Draining E in turns

[F4UDOA]

I would trust his numbers until someone more qualified comes along. Given the mans background as an aeronautical engineer and his access to much more powerful fluid dynamics computations than anyone is capable of making here. This data was written for an article in Sport Aviation Magazine. Not for some flight sim.

Well funny you should say that. Because I don't trust the word of a guy who writes for sports aviation magazines more than I do the engineers at Vought or North American.


I received this document from the Vought archives and scanned it. It shows the P-51B Cdo at .017.



Also in his instantious turn data he shows no weights for the A/C. Without weight you don't know wing loading or power loading so how can you compare?

Also the chart does not show the speed that the G force can be pulled. I assume by the Mustangs approx 2.5 that the speed is around 150MPH but without weight I can't tell what conditions the other A/C are in. Also the P-51D and B have the same intantanious turn rate. This is wrong because the D was heavier empty than the B.

To much assumption in his artical.

[Crumpp]

You don't see the whole article, bro.  It's just exerpts.

Be VERY careful with Co-efficients.

Here is what a NASA Engineer says about Co-efficients:

-----------------------------------------------------------------------------------

Hey XXXX,

The lift coefficient equation (and the whole idea of lift coefficients)
works for both 2D and 3D. The idea was developed many years ago .. before the Wright brothers. In fact, lift coefficients were defined a little bit differently in the days of the Wright brothers than they are today:
http://wright.nasa.gov/airplane/liftold.html
http://wright.nasa.gov/airplane/lifteq.html

but the idea is the same: we relate the lift force to some other known or measurable force, with the lift coefficient just being a factor .. a ratio ..between the lift and some known or measurable force. In the old days, before computers, people would measure the lift of an object .. and knowing the reference force, would generate tables or graphs of lift coefficients for all kinds of shapes, sizes, designs .. etc. The measurements were made on
models in wind tunnels .. and then applied to full scale airplane designs.
As computers came along, we figured out how to calculate the flow around a shape to get the lift coefficient. It's obviously easier to calculate a 2D shape than a 3D shape .. but the idea works for either one. Now, equally obvious .. the value of the lift coefficient for a 2D shape is different
than the value for a 3D wing. So an engineer has to be very careful when using lift coefficients. You have to find out how the particular value was generated (2D or 3D model) .. and there some other aerodynamics effects (like boundary layers and shock waves) which can effect the value as well. You can only apply the lift coefficient to a real case which is similar to how the original model was tested. Check out:
http://www.grc.nasa.gov/WWW/K-12/airplane/airsim.html
for some more details.

Tom
------------------------------------------------------------------------------------

Cdo is even more squirrelly.  The theories change and so do the formulas.  Without knowing what formula, theory, reference area, etc...

That Cdo is useless and could very well be the same thing as what the more modern Aeronautical engineer calculated just using a different scale.

Crumpp

[Crumpp]

He does not list the P51B's drag.  The P51D's Cdo is alot lower on his calculations.  I would say he is using a different formula.


Crumpp

[dtango]

Hiya F4UDOA:

I'm not sure where the perf. numbers on the J22 site come from though.  My impression is Mr. Lednicer does know what he's talking about.  I have several of David Lednicer's papers (very technical) including the one being mentioned.  It (nor the others) doesn't have any reference to turn performance numbers so I can only assume the author of the J22 page calculated those figures.  I agree that the numbers look funny especially in the case of the 190D-9 instantaneous vs. sustained turn.

The CD0 values for the Mustang come from revisiting how wetted surface area used for parasite drag is calculated.

Now crumpp on the other hand - bless his soul, I'm afraid that the more he states about aerodynamics the more I scratch my head!  I don't even know where to start to try and help him "see the light".

Crumpp:

It's simple really.  Try doing some comparative calculations of total drag for different aircraft in a given turn and see what you come up with.  It's pretty clear.  Maybe you'll see it then.

Tango, XO
412th FS Braunco Mustangs

[gripen]

Comparative calculations are easy to do assuming that the the wing area is the referance area and standard conditions.

As an example we can easily do a quick and dirty comparison between calculated high speed Cd0 of the P-51B, Fw 190A and Spitfire IX at the altitude where we know the exact speed and the engine output.

