Explain this and win the prize!

[joeblogs]

Since when did wind tunnels get such a bad rep?

Sure you have to be careful with design, reynolds numbers, etc, but most of these things had been worked out for sub-sonic flows well before the war.

The advantage of a wind tunnel test over flight tests is that the experiment can be better controlled and experiments can be more easily compared with other experiments. The disadvantage is that wind tunnel models may not capture all the features that will affect an actual production model...

-blogs

Originally posted by Crumpp
Windtunnel data on a model has little to do with the actual aircraft with the exception of making general assesments.  You certainly cannot take exact values off it.  Ask Hitech.


You can say:

This design will fly and be stable.
This design will be "X" fast in level flight
etc..

No whether they hold true or on can only be determined by the actual aircraft.  Drag data would have to come from an actual  aircraft in order to have any kind of meaning.

 

Completely worthless for comparision.  We could compare the wooden model of the FW-190 with them but that would be a complete waste of time as well.

 

Ahh, that explains a lot.

Crumpp

[Charge]

"In most cases the wind tunnel data seems to be quite comparable with other wind tunnel tests but the flight tests seem to give lower values. "

I guess that is because there are many minor factors which may have a significant effect combined. Surface design, exhaust system vs. exhaust thrust, cowling fitting, temporal jig misalignment causing badly formed fuselages etc.

I'd imagine that eg. the air that enters the engine cowling of FW is  problematic from aerodynamic modelling point of view. Do they consider the air intake to be closed or to flow through to some extent or what. Considering the size of the air intake it may have a significant effect on how well the model correlates with the real life a/c.



-C+

[gripen]

Hm... Generally the effect of the powerplant (slipstream, radiators, heat effects etc.) is a unknown factor in the all wind tunnel data and it's a problem when testing a scale model or a full size aircraft in the wind tunnel. But otherwise I see wind tunnel as a good and practical way to study planes.

gripen

[Charge]

I agree. I'd imagine that the wind tunnel gives a rather accurate estimate of the behaviour of the aerodynamics and good results when comparing similarly manufactured scale models. The error estimate calculations may be tricky, though.

Otherwise in my opinion a combat aircraft and their abilites cannot be very accurately evaluated by the wind tunnel data alone even if it gives a good estimate of the stall speeds and stall and drag behaviour of the airframe.

I thought the Lednicher article to be a bit torso on part of 190. I dont think he is aware of the possibility of bad aileron tuning which could cause similar effects as torsional warping of the wing in tight turns. Based on the NACA report on roll rate I think is rather unlikely that 190 had a torsionnally loose wing considering its excellent roll rate which would not be possible if his assumption is true. Or is it? Dunno for sure.

-C+

[Crumpp]

But otherwise I see wind tunnel as a good and practical way to study planes.

It definately is and I am not saying wind tunnel data is useless for aeronautical engineers or for drawing general conclusions off a design.

For comparision purposes windtunnel data off of a model and not the actual airplane is worthless for comparision with the real plane.  Not the general conclusions but when you try and get exact figures it most certainly is and can lead to wrong comparison's between different aircraft designs.

In my research I made a similar mistake with FW-190V5g.  V5g is the big wing test prototype with a BMW-801 engine.  Very similar to the production model of the FW-190A.  The engineers who are helping me out immediately pointed out that the actual data is worthless for direct comparision's with other aircraft.  Hitech confirmed this when I offered the report to them as well.

That is why I hunted down some windtunnel test's of the actual aircraft, made the trip, and spent the money to get them.  Those drag polars would be useful for comparing drag polars from another actual plane but not a model.
 
Comparing models is just that.  Comparing a model and not the real thing.  The FW-190 report "Drag data for Aircraft" comes from actual aircraft as well.

I guess that is because there are many minor factors which may have a significant effect combined. Surface design, exhaust system vs. exhaust thrust, cowling fitting, temporal jig misalignment causing badly formed fuselages etc.

