Spitfire XIVs equipped with nitrogen drop tanks

[GregP]

In tests they are good for about 2,500 - 2,800 hp. After that and it's rapidly new engine time. Reno proves that one.

Of course since the Merlin started out at some 740 HP at low altitude, that is pretty darned good for a failure limit. Saying it fails at that power level is a pretty good compliment.

It's just that after WWII, the piston fighter lifetime was pretty well written on the wall for anyone with a bit of vision. The mlitary was well aware of it and I think the last generation of pistons was a damned good one. They are STILL classics of streamlining and efficiency for the types.

I think that fact that the basic Spitfire design was still there at the end says a lot. The Bf 109 might have been, too, except for having the primary country of development lose the war and cease all military aircraft development entirely. I wonder how the Ta 152 might have panned out had it's development continued. It surely had potential. Not sure if any of the Luft 46 stuff was even remotely possible, but you never know.

Nitrous Oxide injection as a reliable system in piston engines has never made it. The failure level is way too high for aviation use. Racing use is one thing,, but service use is another animal entirely.

I have had ZERO good luck with it and have personally blown up $30,000+ in engines following the advice of "experts" in the field, none of whom took any responsibility for the events even when they installed it. One was only supposed to provide a "shot" for drag racing use, but wound up splitting the engine cases into pieces.

I've had MUCH better luck with supercharging and turbocharging than with N2O.

I consider a Nirtous system as an "engine failure desperately seeking a place to happen." I've seen as many "modern" engines with ECUs grenade as I have carubreted engines on N2O and just can't bring myself to trust it ever again. I damned for sure would never FLY behind one, but a turbo is just fine ... if the extra maintenance is done.

 

[pbehn]

In tests they are good for about 2,500 - 2,800 hp. After that and it's rapidly new engine time. Reno proves that one.

Of course since the Merlin started out at some 740 HP at low altitude, that is pretty darned good for a failure limit. Saying it fails at that power level is a pretty good compliment.

If Jet engines were not possible then 70 years of military budgets would have a merlin type engine producing much much more reliable power. Piston aero engines have gone from being devices upon which national security and thousands of lives depend to a rich mans hobby.

 

[GregP]

No doubt with redesigned rods ...

I have no doubt at all that piston engines never reached their zenith in the real world. Engines are tough to design well and tough to make serious improvements upon, but most of the good engines of WWII more than doubled their original outputs after development.

That says a lot for the engineers and the potential of some designs ... and for 150-Grade fuels.

I think from my reading that about 5,000 HP, maybe 6,000 HP, would have been the max without seriously declining returns. The engines would have been large, heavy, and enormously complex ... and would have required some serious maintenance procedures. For fighters, I'm thinking something about the size of a slightly larger P-72, P-75, or Skyradier might be the max without running into scale and weight issues on the power available. No doubt they would have been formidable against similar planes fielded by the competition.

Though I'll snatch a ride in a WWII plane anytime, and have ... I am glad turbines came along when I fly the airlines.

Considering my bad experiences with N2O, it makes me wonder how the stuff might help or destroy a turbine. I have not decided whether or not today's turbine blades could handle it and wouldn't finance it even if I had the money as it's already taken enough money from me to date. If they DID try it, I'm also not sure they could carry enough to make any difference at all except in a very narrow set of circumstances, making me wonder whether it would be worth messing with it.

I suspect not, but also have no proof of same. Who knows? Might be just the ticket for some particular mission.

 

[Mike Williams]

The ratings for GM-1 use on a Ta 152 were 20 minutes at a time presumably a full flow rate. There was 40 minutes total of the stuff.

Do you have any idea of the weight of the complete installation on a Ta 152? For Mosquitoes, the production installation weighed 475 lb. complete with 180 lb. of nitrous. As noted previously the test installation in a Spitfire V weighed 92 lbs. containing 15 lbs. of nitrous oxide.

Some background information on nitrous oxide from a Royal Aircraft Establishment (RAE) Report might be of interest:

 

[Koopernic]

I may be a little hazy as I am commissioning on a mine site but I think that information came from the war prizes book on its performance specifications in terms of length of use. There was some information in Rudiger Kosins book, "the German Fighter" on how it was used ie flow rates. It certainly wasn't for very short bursts. GM-1 was mainly for use above full throttle height. GM1 worked well with MW50 which the Ta 152 could use since it had separate tanks for each liquid.

Kosin argue that when the loss of jet thrust with a turbo supercharger was considered, the increased propeller size and gearbox needed to exploit the turbo was considered that nitrous oxide was a better (lighter) solution for a fighter. I think turbos may have extra intercooling requirements and drag.

