Wildcat intercoolers

[Fernando]

Hi, gentlemen,

 

I am researching to build a Wildcat VI (FM-2) from the Hobbyboss kit, with the Vector conversion. One thing has struck me: were the intercoolers inside the rear engine accesory bay deleted? And so, were they deleted in every R-1820 powered Martlet/Wildcat?

 

The Vector rather sketchy instructions for the conversion, which entails changing the entire nose section, do not show them, but a cylindrical deposit (I guess water for the emergency boost system) just behind the engine, on the lower accesory bay, instead. It wouldn't fit with the intercoolers in place.

 

The otherwise excellent Tamiya F4F-4 comes with only one intercooler, while the Hobbyboss kit comes with a fairly accurate arrangement for two. The nose of the HB FM-2 is rather mismatched, a kind of hybrid, making the conversion necessary. But it comes with the twin intercooler arrangement. I am talking 1/48th scale.

 

Thank you very much!

 

FErnando

[Graham Boak]

If it has a single-stage supercharger, then it wouldn't need the intercooler(s).  This would make it more suitable for lower level operations, which I believe was the reason for the engine change.

[Work In Progress]

Graham's surmise is correct. The R-1820 as used in the FM-2 has a single-stage blower, no intercooler. 

[72modeler]

Both of the gentlemen above are correct; on the F4F-3/4 and export versions powered by the P&W R-1830, there was an oil cooler under each inner wing and an intercooler mounted on each side of the forward face of the wheel bay On the R-1820 powered FM2, the underwing oil coolers were removed and replaced by an oil cooler mounted in the engine accessory section, with cooling air provided by two intakes located in the lower part of the cowling. As the R-1820 used a single stage supercharger, there was no need for the intercoolers, so they were removed.  See the linked photo collection to see the differing supercharger and oil cooler installations between the types. Hope this helps!

Mike

 

 

https://www.angelfire.com/dc/jinxx1/Wildcat/F4F_FM.html

Edited December 16, 2020 by 72modeler
corrected major brain fade!

[Work In Progress]

37 minutes ago, 72modeler said:

on the F4U-3/4

on the what?!

[Fernando]

Thank you, gentlemen; the issue looks as settled.

 

The problem with most pictures (I scrutinized those in the D&S and Squadron Walkaround) is that, first, the accesory compartment is only visible thorugh the wheel wells forward, and that would be either a dedicated or an awkward picture. In the first row of pictures in the site provided by 72modeler (GREAT site, BTW), the intercoolers shows as a big box, but that's hardly the case with most. Second, that some restored F4F-3 or -4s are actually FM-2s! disguised as the earlier machines (usually by painting)!

 

Would also a Martlet IV dispense with the intercoolers?

 

Thnxs!

 

FErnando

[72modeler]

15 hours ago, Work In Progress said:

on the what?!

What the???? Can't believe I did that! I've been doing too much corresponding with CorsairFoxFourUncle and Corsaircorp, and they have been a bad influence on me, as you can see! (Will edit my post forthwith!) 

Mike

Edited December 16, 2020 by 72modeler
corrected spelling

[72modeler]

5 hours ago, Fernando said:

Would also a Martlet IV dispense with the intercoolers?

 

I think so, as the R-1820 Cyclone used in the Mk IV's had a single stage, two speed supercharger, but the oil coolers were still under each wing. I think the intercoolers were only used on the R-1830 powered Wildcats that had two stage, two speed superchargers,

Mike

[Graham Boak]

The intercooler goes between the first and second stage of the superchargers, because compressing the air heats it up, and it needs to be cooled again before the second stage heats it further.  So no second stage no intercooler.

[Dave Swindell]

1 hour ago, Graham Boak said:

So no second stage no intercooler.

Correct in this case, but not always the case. Intercooling can also be used between a supercharger/turbocharger and the engine, but the weight penalties of the intercooler in a single stage design make the advantages for efficiency or increase in power output less attractive in aviation than in other applications where weight isn't a factor.

Two stage charging increases the heating of the charge air significantly more than single stage charging, and as well as having a negative impact on efficiency/power output, it is also problematic because usually you're not just compressing air; the charger is usually downstream of the carburettor, so you're compressing and heating an air/fuel mixture which introduces the risk of pre-ignition before the mixture gets to the cylinders. The intercooler between compressor stages is there to remove this risk as much as it's there to help increase efficiency/power. The engine can handle high temp air (albeit with reduced efficiency/power), but it can't handle a compressed high temp fuel/air mixture.

[gingerbob]

Perhaps a further complication is that, at least to some, an "intercooler" is properly between two stages of compression, whereas between supercharger and engine is an "aftercooler".  It seems that casual, and perhaps even some technical, usage just says "intercooler" for either application.

[alt-92]

I think Greg says it best

 

 

 

[Work In Progress]

In automotive engineering everyone recognises the term "intercooler" regardless of location as long as they are air/air heat exchangers. Some people use the term "chargecooler" for cases where it's part of a liquid cooling circuit.

[MDriskill]

A minor modeling detail sidebar to this discussion...

 

The small teardrop-shaped bulge behind the Twin Wasp engine cowl covered a slightly protruding flange on the intercooler box on each side (F4F-3 in this oft seen photo). So, you would think this bit would be a good indicator of whether or not the two-stage supercharger and intercoolers were fitted. But not necessarily so!

 

 

 

 

As far as I can tell, all production F4F-3's, F4F-4's, and FM-1's (Martlet Mk V), which have intercoolers, did indeed have the buige. But there are some variations on earlier machines.

