really not realistic. The airfoils used on the gliders you
are discussing suffer massive lower-surface separation
over ~110knots depending on wing-loading.

You really need measurements (not extrapolations
of wishful polars ignoring low-CL separation)...

Hope that helps,
Best Regards, Dave

[Greg Arnold[_2_]]

DRN wrote:
> Guys - Using a quadratic to estimate high-speed polar is
> really not realistic. The airfoils used on the gliders you
> are discussing suffer massive lower-surface separation
> over ~110knots depending on wing-loading.
>
> You really need measurements (not extrapolations
> of wishful polars ignoring low-CL separation)...
>
> Hope that helps,
> Best Regards, Dave


Ah ha! My point exactly.

[[email protected]]

On Jan 4, 10:49*am, DRN > wrote:
> Guys - Using a quadratic to estimate high-speed polar is
> really not realistic. The airfoils used on the gliders you
> are discussing suffer massive lower-surface separation
> over ~110knots depending on wing-loading.
>
> You really need measurements (not extrapolations
> of wishful polars ignoring low-CL separation)...
>
> Hope that helps,
> Best Regards, Dave

Yup - I think we're all agreed on that. The best masurement I had was
some logs of fast final glides that showed 25% worse than the
quadratic polar extrapolation - it's rough at best, but some
significant haircut is in order.

The exercise was really focused on whether it was theoretically
advantageous to design a glider for super-strong conditions and high
altitudes. The initial discussion centered on Vne limits, but your
point raises the issue of whether an airfoil designed for cruise at
much higher speed would have an advantage. The general trend in
sailplane design has been to optimize around higher cruise speeds, but
I would observe that racing pilots have been slowing down in cruise
for a host of tactical and strategic reasons, so I guess I don't see
much advantage.

You post made me think of a separate question for you Dave - does the
SN-10 give a haircut to the factory polars above 110kts? I find that
I consistently need to fly 10+ knots slower than the dialed-in
McCready speed to make most final glides work out (sorry I don't have
an SN-10). Also, it would be neat if there were a way for computers to
"learn" the polar of a glider based on actual versus expected
performance - even if it were just for the final glide portion of the
flight. There may well be too many unknown variables to actually do
it. I wonder if there could be a "learn mode" where you take a couple
of high tows on a calm day and do some long runs at 3-4 different
speeds.

9B

[[email protected]]

On Jan 3, 7:24*pm, Eric Greenwell > wrote:
> wrote:

> * > Wouldn't the 200 kt Vne be from sea level up to some limited altitude?
>
> I don't know how Greg sets the Vne, but my ASH 26 E uses the IAS for
> Vne(IAS=146) from sea level to 10,000', and then uses TAS for
> Vne(TAS=170) from point on. So, at 18,000', the Vne is down to ~120
> knots IAS, but still ~170 knots TAS.


My -27 also has Vne "flat rated" up to 10,000' at 151 kts. I would
guess that means that you have a bunch of extra flutter margin at 151
knots at sea level - not that I'm suggesting anyone try it.

9B

[[email protected]]

On Jan 3, 7:24*pm, Eric Greenwell > wrote:
> wrote:
> > Just to finish the thought - you only need 8 knots of lift to maintain
> > altitude at 20:1 and 160 kts.
>
> At 160 knots indicated at 18,000', the TAS would be 216 knots. You'd
> need ~11 knots of lift (216/20). I don't know how common that is along
> the Sierras. We don't get it in Washington State, but possibly along the
> Oregon Cascades.

True - good catch - I believe Vne is likely to still be higher than Va
at that altitude - depending on how they certify it. I think we've
agreed that the L/D would likely be lower than 20, so you're talking
about 15 knots or more, which makes my point even more strongly - you
are unlikely to be able to make practical use of the extra Vne to make
XC speed under just about any expected soaring circumstance.

If they can build the higher Vne into the design for a minimal weight
penalty then, what the heck, they might as well. Otherwise, they still
have a fair amount of weight advantage to play with resulting from
their design and construction techniques. Of course weight translates
to wing loading or the need for wing area to achieve low speed
performance, so presumably they would want the strength for some other
reason.