First we collect a little bit of data:

P-51B => 679 km/h at 4755 m, the first FTH (USAAF test data)
Fw 190A => 537 km/h at sea level (US NAVY test data)
Spitfire IX => 603 km/h at 2896 m, the first FTH (average A&AEE test data)

Then thrust assuming 85% propeller efficiency and 120 kp exhaust thrust:

P-51B (V-1650-3 at 67") => 1600 hp => 6553 N
Fw 190A (1,42 ata 2700 rpm) => 1740 ps => 8470 N
Spitfire IX (Merlin 66 +18lbs) => 1705 hp => 7624 N

Because the thrust equals drag at steady speed, the total drag for the flat plate area with Cd=1 is easy to calculate:

P-51B => 0,381 m2
Fw 190A => 0,486 m2
Spitfire IX => 0,443 m2

Now we can calculate Cd for the reference area:

P-51B => 21,78 m2 => Cd=0,0175 (mach 0,59)
Fw 190A => 18,3 m2 => Cd=0,0265
Spitfire IX => 22,48m2 =>  Cd=0,0205

Then we just calculate Cdi, E factors are purely approximated:

P-51B => 4128 kg AR=5,87 E=0,75 => Cdi=0,00139
Fw 190 => 3942 kg AR=6,02 E=0,8 => Cdi=0,00159
Spitfire IX => 3395 kg AR=5,61 E=0,9 => Cdi=0,00083

Because Cd=Cd0+Cdi, the Cd0 values are easy to solve:

P-51B => Cd0=0,0161
Fw 190 => Cd0=0,0249
Spitfire IX => Cd0=0,0197 (mach 0,51)

In the end we can calculate flat plate area for the Cd0 with the reference area:

P-51B => 0,350 m2 = 3,772 sqft
Fw-190A => 0,456 m2 = 4,913 sqft
Spitfire IX => 0,433 m2 = 4,764 sqft

We can also do a little comparison with the test data below.

gripen

[Crumpp]

I would love to get a copy of the full article.

Now crumpp on the other hand - bless his soul, I'm afraid that the more he states about aerodynamics the more I scratch my head! I don't even know where to start to try and help him "see the light".

See the Light on what?  
That Airplanes should be able to make steep banks and pull high G's all day?

That High Speed turn radius in NOT a function of Wingloading but rather LIFT LOADING??

Ask a fighter pilot what that does for you.

In fact Shaw talks about "load factor" killing speed in a turn citing it is one of the most important things a fighter has to control if he going to turn.

Pulling G's causes a huge rise in your Drag profile.  If you look at the Drag formula it uses AREA not the wieght, the AREA of the surface.  More Area = More Drag

http://www.grc.nasa.gov/WWW/K-12/airplane/sized.html
http://www.grc.nasa.gov/WWW/K-12/airplane/dragco.html


Page 408 "Fighter Combat" reads:

"As a Load factor is increased at a given Airspeed, turn performance improves but total drag increases.  Eventually a load factor is reached in which the entire thrust of the engine is needed to just to offset this drag"
 

In AH we have some planes that can "break turn" all day long and actually seem to gain energy in the turn.  

I have seen planes conduct a tight high angle bank 180 degree LAG turn at the merge.  Then watched them zoom up ABOVE a heavier fighter that pulled a 25 degree zoom at the merge.  All on fighter did was pull up!

Now an Aircraft that just conducted a tight bank will need to bleed some of the energy he had to gain when altitude was lost.  That will be spent regaining to the same or slightly lower altitude he was at in the begining of the turn.

Nobody is saying that a High wingloaded plane should outturn a low wingloaded in the sustained turn realm or anything silly.  

Simply saying there is a price to pay for pulling G's that All A/C have to pay.  Low wingloaded A/C have more surface therefore more drag.

So infact parasitic drag is a HUGE factor in Load factor.

http://www.av8n.com/how/htm/4forces.html#fig-power-ias

http://www.av8n.com/how/htm/4forces.html#fig-force-ias

Crumpp

[dtango]

Hi crumpp:

Try doing the calcs for a relative comparison.  You'll see it then.  You can use gripen's data as a starter.  Now adjust the Cdi relative to a given turn g-loading for comparison between the planes.  See what you get.

Gripen:

Thank you sir .  Separate question for you - I've been trying to find references as it relates to estimating exhaust thrust.  Do you know of any docs that give some principles for doing so?  Thanks!

Tango, XO
412th FS Braunco Mustangs

[Crumpp]

Again,

Yes the value of the co-efficient does go down.

http://www.av8n.com/how/htm/4forces.html#fig-coeff-ias

However the FORCE goes up.

http://www.av8n.com/how/htm/4forces.html#fig-force-ias


Crumpp

[Sable]

Originally posted by Crumpp
Again,

Yes the value of the co-efficient does go down.

http://www.av8n.com/how/htm/4forces.html#fig-coeff-ias

However the FORCE goes up.

http://www.av8n.com/how/htm/4forces.html#fig-force-ias


Crumpp

You seem to be thinking of a situation where one aircraft is going faster then the other and pulling a higher load factor, in which case you are now comparing apples and oranges.  Of course an airplane going 400mph pulling 5 Gs will have more total drag then one going 200mph pulling 2 Gs.  What we were trying to do above is compare two aircraft, at the same speed and load factor.

