Spitfire engine failure in dive?

[antoni]

I haven't a clue what effect various acrobatics have on the carburettor.

The Shilling orifice or restrictor may have been one of several early solutions but I cannot find a reference that clearly explains what they were. Morgan and Shacklady's Spitfire the History surprisingly has little to say on this matter despite explaining at great length some very obscure aspects of Spitfire development. I quote:

"The MK V did need additional power and something needed to be done about the float carburettor, the former being overcome by the installation of more powerful Merlins; the latter by fitting of the 'Shilling' orifice into the carburettor, initially, and the adoption of a modified Bendix Stromberg carburettor later. On 12 May MAP issued a notice to the effect that all new production Merlin 46 and 47 engines should be fitted with the Rolls Royce negative-G carburettor. Also, the 46 was to be given a new mark number."

The new mark number is the 50 series. The Modellers Data File says of the Merlin 50.

"This engine was purely a service trials engine based on the Merlin 46. It used a diaphragm-controlled fuel feed, which was later deleted in favour of Miss 'Shilling's 'restrictor', and then the RAE anti-G device."

There seem to be three solutions. The RAE is Farnborough which is where Miss Shilling was. So what was the RAE anti-G device if it wasn't the Shilling 'restrictor'? Which, if any, was the RR carburettor? The diaphragm-controlled fuel feed?

 

[Sgt. Pappy]

There's an Alfred Price book out there that displays almost (if not all) mods made on the Spitfire throughout its history. I believe it's called Spitfire: A Complete Fighting History. The Spits with regular carburettors also had the problem of fuel mixture becoming too rich if the negative G was held too long since the fuel would pool in the float chamber.

To my understanding the orifice was much like a thin, circular metal plate with a hole in it. It ensured that the fuel in the float chamber was never excessive so that there would be no overflow.

 

[Major]

So the Merlin 46 and Merlin 50 were the same engine O_O?

 

[antoni]

The Merlin 50 was a trials engine based on the 46 and fitted to two squadons of Spitfire Mk Vs at North Weald.

 

[Major]

Ive read that the Merlin 50 was also used in Seafire mk II's and Seafire mk III's, is this true?

 

[antoni]

Seafire Mk IIs were first fitted with Merlin 46s but most interceptions were at lower altitudes. For that reason the Navy wanted them fitted with Merlin 32s but they were hard to come by as they were earmarked for Barracuda Mk II. Eventually a number were diverted. A single Seafire was fitted with a Merlin 55 but never saw service. I cannot find any mention of any being fitted with Merlin 50s.

The Seafire MK III was fitted with Merlin 55s or 55Ms. Again I cannot find any mention of any being fitted with Merlin 50s.

 

[Major]

Seafire Mk. III Trials

British Aircraft of World War II - SUPERMARINE SEAFIRE (Merlin, fighter)

Was the Merlin 55 also fitted with an anti-G carb? I would assume that if the Merlin 46 and 50 were fitted with one, than the 55 was also, just making sure.

thanks

 

[bf109 Emil]

my dad commented on this, as he flew both hurricanes and spits, and to cure, a pilot rolled on his back, and then dove, so fuel was pushed into the carb, rather then nosing over, and g-force would starve the merlin, and allow an adversary to escape. a cumbersome solution until rectified, same as a fault with the 109 in the BoB. as new pilots, or ones whom might be over whelmed with little flight experience where told to stay out of the clouds, for a plane above will spot you 15 seconds before your visibility is suffice, and safest place or altitude for a spit, is to circle at 24 to 25,000 feet as this height was a hinderance to the bf109 ..,

I was unable to find a clip to demonstrate the fuel nemisis to early model Merlins, but if one watches the very opening clip in the movie Battle of Britian, a hurricane pilot does a victory roll over retreating troops and civilians, if you watch closely and listen, the engine cuts out as fuel is thrown from the carbs, and emits black smoke when the merlin cuts back in...but perhaps is summed up by 2 british tankers a few seconds later stating..."Who the hell's he trying to kid"

bf109 Emil

 

[Major]

I never really got the "inverted dive" thing.
So the pilot would roll inverted, than push "up" elevator to make the plane dive, than what? How does he get back to normal level flight?

Also, do you know if the Merlin 55 had anti-G carbs?

thanks for the answer.

 

[claidemore]

Major,
The pilot does a half roll and "pulls" on the stick, his plane is upside down after the half roll, so he pulls back on the stick to push the nose down. Then as he dives he can do a slow roll back to an upright position so he will be pulling positive G when he does his pullout. He'd lose 1-4 seconds, (depending on speed ) if the 109 bunts.

The thing that is almost never mentioned, is that the favorite escape maneuver of the 109s during BoB (and after) was a half roll and dive, which is exactly what the Spit and Hurricnae should be doing anyways.

The Merlin cutting out in a neg G maneuver was a nuisance, but as a tactical disadvantage, it is over stated and over emphasized IMO.

A little footnote:
SU, stands for Skinners Union, for the 3 Skinner brothers who owned the factory that produced those carburators, and also produced the Bendix carbs for Rolls Royce. This company also developed a fuel injection pump which was used on Mosquitos, and which eventually became the Simmonds Fuel Injection pump which is what I have on my 1952 Fordson Major Diesel tractor! How cool is that, to have the same fuel injector that they used on the Mosquito?

