Climb and acceleration(engineers please)

[dtango]

F4UDOA:

I think you're missing it.  Badboy, myself, and Wells have all been saying the same things.

#1 The aircraft with the highest EXCESS POWER / weight has the best rate of climb.  This is what I've said.  This is what Badboy has said.  This is what wells has said before in other posts.  The nuances that you are missing are that:

(a)Engine BHP ISN'T A MEASURE OF EXCESS POWER.  It's more complicated than that.  Try and read through my post up above that I did with all the Pa/Pr graphs etc. to try and explain.

(b)Best rate of climb OCCURS AT A SPECIFIC VELOCITY for an aircraft.  THIS VELOCITY DIFFERS FROM AIRCRAFT TO AIRCRAFT and you have to be careful when you compare BEST rate of climb between aircraft.  E.g. Plane A, Plane B, Plane C are being compared.  Plane A has the best rate of climb between all 3 aircraft.  What that means is Plane A's BEST rate of climb is higher than Plane B and Plane C's BEST rates of climb.  That doesn't mean that at a different velocity Plane A climbs better than Plane B and Plane C, infact it might not at all.

#2 Wells is trying to point out the complexities in statement #1 that engine BHP isn't the measure of excess power.  It is a complex relationship simplified by the express (T-D)*V/W.  He's trying to point out as I was trying to point out in my Pa/Pr curves that excess thrust changes with velocity as thrust, induced drag and parasite drag changes with velocity.  Specifically he's trying to address the specific question you had related to how induced drag factors into the equation and that the F4U has a higher induced drag vs. the F6F and P-51D.

#3 My statements about Cl was directly related to specifics of analyzing induced drag as we were running down the rabbit hole regarding Clmax figures which is Clmax figures doesn't mean squat as it is relates to comparing induced drag between aircraft when analyzing BEST rate of climb.

Tango, XO
412th FS Braunco Mustangs

[wells]

yeah, we're going around in circles here.  Now DOA is talking about optimization...

Look at the thrust/drag curves again.  See where the 2 drag curves cross each other?  That's the lowest drag and Cdi happens to be exactly the same as Cd0 at that point.  The best climb performance is not far from that point.  It's at a little faster speed, but for all intends and purposes, it's close enough!  So, you're given an engine and you're told, "Make a plane that climbs good!"  So, you slap a propeller on the front and you build something that is as light and streamlined as possible.  However, we need to be able to takeoff in 500 ft, so we determine that we will need a wing area of 314 sq ft for our estimated weight of 12000 lbs!  Forget about induced drag for a second...

Using  

roc = (T - D) * V/W  (that's not a Volkswagon)

We can find our 'optimum' climb speed.  We can't possibly make it any lighter and we can't possibly make it any more streamlined and we can't possibly get more power out of the engine.  This is the best we can do!!!  But, we still haven't chosen an aspect ratio for our wing yet!  But, now that we've drawn our graph to find out what the best climb speed is, we're in business!   All we have to do is choose an aspect ratio that will give us Cdi = Cd0 at our best climb speed!  Ta-da!  

I just ran some numbers for the F4u-1.  Best climb speed = 66 m/s (148 mph).  Cd0 ~ 0.0167.  To give a Cdi = 0.0167 @ 66 m/s, we'd need an aspect ratio of about 9.  The f4u probably loses a potential 200 fpm by having a lower aspect ratio.  Is that really worth losing 30% in roll rate?

[Nawc]

For Anyone interested there is another great book on the development and test of the F4U Corsair titled "Whispering Death"  It's written by one of the actual test pilots, I can't for the life of me remember his name..  But check it out, might be able to find it on Amazon.

Nawc

[niklas]

btw: is wingarea the projected area (looking from above) or the "true" wingarea.

Because the inverted gull wing of the F4U reduced effective wingarea imo a bit, especially the inner part has a ~30° angle down looking at it from straight forward, so effective wingare is lower.

niklas

[gripen]

Originally posted by Nawc
For Anyone interested there is another great book on the development and test of the F4U Corsair titled "Whispering Death"  It's written by one of the actual test pilots, I can't for the life of me remember his name..  But check it out, might be able to find it on Amazon.

