F-35 Horizontal Stabilizer Design Change

rheonomic · by **rheonomic** » 16 Jan 2017, 23:34

This has probably been brought up before, although I failed to find anything searching.

Does anyone here know why the design of the horizontal stabilizers was changed?

E.g. AA-1 here:

to the later models here (AF-21 shown):

My assumption is that the change was done to add control effectiveness, since it looks to me like the span is similar with increased chord, so there should be more area, but I'm wondering if there was a different reason.

count_to_10 · by **count_to_10** » 17 Jan 2017, 00:14

I don't see the first image.

Edit: now I do, but I'm apparently too dense to see what is different between the two.

steve2267 · by **steve2267** » 17 Jan 2017, 00:16

I look forward to the replies. I believe you have pointed out the larger surface area of the horizontal tail on AF-21. I assume that AF-2, the aircraft used in the (in)famous High Angle of Attack CLAW test that was widely reported as "the F-35 can't dogfight," had the smaller tail plane area?

I would not be surprised to learn that analysis had determined the original, smaller horizontal tail lacked the necessary area to provide sufficient command authority to generate the pitch rates desired, and this was corrected on later aircraft. (I do not know with which airframe.) But AF-2 was still used for the High AOA CLAW test for whatever reason. (I'm sure it was explained or exposited on in the very long "Can't dogfight" thread, but I don't have time to search for the exact post.)

steve2267 · by **steve2267** » 17 Jan 2017, 00:17

< deleted >

OP updated his first post.

spazsinbad · by **spazsinbad** » 17 Jan 2017, 00:18

DiD Defence Industry Daily does not allow hotlinking of images:

http://media.defenceindustrydaily.com/i ... Top_lg.jpg

'rheonomic' Your info lacks a lot IF we cannot see this image SO PLEASE copy that image to your computer and THEN upload it as an attachment to your post (EDIT is possible) so that WE CAN ALL see what you are on about - thanks.

I see a reply was posted as I typed this - so be it.

cantaz · by **cantaz** » 17 Jan 2017, 00:20

Could be part of the weight reduction program for the B, with the B tails clipped to save weight and the redesign carrying over to the A to maintain commonality.

rheonomic · by **rheonomic** » 17 Jan 2017, 00:26

spazsinbad wrote:'rheonomic' Your info lacks a lot IF we cannot see this image SO PLEASE copy that image to your computer and THEN upload it as an attachment to your post (EDIT is possible) so that WE CAN ALL see what you are on about - thanks.

Rehosted it on Imgur. Saw the image when I posted, must have been in my browser cache. Sorry about that.

spazsinbad · by **spazsinbad** » 17 Jan 2017, 00:29

The GREAT SAGE GOOGLE says: https://books.google.com.au/books?id=49 ... es&f=false

"..."...Based on wind tunnel testing, LM slightly enlarged its X-35 design into the F-35. The forward fuselage is 5 inches (130 mm) longer to make room for avionics. Correspondingly, the horizontal stabilisers were moved 2 inches (51 mm) rearward to retain balance and control...."

That does not answer the question - IF there is one - so I'll gargle some more....

YES that is the wonderful trick of browser CACHE - you see the image when no one else can - MS should allow us to see your browser cache eh. DiD is a shitshower as far as I'm concerned - my three browsers cannot see this page - you may:

http://www.defenseindustrydaily.com/f35 ... 006-02206/

rheonomic · by **rheonomic** » 17 Jan 2017, 00:44

steve2267 wrote:I look forward to the replies. I believe you have pointed out the larger surface area of the horizontal tail on AF-21. I assume that AF-2, the aircraft used in the (in)famous High Angle of Attack CLAW test that was widely reported as "the F-35 can't dogfight," had the smaller tail plane area?

It looks like AF-2 (and AF-01, for that matter) both use the newer design...which makes it look like AA-1 is a one-off.

Control effectiveness seems like the primary reason for the change, but then again as a control engineer, I always think of things in these terms so it could be a case of 'if your only tool is a hammer'...

cantaz wrote:Could be part of the weight reduction program for the B, with the B tails clipped to save weight and the redesign carrying over to the A to maintain commonality.

That's entirely possible. While it looks to me like the new design has more area, I could be misreading the image.

spazsinbad wrote:YES that is the wonderful trick of browser CACHE - you see the image when no one else can - MS should allow us to see your browser cache eh. DiD is a shitshower as far as I'm concerned - my three browsers cannot see this page - you may:

http://www.defenseindustrydaily.com/f35 ... 006-02206/

Doesn't work for me either. I only got the image from DiD since used Google image search to try and find an image showing the planform relatively well and that was one of the better options.

garrya · by **garrya** » 17 Jan 2017, 06:16

Can someone circle the different parts because they looked exactly the same for me

blindpilot · by **blindpilot** » 17 Jan 2017, 06:47

garrya wrote:Can someone circle the different parts because they looked exactly the same for me

: New AF H Stabilz.____________________________Old AA Stab.; AF and AA horiz tails.jpg (39.39 KiB) Viewed 14181 times

BP

rheonomic · by **rheonomic** » 17 Jan 2017, 08:10

So, I went and pulled the JPO 3-view top view and an image of the later version into a vector graphics editor to measure some things. Now, some caveats: I drew outlines by hand, fudged the pixels-to-ft conversion factor to get the wingspans to be the 35 ft reported on the JPO website, used an approximate graphical technique to measure the mean geometric chord, and used a slightly off-angle picture. In other words, these aren't the most accurate numbers in the world.

I get that the area of the horizontals are about the same, that the span is a bit (~1-1.5 ft) shorter on the horizontals, and that the MGC is about a foot longer. (I forgot to add the span of the HT on the right image, I got about 7.9-8 ft.)

So it looks more like a shape change than anything else to me.

spazsinbad · by **spazsinbad** » 17 Jan 2017, 08:51

AF-07 May 2012 from almost just a gnatTit out from directly above:

https://farm8.staticflickr.com/7139/755 ... be_o_d.jpg (6.1Mb)

krorvik · by **krorvik** » 17 Jan 2017, 09:16

Note that the F-35C looks more like AA-1 though.

XanderCrews · by **XanderCrews** » 17 Jan 2017, 16:09

I don't have the exact answer but nearly every difference between AA-1 and the rest of the fleet is to save weight.

steve2267 wrote:I look forward to the replies. I believe you have pointed out the larger surface area of the horizontal tail on AF-21. I assume that AF-2, the aircraft used in the (in)famous High Angle of Attack CLAW test that was widely reported as "the F-35 can't dogfight," had the smaller tail plane area?

AA-1 was destroyed, so all F-35s have the smaller tail planes with the exception of the C which has bigger errrything