9B

[DRN]

On Jan 4, 2:35*pm, wrote:
> You post made me think of a separate question for you Dave - does the
> SN-10 give a haircut to the factory polars above 110kts? *

No, polars are typically fit for the region of "normal" flight,
not for blown final glides or high-speed wave...
Don't know if any instruments try to model high-speed
polars really accurately.

> I find that
> I consistently need to fly 10+ knots slower than the dialed-in
> McCready speed to make most final glides work out (sorry I don't have
> an SN-10). Also, it would be neat if there were a way for computers to
> "learn" the polar of a glider based on actual versus expected
> performance - even if it were just for the final glide portion of the
> flight. There may well be too many unknown variables to actually do
> it. I wonder if there could be a "learn mode" where you take a couple
> of high tows on a calm day and do some long runs at 3-4 different
> speeds.
>
> 9B

A "learn mode" is not practical. The *only* way to get reasonably
accurate polar information is by parallel measurement using a
super-well-calibrated reference glider. To my knowledge, this
is *only* done periodically by the Idaflieg group.

See: Judah Milgram, "Flight Testing at the 1998 Idafleig Meet",
SOARING, April 1999 , page 34, available here:
http://skylinesoaring.org/AUTHORS/

Hope that helps !
Best Regards, Dave

[Kemp[_2_]]

From experience, sustained 10-12 knot wave lift for 100km or longer
sections of the Sierra wave is common enough so that a 200knot redline
can make a significant difference. Doing the math, so long as I have
about 10:1 glide @ Vne that's good enough for me. Selecting a target
indicated cruise speed of say, 120 knots at 17.5K ft. (true 160 knots)
I can push over to 145 knots to handle the lift spikes of 12-16 knots
before having to go upwind to reduce the climb rate. This then allows
me to track straight and modulate altitude with airspeed-only making
for a better net ground speed. Without a Class A clearance, IMHO this
is the only way that a 3000km flight is going to be done in the
Sierra.

Kemp

[[email protected]]

On Jan 5, 10:49*am, Kemp > wrote:
> From experience, sustained 10-12 knot wave lift for 100km or longer
> sections of the Sierra wave is common enough so that a 200knot redline
> can make a significant difference. *Doing the math, so long as I have
> about 10:1 glide @ Vne that's good enough for me. *Selecting a target
> indicated cruise speed of say, 120 knots at 17.5K ft. (true 160 knots)
> I can push over to 145 knots to handle the lift spikes of 12-16 knots
> before having to go upwind to reduce the climb rate. *This then allows
> me to track straight and modulate altitude with airspeed-only making
> for a better net ground speed. *Without a Class A clearance, IMHO this
> is the only way that a 3000km flight is going to be done in the
> Sierra.
>
> Kemp

That's good enough for me - almost no one knows the XC Sierra wave
like Kemp. I wonder if this is the design point they had in mind for
the Duckhawk or if the high Vne happened for other reasons.

Kemp, would you consider the Duckhawk (I can't say I like that name)
as the glider to do a 3,000 km flight in, or if not, why not? There
are already acro gliders that have very high redlines, but for some
reason no one that I know about uses them for big time XC wave flying.

Stay warm up there.

Andy

[Bob Kuykendall]

On Jan 3, 7:46*pm, Eric Greenwell > wrote:
> ...High temperature cured pre-preg allows significantly lighter
> weight than wet layups done by hand, too...

Cite?

[[email protected]]

On Jan 5, 6:16*am, DRN > wrote:
> On Jan 4, 2:35*pm, wrote:

> No, polars are typically fit for the region of "normal" flight,
> not for blown final glides or high-speed wave...
> Don't know if any instruments try to model high-speed
> polars really accurately.

Us western pilots don't think of a 110 kt final glide as "blown"
Dave ;-). Truth be told, I typically find that I am underperforming
the glide ratio in the computer at most speeds, but it really picks up
above 90 knots. I guess I can start moving points on the polar around
until it starts to "feel right" but given all the variables at play
that seems painful.

> A "learn mode" is not practical. The *only* way to get reasonably
> accurate polar information is by parallel measurement using a
> super-well-calibrated reference glider. To my knowledge, this
> is *only* done periodically by the Idaflieg group.

Yeah, I figured. Thanks. I'll check what they've got.

