Max CL and its effect on performance

[Crumpp]

I have read what you have posted on here before, and it seems to me that you are that way. Seems you are almost selective in the information you give out to highlight your point.

That is extremely general and frankly It's quite tough to dispute your opinion based on your assumptions.  There are no real facts or specifics to dispute.  Oh well sorry you feel that way.

Let me explain some things:

1.  I have set some fires in motion (unintentionally) for sure.  Some really good data did comes out.  I am always polite but not the most internet savy guy.  It has amazed me the number of things people take out of context or attach emotions too, which frankly, simply are not there.

2.  I will question when I don't think it's right.


Thank you Bozon for the explaination.  How does a high Max CL benefit a fighter?

Looking forward to your graphs Angus.

Crumpp

[Charge]

Keep up the good work Crumpp!

-C+

[bozon]

Thank you Bozon for the explaination. How does a high Max CL benefit a fighter?

max CL by it self doesn't mean much. What matters more is how much lift can the wing generate at the given speed. This will set the maximum G that can be pulled (if not capped by structure of pilot limitations). This means instantanious rate of turn.

What matters is the entire wing, not just CL. Perhaps the thing to compare between planes is not wing-loading but "max lift-loading": CL*S/m ?

Bozon

[F4UDOA]

Crummp,

I think the answer to your question is yes.

However high Clmax is more of a byproduct of performance than a cause or indicator.

Example all my numbers are from the P-38 flight manual BTW.

The P-38L has extremely high wingloading. 17,000lbs/327sqft=52

However at 17,000lbs it stalls power off at 100mph in the clean condition.

It has a high Clmax which can be calculated this way.

Weight * 391=> airdensity at sea level / Speed ^2 * Wing area

or

17,000lbs * 391 / 100MPH^2 * 327Sqft

6647000 / 3270000

= CLmax =2.03 <==That is really high!

The long wingspan and high aspect ratio increase the Clmax while keeping Cdi(induced drag) low therebye reducing stall speed.

The P-38 does have an odd distinction of having a higher stall power on than off. This has been explained to me as a byproduct of the prop rotation but I do not unstand it enough to explain it.

If you know the FW190's stall speed (power off) you can calculate the Clmax very easily plugging in the speed, weight and wing area.

Most WW2 fighters are between 1.4 and 1.6.

Your number of 1.3 for the 190 is probably from wind tunnel test with no propellor installed. The F4U Clmax with no prop is 1.28 approx but increases to 1.49 with the prop idling.

Also a good trick to come up with 3G, 4G etc stall speeds is to multiply the 1G stall speed by the square of the G force.

For instance if the 1G stall is 100MPHthen to get the 3G stall speed multply the square route of 3 which is 1.73 by 100MPH and you get 173MPH 3Gstall. This is a rough number but you get the idea. This is why stall speeds are so important and why Clmax is important. This is only instanious turning. Sustained is more a function of thrust to weight.

Now remember Clmax remains the same regardless of weight. So if the P-38 weight is reduced then the stall speed is also reduced but the Clmax is constant.

So you can take that Clmax calculation and figure out the stall at any given weight. From there you can figure out the 3G stall at any given weight and then make your own EM diagram.

Of course remember I have learned these calculations on these and other boards so my numbers are very primitive compared to what HTC is doing.

[F4UDOA]

My bad on the P-38 Clmax. I didn't check the CAS chart.

If the P-38 is indicating 106MPH you are really flying at 120MPH so there is a minimum 14MPH adjustment. It gets worse as you go slower.

So try this

17,000MPH * 391 / 114MPH^2 * 327sqft

6647000 / 4249692

Clmax = 1.56

That is more in line with everyone else.

Note: Always check airspeed indicator error IE. CAS chart

[Crumpp]

So the P38's is 1.56
The Spitfires is 1.3

Max CL has to be combined with wingload

Your number of 1.3 for the 190 is probably from wind tunnel test with no propellor installed. The F4U Clmax with no prop is 1.28 approx but increases to 1.49 with the prop idling.

The 1.3 is the Spitfires.  The NACA tested it and found a Max CL of 1.1.  The RAE tested it and found 1.3, AFAIK.

What matters is the entire wing, not just CL. Perhaps the thing to compare between planes is not wing-loading but "max lift-loading": CL*S/m ?

Thanks Bozon.  Was it you who was doing the EM diagrams for some of the fighters?

Crumpp

[bozon]

sorry crumpp, but no. I'm no aeronotics engineer so such stuff will be too much of an effort for lazy me...

btw, I wrote the lift load upside down, should have been m/(maxCl*S).

Bozon

[pasoleati]

What book and when? I am a new member and this is my first time to drop in this forum so please enlighten me!

[pasoleati]

Do you have a source for the higher power on stall speed of the P-38? I have a  pilot manual for the plane and it does not mention this phenomenon. Do you have speed figs for power on stall speeds? Is the effect similar clean vs. landing condition? Sounds honestly speaking a bit odd.

[F4UDOA]

Bozon,

What is the "M" stand for in your lift load equation?

[F4UDOA]

pasoleati,

My source of that data is a book which is actually the record of the 1944 Fighter Conferance held by the Navy. The Book/Transcript is called "Report of Joint Fighter Conferance" NAS Patuxent River MD 16-23 Oct 1944. It is easily found and purchased and full of information.

The stall speeds themselves I rely on the manuals for because the stalls in the book are in a range with no weight, condition or power listed. However the one thing that stands our about the P-38 stall is that it is higher power on than off. I though it was a misprint at first but a guy who used to be on these boards explained to me that it was really a function of the propwash on the P-38. The guy goes by "Wells". He is one of the creators of the online simms Target Korea and Target Rabaul.

In anycase get the book. It is one of the best sources of data I have found and lets you know what the actual fighters pilots thought in 1944.

[pasoleati]

I have the book in my shelf. I really have to check the figures. I do agree that the book is essential reading for serious fanatics!

[pasoleati]

[Since you are a Corsair man, do you have any info whether installing outerwing slats were considered for curing the bad stalling characteristics? BTW, Corwin Meyer made some interesting comments on the subject in his pilot report of the Corsair is Flight Journalīs F4U special issue!

[F4UDOA]

I have never been a fan of the outer wing slats such as the ones on the 109 or La-7. They seem to have caused more of a problem than anything else during combat maneuevers. The F4U had a spoiler on the starboard wing to give it more of a symetrical stall but it lowered the overall Clmax of the A/C. This fix was implemented after the first 800 F4U's built and continued throughout the production so apparently it was deemed a sucess by Vought.

The stall of the F4U is somewhat subjective. It was harsh for a Navy A/C of the time but when compared to it land based contemporaries it was considered gentle in that respect.

Corkey Meyer has been writing the same artical for 20 years. It is just a shame that Boone Guyton is no longer around to give the Vought perspective. Some of his points are very valid. He doesn't really get into performance comparisons very much. Just where Vought could have done better. I would luv to talk to that guy about the F6F and F4U.

[VO101_Isegrim]

Originally posted by Furball
I understand you are completely biased to 190's, and thus a book you write about them will not be an accurate resource to quote or base opinions on.  Its like that isigrim guy writing a book on 109's.

You`d be surprised.