That is absolutely correct as I understand it.  Even with the actual aircraft you have to be careful.  Just look at the P51 wind tunnel test reports.  Several of them were done with a preproduction model that did not have simple things like exhaust stacks mounted.  These simple things add up and this is why you see some claims of extremely low drag on the 51.  It was a low drag design but not nearly as low as some of the claims.

The intakes are problematic for any model.  In the case of the FW-190A, since plane itself is such a small physical size, the intake area is very compariable to the Spitfires radiators.  Just a different shape.

Crumpp

[Crumpp]

I thought the Lednicher article to be a bit torso on part of 190. I dont think he is aware of the possibility of bad aileron tuning which could cause similar effects as torsional warping of the wing in tight turns. Based on the NACA report on roll rate I think is rather unlikely that 190 had a torsionnally loose wing considering its excellent roll rate which would not be possible if his assumption is true.  Or is it? Dunno for sure.

One thing for sure Charge.  The FW-190 had extremely sensitive ailerons that needed precise adjusting.  Additionally according to both the pilots who flew it and the manuals, the FW-190 had multiple hinges to "tune" the ailerons to a desired performance band.  The hinges adjusted the height of the aileron in it's mounting giving the pilot different "max roll" performance at different parts of the envelope.

If I had to say the achilles heel of the 190, it would be it's aileron adjustments.  They are simple machined blocks of duraluminum with grooved slots for the mounting bolts.  These blocks fit on top of the aileron mounting block in the wing which is simply a fixed flat block.  The aileron is mounted (with whatever hinges) on this flat block and set in the correct position.  The bolts are then tightenend down and they are the only thing holding the aileron in it's adjustment point.  I imagine those blocks could slide and the aircraft required constant inspection of the adjustment.

The aileron adjustment had severe effects on the handling qualities of the design.  I know that the FW-190A5 the USN tested had out of adjustment ailerons.  When you read the Luftwaffe caution statements, advisory reports, and Focke-Wulf data it becomes obvious.

Being that the main wing spar is solid on the FW-190 and runs the entire length of the wing underneath the fuselage, I imagine it torsionally strong.  I have the complete report of RAE 1231 which the NACA graph is based on.  In it the test pilot states the FW-190 flown has the stiffest ailerons of the three FW-190's he has flown.  Additionally with Frise alerions you are going to get a rather wide performance band, AFAIK.

Crumpp

[Charge]

"The intakes are problematic for any model. In the case of the FW-190A, since it is such a small physical size, the intake area is very compariable to the Spitfires radiators. Just a different shape."

Edit: Different shape yes, but also probably causing rather much drag in the process, too, by increasing the face area of the a/c.

Yes, but their placement may have effect on other factors again, as noted of the Spitfires radiator which, AFAIK, had somekind of  effect on wing lift. Don't remember exactly if it was considered good or bad or insignificant. And to me it seems that it has quite a bit effect if the radiator is able to close completely or not.

I have never understood where the cooling air exits in 190A. In first models the only vents in the cowling were for the exhaust tubes and because of overheating the cooling louveurs were made in the aft cowling to allow exit of hot air. To me it seemed like a bit idiotic design flaw to leave them out in the first place...

Maybe that centralized drag was one of the factors which gave the 190 such a good rollrate as there was no off-balancing drag effect anywhere else but just around the thrust line vector (ie. engine camshaft?) And maybe that is the reason they decided to use similar cowling design in D-models. So I'm guessing  that if they had made a different eg. P51 style radiator on D9 the drag could have been less, but the roll rate could have suffered too?

-C+

[gripen]

Originally posted by Crumpp
Comparing a model and not the real thing.

Well, as noted above, the Fw data seems to be based on wind tunnel data possibly with some kind of model.

Besides I don't see any reason why the data determined with a model in the wind tunnel should not be comparable with the data determined with a full size aircraft in the wind tunnel.