And as for you statement about area above, please re-read my earlier post.  The area reffered to in the drag equation is "Reference Area".  It's a guesstimate of the total surface area of the aircraft, and doesn't change with the aircrafts angle of attack.  Because the air streamlines around the airplanes body there is really no additional parasite drag up until a stall (at which point a large wake forms behind the wing).  That is why the coefficient of parasite drag is basically unchanged vs. angle of attack right up until a stall.

There is additional drag as angle of attack increases from the lift created by the wings and this is calculated with the induced drag formula.

[dtango]

Crumpp:

I would love to get a copy of the full article.

I missed this earlier.  I'll post it later this PM when I get home from work.

Yes the value of the co-efficient does go down....However the FORCE goes up.

This is all true.  The problem is you're taking this statement and making a leap to an incorrect conclusion.  The statement means nothing until you understand the drag relationship in its entirety and relative to aircraft in comparison.  

The best way to understand it all is to do the calculations.  The mathematics represent the relationship in it's entirety.  Gripen already has given you a set of data to start and work from.  Now just vary the Cdi values per plane per turn g-load per velocity and see what it tells you.

Tango, XO
412th FS Braunco Mustangs

[gripen]

dtango,
So far the best reference I have found on the exhaust thrust is an article, "The Utilization of Exhaust Thrust" by N. Ya. Litvinov,  in the old British magazine called "Aircraft Engineering" July 1944. Actually it's a translation from the Russian article and it's based on Russian tests on  the Klimov M-105 and Yak-1. Another pretty good one is a NACA test report on the Spitfire V ejector pipes.

For  quick and dirty comparison calculations generic assumptions on the exhaust thrust will do good enough; there should be no big differences between above mentioned  planes.

gripen

[dtango]

Gripen- OK thanks.  I'll try looking them up.  Yeah, I was more interested in some of the nitty-gritty - nothing related to your calcs above.

Tango, XO
412th FS Braunco Mustangs

[Crumpp]

Try doing the calcs for a relative comparison. You'll see it then. You can use gripen's data as a starter. Now adjust the Cdi relative to a given turn g-loading for comparison between the planes. See what you get.

As far as Cdo calculations go, I will trust David Lednicer's calculations over Gripen.  

1. We have three different Airplanes under 3 different conditions.  It's impossible to make a valid comparision using co-efficients.

------------------------------------------------------------------------------------
P-51B => 679 km/h at 4755 m, the first FTH (USAAF test data)
Fw 190A => 537 km/h at sea level (US NAVY test data)
Spitfire IX => 603 km/h at 2896 m, the first FTH (average A&AEE test data)
------------------------------------------------------------------------------------

2.  We are using drag co-efficients calculated in the 1940's when MANY Aeronautical Engineers would have argued with a slide rule til their last breath that man would never fly in space or break the sound barrier as our "check" to calculations.  

Lastly All that is going to prove what I already know and what NOBODY it disputing.  In the sustained turn realm.  Lower Wingloaded plane have better sustained turn rates.


That is NOT the issue.  The issue is the ability to pull SHARP TURNS at High Speed and High G's and still come out with energy to spare.

This issue greatly contributes to the "Bore and Snore" style of energy fighting people complain about.

In AH the penalty for pulling a "break turn" is pretty small.  The planes lose no altitude and little speed.  In fact they should lose either speed or altitude drastically.  In combat nobody break turns except in immediate defense.

Crumpp

[hitech]

Crumpp wrote

In AH the penalty for pulling a "break turn" is pretty small.  The planes lose no altitude and little speed.  In fact they should lose either speed or altitude drastically.  In combat nobody break turns except in immediate defense.

Crumpp: You do not have the background to even begin to evaluate that situation.

You might wish to do a lot of research before making that statment. Infact you better be able to post exact numbers on the amount of speed loss for a given condition. If you can't post the calculations and numbers required for that evaluation. Then it is imposible to even make an evaluation on your claims. Please start listening to other people like sable,karnak,tango,gripen and myslef who do have a strong knowledge in this subject area.

HiTech

[Crumpp]

Sure I will sit down and calculate you some numbers then.

Crumpp: You do not have the background to even begin to evaluate that situation.

How do you know my background and WHO ARE YOU to make that Judgment?

Crumpp