Painted exhaust

There have been several examples of painted on exhaust stacks on semi-scale airplanes which are very realistic. for me, I'll stick with 3 dimensional stacks. Here is Bene Rodriguez's 4 stroke F-51 and Keith Trostle's Bearcat.

LAST EDITED ON Jul-14-04 AT 00:46 AM (CDT)
 
Something I've wanted to know a long time (and I figured you'd probably know the answer if anyone did) was why the RAF changed the exhaust stacks on the Spitfire. Pictures of Mark Vs (and earlier marks) show the ganged up, 3 to a side large stacks, while Mark IXs and later have the smaller 6 to a side ones. Did this have something to do with moving to the two stage Merlin? Some Mustangs I've seen at airshows have the side-ejecting stacks (like on the Bene Rodriguez model, above) rather than the more common rearward facing funnels, too.

>Something I've wanted to know a long time (and I figured
>you'd probably know the answer if anyone did) was why the
>RAF changed the exhaust stacks on the Spitfire. Pictures of
>Mark Vs (and earlier marks) show the ganged up, 3 to a side
>large stacks, while Mark IXs and later have the smaller 6 to
>a side ones. Did this have something to do with moving to
>the two stage Merlin? Some Mustangs I've seen at airshows
>have the side-ejecting stacks (like on the Bene Rodriguez
>model, above) rather than the more common rearward facing
>funnels, too.
>
>
>
>
>
>

Ron B.

The later Marks got a useful amount of additional thrust from the rearward facing funnels,and by reshaping them,a reduction in frontal area and parasitic drag,or so I'm told.

Ron B.
F4Fguy

What you see at airshows are often what is available to the restorer at the time of assembly, or what was on that airplane for some period of time.

I flew warbirds for a while and was puzzled to hear people ask why this airplane had that piece of equipment, or didn't. I told them I was busy keeping what we had operational so we could get the airplane to the show so they could ask me that question! Trying to keep it good natured of course.

As historical correctness becomes more important, the restorations will become more correct. A lot of Mk.II Spitfires have 4 bladed props because they are available. Hoffman could probably make the blades for a composite type like a Rotol, but you must have a serviceable hub and blade shanks. Props are expensive now days, a Hamilton Standard cuffed four blade for a Mustang will cost over 75,000 dollars outright. The Mustangs you see on the ramp with the non-cuffed round shank Hamilton Standards will most likely be some form of cut and shaped Convair or Northstar airliner blades.

As for exhausts on the Mustang, the big straight angle jobs are from late model F-51D series airplanes. These are the stacks you see at Reno on the speedy ships. They are able to process a lot of exhaust with out failure. In the sixties, guys experienced a lot of failures of the older wartime P-51D stacks of the necked down variety while using high power settings. These high power settings were way above the factory limits, and so the exhaust temperature and velocity would overtax the stacks structure. During racing at Reno these type failures in present day do not occur, at least I cannot recall one in a long time.

Ron is correct about the Spitfire exhaust, the grouped type gave way to the single ejector type like on the Mk.16 he has pictured because it was superior in jet thrust to the grouped type.

An interesting note; The Mk. 16 has a low altitude Merlin 266 built by Packard. Side by side, at the same power setting, the Spifire will walk away from a D model Mustang at 10,000 feet.

Sorry to go on,
Chris...

How about a turbocharger? The turbos (4 ea) behind the LG on PW's B-17 #909 look like they are carved or molded. Totally not so. Actually, decals, computer generated by Howard Rush. The cowl flaps are functional, too. Fixed, but funtional. Steve

What about them wheel wells? Are those painted on?

You can see the bladder hole in that photo.

I'd heard about the exhaust thrust, but I didn't know if that was the reason they changed to the single stacks. RR was developing a 2 stroke engine during the war (the Crecy) that was supposed to be a drop-in Merlin replacement, and planes powered by this engine were supposed to get 30% of the thrust from the exhaust. Very, very loud engine - like most 2 strokes, the exhaust port opened while the pressure in the cylinder was still high.

Interesting that they don't use some form of rear ejector exhaust on the Reno racers, since there's more thrust that can be recovered from the exhaust when you have a higher gas flow at high power settings!