9B

[Eric Greenwell]

Bob Kuykendall wrote:
> On Jan 3, 7:46 pm, Eric Greenwell > wrote:
>> ...High temperature cured pre-preg allows significantly lighter
>> weight than wet layups done by hand, too...
>
> Cite?

I'm not the best person to ask, since all I can do is repeat what Greg
Cole tells me. Here's where he gets his pre-preg:

http://www.toraycompam.com/index.php?option=com_content&task=view&id=14&Itemid=32

They are in Tacoma, WA. Summarizing as best I can from conversations
with Greg:

"Hand layup requires carbon fiber and epoxies that can be applied by
hand and at room temperature, and will reliably "wet" under those
conditions. Applying by hand makes it difficult to exactly the right
amount of epoxy, which means too much is always applied to compensate
for the variations of hand layup and the difficulty of testing the final
product.

By impregnating the carbon fiber at the factory,the epoxy is applied by
machine to a very close tolerance so there is no excess weight. This
allows a much wider choice of carbon fibers and epoxies to be used.

The product (fiber + epoxy) can be inspected and tested before delivery
to the customer, so tolerances are tighter. As a result, you can have a
stronger, stiffer material for the same weight. Or, use less material
(less weight) for the same strength."

The high temperature cure (250F) used for these pre-pregs is probably an
important part of getting the better strength and stiffness per pound,
but I don't recall what he's said about it.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[Greg Arnold[_2_]]

Eric Greenwell wrote:
> Bob Kuykendall wrote:
>> On Jan 3, 7:46 pm, Eric Greenwell > wrote:
>>> ...High temperature cured pre-preg allows significantly lighter
>>> weight than wet layups done by hand, too...
>>
>> Cite?
>
> I'm not the best person to ask, since all I can do is repeat what Greg
> Cole tells me. Here's where he gets his pre-preg:
>
> http://www.toraycompam.com/index.php?option=com_content&task=view&id=14&Itemid=32
>
>
> They are in Tacoma, WA. Summarizing as best I can from conversations
> with Greg:
>
> "Hand layup requires carbon fiber and epoxies that can be applied by
> hand and at room temperature, and will reliably "wet" under those
> conditions. Applying by hand makes it difficult to exactly the right
> amount of epoxy, which means too much is always applied to compensate
> for the variations of hand layup and the difficulty of testing the final
> product.
>
> By impregnating the carbon fiber at the factory,the epoxy is applied by
> machine to a very close tolerance so there is no excess weight. This
> allows a much wider choice of carbon fibers and epoxies to be used.
>
> The product (fiber + epoxy) can be inspected and tested before delivery
> to the customer, so tolerances are tighter. As a result, you can have a
> stronger, stiffer material for the same weight. Or, use less material
> (less weight) for the same strength."
>
> The high temperature cure (250F) used for these pre-pregs is probably an
> important part of getting the better strength and stiffness per pound,
> but I don't recall what he's said about it.


And if you are vacuum bagging, excess resin is forced out of the
laminate. High end sailboats have used such techniques for years, and
reportedly save a lot of weight. The light weight of the Sparrowhawk is
another datapoint that suggests you can save a lot of weight.

[[email protected]]

On Jan 5, 4:31*pm, Bob Kuykendall > wrote:
> On Jan 3, 7:46*pm, Eric Greenwell > wrote:
>
> > ...High temperature cured pre-preg allows significantly lighter
> > weight than wet layups done by hand, too...
>
> Cite?

My estimate is that the prepregs save about 10% per square.
On other 15% due to the smaller wing. The biggest saving would be on
the spar due to use of pulltrusion which could be as High as 40%.
Allowing for a thinner airfoil, smaller root chord and an higher
aspect ratio the saving on the spar would be cut down to only 5%.
There other weight savings, hardware in the wing is lighter (made from
carbon) also a thin poly coat of paint.
In all a weight saving of 35% on the wing is doable, maybe even more.