 

The XF4F-3 prototype, two F4F-3 pre-production aircraft (one of which is in this photo), and first small F4F-3 production batch, did have intercoolers. But these had a slightly different mount not requiring the bulges.

 

 

 

The F4F-3A (including its prototype designated XF4F-6), and the Martlet II did not have intercoolers. Logically enough some of the early "A.M." serial Mk II's did not have the bulge...

 

 

 

...but later Martlet Mk II's ("AJ" serials), and all production F4F-3A's (Martlet Mk III), do have the bulge. Though functionally superfluous, they may have been retained in the interest of parts commonality with other variants being constructed simultaneously.

 

 

 

 

The little bulge is not present on any of the Cyclone-engined F4F variants - the G-36A (Martlet Mk I), F4F-4B (Martlet Mk IV), or FM-2 (Wildcat Mk VI). On these the area between the firewall and cowl is really more different from the Twin Wasp variants, than is commonly realized.

Edited December 24, 2020 by MDriskill

[72modeler]

Very nice detail photos! I had not noticed that it was the flange on the intercooler that required the bulge- many thanks @MDriskill!

Mike

[Fernando]

Hello, gentlemen, have a nice year 2021.

 

Very interesting details on Martlet IIs/IIIs.

 

As a follow up to the Wildcat VI, were drop tanks normally carried by FAA machines?

 

Fernando

[Mick4350]

I just had to look this up in my copy of Capt. Eric Browns Wings of the Navy book and looking at the exploded view drawing on page 46, item number #31, I noticed that it's called an interdooler in my copy that was published in 1987.

[Work In Progress]

33 minutes ago, Fernando said:

As a follow up to the Wildcat VI, were drop tanks normally carried by FAA machines?

The only FAA Martlets and Wildcats I've ever seen carrying external tanks are Wildcat VI / FM-2 . There was no technical plumbing reason why a Wildcat V / FM-1 could not have done, and I've put some on my own Wildcat V model, but I don't have a photo to justify it.

[alt-92]

On 12/18/2020 at 4:37 PM, MDriskill said:

The XF4F-3 prototype, two F4F-3 pre-production aircraft (one of which is in this photo), and first small F4F-3 production batch, did have intercoolers. But these had a slightly different mount not requiring the bulges.

 

 

Out of curiosity, the front F4F, apart from what appears to be a more squared-off panel over the intercooler, what is the groove on the port side? Machine gun?
(also intake on the top of the cowling and very visible fasteners as opposed to the other one - which exactly is the "YF" ? ) 

[Work In Progress]

It's a .30 Browning and there's likely one on the other side too

Edited January 4, 2021 by Work In Progress

[MDriskill]

8 hours ago, alt-92 said:

 

Out of curiosity, the front F4F, apart from what appears to be a more squared-off panel over the intercooler, what is the groove on the port side? Machine gun?
(also intake on the top of the cowling and very visible fasteners as opposed to the other one - which exactly is the "YF" ? ) 

Correct, the machine in the foreground is one of the first two pre-production F4F-3's, which carried nose-mounted guns. All subsequent Wildcats actually retained the basic gun bay structure, with flush access doors as opposed to these operational bulged ones, but did not carry weapons there.

Edited January 5, 2021 by MDriskill

[Fernando]

10 hours ago, MDriskill said:

Correct, the machine in the foreground is one of the first two pre-production F4F-3's, which carried nose-mounted guns. All subsequent Wildcats actually retained the basic gun bay structure, with flush access doors as opposed to these operational bulged ones, but did not carry weapons there.

Amazing the panelling in that area was never fully upgraded, retaining that funny looking panels which were for sure a production hindrance, much less efficient than simple, square ones.

 

Fernando

[Fernando]

19 hours ago, Work In Progress said:

The only FAA Martlets and Wildcats I've ever seen carrying external tanks are Wildcat VI / FM-2 . There was no technical plumbing reason why a Wildcat V / FM-1 could not have done, and I've put some on my own Wildcat V model, but I don't have a photo to justify it.

That's what I thought. I have seen a few pictures and only one shows the tanks fitted, only to a VI. Of course the plumbing was there on the rest of the models if appropriate, but the tanks are not present. I guess there was something related to doctrine and use. Also, a drop tank is only useful as long as you have enough supply of them to replace them as they are dropped (we know that very well from experience); if you do not, you better not count the extended range in your operational planning, or assume them as "non-droppable"!

 

Fernando

[Work In Progress]

52 minutes ago, Fernando said:

if you do not, you better not count the extended range in your operational planning, or assume them as "non-droppable"

And carriers are perpetually short of space, especially British carriers. And very little eats space quicker than large empty cylinders. Plus, the Wildcat has a good amount of internal fuel anyway. 

There are other tactical considerations too. I just found this piece, which is interesting on the human factors which led to limiting air defence missions to two hours on station, which the Wildcat can do on internal fuel. 

https://www.armouredcarriers.com/grumman-f4f-martlet-variants

 

If you use your Wildcats purely as defence for the carrier group I suppose you don't need any more. If you want to use them more as an escort fighter accompanying bomber/torpedo raids on the enemy carrier group then range and endurance are definitely more important. 

[MDriskill]

On 1/5/2021 at 7:26 AM, Fernando said:

Amazing the panelling in that area was never fully upgraded, retaining that funny looking panels which were for sure a production hindrance, much less efficient than simple, square ones.

 

Fernando

Agreed, have always thought it odd that the Wildcat retained the structure around the gun bays. Perhaps it was easier than changing design and tooling once production got rolling.

 

Or maybe there was some thought that nose guns might re-appear...a classic case of, "better to have it and not need it; than to need it and not have it," LOL!

Edited January 15, 2021 by MDriskill