PDA

View Full Version : P-51Ds without the dorsal fin?



mortoma
12-15-2009, 11:59 AM
Seeing is believing, here are four P-51Ds in formation and only one has the dorsal fin extension for the vert stab. Here: http://en.wikipedia.org/wiki/File:Bott4.jpg

I never knew they had D models without the extension. Very interesting as you learn something about warbirds every day.

psykopatsak
12-15-2009, 12:25 PM
or maybe the info about the photo is incorrect?

Mr_Zooly
12-15-2009, 12:37 PM
http://www.aviation-history.co...th-american/p51.html (http://www.aviation-history.com/north-american/p51.html)

The first P-51Ds types were delivered without dorsal fins, but this feature was added to compensate for keel-loss when the bubble canopy was adopted.
Maybe they ran out of fillets.

na85
12-15-2009, 12:51 PM
Originally posted by mortoma:
Seeing is believing, here are four P-51Ds in formation and only one has the ventral fin extension for the vert stab. Here: http://en.wikipedia.org/wiki/File:Bott4.jpg

I never knew they had D models without the extension. Very interesting as you learn something about warbirds every day.

You mean dorsal. Ventral implies "stomach" or "underneath" http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

berg417448
12-15-2009, 01:11 PM
The 4th plane in the formation is a B model.


http://www.361fg.com/images/other/P51gr.jpg


The dorsal fin was added to the P-51D-10NA and later versions at the factory. Other P-51s received the modification in the field.

horseback
12-15-2009, 01:40 PM
The P-51Ds started arriving in the ETO around June of 1944, and none of them had the dorsal fin extension until mid August. As I recall, the D models started coming out of production around late February--early March of that year.

NAA was aware that the loss of 'keel' area would have a negative effect on high speed handling, but they hadn't arrived at a fix for it when the first examples were being shipped to the UK. What interests me is how many B/C models also got the dorsal fin extension fitted to them.

I have to think that the Merlin's torque and greater power were a bit much for the original design specs (which were developed with the Allison V-1710 in mind) and it wasn't until the F/H models with the taller fin until all the differences were sorted out.

cheers

horseback

mortoma
12-15-2009, 02:14 PM
Originally posted by na85:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by mortoma:
Seeing is believing, here are four P-51Ds in formation and only one has the ventral fin extension for the vert stab. Here: http://en.wikipedia.org/wiki/File:Bott4.jpg

I never knew they had D models without the extension. Very interesting as you learn something about warbirds every day.

You mean dorsal. Ventral implies "stomach" or "underneath" http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif </div></BLOCKQUOTE>Oops!!

staticline1
12-15-2009, 02:29 PM
Just to add what horseback said. I believe it was the -5 models that did not have the dorsal fin. All the photos I've seen of the -10 and later runs had the fin but I'm sure there are a few exceptions to the rule.

jarink
12-15-2009, 02:41 PM
Originally posted by horseback:
The P-51Ds started arriving in the ETO around June of 1944, and none of them had the dorsal fin extension until mid August. As I recall, the D models started coming out of production around late February--early March of that year.

NAA was aware that the loss of 'keel' area would have a negative effect on high speed handling, but they hadn't arrived at a fix for it when the first examples were being shipped to the UK. What interests me is how many B/C models also got the dorsal fin extension fitted to them.

I have to think that the Merlin's torque and greater power were a bit much for the original design specs (which were developed with the Allison V-1710 in mind) and it wasn't until the F/H models with the taller fin until all the differences were sorted out.

cheers

horseback

The fillet mod (which actually was a package of several modifications) was also supposed to fix some problems with rudder reversal.

These are quotes from the NAA bulletin, #102-31-129) on DFF installation:


From an analysis of the load encountered under these conditions, it was concluded that the asymmetric horizontal tail loads responsible were caused by rudder reversals. These reversals were found to exist for angles of sideslip in the vicinity of approximately fifteen degrees left or right. Such characteristics may contribute to inadvertent snap rolls occurring during slow rolls made with large angles of yaw.


The reverse boost installation used on the P-51D Airplanes will be identical to the installation on P-51B and P-51C Airplanes. It will provide an increase in rudder forces over and above that provided by the dorsal fin, lessening the possibility of overcontrolling the rudder at large angles of yaw.

I've heard that the main purpose of the DFF itself was to slow down the rate of yaw so that a violent snap roll was not accidentally induced.

Bogustogus
12-26-2009, 11:03 AM
What interests me is how many B/C models also got the dorsal fin extension fitted to them.