Example The total weight of an ASW 27 is 230lb.
If you add the savings up, the weight of a wing of a new design like
the Duck Hawk, could end up near a 150 lb or 75 lb per panel.
The fuselage also can come in at 150lb.
Regards
Udo

[Udo Rumpf[_2_]]

Fourth line from the bottom should read:
the total weight of an ASW27 "wing" is ~ 230 lb

>My estimate is that the prepregs save about 10% per square.
>On other 15% due to the smaller wing. The biggest saving would be on
>the spar due to use of pulltrusion which could be as High as 40%.
>Allowing for a thinner airfoil, smaller root chord and an higher
>aspect ratio the saving on the spar would be cut down to only 5%.
>There other weight savings, hardware in the wing is lighter (made from
>carbon) also a thin poly coat of paint.
>In all a weight saving of 35% on the wing is doable, maybe even more.
>
>Example The total weight of an ASW 27 is 230lb.
>If you add the savings up, the weight of a wing of a new design like
>the Duck Hawk, could end up near a 150 lb or 75 lb per panel.
>The fuselage also can come in at 150lb.
>Regards
>Udo

[[email protected]]

On Jan 5, 7:15*pm, Udo Rumpf > wrote:
> Fourth line from the bottom should read:
> the total weight of an ASW27 "wing" is ~ 230 lb
>
> >My estimate is that the prepregs save about 10% per square.
> >On other 15% due to the smaller wing. The biggest saving would be on
> >the spar due to use of pulltrusion which could be as High as 40%.
> >Allowing for a thinner airfoil, *smaller root chord and an higher
> >aspect ratio the saving on the spar would be cut down *to only 5%.
> >There other weight savings, hardware in the wing is lighter (made from
> >carbon) also a thin poly coat of paint.
> >In all a weight saving of 35% on the wing is doable, maybe even more.
>
> >Example The total weight of an ASW 27 is 230lb.
> >If you add the savings up, *the weight of a wing of a new design like
> >the Duck *Hawk, could end up near a 150 lb or 75 lb per panel.
> >The fuselage *also can *come in at 150lb.
> >Regards
> >Udo

Thanks for the correction Udo - I was starting to feel bad about my
grossly overweight -27.

9B

[Kemp[_2_]]

> Kemp, would you consider the Duckhawk (I can't say I like that name)
> as the glider to do a 3,000 km flight in, or if not, why not? There
> are already acro gliders that have very high redlines, but for some
> reason no one that I know about uses them for big time XC wave flying.
>
> Stay warm up there.
>
> Andy

I looked at some acro ships and the highest redline I could find was
180 knots (Windex I think), which, yes is better than 150knots, but
the lightweight is really a nice benefit. Yes, the Duckhawk is very
interesting and for me, esp. with a self-launch version, a very
compelling machine. Easy assembly due to light wings, high Vne, good
enough performance even allowing for some marketing. I've visited
Greg's facility twice and am impressed with the approach and the
Sparrowhawk too. I have a 3 view printout with specs tacked to my
office wall as a reminder........

Kemp

[Bob Kuykendall]

On Jan 5, 5:29*pm, wrote:
> On other 15% due to the smaller wing. The biggest saving would be on
> the spar due to use of pulltrusion which could be as High as 40%...

Funny, I heard Greg wasn't planning on using pultrusions. He's never
seemed very keen on them.

[Greg Arnold[_2_]]

Bob Kuykendall wrote:
> On Jan 5, 5:29 pm, wrote:
>> On other 15% due to the smaller wing. The biggest saving would be on
>> the spar due to use of pulltrusion which could be as High as 40%...
>
> Funny, I heard Greg wasn't planning on using pultrusions. He's never
> seemed very keen on them.

Are pultrusions lighter than something made with vacuum bagged
pre-pregs? If so, why are they lighter?

[Udo Rumpf[_2_]]

At 02:30 07 January 2009, Bob Kuykendall wrote:
>On Jan 5, 5:29=A0pm, wrote:
>> On other 15% due to the smaller wing. The biggest saving would be on
>> the spar due to use of pulltrusion which could be as High as 40%...
>
>Funny, I heard Greg wasn't planning on using pultrusions. He's never
>seemed very keen on them.

Maybe he will not use a spar at all. Who knows
We all shall be surprised or not.
Udo

[Udo Rumpf[_2_]]

>Are pultrusions lighter than something made with vacuum
>bagged pre-pregs? If so, why are they lighter?