According to those who know, Mustangs powered by the famous Dwight Thorn "Mouse" engine have a measureable increase in jet thrust at certain super high power settings. Evidently the last 20 in hg of manifold pressure are not really making it to the propeller reduction gearbox, but raise the airplanes speed by jet thrust. To make the difference between 120 and 140 in hg of manifold pressure the blower uses all the additional torque. It is possible that one might see different and optimised exhaust stacks in the future at Reno, but these racers evolve over time.
The Super Corsair with the R-4360 that was lost at Phoenix in 1994 had an elaborate jet thrust exhaust scheme that was in part responsible for it's sterling performance at the 1985 Reno Nationals in which it won the Gold final at a then record of 438+ mph. So, jet thrust is not only well known, it is used to advantage on the racers.
Chris...

Isky: I think the change to six stacks occurred with the Spitfire VII and VIII. These had the Merlin 60 and 70 Series, with a two speed, two stage supercharger. Currell

LAST EDITED ON Jul-16-04 AT 06:10 AM (CDT)
 
Ah OK, that would make sense. So I was wondering why did the change took place at that time - was it coincidental, or did it have something to do with the switch over to the two stage Merlin?

I came across an account written by the wing commander of a wing where one of the squadrons was equipped with Mark VIIs. Uncommon Spitfire! I think the other two squadrons in the wing had Mark XIVs at the time. This was 1944, I think, southern or eastern England.

I can't recall much about the Mark VII, the VIII was a revised airframe, with additional tankage, and I think a bigger tail and a few other improvements including tropicalization. They didn't fly these in the ETO, most were sent to the Far East and elsewhere. This airframe also became the basis of the Mark XIV. The IX was actually a stopgap measure - they fitted the Merlin 60 series engines to what was essentially a Mark V airframe, and IIRC, many Mark Vs were converted to the IX. This was the main type used in the ETO in 1943 and onwards.

>An interesting note; The Mk. 16 has a low altitude Merlin
>266 built by Packard. Side by side, at the same power
>setting, the Spifire will walk away from a D model Mustang
>at 10,000 feet.

That's an interesting observation. Were all Mk. 16s fitted with the low altitude Merlins while P-51Ds were all fitted with the high altitude one (presumably the Packard version of the Merlin 61)? The Brits made three versions of the Mark IX (which is supposedly the same thing as the XVI) with low, medium and high altitude engines.

I don't know. Our museum had a low altitude Merlin equipped Mk.XVI with full span wings. The cruise power setting was 30 in hg and 2450 rpm. This would give you 245 to 255 IAS, which was the same as the museum Mustang at 36 in hg and 2450 rpm. If you would cruise them side by side , and run the boost up on the Spitfire to the same manifold pressure as the Mustang it would accelerate away. The D just has more drag than a Spitfire at those speeds. Same thing happens with an A model Mustang, the A will walk away from the D at the same hp at low altitude.

Trouble with these comparisons of all these airplanes is the modifications done to them through the years. The museum Mustang was the famous Jay Dee, owned by Dale Fulton and flown by George "Wheaties" Welch in the 1946 Thompson, and then sold to J.D. Reed, owner and co-conspirator of the infamous Beguine. It was flown by Ken Cooley, Charles Walling and Ken Hagerstrom for J.D. through 1949. This airplane had a long career of racing and modification. When I was familiar with it it had an airline version, fuel injected, "highway gears" Merlin 700 series engine that made about 2000 hp dry. At 24,000 feet in high blower it would true out at high power over 400 and that was not wide open. It was never flown to max power at critical altitude that I know of so I don't know how fast it would really go. But it was fast.
Chris...

It's interesting that the Japanese did the same on a later model of the A6M- Zero Sen. I believe it was on the -5 model. The stacks gave a few more kts.

As clever and well done as the painted on stacks are, I agree with you, Al!

To me it seems to "cheap out" on an otherwise fine ship. JMNSHO.

[photo not recovered: 3e69bb3870f12ad5.jpg]

"Yesterday is but today's memory, and tomorrow is today's dream." -Kahlil Gibran