Answer: none, because those models had more vertical area than the D series.
The only need for the extension was the loss of vertical surface due to the cutting down of the fuselage to create the bubble canopy. http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

The fitting of a Merlin instead of an Allison had nothing to do with that.

yuuppers
12-26-2009, 01:10 PM
Originally posted by Bogustogus:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">What interests me is how many B/C models also got the dorsal fin extension fitted to them.

Answer: none, because those models had more vertical area than the D series.
The only need for the extension was the loss of vertical surface due to the cutting down of the fuselage to create the bubble canopy. http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

The fitting of a Merlin instead of an Allison had nothing to do with that. </div></BLOCKQUOTE>
Many B/Cs got the fillet as they to had the same problem as the early Ds but was not as bad as the Ds. http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

yuuppers
12-26-2009, 01:12 PM
http://www.wwiivehicles.com/usa/aircraft/fighter/north-american-p-51-mustang/north-american-p-51-b-mustang-01.jpg

http://www.cybermodeler.net/history/354fg/images/5318xac.jpg

http://mm04.nasaimages.org/MediaManager/srvr?mediafile=/Size4/nasaNAS-2-NA/15269/EL-2003-00314.jpg&userid=1&username=admin&resolution=4&servertype=JVA&cid=2&iid=nasaNAS&vcid=NA&usergroup=nasa&profileid=9

http://www.456fis.org/THE%20P-51/P-51B-5NA_2%5B1%5D.jpg

Airmail109
12-26-2009, 01:26 PM
Okay, the C model with the dorsal fillet is my new fav!

Kettenhunde
12-26-2009, 02:27 PM
That problem is a vertical stabilizer flow separation. That is why the yaw-wise force reversal occurred. The vertical stabilizer is stalled and does not produce any force 90 degrees to the separated flow vector.

That means, even though we are putting control input to yaw to the left the airplane suddenly and violently yaws to the right when the vertical tail stalls.

The purpose of the fillet is energize the boundary layer by generating a vortex to delay the onset of separation. It is just a strake.

I am sure NA probably thought removal of the turtle-back would unmask the vertical stabilizer increasing pressure in large yaw angles and eliminate this problem.

koivis
12-26-2009, 02:46 PM
C model with the dorsal fillet

Just to add:

The main difference between P-51B and P-51C is that B's were built in Inglewood, California while C's were built in Dallas, Texas. Both could have either flat-top or bulged canopy. Bulged ones were first introduced by British, later used in 8th AF Mustangs too. And yep, Brits called both B & C "Mustang Mk III".

http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

horseback
12-26-2009, 06:48 PM
Originally posted by koivis:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">C model with the dorsal fillet

Just to add:

The main difference between P-51B and P-51C is that B's were built in Inglewood, California while C's were built in Dallas, Texas. Both could have either flat-top or bulged canopy. Bulged ones were first introduced by British, later used in 8th AF Mustangs too. And yep, Brits called both B & C "Mustang Mk III".

http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif </div></BLOCKQUOTE>Same airplane, same manufacturer, just paid for with a different checking account.

cheers

horseback

Feathered_IV
12-26-2009, 07:49 PM
I use the mod that removes the dorsal fin for the earlier stock D. I'd read that they also had a tendency to shed their wings in the early days before being strengthened, so it seemed appropriate.

Bogustogus
12-28-2009, 09:05 AM
Originally posted by yuuppers:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Bogustogus:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">What interests me is how many B/C models also got the dorsal fin extension fitted to them.

Answer: none, because those models had more vertical area than the D series.
The only need for the extension was the loss of vertical surface due to the cutting down of the fuselage to create the bubble canopy. http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

The fitting of a Merlin instead of an Allison had nothing to do with that. </div></BLOCKQUOTE>
Many B/Cs got the fillet as they to had the same problem as the early Ds but was not as bad as the Ds. http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif </div></BLOCKQUOTE>

I stand corrected.... thx for the heads- up! http://forums.ubi.com/images/smilies/25.gif

sveper
12-31-2009, 02:15 AM
Parts list of modification(numbers only).
http://www.silvervingar.se/J26_dorsal_fin.jpg

ElAurens
12-31-2009, 09:06 AM
Now if the B and C in the sim only performed at the levels they did IRL we'd really have something. The B/C should be considerably faster in top speed and have a higher rate of climb compared to a D. This is because the conversion to the bubble type canopy increased drag do to increased turbulence behind it, compared to the "razor back" versions.