F4F-4 technical issue - help please

[Jindřich Nepevný]

Dear All,

I very appreciate some help with two F4F-4 technical issue that I am not able to identify properly. This is small airscoop on the right side behind the cockpit, respectively opened canopy, plus small round opening/hole (unknown purpose for me) in close area and located slightly higher then airscoop but within one fuselage segment.

Both feature was not intruduced on F4F-3 or 3A with the exception of last production run of 100 planes that was built in spring 1943 after ceasing production of F4F-4 serie at Grumman factory.

Many pictures of F4F-4 show this both feature but not every ones, unfortunately. It seems that this both feature was introduced gradually somewhere during second production run (BN 5030 – 5262) in early Spring of 1942, i.e. not from the beginning. Several pictures show F4F-4 without airscoop as well as round hole (aproximately till Guadalcanal campaign), some only with the round hole and mostly ones with both feature.

For example – picture of white 10 of VF-3 (BN 5149) from Midway or black 41-F-8 of VF-41 (BN 4084) from April 1942 clearly show planes without any of a/m features.

On the contrary, F4F-4 black 13 of VF-6 (BN 5193) from the beginning of Guadalcanal campaign has only round opening/hole and no unit-marked F4F-4 of BN 5262 (served for testing of new system of double flaps) as last machine of second production run has already both fearures,   

Well, there is several related questions,

a/ when was airscoop officialy intruduced and based on what (some technical USN bulletin or so)?

b/ purpose of round opening/hole (perhaps first unsuccessfull attempt for better ventilation of radio and other avionic equipment in fuselage, my guess)

Many thanks in advance.

 

 

Edited November 7, 2022 by Jindřich Nepevný
picture adding

[dragonlanceHR]

I see it on F4F-7 and FM-1 photos, but none of my references say what is it. Even the Dana Bell aircraft pictorial, which makes me sad. I wish someone would do a definitive modellers book in Wingleader format.

 

Edit: see also

 

 

Edited November 7, 2022 by dragonlanceHR
update

[Troy Smith]

2 hours ago, Jindřich Nepevný said:

I very appreciate some help with two F4F-4 technical issue that I am not able to identify properly. This is small airscoop on the right side behind the cockpit, respectively opened canopy, plus small round opening/hole (unknown purpose for me) in close area and located slightly higher then airscoop but within one fuselage segment.

Hi Jindrich

I suggest posting a photo of the detail in question.

 

There have been some very indepth discussions in this thread recently,  

I would suggest posting the above question in that thread,  and use the name tag facility,  type @

and then the members name like  @Jindřich Nepevný    as there are some very knowledge people posting there, and see if they can help. 

These seems like the folks to ask

@mdesaxe  @captnwoxof @detail is everything @MDriskill @Dana Bell

 

HTH

[dragonlanceHR]

Troy, it is visible on photo no.2 of MDriskill's Sep 27th post I linked. Blue arrow.

[Troy Smith]

39 minutes ago, dragonlanceHR said:

Troy, it is visible on photo no.2 of MDriskill's Sep 27th post I linked. Blue arrow.

this one?

  

On 27/09/2022 at 15:04, MDriskill said:

Small radio bay cooling scoop

 

 

3 hours ago, Jindřich Nepevný said:

b/ purpose of round opening/hole (perhaps first unsuccessfull attempt for better ventilation of radio and other avionic equipment in fuselage, my guess)

 

[tempestfan]

Jumpei Temma's drawings show both features, though without further explanation - his -4 stbd side view is labelled "early production". Given his (I repeat myself) is the only set of drawings I am aware of that feature the small blister in front of the outboard shell ejector, I think he did a very serious study of pics. I have no idea if he could answer your questions if you contact him via the "mail to" feature on his start page - but it may be worth a try.

[Jindřich Nepevný]

Many thanks to all,

 

and, yes the blue arrow pointed out on fuselage airscoop of one of the last 100 F4F-3 batch manufactured after finishing F4F-4 series, purpuse is clear - cooling.  

 

But the second unknown feature is round opening/hole visible on the picture but higher and closeer to the US star marking.  