Yes. Due to the alignment of the fibres and the higher tensile strength of
the resin, plus the high cure temperature.
Hand lay-up and vacuum bagging can only achieve a fraction of the
potential strength of the carbon fibre.
Unidirectional preprec have some of the same benefits but not to the same
extent as pultrusions.
Udo

[Greg Arnold[_2_]]

Udo Rumpf wrote:
>> Are pultrusions lighter than something made with vacuum
>> bagged pre-pregs? If so, why are they lighter?
>
> Yes. Due to the alignment of the fibres and the higher tensile strength of
> the resin, plus the high cure temperature.
> Hand lay-up and vacuum bagging can only achieve a fraction of the
> potential strength of the carbon fibre.
> Unidirectional preprec have some of the same benefits but not to the same
> extent as pultrusions.
> Udo
>

Does a pultrusion work with a spar that is tapered as you get further
from the fuselage?

[Darryl Ramm]

On Jan 6, 9:16*pm, Greg Arnold > wrote:
> Udo Rumpf wrote:
> >> Are pultrusions lighter than something made with vacuum *
> >> bagged pre-pregs? *If so, why are they lighter?
>
> > Yes. Due to the alignment of the fibres and the higher tensile strength of
> > the resin, plus the high cure temperature.
> > Hand lay-up and vacuum bagging can only achieve a fraction of the
> > potential strength of the carbon fibre.
> > Unidirectional preprec have some of the same benefits but not to the same
> > extent as pultrusions.
> > Udo
>
> Does a pultrusion work with a spar that is tapered as you get further
> from the fuselage?

Yes, usually just like spar caps on conventional I beam spars also
allow tapered wings (was this a trick question?). See
http://continuo.com/marske/ARTICLES/Carbon%20rods/carbon.htm

---

I'll suggest a marketing program to Greg Cole... let the first handful
of position holders rename the Duck Hawk. Peregrine (i.e. what a Duck
Hawk is) works for me. Ooops I'm not a position holder.

Darryl

[Greg Arnold[_2_]]

Darryl Ramm wrote:
> On Jan 6, 9:16 pm, Greg Arnold > wrote:
>> Udo Rumpf wrote:
>>>> Are pultrusions lighter than something made with vacuum
>>>> bagged pre-pregs? If so, why are they lighter?
>>> Yes. Due to the alignment of the fibres and the higher tensile strength of
>>> the resin, plus the high cure temperature.
>>> Hand lay-up and vacuum bagging can only achieve a fraction of the
>>> potential strength of the carbon fibre.
>>> Unidirectional preprec have some of the same benefits but not to the same
>>> extent as pultrusions.
>>> Udo
>> Does a pultrusion work with a spar that is tapered as you get further
>> from the fuselage?
>
> Yes, usually just like spar caps on conventional I beam spars also
> allow tapered wings (was this a trick question?). See
> http://continuo.com/marske/ARTICLES/Carbon%20rods/carbon.htm

So just the caps, rather than the entire spar, are pultruded.


>
> ---
>
> I'll suggest a marketing program to Greg Cole... let the first handful
> of position holders rename the Duck Hawk. Peregrine (i.e. what a Duck
> Hawk is) works for me. Ooops I'm not a position holder.
>
> Darryl

[Darryl Ramm]

On Jan 6, 9:56*pm, Greg Arnold > wrote:
> Darryl Ramm wrote:
> > On Jan 6, 9:16 pm, Greg Arnold > wrote:
> >> Udo Rumpf wrote:
> >>>> Are pultrusions lighter than something made with vacuum *
> >>>> bagged pre-pregs? *If so, why are they lighter?
> >>> Yes. Due to the alignment of the fibres and the higher tensile strength of
> >>> the resin, plus the high cure temperature.
> >>> Hand lay-up and vacuum bagging can only achieve a fraction of the
> >>> potential strength of the carbon fibre.
> >>> Unidirectional preprec have some of the same benefits but not to the same
> >>> extent as pultrusions.
> >>> Udo
> >> Does a pultrusion work with a spar that is tapered as you get further
> >> from the fuselage?
>
> > Yes, usually just like spar caps on conventional I beam spars also
> > allow tapered wings (was this a trick question?). See
> >http://continuo.com/marske/ARTICLES/Carbon%20rods/carbon.htm
>
> So just the caps, rather than the entire spar, are pultruded.
>
>
>
> > ---
>
> > I'll suggest a marketing program to Greg Cole... let the first handful
> > of position holders rename the Duck Hawk. Peregrine (i.e. what a Duck
> > Hawk is) works for me. Ooops I'm not a position holder.
>
> > Darryl
>
>

The caps are where the compression and tension strength is gained. In
Duck Hawk who knows if they are being used at all?

