Jump to content


Photo
- - - - -

How to do the Albatros series justice


  • Please log in to reply
155 replies to this topic

#121 gavagai

gavagai
  • Posts: 15542

Posted 15 December 2011 - 00:35

I was wondering just how sensitive it is to airspeed data. So, for example, if we use the D.III CDo value, and compare 109mph to 116mph:

CDo is proportional to 1/(116/109)^3 = .83

0.0465 * .83 =.0386

A 6% increase in airspeed suddenly makes it appear much more streamlined.

————-

Or, for example, comparing the D.III's 109mph (which our more powerful OAW cannot do) to the 117mph D.Va data I posted:

(180hp/170hp)/(117/109)^3 = .856

In other words, it would indicate that the D.Va's CDo was almost 15% less than the D.III's, which seems rather extreme. I think it's more fair to say that the airspeed data is all over the place and is hard to trust.
  • 0

#122 Chill31

Chill31
  • Posts: 1892

Posted 15 December 2011 - 01:44

With regard to climb rate: The Alb D5a and the N17 have almost identical Power to weight ratios. However, the AlbD5a has a 13% higher wingloading (which equates to an increase in drag) AND it also has a 13% slower climb rate at low-mid altitude. This is why I dont think that its climb rate is far off.

Lets say we have two planes with identical power to weight ratios and identical drag profiles and similar airfoils. These two planes should have very similar climb rates. If one of those planes had more drag (in the above example, drag due to lift) than the other, he will have less excess power and thus will have a slower climb rate. I hope that explains my above statement. It is purely coincidental that the Alb has 13% increased wingloading AND 13% lower climb rate as it could vary somewhat, but the correlation is not a coincidence.



As for the difference in climb between the Fokker D7 FM and the AlbD5, it comes down to drag and lift again. The D7 is a very clean airplane aerodynamically (relatively speaking) AND he has a high lift wing. So even if we say that the D7 had identical parasite drag (zero lift drag), the D7 will have a higher Coefficient of lift (possibly around 50% more) for a given AOA, ie a higher L/D. So you can see that he would have a slightly better climb rate. For ROF D7 vs Alb D5, the D7 is about 13% better in climb.

***side note: On reason for the Alb performance drop compared to the Pup, possibly even more than the engine, is the steep increase in drag due to lift (it is exponential with increasing AOA). As it gets higher in altitude, the IAS drops off and requires increased AOA (drag)to stay flying. The Pup, with a very low wing loading will not have the same drag increase based on AOA. The thick airfoil of the D7 handles increasing AOA in a MUCH better manner, ie his drag increases slower with AOA increase than the thin wing of the D5. This is also a contributing reason for the better performing Fokker Dr1 at altitude.

Finally, if you have the time and desire, you can play with this airfoil computer. Its not perfect, but it gives a nice demo of what you can expect and even reproduces stall curves which look as you would expect them too: http://www.mh-aeroto...ls/javafoil.htm" onclick="window.open(this.href);return false;">http://www.mh-aeroto...ls/javafoil.htm
  • 0

#123 piecost

piecost
  • Posts: 1318

Posted 15 December 2011 - 02:16

Interesting stuff,

I find it difficult to interpret the performance characteristics of these planes since there are so many factors varying and the original data was so error prone. For goodness sake, one report mentioned that performance tests should use the exact same propeller each time, since differences between identical propellers varied so much (due to warping, I assume).

In interpreting non-dimensional data, a plane with a small wing may have a larger looking drag coefficient. The dimensional drag is the one that really matters.

This may be a good time to post a wind tunnel test of the Fokker DVII wings. Note that the test were only performed on the wings and not the fuselage, tail or other bits.

A caveat must be applied to the results since Reynold's number effects were not fully understood the results may be in error due to lack of model transition fixing etc. Differences between tunnel and flight results may significantly differ to those for thin wings.

I had somewhere, some wind tunnel data for Albatross sections (not whole biplane wings)

It would be fantastic if someone has the time and inclination to simulate the various wing sections. We would then have a level playing field to compare.

Wind Tunnel Tests on a Fokker Biplane

Reports & Memoranda No. 817

Attached Files


  • 0

#124 JimmyBlonde

JimmyBlonde
  • Posts: 2346

Posted 15 December 2011 - 02:19

Did anyone else get an acid flashback from trying to read Chill's last post???
  • 0

#125 Chill31

Chill31
  • Posts: 1892

Posted 15 December 2011 - 04:04

haha, sorry about that…

I think the point of this post has been made perhaps?