Nawc

I have been under impression that it was the Beaufighter which was called "Whispering Death" due to it's quiet sleeve valve engines. I think  the F4U was called "Whistling dead" due to whistling sound from oil cooler intakes.

gripen

edited: Oops I mean "Whistling death"

[GRUNHERZ]

F4UDOA

Most of the entire outer wing panels on all WW2 F4Us were covered in fabric. Not just control surfaces, in fact the ailerons were metal in Corsairs IIRC.

So why?

[Nawc]

Gripen,

You are indeed correct, and I did mean Whistling, just a brain fart I guess.  I'm embarrased since my grandfather used to build Corsairs for chance vought during ww2 in Bridgeport Conneticut.  He's told me many stories.  He has some nice cockpit instrumentation to go along with them too.  Leftovers after the war I guess.

The book is titled: "Whistling Death" by Boone T. Guyton  who was a test pilot on the program.  It was pretty interesting reading, not exactly a page turner, but filled with the little quirks about the aircraft and some interesting stories about some crash landings, and performance.  Great book for any aviation-historian.

Thanks for the catch Gripen.
Nawc

[F4UDOA]

Nawc,

Hehe, I new you would get that title right eventually.

I have Whistling Death as well as "I flew them first" by Don Armstrong who was the lead test pilot for Goodyear on the F2G. Also I believe the other book you mentioned "The fundamentals of Fighters design" by Ray Whitford(sp).

Frankly Wells hit the nail on the head when he said that Vought was trying to meet specs and at the end you have to choose between induced drag and roll rate. I would take the roll too. I just like to get inside the engineers heads that built these things. Not the cookie cutter government funded stuff that gets built today. I would luv to talk to Steve Hinton who won at Reno in 1985 with a F4U-1 with a R4300 on it. He did some wing modifications to lower the drag.

Grunherz,

I get the feeling your going somewhere with this. What is the answer?? I can tell you that most WW2 A/C were a combination of fabric and stressed metal. What do you think?

[Nawc]

DOA,

The other book I was refering too is a current day guide to Introductory Aircraft Design, published by the AIAA and authored by Raymer, sorry can't remember his first name.  This book takes you through the whole design process as it should occur.  So you get a great perspective on how design decisions are made.  If you really want to get into it, get a program such as mathcad or tksolver and run all the equations yourself and you can see all the relations.  I used this book as a bible for my first aircraft design project for my Senior project in college.  I used the 4th edition I believe.

Take a look, you can probably find it on AIAA's web site.  Actually I just looked it up it's called "Aircraft Design a Conceptual Approach" I know, I don't have a good average on titles today.  By Daniel Raymer.  http://www.aiaa.org/store/storeproductdetail.cfm?id=529

Have fun,
Nawc

[funkedup]

DOA you should come to the airshow at Chino next year.  During the show Steve is quite busy flying several planes, but at the end of the day they open up the flight line and he is very friendly and willing to answer questions.

[GRUNHERZ]

Nowhere in particular F4UDOA. I'm just saying that all sorts of planes have odd or non standard buliding and design decisions. Like fabric covered outer wings of F4U, or its very broad low aspect ratio wing.

[Holden McGroin]

Constants are for English units, not SI

Rate of Climb = 60 x V x Angle of Climb (in radians)

Angle of Climb = [550 X Prop Eff x sq rt of (Airdensity / 2)]

all divided by {Gross WT/ Power} x sq rt of {GWT/ Wing Area}

inhale

then subract total aircraft drag coeff and subtract 1 / { pi x AR }

AR = wing aspect ratio....

so by equating climb to hp, you only neglect aspect ratio, prop effeciency, air density, gross weight, wing area, and overall drag.

otherwise, it is a perfect ratio.

Accelleration related only to the balance / imbalance of thrust vs drag, and the mass (inertia) of the aircraft  F=MA.... A = F / M

As for Wing design, the F4U was originally planned as a straight winged aircraft, but after some of the design had been finished, they decided to install a larger engine.  This required a larger prop diameter, and they bent the wings down so that the landing gear would not be long and weak for carrier crashes (landings)

All design is a compromise among competing factors.