Polar Data for Phoebus A1

[John Foster]

I'm looking for polar data on the Bolkow Phoebus A1.  I've done an internet search, but nothing comes up.  But I know it is available on a number of flight computer devices as a pre-set for the glider.  Is anyone able to give me the 3 different numbers (A, B, C) to enter in for a custom polar?  Thanks.

[Stefan Will]

Looks like XCSoar only has built-in polar data for the Phoebus C (https://github.com/XCSoar/XCSoar/blob/master/src/Polar/PolarStore.cpp#L196). 

Does your POH have a polar in it? All you need are three airspeed / vertical velocity pairs, and the coefficients can be calculated from those.

On Mon, May 5, 2025 at 11:00 PM John Foster <johngf...@gmail.com> wrote:

I'm looking for polar data on the Bolkow Phoebus A1.  I've done an internet search, but nothing comes up.  But I know it is available on a number of flight computer devices as a pre-set for the glider.  Is anyone able to give me the 3 different numbers (A, B, C) to enter in for a custom polar?  Thanks.

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[John Foster]

Those are the three numbers I'm looking for.  My POH does NOT have a polar in it, unfortunately.

[Dan Daly]

Searched on Phoebus and a hit on Deutsches Museum came up with some data included

• Manufacturer: Bölkow-Entwicklungen KG, Laupheim, 1967
• Wingspan: 17.0 m
• Wing aspect ratio: 20.5
• Weight, empty: 240 kg
• Minimum sink rate: 0.63 m/s at 83 km/h
• Best glide ratio: 39 at 93 km/h

You could start with something similar - perhaps ASW-15, or Standard Cirrus, and see if they work (maybe with tweeking).

You could ask the Idaflieg at https://idaflieg.de  ; they may have oldtimer data. The list of measured aircraft is long; perhaps they have data, or something close. From the website:

"This is the (abbreviated english) version:
Available flight performance reports are listed below. Please write a short email to vorstandÃ3idaflieg.de to request a report. The list might be incomplete. If you can't find your desired sailplane, feel free to ask anyways. We charge a fee of 15€ per report. The bank account is mentioned above. Additional donations to support the scientific work of our student group are always welcome!"

Dan

[Dan Daly]

And, possibly found a polar at:

https://www.stolaf.edu/people/hansonr/soaring/spd2fly/index.htm then select "Phoebus C" from drop-down list.

Dan

[Martin Brugger]

I have the polar for the Phoebus C which  isn't really what you want.  Your are looking for the A model which had 15m wings.  I believe the wing profile was the same.

90km/hr    0.67m/s

145km/hr  1.71m/s

199km/hr  3.84m/s

Not sure on the meaning, as it was some years ago,  but with that is:  a  1.88,  b -2.54,

c 1.43  with polar.exe written beside those numbers.

Martin

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[Martin Brugger]

Failing that you could contact Lindner Technik,  the son of one of the designers  for things Phoebus.

[Stefan Will]

I found this old spreadsheet that has a polar for the Phoebus A (and B and C): https://web.archive.org/web/20170215203138/https://www.gliding.com.au/assets/docs/Polar10.xls

On May 6, 2025, at 3:08 PM, Martin Brugger <flying...@gmail.com> wrote:



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[Stefan Will]

Sorry, just for the A, apparently sourced from Idaflieg.

[Chip Bearden]

In my experience, we tend to get caught up in trying to input precise numbers for these polars--and then fly around with different wingloadings, wing profile distortions due to curing over the years, bugs, dirt, sealing (varied widely in those days), wind gradients, turbulence, etc. And that ignores the fact that most testing to develop these precise polars must be done early in the morning on stable days because natural movement of the air can have an enormous impact on performance. 

I've been using a handheld "prayer wheel" calculator I developed years ago for my old LS3 to "sanity check" my electronic glide calculators in my ASW 24 for over 30 years. So I suggest that you just pick something comparable from that era--ASW 15, Libelle 201, Standard Austria SH1, or even a K6E--and go with that. As I recall, the early Phoebus gliders had fairly low wing loading and were sensitive to rain, roughness, etc. So any differences you see in the real world will almost certainly be due to all of the above factors, not from having a polar that isn't perfect for your specific glider. Speaking of that, it's also commonly accepted that gliders from that era often varied significantly from one sailplane to another even of the same identical model owing to variations in how the parts were molded and then hand finished. So even if you find the exact polar you're seeking, there's no guarantee it will be representative of your glider. 

Chip Bearden

JB

[Moshe Braner]

Thanks Chip for the dose of reality.  That said, does anybody have polar data for the HPH 304C?  We have that glider in our club.  I've used the LS4 polar in a glide computer while flying the 304C, thinking it is "close enough".

[Steven Leonard]

John, the polar for YOUR Phoebus A was reported in the June 1970 issue of SOARING magazine, on page 19.  Tabulated data on page 17.

Steve Leonard 

[John Foster]

I'm actually looking for data for a Phoebus A1, not C model.  C model has 17m wings and retractable undercarriage.  A1 model is 15m and fixed gear.

[Steven Leonard]

Copied from the June 1970 issue of SOARING magazine.  Not sure if the plane is not better or worse than this.

Steve Leonard