Is there anyone who still has questions regarding albatross performance? Does anyone dispute what we have laid out here?

Piecost, do you have anything to pile on?
  • 0

#126 piecost

piecost
  • Posts: 1318

Posted 15 December 2011 - 04:59

Nothing constructive
  • 0

#127 J2_Adam

J2_Adam
  • Posts: 2453
  • LocationVancouver, BC

Posted 15 December 2011 - 05:03

Did anyone else get an acid flashback from trying to read Chill's last post???

I did and enjoyed it. :ugeek:
  • 0

#128 gavagai

gavagai
  • Posts: 15542

Posted 15 December 2011 - 05:25

Chill31, I would like to hear something from viks or another green name before we call the thread good. I've been waiting for 2+ years to see the Albatros get its due in RoF, and what does any of this mean without an acknowlegement that there was a poor choice of data for the DVa?
  • 0

#129 =FB=VikS

=FB=VikS
  • Developer
  • Posts: 1246

Posted 15 December 2011 - 12:25

Chill31, I would like to hear something from viks or another green name before we call the thread good. I've been waiting for 2+ years to see the Albatros get its due in RoF, and what does any of this mean without an acknowlegement that there was a poor choice of data for the DVa?

To hear what?
Im not going to make any conclusions - as Andrew will do it in case of Alb.D.Va FM revision.
Our task - is to give him information to think on and work with it.
  • 0

#130 gavagai

gavagai
  • Posts: 15542

Posted 15 December 2011 - 15:54

Chill31, I would like to hear something from viks or another green name before we call the thread good. I've been waiting for 2+ years to see the Albatros get its due in RoF, and what does any of this mean without an acknowlegement that there was a poor choice of data for the DVa?

To hear what?

To hear that you're no longer supremely confident in the correctness of the D.Va's current flight model. In past conversations you insisted on it, and insisted that e.g. the Sopwith Camel and Dr1 were faster, no matter how many eye witness accounts said otherwise.

Anyway, I do look forward to Petrovich's investigation.

Thank you.
  • 0

#131 elephant

elephant
  • Posts: 1156

Posted 15 December 2011 - 16:30

:D
  • 0

#132 =FB=VikS

=FB=VikS
  • Developer
  • Posts: 1246

Posted 15 December 2011 - 17:01

To hear that you're no longer supremely confident in the correctness of the D.Va's current flight model. In past conversations you insisted on it, and insisted that e.g. the Sopwith Camel and Dr1 were faster, no matter how many eye witness accounts said otherwise.

I "insisted on it"?
Where?
Maybe i insisted on position that actual numbers is better than words? Its different things.

PS: im never confident in anything, as everyone has his own truth ;)
  • 0

#133 gavagai

gavagai
  • Posts: 15542

Posted 15 December 2011 - 17:08

We talked about it on at least two occasions on the syndicate server. 8-)
  • 0

#134 ImPeRaToR

ImPeRaToR
  • Posts: 7902

Posted 15 December 2011 - 17:08

Never trust statistics that you haven't faked yourself :)
  • 0

#135 gavagai

gavagai
  • Posts: 15542

Posted 15 December 2011 - 17:11

Lies, damned lies, and statistics!
  • 0

#136 Tom-Cundall

Tom-Cundall
  • Posts: 5549

Posted 15 December 2011 - 17:24

My favourite is

"I can prove anything with statistics, except the truth" George Canning.

&


“Definition of Statistics: The science of producing unreliable facts from reliable figures.” Evan Esar

&

“Statistics are no substitute for judgment” Henry Clay

All fit well here… :)
  • 0

#137 =FB=VikS

=FB=VikS
  • Developer
  • Posts: 1246

Posted 15 December 2011 - 17:36

We talked about it on at least two occasions on the syndicate server. 8-)

Can`t remember, any screenshots? :lol:
  • 0

#138 Pimpin

Pimpin
  • Posts: 1066

Posted 15 December 2011 - 17:39

We talked about it on at least two occasions on the syndicate server. 8-)
That'll never stand up in court! :D
  • 0

#139 BraveSirRobin

BraveSirRobin
  • Member
  • Posts: 6582
  • LocationHackistan

Posted 15 December 2011 - 17:47

If you had all the statistics you needed you wouldn't be bickering over flight models.
  • 0

The toughest part of my job is dealing with incompetent clowns who think they're good at their job.

Free Plank!

