Author Topic: Question about Flaps Deployed at High Speeds.. (Read 2349 times)

hitech · « **Reply #45 on:** January 06, 2003, 08:40:26 AM »

F4udoa: You sure your not readying the cas ias table backwards?

HiTech

F4UDOA · « **Reply #46 on:** January 06, 2003, 10:37:52 AM »

Hitech,

No I'm sure HT. I'm reading it right out of the F4U, F6F and P-38 manuals.

For the F6F it has two CAS correction tables. One for the F6F-3 and one for the F6F-5. The one for the F6F-5 reads as follows.

Flaps retracted

100Knots subtract 5 knots
120Knots subtract 6.5 knots
140Knots subtract 7 Knots

Flaps extended

80 Knots Add 6.5 Knots
100 Knots Add 4.5 Knots
120 Knots Add 2 Knots

The F4U Manual is for the -1 and -1D series.

The manual list the indicated airspeed, corrected airspeed and the correction in Knots.

Flaps retracted

90 knots IAS = 88Knots -2Knots
100Knots IAS = 99Knots -1Knot
110Knots IAS = 110Knots 0Knots
300Knots IAS= 308Knots +8Knots

Flaps extended

70Knots IAS = 67Knots -3Knots
80Knots IAS = 78Knots -2Knots
89Knots IAS = 100Knots -1Knots
100Knots IAS = 100Knots 0Knots
110Knots IAS = 111Knots +1Knots

These two birds stall way too high according to these charts with flaps and the F6F stalls way too high period. The F4U stall is more modestly off with no flaps. But with flaps there is about a 15% to 20% difference between AH and the manual.

I think this is why the F4U carrier takeoff is sooo difficult.

F4UDOA · « **Reply #47 on:** January 06, 2003, 12:51:43 PM »

Dtango,

I think you are falling into the same trap I just did doing the same calculations.

Here is the calculation I am doing for the F4U.

Cl = Lift * 391 / (V^2 * Area)
= 11300 * 391 / (97^2 * 314)
= 1.49

But if I use 76MPH (the F4U full flap stall) as the speed my CLmax comes out to 2.4 something which is to high. The reason is because you are not adding the extra wing area to the 314 created by the flaps. If you did the number would be approx 1.90 (power on).

The F6F as you pointed out is coming up with a very high Cl max of 2.4 with no flaps.

Here is the F6F power on at 11,250LBS no flaps power on.

Cl = Lift * 391 / (V^2 * Area)
= 11,250 * 391 / (74^2 * 334)
= 2.4

This page shows A/C#5 the F6F to have a Clmax prop idling of Approx 1.9. full flap. This would be higher if the A/C had airflow as there is no wind over the wing. Based on the F4U pre-spoiler clmax of 2.30 I would assume the F6F's to be slightly higher. But I agree 2.4 no flap seems to high and must be a pitot tube error.

Even with that the F4U and F6F stalls are too high even with an questionable Clmax for the F6F.

dtango · « **Reply #48 on:** January 06, 2003, 02:33:44 PM »

Not sure what you mean about fallling into the same trap

. The calcs I ran for the F6F-5 was with no flaps based on your quoted no flap stall speed for the F6F-5 at 74 mph.

I have the same NACA report. Here's another one to look at as well (very large).
NACA Report 824

It shows the F6F-5 (model XV in chart) clean with a Clmax of 1.6. If I use this figure I get a stall speed of 90mph which is pretty different from 74mph. My point is that I couldn't say that there is something wrong with the AH F6F-5 FM when the physics don't agree with the numbers you have quoted.

So why the difference in the Clmax figures even quoted by NACA for the F6F-5?

Perhaps the following:
(1) the NACA 829 report you are pointing to was meant to study the effects of stall characteristics and factors - not a report to to determine exact Clmax of a certain airframe but to determine what influences the change in Clmax for a given airframe.

(2) The NACA 824 report difference uses a simplified approach for calculating the average CL across the span of the wing resulting in the 1.6 at rn of 5.0 x 10^4. The 1.41 figure was I believe from using modern CFD wing analysis software now that we have computers that can make those computations.

I haven't commented on the F4U. BTW- model XIII in the 824 report is an F4U with the Clmax figures for the various flight conditions. Cool stuff. You might try running some of the calcs with that data to see what you come up with for the F4U and see how that matches with other data you have.

Tango, XO
412th FS Braunco Mustangs

hitech · « **Reply #49 on:** January 06, 2003, 02:51:56 PM »

Now you realy lost me F4UDOA wing area increasing with flaps? The f6f didn't have fowler flaps.

HiTech

hitech · « **Reply #50 on:** January 06, 2003, 02:54:54 PM »

BTW pulled out the f6f manual. Somthing is realy strange in the -5 IAS to CAS conversion table. The flaps up / flaps down entry dosn't seem to pass a smell test because the direction of IAS to CAS reverse with flaps up & flaps down to AOA increase.

