Kawanishi H6K Mavis flying boat v Blenheim IF long range fighter

[Fatboy Coxy]

Hi all, I was just looking at a Kawanishi H6K Mavis flying boat v Blenheim IF long range fighter, match up

With a cruising speed of 138mph, and a top speed of 210mph, the Mavis is as slow as an old London bus compared to a Blenheim IF long range fighter, who is cruising at 165mph, and a top speed well over 210mph.

The interest is how each sees the other as a potential threat. Initially the Japanese may not appreciate the Blenheim is a fighter, until she opens up with her four 0.303 in (7.7 mm) machine guns in the gun pack under the fuselage. Nevertheless, her speed advantage would have been immediately obvious, enough to make any Japanese pilot very wary of a Blenheim.

The Blenheim, however, sees a slow lumbering, four engined, flying boat, a very easy target, so what angle how does he attack from. The Mavis has a number of single 7.7mm machine guns to defend herself, but should the Blenheim close from the rear, the Mavis had a terrible sting in the 20mm cannon in a tail turret.

Your thoughts are welcomed

 

[Thumpalumpacus]

Hi all, I was just looking at a Kawanishi H6K Mavis flying boat v Blenheim IF long range fighter, match up

With a cruising speed of 138mph, and a top speed of 210mph, the Mavis is as slow as an old London bus compared to a Blenheim IF long range fighter, who is cruising at 165mph, and a top speed well over 210mph.

The interest is how each sees the other as a potential threat. Initially the Japanese may not appreciate the Blenheim is a fighter, until she opens up with her four 0.303 in (7.7 mm) machine guns in the gun pack under the fuselage. Nevertheless, her speed advantage would have been immediately obvious, enough to make any Japanese pilot very wary of a Blenheim.

The Blenheim, however, sees a slow lumbering, four engined, flying boat, a very easy target, so what angle how does he attack from. The Mavis has a number of single 7.7mm machine guns to defend herself, but should the Blenheim close from the rear, the Mavis had a terrible sting in the 20mm cannon in a tail turret.

Your thoughts are welcomed

Pepper-pot the hull of the flying boat and/or aim for the engines, either way from underneath?

As an aside, the Mk IV's top speed is quoted in Wiki as 267 mph, but I can't find info on the IF's top speed. How much faster was it than the Mavis, if you or anyone else knows?

 

[Greg Boeser]

My references give the top speed of a Blenheim Mk I as 278 at 15,000'
I imagine the Mk IF would be slightly slower due to the induced drag of the belly gun pack.

 

[fubar57]

This is from the Warpaint Series by Andrew Thomas*

​

*your references may vary

 

[Thumpalumpacus]

My references give the top speed of a Blenheim Mk I as 278 at 15,000'
I imagine the Mk IF would be slightly slower due to the induced drag of the belly gun pack.

Fantastic, thanks. I'd found myself assuming that because the Mk IV's cruising speed was much higher than the OP's statement regarding the IF's cruising speed that the latter would have a lower top speed as well.

In an event it appears the IF had a marked turn of speed over the Mavis. Thanks for clearing that up for me.

 

[special ed]

Apparently speed has little to do with the combat. Elsewhere on this forum are accounts of B-17s and B-24s attacking Japanese flying boats with less than the desired results by the US crews. Reminded me of old sailing ships broad siding each other.

 

[GrauGeist]

The H6K had an Achilles Heel like most flying boats - no lower turrets because of the hull.
The best attack solution would be a climbing attack from astern (rear gunner can't depress the cannon far enough).

Also, like most flying boats, the bulk of their fuel is stored in the hull.

 

[nuuumannn]

Just a wee note, book sources and so forth quoting the maximum speeds for the Blenheim IF have to be taken with a grain of salt, as according to the Pilot's Notes for the type, there is no maximum level speed listed, but there is a maximum diving speed:

"For all-out level flight a maximum speed of 2,750 rpm and a boost pressure of +5 psi must not be exceeded; this speed must not be employed for a period of more than five minutes."

Based on that sentence, the maximum IAS will be whatever the aeroplane is doing when those parameters are reached. Individual aeroplanes might register different speeds to one another, as, for some inexplicable reason it has been recorded that Avro built Blenheims had on average lower performance than Bristol built Blenheim Is.

Under the Diving Speed heading is the following: "The maximum diving speed is 285 mph ASI reading. At less than one-third throttle opening the engine speed must not exceed 2,750 rpm for periods of not more than 20 seconds with a momentary maximum speed of 3,120 rpm."

"The maximum diving speed of 285 mph ASI reading is permissible in a steady dive only."

 

[Shortround6]

The Blenheim has several problems in to regards to published performance tables.

The Blenheim MK I was supposed to be good for 285mph at 15,000ft.
Yes the gun pack was supposed to be 10-15mph (or more) less due to drag.