Galland didn't like it because a high proportion could evaporate when fighters were on standby on a summers day. Probably could've been solved with a dewar style vacuum container.

Do you have any idea of the weight of the complete installation on a Ta 152? For Mosquitoes, the production installation weighed 475 lb. complete with 180 lb. of nitrous. As noted previously the test installation in a Spitfire V weighed 92 lbs. containing 15 lbs. of nitrous oxide.

Interesting to note that 160lbs of Nitrous is the equal in weight of about 100L of gasoline or about 24Imp gallons. A spitfire or P-51 tail tank would accept this kind of change of Centre of Gravity without much handling issues noticeable. The weight of the installation would simply be corrected by adding nose counterweights or more likely removing tail counterweights.

I suspect the Ta 152H tank was much larger than 160lbs.

 

[kool kitty89]

On the British end of things, it seems like nitrous systems would have been most useful if they'd been ready for deployment prior to the 2-stage merlins entering mass production. With the high-alt rated 2-stage merlin models, the effort seems to make less sense. I suppose it might be useful on Hercules powered aircraft as well.

That's short of extremely high altitude performance that never ended up materializing during WWII ... and as a partial alternative to turbochargers.

 

[GregP]

If you get N2O injection right, it seems reliable enough. A 15 pound bottle in a car with an LS-1 V-8 will give you shots for about 10 - 15 trips down the drag strip. That's with 346 cubic inches displacement at 6,500 rpm.

For a Merlin at 3,000 rpm and 1,649 cubic inches of displacement, you'd need to carry quite a load for 20 minutes and N2O is almost always used only at full throttle, but at least that is worthwhile time. 1 minute might let you escape once from something and that's about all. It might make you THINK you could escape, but not really.

If I could choose, I like the 2O minutes at least an order of magnitude more than the 1 minute. I am making the assumption that if the military installed it as standard equipment, it wouldn't blow the engine right away. That being the case, emergency power is nice every great once in awhile during an extreme emergency. If you get used to using it, you WILL have engine issues sooner or later, military stock or not. N2O is not "engine friendly" by any stretch of the imagination and I would seriously hate to take a bullet in the N2O tank! In fact, if the tank wasn't located some distance from the cockpit, I might not let them fill it at all. If it DOES blow up, you need at least a chance to escape.

 

[kool kitty89]

There's still the difference of context here as well. Unless you're using nitrous oxide to boost auto-engine performance at rather high altitudes and not go much/at all beyond similar performance obtained with the same vehicle at sea level, it's not the same context as the military engines. (granted you're also talking aircraft engines that were all already using superchargers too)

 

[Mike Williams]

As an aside, Liquid Oxygen installations were fitted to a number of Spitfires, including Spitfires II, V, VI and VII. At least one Spitfire VI (Merlin 47) was fitted with an LOX system which served with the High Altitude Flight at Northolt and then 124 Squadron. A couple of Spitfire VIIs were also equipped with LOX. Weight of the complete system on the VII, including LOX, was 130 lb.

 

[parsifal]

Mods, anyone - Does this board have an ignore member capability? I can't seem to find it anywhere here. Thanks.

Click on the members active link. that's his name with the line under it. that will take you to his profile, and from there you can do stuff....add him as a friend, add him to your ignore list and other stuff as well

 

[GregP]

It is exactly the same as in a car with the only difference being jetting for altitude.

You use N2O to boost the power level at full throttle only. Jetting it correctly at partial power is hardly ever done, not because it can't be done, but because it is waste. If you USE it at partial power, you are using it unnecessarily. Just move the throttle forward and you get the same effect wihtout using the Nitrous, right up until full power. At that point, it makes sense to use N2O if you want a 15 - 35%+ power shot for some period of time and if the engine components can handle the extra power without breaking.

I have already said in here that Merlin rods were good for 2500 - 2800 HP only, so using Nitrous for more than that might be reserved for setting world records or racing only. If you had a Merlin that made 1700 - 2200 HP. you could use Nitrous to get to 2500 HP. More than that and you are betting the farm against the livestock that you will make it home with a running engine.

You might do it for a record or a race or good publicity, but you certainly wouldn't install such a system (more than 2500 HP from a Merlin) in a service aircraft and expect people not to try it out. I'd install it ... assuming correct system ... in a wartime service plane, but NOT in a peacetime service plane. In peacetime, I'd disable the boost system or prevent it from being filled by removing the tank and capping the lines.

 

[Mike Williams]

Thanks parsifal, I have it sorted out now

 

[Koopernic]

My expectation is this:

The RAF was experimenting with Nitrous Oxide on the Mk XIV Spitfire. The note Mike William's posted indicate that there was interest in using NOX not only above the aircrafts full throttle height but at low altitude. The problem being that improvements above 150PN fuel were unlikely and that seemingly the Griffon could take a much higher PN fuel. NOX was seen as a way of increasing the knock rating of the mixture.