I don't know if anybody has used tapered pultruded rods in a spar as
well but it may be a possibility given the complex rods and tube shape
being manufactured for other applications.

Darryl

[Udo Rumpf[_2_]]

>Does a pultrusion work with a spar that is tapered as you get >further
from the fuselage?

The Genesis is an example, the Lak 17 maybe as well.
Udo

[Udo Rumpf[_2_]]

>I don't know if anybody has used tapered pultruded rods in a >spar as
well but it may be a possibility given the complex rods >and tube shape
being manufactured for other applications.

Rectangular profiles are made, the smaller the cross section of the
Pulltrusion the better you are able to match the bending moment. Naturally
it is more effort to built with smaller sections
but it provides for a near optimum spar.
Udo

[Udo Rumpf[_2_]]

>I don't know if anybody has used tapered pultruded rods in a >spar as
well but it may be a possibility given the complex rods >and tube shape
being manufactured for other applications.

Rectangular profiles are made, the smaller the cross section of the
Pulltrusion the better you are able to match the bending moment. Naturally
it is more effort to built with smaller sections
but it provides for a near optimum spar.
Udo

[Bob Kuykendall]

On Jan 6, 8:30*pm, Udo Rumpf > wrote:

> Yes. Due to the alignment of the fibres and the higher tensile strength of
> the resin, plus the high cure temperature.
> Hand lay-up and vacuum bagging can only achieve a fraction of the
> potential strength of the carbon fibre.
> Unidirectional preprec have some of the same benefits but not to the same
> extent as pultrusions.

To expound on what Udo writes:

Pultruded carbon fiber strips (or rods or ribbons or whatever profile)
are a neat way to make spar caps for wing spars because they have
great properties and don't require heroics in terms of fiber
alignment, lamination conditions, and climate control. Their
application to sailplane design was Pioneered (pun intended) by Jim
Marske who tested and developed a variety of ways to design and work
with them. Jim further did tests on a variety of hand-laminated
unidirectional carbon fiber test coupons and found that it is very
difficult, and sometimes impossible, to achieve handbook properties
without extreme control of fiber alignment and curing conditions.

Offhand, I think that pultruded strips offer max tensiles of around
300 ksi and (this is the important part) max compressive of around 275
ksi. That's around five times what you get in compression strength
from hand-laminated uni carbon. Their Young's modulus is somewhere
around 20 million.

The biggest arguement against pultrusions (and this might be the most
compelling thing for Greg), is that while they offer great strength,
their stiffness (as in Youngs modulus) has only a 10% to 15%
improvement over hand-laid uni. Since a lot of sailplane design
considerations are bound by stiffness more than by strength, the extra
strength of pultruded carbon doesn't have all that much effect on the
finished product.

I suspect that since Greg has good access to high-tech prepreg
materials, and more importantly to the expensive autoclaving equipment
and energy it takes to press and cook it, Pultrusions don't hold as
much advantage in his shop as they do in my more lowbrow and low-
dollar operation.

Thanks, and best regards to all

Bob K.
www.hpaircraft.com/hp-24

[DRN]