Regarding ailerons, the Brits captured at least three Fw 190s intact (landed intact to the British air fields for various reasons) so the adjustment of the ailerons is very unlikely the reason for tendency to stall from the turn. But that is not a subject of this thread.

gripen

[Charge]

Yes Gripen, I believe the Lednichers article on that part that the wing profile was prone to a sudden stall but when it is considered a design flaw despite washout and all I'm bound to think that the ailerons where not properly adjusted on that particular aircraft Brown flew.

Sorry 'bout this off current in your thread on my part Gripen.

-C+

[rshubert]

Originally posted by Angus
So, if you have a dihedral, you have to increase washout right?

rshubert, either you are very well read, or a pro, must be.

I am honoured to be exchanging words with you M8

Not a professional--just an electrical engineer who flies for fun.  As to the question, I don't know.  It doesn't necessarily follow, does it?   The stall is purely an angle of attack question, and the washout affects the wingtip angle of attack.  Dihedral doesn't affect angle of attack, so I guess that playing around with dihedral would not have any effect on the amount of washout needed to provide control on the edge of a stall.  But that is a GUESS, not a known fact.

It is an interesting question, though--and points out that the subject of wing design is not easily explained in terms of one or two factors.  NACA (NASA's predecessor), the Brits, the Germans, and everybody else spent a LOT of time on wing designs during the '20s and '30s, many of which are still in use today.



shubie

[gripen]

Originally posted by rshubert

Dihedral doesn't affect angle of attack, so I guess that playing around with dihedral would not have any effect on the amount of washout needed to provide control on the edge of a stall.  

Yep, extreme amount of dihedral "might" have a similar effect as swept back wing due to increased downwash at low speeds but generally it's there just for stability.

gripen

[Crumpp]

Edit: Different shape yes, but also probably causing rather much drag in the process, too, by increasing the face area of the a/c.

I don't think they would cause anymore drag than a radiator.  In fact I would think less.  Drag is caused by surface area, correct?  Sure cooling fins on an air cooled radial are there to increase the surface and would increase drag.  Compared to radiators which are fairly large as were the Spitfire Mk IX's, I don't see that the difference is that great.

In fact Lednicer seems to be correct.  If the FW-190 was as big as the spit it would have more drag.  It's smaller physical size though gives it less form drag than the Spitfire.

I have never understood where the cooling air exits in 190A. In first models the only vents in the cowling were for the exhaust tubes and because of overheating the cooling louveurs were made in the aft cowling to allow exit of hot air. To me it seemed like a bit idiotic design flaw to leave them out in the first place...

Air can exit around the exhaust stubs.  Got to agree though.  The space in not very big and someone was surely being overly optimistic that the small volume exiting the space would carry off the excess heat.  

Got a nifty report examining different ways to seal the cowling.

They were going for minimum drag on the cowling job and tried to get away with as little excess space under it as possible.  What I don't understand is why they put them on the inside at first in the FW-190A1-A4.  The FW-190A5 and later gills are louvers on the outside and are much more aerodynamic.  They work better too.  Putting the louvers on the inside makes no sense to me!  Your trying to get the air out and the slit for the gills is certainly not aerodynamic.

Regarding ailerons, the Brits captured at least three Fw 190s intact (landed intact to the British air fields for various reasons) so the adjustment of the ailerons is very unlikely the reason for tendency to stall from the turn.

The Geschwaders had a hard time keeping the ailerons adjusted.  Why would the RAF be any better at it?

Besides I don't see any reason why the data determined with a model in the wind tunnel should not be comparable with the data determined with a full size aircraft in the wind tunnel.

Give Pyro a call and ask him this.

Crumpp

[gear]

Originally posted by Guppy35 .Keep in mind the 190s were actually Rumanian IAR80s  

The FW190 is not a Romanian IAR 80.

[gripen]

Originally posted by Crumpp

In fact Lednicer seems to be correct.  If the FW-190 was as big as the spit it would have more drag.