However was the problem was that the MK I was 'supposed' be only good for 240mph at sea level and 254mph at 5,000ft using 87 octane fuel'.
So the "fighter" MK IF might have good for 225-230mph at sea level?
The engines were only rated for 725 hp at sea level compared to the 840 hp at 15,000ft.

The Mavis didn't have quite the drop off in top speed.

If the Blenheim MK IF was running at 10,000-12,000ft it might have had around 250 mph.

There may also be an an issue with those crappy two pitch propellers.

Somebody has quoted the dive speed of the Blenheim but the 285mph speed at 15,000 is also the limiting of the speed of the propeller at max engine speed.
Is the problem the plane itself can't fly without structure failure or the propellers while fail (or while break the engines through over speeding?)

attempts with the MK IF (and indeed the MK IVF) at lower altitudes and/or lower speeds have problems with the engines forcing to be used used either less than full throttle settings or use higher engine speeds but less than optimum propeller pitch settings.

Actually the the two pitch props have only one setting below under 100-120mph at full power. If the engine requires less than full pitch then the engine needs reduced rpm (and reduced power) to match the props so that the props aren't too mismatched.

 

[nuuumannn]

Somebody has quoted the dive speed of the Blenheim

That's the maximum diving speed according to the Pilot's Notes, AP1530A, not just some random quote from a book or such.

 

[Greyman]

Repost (ish) from another thread:

Blenheim I - weight supposedly 10,960 lb
Blenheim IF - figure from 'The British Fighter Since 1912'
Blenheim I - 11,776 lb (+5lb sq/in)
Blenheim IV - 14,500 lb (+5lb sq/in) - boost override (+9lb sq/in)
Blenheim IV - 13,190 lb (same aircraft)

No mention of the turret's position on any of the tests. If I was forced to make a guess I'd say it was retracted.

I suspect the two blue Mk.I points are for +3.5 lb boost, which was the Mercury VIII without the boost override pulled. For +5 lb they'd be about 2 mph faster and 2,000 feet lower (lines added to sketch this out).

A couple of different sources have the speed loss by adding the gun pack as about 6 mph.

 

[Shortround6]

That's the maximum diving speed according to the Pilot's Notes, AP1530A, not just some random quote from a book or such.

The Pilot's notes are as you state, at least as what I have seen for the MK IV. I don't have the notes for the MK I ( or for the fighter versions)
I would no see reason for the MK I to be any deferent for the propeller speed number/s.

The comments about the dive speed come from the later MK V and the plane being rated at 325mph for diving and the dive rate in a different paragraph than the earlier notes.
The speeds were the same for the same for the propeller pitch.

It just seems a bit strange that the dive speed was so close to the RPM limit.
The Hamden was rated at as a 290mph dive speed but it both the Hampden and the Blenheim V had constant speed propellers.
Perhaps the required procedures were a bit different with two speed propellers?

 

[GrauGeist]

A B-17 could catch an H6K, and did.

Here is an actual encounter between the two, recollected from the H6K's pilot:
Clash of the Titans

 

[nuuumannn]

I don't have the notes for the MK I ( or for the fighter versions)

The Mk.I doesn't have separate pilot's notes for different variants, they apply to the Mk.I in general.

I have Mk.I, IV and V pilot's notes for the Blenheim. In the Blenheim IV Pilot's Notes (AP.1530B) the reference is the same, there is no maximum IAS stipulated except for diving speed, which is the same as the Mk.I, 285 mph at 2,750 rpm at one third throttle opening, at more than one third throttle opening maximum rpm is 3,100 "for a momentary period only".

So again, variations are going to be encountered depending on the conditions of the aeroplane and weather etc...

 

[Wildcat]

A RAAF Hudson MkIIIA engaged and shot down a Mavis in June 1942 off Bougainville. Probably the closest comparable aircraft to the Blenheim.

 

[Graeme]

 

[Greg Boeser]

With only 166 built and the frequency with which they were shot down, it's a wonder any survived the war

 

[nuuumannn]

it's a wonder any survived the war

None did. The H6K is extinct. Above water, that is.

A single H8K survives, only because it was taken to the USA for evaluation post-war. It's now at the naval base museum at Kanoya.

 

[Greg Boeser]

I had read there were still 5 at the end of the war. But they didn't survive long.

 

[nuuumannn]

I had read there were still 5 at the end of the war. But they didn't survive long.

Ah, copy that, I misunderstood you. My mistake.

I vaguely remember reading something somewhere that stated the Dutch/Indonesians had one or two operational post-war?

Ah, Yup. answered my own question...

"Air Service Volunteer Corps - A single H6K5 flying boat was restored to flight by Indonesian forces during the Indonesian War of Independence."

Picture:

Kawanishi H6K - Wikipedia

en.wikipedia.org

From here:

Kawanishi H6K - Wikipedia

en.wikipedia.org