IronJockel Posted August 22, 2016 Posted August 22, 2016 The effect of negative g on the early Merlin engines probably is one of the most discussed subjects in flight sims, yet I can’t find real data about how severe it was. All I could find so far did not let me make a final conclusion. What I would like to know is if it was possible to completely shut off the engine during a negative g maneuver and how long it took on average for it to recover and operate at desired mixture levels. According to these sources it was possible to completely shut off the engine. The early versions of the Rolls-Royce Merlin engine came equipped with a SU carburetor. When these aero planes performed a negative G force maneuver (pitching the nose hard down), fuel was forced upwards to the top of the float chamber of the carburetor rather than into the engine, leading to loss of power. If the negative G continued, the fuel would collect in the top of the float chamber, forcing the float to the floor of the chamber. This would in turn open the needle valve to maximum, flooding the carburetor with fuel and drowning the supercharger with an over-rich mixture. This would lead to a rich mixture cut-out, which would shut down the engine completely, a serious drawback in combat. [1] https://en.wikipedia.org/wiki/Miss_Shilling%27s_orifice https://youtu.be/BpTrygZfC-g?t=934 (in this clip the mechanic doesn’t use a merlin for his demonstration) [ame] [/ame] But I failed at finding actual combat reports about this happening so far. So was it only theoretical possible? This article mentions the merlin’s disadvantage but sadly no technical data on it. http://www.spitfireperformance.com/spit1vrs109e.html If anybody more information on this I would be very grateful if he could post them here. Please do not drive this into a discussion about simulations of this. All I care about is reality. [sIGPIC][/sIGPIC]
whiteladder Posted August 22, 2016 Posted August 22, 2016 I suspect you will find very few combat reports (if any) of this happening, because as it was a know problem with the engine the pilots knew they needed they had to perform a half roll before starting a dive.
WinterH Posted August 22, 2016 Posted August 22, 2016 I may be mistaken but, I have always been under the impression that this issue plauged mainly earlier Spitfire versions, and was fixed on later ones using later variants of Merlin engine. If you think about it, P-51D and later Mustangs also are powered by a (later) Merlin, and diving is one of their party tricks, not one of their weaknesses. Spit and Hurri engines cutting off at negative g seems more associated with Battle of Britain period, rather than much later Spitfire IX ED is developing. Wishlist: F-4E Block 53 +, MiG-27K, Su-17M3 or M4, AH-1F or W circa 80s or early 90s, J35 Draken, Kfir C7, Mirage III/V DCS-Dismounts Script
IronJockel Posted August 22, 2016 Author Posted August 22, 2016 But wouldn't a rookie in the heat of the moment possibly do a mistake and be forced to glide back or bail? Out of some may filed reports they should be something ... Especially when many sources claim the possibility of this to happen. I suspect you will find very few combat reports (if any) of this happening, because as it was a know problem with the engine the pilots knew they needed they had to perform a half roll before starting a dive. [sIGPIC][/sIGPIC]
IronJockel Posted August 22, 2016 Author Posted August 22, 2016 I may be mistaken but, I have always been under the impression that this issue plauged mainly earlier Spitfire versions, and was fixed on later ones using later variants of Merlin engine. If you think about it, P-51D and later Mustangs also are powered by a (later) Merlin, and diving is one of their party tricks, not one of their weaknesses. Spit and Hurri engines cutting off at negative g seems more associated with Battle of Britain period, rather than much later Spitfire IX ED is developing. You're correct, but this topic isn't about the Mustang or the Spit MkIX. [sIGPIC][/sIGPIC]
WinterH Posted August 22, 2016 Posted August 22, 2016 Ah, sorry, I've automatically assumed this being about upcoming module, without even checking what forum it is under, duh... :) Wishlist: F-4E Block 53 +, MiG-27K, Su-17M3 or M4, AH-1F or W circa 80s or early 90s, J35 Draken, Kfir C7, Mirage III/V DCS-Dismounts Script
IvanK Posted August 23, 2016 Posted August 23, 2016 The effect of negative g on the early Merlin engines probably is one of the most discussed subjects in flight sims, yet I can’t find real data about how severe it was. All I could find so far did not let me make a final conclusion. What I would like to know is if it was possible to completely shut off the engine during a negative g maneuver and how long it took on average for it to recover and operate at desired mixture levels. According to these sources it was possible to completely shut off the engine. https://en.wikipedia.org/wiki/Miss_Shilling%27s_orifice https://youtu.be/BpTrygZfC-g?t=934 (in this clip the mechanic doesn’t use a merlin for his demonstration) But I failed at finding actual combat reports about this happening so far. So was it only theoretical possible? This article mentions the merlin’s disadvantage but sadly no technical data on it. http://www.spitfireperformance.com/spit1vrs109e.html If anybody more information on this I would be very grateful if he could post them here. Please do not drive this into a discussion about simulations of this. All I care about is reality. I have specific Flight test data on this from the UK National Archives. This was used to tune the sad state it was in IL2 CLOD. Away from home but will post it here once back home.
NeilWillis Posted August 23, 2016 Posted August 23, 2016 Nice one IvanK, but it is a pity everyone has latched onto something that affected earlier models of the Spitfire, and not a factor regarding the Mk IX! IO guess we'll be having a debate about the wooden two bladed props fitted to the Mk1a next!!!
IvanK Posted August 23, 2016 Posted August 23, 2016 Here is a Snippet that I can access whilst away with my G line on the bottom. As Neil says this -Ve G cutout is however irrelevant for the Merlin's in DCS !
NeilWillis Posted August 23, 2016 Posted August 23, 2016 Any idea when the fault was rectified IvanK? I'm guessing it took quite a radical redesign of the carb float chamber, so I dare say it was well after September 1940?
Random Posted August 23, 2016 Posted August 23, 2016 Merlin 66 had a pressure injection carb that cured the issue. But it wasn't fitted on ALL subsequent variants.... So some MkIX Spitfires were OK and I think later variants were mostly OK too. But I'd have to dig a bit.
IronJockel Posted August 23, 2016 Author Posted August 23, 2016 Thanks IvanK! From this i can read that the stutter starts more or less around 0 G what is relatively gentle pitch down. Nice one IvanK, but it is a pity everyone has latched onto something that affected earlier models of the Spitfire, and not a factor regarding the Mk IX! IO guess we'll be having a debate about the wooden two bladed props fitted to the Mk1a next!!! Who is everyone? Until now 5 people have posted here. There is a whole forum section for the Mk IX and I didn't open this topic in there. [sIGPIC][/sIGPIC]
Recommended Posts