Not a subeject of this thread but Lednicer's numbers give 3,5% difference in drag and the values for the Fw 190 are based on manufacturers data. Basicly a neglible difference.

Originally posted by Crumpp

The Geschwaders had a hard time keeping the ailerons adjusted.  Why would the RAF be any better at it?

Not a subject of this thread but my understanding is that this theory is borne out in the same place as "wet lifting area", strange theorie on swept back wings and pressure distribution etc...

Start a new thread and show the physical connection between stall in the turn and the ailerons.
 

Originally posted by Crumpp

Give Pyro a call and ask him this.

Pyro is most wellcome to join in discussion any time.

Basicly you are changing your argument all the time depending on which seem to support your agenda on the Fw 190. In the beginning of this thread you were arguing that some aspect ratio based formulas give correct value of e. Then you created various strange theories on lift distribution. Now you claim Fw data flight tested despite it's very unlikely. Still, you have not been able to bring in any evidence nor calculate something properly so far.

gripen

[Crumpp]

Basicly you are changing your argument all the time depending on which seem to support your agenda on the Fw 190.

BS Gripen.

I thought you knew about aeronautics to know better.  I assumed you were smart enought to use good data in the first place.  This entire argument would have never happenend had I known your drag polars came off of 1/6 wooden models and not an actual aircraft.

Not a subeject of this thread but Lednicer's numbers give 3,5% difference in drag and the values for the Fw 190 are based on manufacturers data. Basicly a neglible difference.

Was not neglible when you were claiming it was not true.

 

Not a subject of this thread but my understanding is that this theory is borne out in the same place as "wet lifting area", strange theorie on swept back wings and pressure distribution etc...

Yeah, OK.  Guess the Luftwaffe just killed trees by writing memo's, manuals, and tons of reports detailing the importance of properly adjusted ailerons to turning performance and stall.

Still, you have not been able to bring in any evidence nor calculate something properly so far.

Lets see and compare total drag @ 440fps at the Spitfires FTH altitude with the correct data:

BF 274 - 795.641828 @ 440 fps
Total Drag FW-190A5 -718.2845242@ 440 fps

BS354 - No data listed except the A/C was 7 mph slower w/50 bhp more output than the Merlin 66 @ (+18)

BS543 - 810.863789
FW-190A5 - 705.7484202

BS551 - 758.4823884
FW-190A5 - 704.890256

EN524 with 4 bladed prop - 765.4635575
FW-190A5 - 702.4712376

BS310 with 4-bladed prop - 793.0539968
FW-190A5 - 751.8834689

BS310 with 5 bladed prop - 794.0663191
FW-190A5 - 749.7161496

JL165 - done to death

MA 648 Merlin 66 (+18) SU Pump - 838.0549776
FW-190A5 - 804.8037275


BS310 - 792.6552588 Parasitic drag - 691.672177

FW-190A8 - 794.3964059 Parasitic drag - 606.4158622

At 315mph the total drag situation changes completely in the FW-190A8 favor.

JL165 vs FW-190A8 has been done to death, again in the FW-190A8's favor.

MA 648 is the ONLY Spitfire Mk IX to beat the FW-190A8 for drag and here is why:


quote:
--------------------------------------------------------------------------------
External equipment of the above four aircraft was similar with the exception that MA.648 had the new pattern of air intake.
--------------------------------------------------------------------------------

MA648 - 837.1701001 parasitic drag - 751.6212076
FW-190A8 - 869.2121249 parasitic drag - 709.9624067

The parasitic drag is always in the FW-190's favor but the total drag drops to within a few pounds of each other at 315 Mph but never swings in the FW-190's favor.

So ONE example of the Spitfire Mk IX with an experimental air intake beats the FW-190A8 in total drag. The others are behind their FW-190A contemporary the whole way.

That about covers the Spitfire Mk IX's vs. their contemporary FW-190 adversary.

Crumpp