On Jan 7, 1:40*pm, Bob Kuykendall > wrote:
> On Jan 6, 8:30*pm, Udo Rumpf > wrote:
>
> > Yes. Due to the alignment of the fibres and the higher tensile strength of
> > the resin, plus the high cure temperature.
> > Hand lay-up and vacuum bagging can only achieve a fraction of the
> > potential strength of the carbon fibre.
> > Unidirectional preprec have some of the same benefits but not to the same
> > extent as pultrusions.
>
> To expound on what Udo writes:
>
> Pultruded carbon fiber strips (or rods or ribbons or whatever profile)
> are a neat way to make spar caps for wing spars because they have
> great properties and don't require heroics in terms of fiber
> alignment, lamination conditions, and climate control. Their
> application to sailplane design was Pioneered (pun intended) by Jim
> Marske who tested and developed a variety of ways to design and work
> with them. Jim further did tests on a variety of hand-laminated
> unidirectional carbon fiber test coupons and found that it is very
> difficult, and sometimes impossible, to achieve handbook properties
> without extreme control of fiber alignment and curing conditions.
>
> Offhand, I think that pultruded strips offer max tensiles of around
> 300 ksi and (this is the important part) max compressive of around 275
> ksi. That's around five times what you get in compression strength
> from hand-laminated uni carbon. Their Young's modulus is somewhere
> around 20 million.
>
> The biggest arguement against pultrusions (and this might be the most
> compelling thing for Greg), is that while they offer great strength,
> their stiffness (as in Youngs modulus) has only a 10% to 15%
> improvement over hand-laid uni. Since a lot of sailplane design
> considerations are bound by stiffness more than by strength, the extra
> strength of pultruded carbon doesn't have all that much effect on the
> finished product.
>
> I suspect that since Greg has good access to high-tech prepreg
> materials, and more importantly to the expensive autoclaving equipment
> and energy it takes to press and cook it, Pultrusions don't hold as
> much advantage in his shop as they do in my more lowbrow and low-
> dollar operation.
>
> Thanks, and best regards to all
>
> Bob K.www.hpaircraft.com/hp-24

Another consideration is transferring the shear loads
out of the caps at the root. With prepreg or wet-layup,
you can wrap the caps part way around the end of the
spar to help with this; not so with pultrusions. I don't
know how important this is...

Wet lay-ups in a glider factory environment are not
too hard (not at all trivial, but control of wetting and
fiber-straightness are understood). Perhaps not to
"handbook values" (nor designed to) ;-)

See ya, Dave "YO electric"

[Bob Kuykendall]

On Jan 7, 1:01*pm, DRN > wrote:

> Another consideration is transferring the shear loads
> out of the caps at the root. With prepreg or wet-layup,
> you can wrap the caps part way around the end of the
> spar to help with this; not so with pultrusions. I don't
> know how important this is...

The spars that Jim Marske has helped develop for the Genesis and LAK
ships, and the static tests that they survived, seem to demonstrate
that this is not a critical issue.

> ...control of wetting and fiber-straightness are understood...

1. >O {Press Button}
2. ~~~ {Receive Ondulation}

Thanks, Bob K.

[Darryl Ramm]

On Jan 7, 2:11*pm, Bob Kuykendall > wrote:
> On Jan 7, 1:01*pm, DRN > wrote:
>
> > Another consideration is transferring the shear loads
> > out of the caps at the root. With prepreg or wet-layup,
> > you can wrap the caps part way around the end of the
> > spar to help with this; not so with pultrusions. I don't
> > know how important this is...
>
> The spars that Jim Marske has helped develop for the Genesis and LAK
> ships, and the static tests that they survived, seem to demonstrate
> that this is not a critical issue.
>
> > ...control of wetting and fiber-straightness are understood...
>
> 1. >O * *{Press Button}
> 2. ~~~ *{Receive Ondulation}
>
> Thanks, Bob K.


....
o
/|\
5. _/ \_ {walk on it} :-)


Darryl

[Nyal Williams[_2_]]

The name is taken for a metal trainer made by a glider manufacturer in
Florida(?)

I never heard of a pulltrusion and can only guess what it means; I'm a
poltroon, my self.