 

best regards

 

JN

[Jindřich Nepevný]

to Toryu,

 

it is very close, but most drawings (may by inaccurate) as well as few picture shows wire ending from horizontal stabilizers in fuselage segment closer to tail, and little bit lower then "opening/hole"; see for example picture of F4F-4 demontrating how to use . . . . life  raft.  It is quite well-known, I have still difficulty tu put here pictures. It is G-11021 from 19/11/1942.  

 

JN

[Jindřich Nepevný]

to Toryu,

 

not exactly,

 

round opening/hole was introduced earlier than airscoop - see my BN research above.

 

best regards

 

JN

[captnwoxof]

Hello

I've been looking over my references, hoping to find a concrete answer to your question, but so far it has eluded me. Your observations appear to be correct (good eye!), all I can do is confirm them and add a few additional ones, particularly regarding the British Martlet varients.

 

I have found four configurations:

1)   No hole or scoop

2)   Hole only

3)   Hole and scoop

4)   Scoop only (tentative-the hole may be there, but taped/sealed over)

 

Breakdown by varients:

 

USN

F4F-3 & 3A:  All photos show no hole or scoop, with the exception of the "oddball" last 100 F4F-3s (12000 series BuNos) that were built after F4F-4 production had ended.                         Apart from the fixed wing (which defined them as -3s) they were essentially identical to late production -4s. I can confirm that they had both the hole and scoop.

F4F-4:          Mix. Very early production display neither. Hole appears to have been introduced first, as some airframes have it without the scoop. If the scoop was introduced                      at some later point, the hole was retained, as I cannot find an example that has the scoop without the hole.

FM-1:           Somewhat to my surprise, they are a mix. What I have found so far is either no hole or scoop, or both.

FM-2:           Again, a mix.  Operational photos show no hole or scoop. Some restored examples have both, but this may be an inaccuracy in the restoration.

 

FAA (British)

Martlet I (G-36A):      No hole or scoop.

Martlet II (G-36B):     Hole only. This includes the first ten fitted with fixed wings. Their fuselages were built in Dec 1940, so I believe this is the earliest example of this feature.

Martlet III (F4F-3A):   No hole or scoop (these were stock F4F-3As requisitioned from USN inventory for Lend-Lease).

Martlet IV (F4F-4B):   Mix, Most in service have both hole and scoop.

Martlet V (FM-1):       Most have both hole and scoop. Some appear to have scoop only.

Martlet VI (FM-2)       No hole or scoop.

 

Richard Dann has stated that the scoop was for avionics cooling. I don't know what his source is, but he has had extensive access to Grumman's archives and files, In any case, it is apparrant that the scoop provides ram air venting into the fuselage where the radio gear is located. The hole might also provide airflow, either as an outlet or inlet by venturi effect (if that is its purpose). I cannot find any photos of the interior that show the hole or scoop from the inside. Looking at reports and requests for modifications, I cannot find anything noting a need for increased cooling of the radios. (My sources are admittedly limited).

What I did find was considerable correspondance from the British regarding carbon monoxide levels in the cockpit. The USN make a brief mention of it, but considered the problem "corrected".

Not so the British, who were very concerned with the matter. The problem was found to be that the exhaust, vented down and below the fuselage into the slipstream, was sucked back in through openings in the rear fuselage and drawn back to the cockpit by venturi effect. Each mark of Martlet was evaluated independently. and all were found unsatisfactory to some degree. They undertook all sorts of modifications of the exhaust pipes and interior sealing. The report on the Mk IV is interesting. It notes that the aircraft tested (FN111) had a small sccop fitted to the starboard fuselage aft of the cockpit, providing ram air inside the aft fuselage, countering the venturi effect and helping to prevent the exhaust from reaching the cockpit. So perhaps this was the intention of the scoop. The jet exhaust of the FM-2/Martlet VI alleviated much of the problem, and could be why they do not have the scoop.

 

That's all I know. The lack of a clear pattern is frustrating, Hopefully someone with better access to Grumman's files can say more.

 

 

 

Edited November 11, 2022 by captnwoxof