In Luftwaffe usage GM-1 (Goering Mixture 1, cryogenic nitrous oxide) was used above the engines full throttle height (where the engine could take the full unthrottled throttled force of the supercharger) whereas MW50 (water methanol) injection was applied below the engines full throttle height. Late war Me 109K4, Fw 190A9, Fw 190D9 had a tail tank of around 115-130 litres that was to carry either extra fuel (either B4 or C3), GM-1 or MW50 depending on mission and availability. Only production/delivery issues prevented the delivery of the plumbing though two Fw 190D9 were flown, in service, with GM-1 in the tanks.

There is nothing to prevent us from using nitrous oxide at low altitude so long as the same power limits are observed to prevent bearing damage and to not exceed thermal limits as were imposed on use of MW50 (ADI injection in allied terminology). It was just more convenient and cheaper to use MW50 for low altitude and GM-1/Nitrous for high altitude. The DB605DB/DC went from about 1450hp on B4 to 1800hp on B4+MW50. So long as the nitrous was used judiciously and max power kept below the 1800hp certified for MW50 the engine should be fine. I rather suspect nitrous was kinder and less corrosive and as the RAF papers noted it relieved the supercharger of having to supply the power for over boosting.

I do not see it a problem to apply Nitrous Oxide to the Spitfire XIV. There was a tail tank after the pilots seat I believe it was 44 gallons and that it was considered only suitable for ferrying as it upset the centre of gravity too much for good handing. 44 gallons of fuel weights about 130kg or 285 pounds. That's more than the 160lbs night fighter Mosquito were using. I'm sure that the Mk XIV would have coped with less than half that amount of nitrous, say 140lbs with little effect on handling. The Night fighter mosquitos were getting results from only 160lbs.

The Griffon clearly still had reserve and as was noted Nitrous Oxide could be used to relieve the power draw on the supercharger substantially and prevent pre ignition.

The RAF had the problem of potentially having to deal with flying bombs at low altitude and to get an intercept on say an Ar 234 reconnaissance jet. In such a situation the nitrous could both dramatically increase climb rate (and burning of any handling issues during medium altitude and speed.)

The Ta 152H had both M50 and Nitrous and could use them concurrently. Obviously since the RAF had a 150PN fuel they could more easily avoid water injection. They probably desired 160PN fuel but that was unlikely to be made available in quantity.

Below is the 2015 Volkswaggon Tiguan people mover used by moms to drop of children at school and go shopping at supermarkets. It's 1.4L TSi engine has a specific output of 100hp/Litre on 95 (or less) RON with lean mixture thus handsomely exceeding the performance of the Merlin or Griffon. That's equal to the Merlin producing 2600hp on 95 octane.

 

[kool kitty89]

You use N2O to boost the power level at full throttle only. Jetting it correctly at partial power is hardly ever done, not because it can't be done, but because it is waste. If you USE it at partial power, you are using it unnecessarily. Just move the throttle forward and you get the same effect wihtout using the Nitrous, right up until full power. At that point, it makes sense to use N2O if you want a 15 - 35%+ power shot for some period of time and if the engine components can handle the extra power without breaking.

I have already said in here that Merlin rods were good for 2500 - 2800 HP only, so using Nitrous for more than that might be reserved for setting world records or racing only. If you had a Merlin that made 1700 - 2200 HP. you could use Nitrous to get to 2500 HP. More than that and you are betting the farm against the livestock that you will make it home with a running engine.

The difference here is most cases wouldn't be boosting power BEYOND existing military or emergency power ratings (or max continuous for boosted cruise sorts of scenarios) but to allow those ratings to be achieved well above their normal full throttle heights.

We're not talking 2500 hp on a merlin ... but say maybe 1700 hp at an altitude it would normally be struggling to produce 1200, or back with the single-stage merlins, say more around 1500 hp at an altitude it was making less than 1000 hp. (same could hypothetically be said for nearly any other engine that lacked high power at altitude, but most useful for engines with relatively limited altitude performance and/or when turbocharging wasn't available ... superchargers lacking good intercooling would be a big issue as well -N2O injection would cool the charge to some extent rather than heating it as added supercharger compression would do)

For that matter, developing nitrous boosting systems for single stage allison engines might have been useful too. (practically speaking, if no added funding was provided, that likely would have delayed other developments though ... had the USAAC considered 'turbochargers for high alt bombers and heavy fighters, low/medium altitude superchargers for patrol/CAS aircraft, and nitrous -or perhaps LOX- boosting for small high alt fighters/interceptors' the overall doctrine might have made more sense)

A nitrous injection system (particularly one only sufficient for typical military or emergency power duration) should be much easier to fit into small single engine fighters of the period than turbochargers and intercoolers and possibly even useful for some larger aircraft. (still probably mostly for fighters, possibly some dedicated recon aircraft)

In terms of battle damage vulnerability, you'd tend to have similar concerns as with the pilot/crew oxygen system but on a larger scale of vulnerable area.