At 05:46 07 January 2009, Darryl Ramm wrote:
>On Jan 6, 9:16=A0pm, Greg Arnold wrote:
>> Udo Rumpf wrote:
>> >> Are pultrusions lighter than something made with vacuum =A0
>> >> bagged pre-pregs? =A0If so, why are they lighter?
>>
>> > Yes. Due to the alignment of the fibres and the higher tensile
>strength=
> of
>> > the resin, plus the high cure temperature.
>> > Hand lay-up and vacuum bagging can only achieve a fraction of the
>> > potential strength of the carbon fibre.
>> > Unidirectional preprec have some of the same benefits but not to the
>sa=
>me
>> > extent as pultrusions.
>> > Udo
>>
>> Does a pultrusion work with a spar that is tapered as you get further
>> from the fuselage?
>
>Yes, usually just like spar caps on conventional I beam spars also
>allow tapered wings (was this a trick question?). See
>http://continuo.com/marske/ARTICLES/Carbon%20rods/carbon.htm
>
>---
>
>I'll suggest a marketing program to Greg Cole... let the first handful
>of position holders rename the Duck Hawk. Peregrine (i.e. what a Duck
>Hawk is) works for me. Ooops I'm not a position holder.
>
>Darryl
>

[[email protected]]

On Jan 7, 2:30*pm, Nyal Williams > wrote:
> The name is taken for a metal trainer made by a glider manufacturer in
> Florida(?)
>
> I never heard of a pulltrusion and can only guess what it means; I'm a
> poltroon, my self.
>

Opposite of an extrusion - which had already been named or it would
have been called a push-trusion I suppose.

Calling the opposite of an extrusion an intrusion didn't work either
so there you go...

9B

[Bruce]

wrote:
> On Jan 7, 2:30 pm, Nyal Williams > wrote:
>> The name is taken for a metal trainer made by a glider manufacturer in
>> Florida(?)
>>
>> I never heard of a pulltrusion and can only guess what it means; I'm a
>> poltroon, my self.
>>
>
> Opposite of an extrusion - which had already been named or it would
> have been called a push-trusion I suppose.
>
> Calling the opposite of an extrusion an intrusion didn't work either
> so there you go...
>
> 9B
Maybe we can be more specific. A Pultrusion is where a solid is made in
a continuous process from a collection of fibres that are embedded in a
solid (usually resin - but also metals etc).
The process is to progressively pull a set of fibres off spools under
substantial tension through a shaped hole (former), while one of a
couple of processes apply the substrate (resin). This gives you a close
to perfectly aligned set of fibres in a very uniform substrate. Then the
result is usually heat cured in a die and cut to length...

Very uniform result - both dimensionally and in strength and also close
to theoretical strength limits, but typically quite "floppy"

[Bob Kuykendall]

On Jan 6, 9:16*pm, Greg Arnold > wrote:

> Does a pultrusion work with a spar that is tapered as you get further
> from the fuselage?

[Warning: I am not an engineer. The following is not engineering
advice. Read and apply at your own risk. Via con Dios, Amigo!]

You have to make them work.

Designing economically with pultrusions is all about using
commercially-available profiles. You can order entire custom mondo
bars or strips or even angles or T-sections if you want, but the cost
per unit strength and stiffness is through the roof. Economically, it
makes better sense to select smaller strips or rods that have wide
application in consumer goods, and take a free ride on their economies
of scale.

Basically, you assble the spar as a box, I-beam, or C-section using
relatively conventional composite construction techniques, and use a
matrix (columns and rows) of pultruded elements in the spar caps to
collect the tensile and compressive loads. LAK has used 1/8" dia
pultruded rods in the past, as did the Genesis. I think LAK's recent
designs might tend towards the use of rectangular-section strips as do
mine.

You taper the spar in depth to match the wing depth by making the
shear web in the shape of one or more elongated trapezoids. You taper
the spar caps in cross-section to match the sectional moment of
inertia to the local bending moment by ending the pultruded elements
(or entire columns or rows of elements) at various spanwise stations.
So out by the tip there might be only an eighth or a tenth of what you
have at the side-of-body where the bending moment is at its maximum.

As Dave Nadler suggests, transferring loads between the upper and
lower spar caps in the spar stub, and transferring the moment from one
spar butt to the other through the main pins, is not trivial. However,
what I've seen of crashed and otherwise torn apart European racers
suggests that if you're methodical and consistent you can approach it
relatively casually and still have plenty of margin.

The tooling required to make spars using pultrusions can be as
substantial or as hokey as your workshop environment lets you get away
with. I've seen it done successfully with a pair of sharpie lines
drawn on a long level Formica tabletop. Using strips of wood on the
tabletop to guide the spar cap matrix alignment has also worked well.

Thanks, Bob K.