 

[Major]

Ahh i see.

 

[kool kitty89]

It was basicly a split-S dive...

Really the only major time this cut out is a problem is during aiming when you may need to pull a little -G.

An interesting thing to mention is that the Il-2 Sturmovik combat flight sim models this effect quite well on the Hurricane Mk.I and the Gloster Gladiator. (both used by the Finns)

 

[Major]

Wait, how come rolling inverted before the dive does not make the engine cut out? I thought inverted flight would pull negative G and mess up the engine.....

 

[kool kitty89]

It's not inverted flight since you could roll and continue to pull +G's. (by applying elevator during the roll) Even if just rolled and then pulled back into a dive the period when 0/-G's would be experienced would be something on the order of 1 sec. (enough for the engine to sputter, that's all)

 

[claidemore]

Don't forget that this was not a gravity fed fuel system, there was an engine driven fuel pump that was pushing fuel from the tanks to the carburators and an immersed pump in the lower tank (Mk V) to maintain pressure at high altitudes. The pump operated in inverted and negative G flight, the problem was the mixture of fuel to air in the carburator.
Basically the engine was still getting fuel, it just wasn't mixed properly, and so the engine would run 'rough', sputter etc.

If flying inverted, the pilot had to pull the throttle back so the engine would not get 'flooded', once he returned to a normal flight attitude, he could throttle up and the engine would roar to life again. They were actually more worried about fouling the engine with coolant and oil than starving it of fuel.

Pilots were also taught to 'barrel' the roll during aerobatics to maintain positve G and keep the engine running smoothly, as KK mentions.

 

[Major]

Wait a sec, so the engine would sputter if the pilot just did a simple roll O_O ?

 

[antoni]

Seafire Mk. III Trials

British Aircraft of World War II - SUPERMARINE SEAFIRE (Merlin, fighter)

Was the Merlin 55 also fitted with an anti-G carb? I would assume that if the Merlin 46 and 50 were fitted with one, than the 55 was also, just making sure.

thanks

To speed up production the first 32 Seafire Mk IIIs were built with fixed wings. They fior this reason they were redesignated MK IIc (Hybrids). The last MK II LR764 was fitted with a Merlin 55 and MK II tail unit. The first MK III/II Hybid,LR765 was fitted with a Merlin 50 as was LR766. All three were trials aircraft. There are some MK III serials listed as fitted with Merlin 45Ms and Merlin 55Ms but it is tedious to look down lists of serials for entries with an engine specified. They also seem to be trails aircraft. As most have no engine listed I assume that means they were fitted with the engine specified, which for the MK III, was the Merlin 55. Does that mean that the other serial numbers for the MK III/IIc Hybrid were fitted with MK III engines or MK II engines I don't know but I am inclined to think that as they were originally built as MK IIIs they had the Merlin 55

I am not sure what type of carburettor was fitted. The 50A and 56 had the same carburettor as the 50. I don't think it is a simple case of a 50 series engine being the 40 series engine fitted with a new carburettor. For example the 55 was a modified 50 with a two piece engine block.

 

[claidemore]

I highly recomend reading the Spitfire Mk II pilots notes, very good information on aerobatics with the float carburater engines.

Can download a pdf from these forums here:

http://www.ww2aircraft.net/forum/other-mechanical-systems-tech/spitfire-manuals-9050.html

Or a zip file with scans here:

Free Supermarine Spitfire Checklists to Download

 

[bf109 Emil]

Major,
The pilot does a half roll and "pulls" on the stick, his plane is upside down after the half roll, so he pulls back on the stick to push the nose down. Then as he dives he can do a slow roll back to an upright position so he will be pulling positive G when he does his pullout. He'd lose 1-4 seconds, (depending on speed ) if the 109 bunts.
from claidemore...thank you for enlightening an earlier reply as to my posting...

The thing that is almost never mentioned, is that the favorite escape maneuver of the 109s during BoB (and after) was a half roll and dive, which is exactly what the Spit and Hurricnae should be doing anyways.

The Merlin cutting out in a neg G maneuver was a nuisance, but as a tactical disadvantage, it is over stated and over emphasized IMO.

as said, someone can notice this at the VERY begining of the movie Battle of Britian...turn up the sound, and it shows a hurricane doing a roll, and listen, as the fuel is forced from the carb., the engine cuts out, as it continues, the engine cuts back in, now to rich from fuel being forced into carb., and leaves a trail of black smoke...perhaps the best example or view of the merlin cutting out, then coming back to life...

bf109 Emil

 

[SoD Stitch]

Major,
The pilot does a half roll and "pulls" on the stick, his plane is upside down after the half roll, so he pulls back on the stick to push the nose down. Then as he dives he can do a slow roll back to an upright position so he will be pulling positive G when he does his pullout. He'd lose 1-4 seconds, (depending on speed ) if the 109 bunts.
from claidemore...thank you for enlightening an earlier reply as to my posting...bf109 Emil

Yes, by pulling back on the stick in the inverted position, the so-called centrifugal gravity exerts a force on the aircraft (and, hence, the engine) of ~1G, thereby imitating normal gravity.