There is nothing to prevent us from using nitrous oxide at low altitude so long as the same power limits are observed to prevent bearing damage and to not exceed thermal limits as were imposed on use of MW50 (ADI injection in allied terminology). It was just more convenient and cheaper to use MW50 for low altitude and GM-1/Nitrous for high altitude. The DB605DB/DC went from about 1450hp on B4 to 1800hp on B4+MW50. So long as the nitrous was used judiciously and max power kept below the 1800hp certified for MW50 the engine should be fine. I rather suspect nitrous was kinder and less corrosive and as the RAF papers noted it relieved the supercharger of having to supply the power for over boosting.

Indeed, you'd have the same structural considerations of net power consumption (including that used to drive the supercharger) as with any engine ... applying too much N2O or LOX would be much like overboosting with a turbocharger and intercooler sufficient to keep the charge cool. Using nitrous boost at lower altitudes in low-gear is an interesting idea too, obviously also useful for single-speed supercarged engines limited to low altitudes in general, but still useful on multi-speed engines given the lesser power consumed by the supercharger (and less heat introduced into the charge).

I wonder if nitrous oxide injection systems might have some advantages over water injection systems in terms of serviceability. I understand the differences between the two and the different performance envelopes they operate in, but I meant more the trade-offs between containment/storage of the N2O along with injection jet regulation compared to concerns over corrosion from introducing water (and methanol) into the fuel system and cylinders of an engine. (particularly in terms of the feasibility of it already being in use at/near the start of WWII had interest in developments been heavier pre-war -like the USAAC focusing on that for altitude boosted installations where turbos were less practical)

N2O also seems much safer and easier to contain and transport than LOX and less dangerous in the case of leak or rupture (in terms of cryogenic temperature extremes, containment pressure, and accelerant/oxidizer properties)

 

[Shortround6]

Below is the 2015 Volkswaggon Tiguan people mover used by moms to drop of children at school and go shopping at supermarkets. It's 1.4L TSi engine has a specific output of 100hp/Litre on 95 (or less) RON with lean mixture thus handsomely exceeding the performance of the Merlin or Griffon. That's equal to the Merlin producing 2600hp on 95 octane.

I wonder how much power it makes at 3000rpm?

 

[pbehn]

I wonder how much power it makes at 3000rpm?

I have made the same point a few times here. My Audi is a 3.0 Litre diesel which produces 256 BHP and although a bit sporty is nowhere near being highly tuned 0-60 is 5.9S max speed is restricted to 155MPH but it stil returns 40-45 MPG in almost all situations, servicing is once per year and engine problems are rare. F1 engines have in the past produced 1000BHP from 1.5L engines. No one would fly an aircraft with those engines without an ejector seat or parachute system but it gives an idea of what is possible.

 

[GregP]

About the Tiguan's engine above, they didn't have ECUs in WWII; they had carburetors. They didn't have mass airflow sensors either. The mixture could vary inside the intake manifolds so some cylinders were lean and others were rich. The Allison V-1710 had to address that issue, among other things.

Getting 100 HP/liter withotu computers helping was a good way to toast your cuarbureted, old-style powerplant. They blew up many engines getting things right. I'm not saying they could not get 100 HP/liter ... I'm saying it was much harder before computers came along to keep watch on things and make adjustments as the engine runs.

 

[Milosh]

The Germans with their MW50 and GM1 systems seemed to have been able to make it work.

 

[GregP]

Most WWII engine got that level of power eventually, but they didn't strat there. The ALlison, Merlin, DB, Hiso-Suiza and a LOT of others started at less than 1,000 HP nefore they started developing the engines. It certainly wasn't impossible, but computers really amde things a LOT easier when you can sense the air-fuel atio and adjust it it real time.

The engine guys back then were pretty good, but it took a lot of effort to get there while being reliable and long-lived at the same time. If you look at the length of time it took to go from the firste ngines to the best service variants, you might find out the level of effort to get tehre during wartime with money and priority took a lot of man-hours before it was just right.

 

[fastmongrel]

You take the VW Tiguan above 10,000ft and it would struggle to pull the skin off a Rice Pudding. In fact the ECU would probably go into limp mode or even shut the engine down completely.