 


#140 SYN_Vander

SYN_Vander
  • Tester
  • Posts: 4710

Posted 15 December 2011 - 17:49

Be careful with what you say, we do keep chat logs you know! (thanks to Vaal ;) )
  • 0

#141 gavagai

gavagai
  • Posts: 15542

Posted 15 December 2011 - 18:11

We talked about it on at least two occasions on the syndicate server. 8-)

Can`t remember, any screenshots? :lol:

Of course, I snapped lots of pics because I was waiting for this day.

But IIRC you did say something like "data is more reliable than quotes," or something to that effect, and that was your basis for saying that the Albatros D.Va was slow.

Anyway, Viks, you need to adopt a more holistic approach to this stuff. WW1 aircraft data is not reliable by itself.
  • 0

#142 piecost

piecost
  • Posts: 1318

Posted 15 December 2011 - 19:27

This attachment is not very helpful as such but illustrates how quickly a new aeroplane degraded. Did soggy fabric relate to the strength or tautness of the fabric i.e. its airworthiness without impacting the performance? Or, did soggy fabric incur significant billowing and permeability (with a performance impact)? I don't know.

I am starting to believe that the difference between a brand new and an old example of one type of plane may outweigh the differences between different types of planes (assuming they are similar types and in similar condition).

From Aeronautic Journal April 1919

Attached Files


  • 0

#143 gavagai

gavagai
  • Posts: 15542

Posted 15 December 2011 - 21:23

Piecost posted this is another thread, but it's worth posting here:

Image

So a German or French scout would have lost 2.5% of its airspeed by not using the streamlined RAF bracing wires, i.e. it cannot, by itself, explain the slow speed of the Albatros series in RoF.
  • 0

#144 piecost

piecost
  • Posts: 1318

Posted 16 December 2011 - 23:00

This is the only Albatros information I have, I am not sure which type the section is taken from. The caveats about the data, which I have referred to in the past apply. This data is not truly 2 dimensional but tested on an aspect ratio of 6 wing. The comparison with the SE5a wing section is interesting

Standard Tests of Two Aerofoils… Albatros Sections and a Comparison with RAF15

Reports & Memoranda No. 375

Attached Files


  • 0

#145 piecost

piecost
  • Posts: 1318

Posted 16 December 2011 - 23:01

Standard Tests of Two Aerofoils… Albatros Sections and a Comparison with RAF15

Reports & Memoranda No. 375

…continued

Attached Files


  • 0

#146 ImPeRaToR

ImPeRaToR
  • Posts: 7902

Posted 16 December 2011 - 23:28

It's the lower wing of a "V-strut albatros", afaik D.III, D.V and D.Va had the same wings.
  • 0

#147 NickM

NickM
  • Posts: 1625

Posted 18 December 2011 - 17:42

Piecost posted this is another thread, but it's worth posting here:

Image

So a German or French scout would have lost 2.5% of its airspeed by not using the streamlined RAF bracing wires, i.e. it cannot, by itself, explain the slow speed of the Albatros series in RoF.

No, that's not what it says. It say a difference of about 2.5 % on small machines. But not all scouts were small machines. I would argue that aircraft like the N.11 or Pup are significantly smaller and lighter than the next generation of scouts like the SE5a, D.VII or Albatros D.Va which could have take-off weights almost twice as large. Lighter aircraft require less in the way of bracing and so will almost certainly use thinner wires.

If you are looking for an effect of bracing wires on the top speed of an Albatros fighter, probably all we can say with confidence from the above quote is that not using streamlined wires reduced the top speed by a few %.
  • 0

#148 gavagai

gavagai
  • Posts: 15542

Posted 19 December 2011 - 18:04

That is pure speculation Nick (what was small and what was large in 1919?), but even if we accepted a figure like 3-4%, my point would still stand. I think the correct explanation of the slower airspeed of the Albatros series would have to make use of both the high camber wing profile, and the higher drag bracing wires, with a greater burden of explanation on the highly cambered wing. Then it begins to make sense that you can get 219kmh from a 180hp Spad 7, and only 187kmh from the 180hp D.Va (more than a 15% difference!) at sea level. But the slower 165-170kmh figures for the D.Va I reject outright as the consequence of captured aircraft with "soggy" canvas, slightly warped propellers, etc. As Piecost mentioned, what seems to have been very important was not so much the type of aircraft facing each other, but their relative conditions!
  • 0

#149 piecost

piecost
  • Posts: 1318

Posted 19 December 2011 - 22:39

In addition, I believe that the Albatros wing radiator may have been a draggy installation. Apparently a better installation than fuselage mounted ear radiators, but I am not sure why. (why did the Dolphin change from a neat nose radiator to the archaic ear radiators?)