HiTech

F4UDOA · « **Reply #51 on:** January 06, 2003, 03:21:36 PM »

HT,

Your right on both things.

1. The F6F does not use fowler flaps but they are extention flaps. And I believe they extend as well as deflect. Similar to the F4U if you look at Dtango's link.

2. The stall speeds listed in the F6F manual are a little fishy. But even with a calculated stall of 90MPH clean and 76MPH dirty it still does not match AH.

3. The F4U data is correct and does not match either. 11,300 is a little less than 50%fuel. You still can't fly into the 80MPH range regardless of fuel or ammo load in either the -1 or -1D/C.

hitech · « **Reply #52 on:** January 06, 2003, 03:28:34 PM »

And in the F6F FLight Operations manual. It show dirty power off stall at 80mph with 11,000 Lbs. This equates to an MaxCL of about 2.0. Now the chart with stall speeds is not labled IAS or CAS. If its IAS per there conversion table it realy should be around 90mph CAS. Belive our CLMax is around 1.98.

Just curious where you got a clean stall speed of 74 mph.

HiTech

F4UDOA · « **Reply #53 on:** January 06, 2003, 03:58:14 PM »

HT,

Look in your Pilots Flight operations manual for the F6F page 44.

Section 18 paragraph B. Stalling

Clean Power on- 62Knots
Clean Power off- 64 Knots

LG&Flaps down- power on- 50Knots
LG&Flaps down- power off- 53Knots

????????????????????????????????

Are the manuals different?

Don't see the weight listed now. Must have been looking at the spin characteristics listed beneath. Never the less they are very low speeds.

BTW the slotted flaps definitely extend as well as deflect increasing wing area. Scews up the cl max calculation a bit.

Dtango,

In the NACA report 824 your looking at the wrong bird. A/C XV is a FW190A. A/C XIV is the F6F and A/C XIII is the F4U.

But I still can't tell how your reading the Clmax from that data.

F4UDOA · « **Reply #54 on:** January 06, 2003, 04:01:15 PM »

BTW,

What is geometric washout?

dtango · « **Reply #55 on:** January 06, 2003, 04:04:41 PM »

F4UDOA:

The 824 report shows the F6F with just slotted flaps with no extension (model XV with airfoils 23015.6 and 23009 in the report). I am not at home so can't reference USA's 100,000 to check to see what it says there.

The difference between CLmax 1.6 vs. 1.41 could be attributable to methods for deriving the pressure distribution across the wing (e.g. simplified in the NACA report vs. CFD s/w approach). I can't speak to the difference in accuracy this may introduce and would be hesistant to make the claim the F6F FM is off until I could settle this in my mind.

The 824 report also shows the F6F with dirty CLmax of 2.48-2.5.
HT - are you saying the F6F-5 in AH has a dirty CLmax of 1.98?

Tango, XO
412th FS Braunco Mustangs

hitech · « **Reply #56 on:** January 06, 2003, 04:16:21 PM »

F4UDOA Look at page 59.

HiTech

dtango · « **Reply #57 on:** January 06, 2003, 04:26:34 PM »

Geometric washout = wing twist.

Hmmm, XV is the FW-190? The F6F has airfoil root and tips of NACA 23015.6 and NACA 23009. Interestingly enough the FW-190 has pretty much the same - 23015.3 23009. I didn't check the AR's against the AR's shown so you might be right - XV is the 190. Model XIV I didn't think was the F6F because of the root and tip airfoils listed there weren't the right ones for the F6F (unless I'm not translating the NACA designations correctly).

I'm reading CLmax in the next to the last column.

I just realized something as well. The RN listed are pretty low too since RN's for the velocities we look at are typically in the 10^6 range not 10^4. Heh, not sure we can use these charts anymore until someone reads through the report to try and make sense of it all.

Tango, XO
412th FS Braunco Mustangs

F4UDOA · « **Reply #58 on:** January 06, 2003, 04:45:37 PM »

Page 59!!!

What the fark is that??

The numbers on page 44 must be without seats and a bunch of helium balloons or something?

Honestly dude were looking at the same manual. I can't even imagine what gives there?

But as long as your looking at that chart notice the ground run for takeoff in a 25Knots wind at 12,000LBS is about 320FT. That's before you hit the control tower on the CV.

Also notice in the F4U manual page 64 the stall speed power off is 74knots at 11,000LBS and the takeoff run at 12,000LBS is aound 340ft. Much sooner than AH allows.

Dtango,

I see all the Clmax numbers on the right side there. I just don't know which one is no flap and which one is full.

Also it shows slotted extensor flaps for the F4U and F6F. I'm pretty sure that's a 190A with the plain flaps.

Let me know what you think of that doc when you get a chance.

Thanks
Guys!

hitech · « **Reply #59 on:** January 06, 2003, 05:10:17 PM »

Ahh lets finish this topic first? I would tend to belive the Page 59 chart, it passes smell test, other speeds don't.

HiTech