I read (but didn't bother copying) a post-war British paper with a one-line critique of the wing radiator suggesting that it was draggy. Perhaps a biased view, but it is telling that the ultimate water-cooled biplanes (Hart, Heinkel He 51, etc) used a body mounted, underslung installation.

The wing radiators were significant relative to the wing area and, by design, allowed air to pass though the wing. This sounds terrible for wing efficiency. A Sopwith Camel biplane cellule (without fuselage) was wind tunnel tested with the mid chord hole for improved view. It incurred a 20% increase in drag! The Albatros radiator would have less airflow than the hole (due to the blockage from the radiator elements), but over a greater area. I wonder if a performance advantage was to be had with the shutters closed!

We should not look at the bluff noses of the SE5a and the SPAD and assume that their radiators were relatively draggy.
  • 0

#150 gavagai

gavagai
  • Posts: 15542

Posted 19 December 2011 - 23:52

Interesting Piecost, what you say makes sense. The wing mounted radiator was supposed to be more effective for cooling than a nose mounted radiator (but our Albatrosses never have overheat problems), but the drawback is evident.

I wonder if the F1/3 Camel prototype had the wing cutout? Could that play a role in an explanation of why the initial production models were disappointing compared to the prototype's performance?
  • 0

#151 piecost

piecost
  • Posts: 1318

Posted 20 December 2011 - 08:32

Sopwith Camel by J. M. Bruce, Windsock Datafile No 26

On March 2 1917, a sample Camel was flown at No 1 Aircraft Depot, St-Omer, by 2/Lt K L Caldwell of No. 60 Squadron, FRC, and on March 4 by Capt\ain A M Lowry of No 70 Squadron, FRC. A note of March 5 1917 suggested that this Camel had a central cut0out in the upper wing whereas the Navel Camel did notl the RFC concluded that it wanted this cut0out to be standardised, but it did not say why.

As it was of little use as a means of improving the pilot's upward view; a more compelling reason for its use might have been the alleviation of the Camels pronounced tail-heaviness. The Pup had been similarly afflicted, and it had been found that an improvement was brought about by making a small central cut-out between the spars of its central section.

The identity of the Camel tested bty the RFC in early March seems not to have been recorded, but it might have been the prototype that Martlesham Heath was to record as F1/3.

With the benefit of RoF experience I dispute Bruce's conclusion about the little improvement in pilots view. The upward view is so poor that even a small cut-out is really helpful. There are other ways to combat tail heaviness - without incurring a performance loss. Since the cut-out was further enlarged by some, it must have been of use. I have read elsewhere, Surprisingly, that the enlarged cut-out had little further reduction in performance.

It was known that cutting the hole would degrade performance, hence the fitting of the washboards to the edges, but the wind tunnel test was only performed after the Camel had been in service many months


On the Effect of Cutting a Hole in the Top Plane of a Biplane


Reports & Memoranda No. 419

Attached Files


  • 0

#152 elephant

elephant
  • Posts: 1156

Posted 20 December 2011 - 13:48

gavagai's question about the prototype Camel and the upper wing view cut stil stands…

PS: I found this photo of the prototype? :?
Seems the cut was there…

Image

PS: Found this one too, from Xmas 1916 and the cut is lacking!

Image

:S!:
  • 0

#153 gavagai

gavagai
  • Posts: 15542

Posted 20 December 2011 - 14:26

Image

Another one.

Image
  • 0

#154 Tom-Cundall

Tom-Cundall
  • Posts: 5549

Posted 20 December 2011 - 16:32

I remember reading that the Camel prototype had a single piece upper wing unlike production models which had three segments.

Not sure what difference if any that would have made. I think the engine was the big thing.

Those initial 130/140hp Clergets were terrible - nowhere near the quality of the 110 Le Rhones and performance suffered as a result.

Sorry for the OT.
  • 0

#155 piecost

piecost
  • Posts: 1318

Posted 20 December 2011 - 21:31

Back to Albatros deterioration in service

Report on the Comparative Weathering of British & German Doped Fabric

Reports & Memoranda No. 446

Attached Files


  • 0

#156 piecost

piecost
  • Posts: 1318

Posted 20 December 2011 - 21:37

More on the deteriation of fabrics with age.

It seems that the fabric could slacken which would effect the aerodynamic profile and hence the performance. I have not found specific mention of change in the permiability of the doped fabric. It must not have been an issue (provided the dope remained intact).

Table from

Report on the Use of Dopes & Fabrics in Egypt

Reports & Memoranda No. 318

Attached Files


  • 0


0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users