More fuel in Hurricane? (1 Viewer)

[SaparotRob]

Notwithstanding the gph consumption figures in post #19 above, it should be appreciated that the best range performance, or air nautical miles per gallon (anmpg), for the Merlin engine was generally achieved by flying with low revs, throttle wide open and relatively high boost. Engine handling wise this was roughly achieved by reducing the revs by the constant speed propeller control, opening the throttle wide and being high enough that the achieved boost was just at the weak mixture limit. This procedure increased range due to the engine operating with minimum throttling and reducing internal losses whilst still having high overall compression. With high altitude, low temperature and TAS/IAS ratio's helped.
Individual aircraft types would have further airframe drag effects and operating weights would limit the altitude, according to the task.
Alec Harvey-Bailey in his great book "The Merlin in Perspective" (RRHT), lists the later bomber ops into Germany flying 1800rpm/7lb boost cruise for best range. The Mosquito had to hold higher rpm to avoid propeller vibration effects and had a good cruise performance carrying a 4000lb cookie to Berlin, cruising at 30,000 feet, full throttle, 2300 rpm, giving 4 lb boost and close to 360mph TAS.

Eng

Was this figured out by trial and error or by engineers from RR and Hawker? Today, an IC chip would come up with the engine management settings.

 

[Engineman]

Was this figured out by trial and error or by engineers from RR and Hawker? Today, an IC chip would come up with the engine management settings.

That is a good question. Generally, testing the engines against a brake dynamometer in an altitude test cell can give you accurate results for HP per pound of fuel per hour. This is possible to equate with the drag performance of a particular aeroplane and so give estimates of range etc. Also, the effects of running the engines on test at low/high revs etc with different boost can be explored to see the way the engine responds to the circumstances. Beyond that, actual trials of the aircraft would provide the real in-flight performance that was used in the aircraft performance manuals.
I think that the overall effects of lower rpm and higher boost with wide open throttle on range performance were understood from long distance flights before WW2. However, actually
using these techniques with Military aircraft in Service was a developing process. Many forms of Military operations were not compatible with getting the very best efficiency out of the engines, but some long range and long endurance flying demanded using the most efficient techniques of operation, or you ran out of fuel!

Cheers

Eng

 

[Engineman]

Was this figured out by trial and error or by engineers from RR and Hawker? Today, an IC chip would come up with the engine management settings.

Hi again,
There are also aspects of engine management such as Air/Fuel (A/F) ratio, boost and ignition timing to consider, as you allude.
Most WW2 piston engines had relatively simple, even primitive, engine management. Most carburettor systems that had automatic mixture control were basic fuel mixture control due to ambient pressure (altitude) and with an extra richening jet for variation in boost, some still had manual selection of Rich or Weak bias. Ignition timing usually followed a pre-set advance profile that started from approximately 0 degrees at closed throttle, increasing to approx 45 degrees advance at max continuous power, then retarding to around 35 degrees advance at Emergency or T/O power. Many of the Magneto's only varied the timing of the spark by adjusting the position of the LT points, which mean't that the optimum flux spark energy would not be available in sections of the timing range. Better timing systems used adjustment of the magneto drive to vary the timing, which kept the spark strength at optimum, whatever the timing.
Available boost on gear driven superchargers was rpm dependent, so single speed supercharge was quite limited, with little boost below the maximum engine rpm. Later 2 or 3 speed supercharger ratio's increased the altitude range of performance, and boost limiters or controllers prevented overboosting. However, an engine operating in boost limiting was being throttled, which is inefficient.
So, it can be imagined that it was sometimes difficult to operate an engine efficiently in different circumstances. For instance, operating an early-ish Merlin for long range at low rpm and wide-open throttle might not have the absolute optimum ignition timing or A/F ratio. But these conflicting requirements were usually accommodated, although limitations were sometimes applied and the absolute optimum performance was not always achieved.

Eng

 

[SaparotRob]

1. Thank you for spoon feeding me this.
2. Yes, I reread these a few times. Glad I adjusted the timing on my Dodge Dart way back when. That helped.
3. Were there detrimental effects to the plugs, pistons or carbon (?) build up in the exhaust?

 

[Engineman]

1. Thank you for spoon feeding me this.
2. Yes, I reread these a few times. Glad I adjusted the timing on my Dodge Dart way back when. That helped.
3. Were there detrimental effects to the plugs, pistons or carbon (?) build up in the exhaust?

Very generally, the high-Octane fuels got greater and greater amounts of Tetra-Ethyl Lead in them and the sparkplugs were developed to operate at very high BMEP levels. This caused problems with low power operation, where the plugs ran cooler than their self-cleaning temperature and Lead deposits built up. This was cured by periodic opening-up of the engines to burn off the deposits.
Rolls-Royce found that the low rpm/high-ish boost operation could cause piston ring gumming, so they changed to heavier piston-rings to combat this.
More modern technology has seen very big developments in wide-range spark plugs and very clean burning ashless oils and hIgh grade synthetic oils.

Eng

 

[special ed]

I filled my ex-M in Law's Buick Gran Sport with high test pump gas and adjusted the timing. Super performance and she liked. When she went home and bought regular gas, the knocks began so she had it readjusted to normal. She preferred economy to performance.

 

[Tiv]

Regarding the CoG issue, in the withdrawal from Norway it was decided to try and save the Hurricanes by flying them out to HMS Glorious and some tests were made on short landing. It was found that under fierce braking the Hurricane had a tendency to nose over so to counter this a sandbag was placed in the tail of each aircraft. Thus fitted the whole squadron was subsequently landed on Glorious with a couple having broken tail wheels. All to no effect in the end as Glorious was sunk on the way home though it did point the way to the Sea Hurricane.

 

[don4331]

Regarding the CoG issue, in the withdrawal from Norway it was decided to try and save the Hurricanes by flying them out to HMS Glorious and some tests were made on short landing. It was found that under fierce braking the Hurricane had a tendency to nose over so to counter this a sandbag was placed in the tail of each aircraft. Thus fitted the whole squadron was subsequently landed on Glorious with a couple having broken tail wheels. All to no effect in the end as Glorious was sunk on the way home though it did point the way to the Sea Hurricane.

I'm not sure jamming a sandbag between the spars of the horizontal stabilizer exactly pointed the way to the Sea Hurricane.*

The actual Sea Hurricane having an arrestor hook so it could use the wires to stop - versus jamming on the brakes.​

​

*Having a very rear CoG combined with flying at Swordfish speeds from Norway to Glorious was supposedly extremely tiring on the RAF pilots.

The Swordfish being necessary for the Hurricane pilot to be able to find the carrier in the open sea.​

 

[Shortround6]

Well, when they got 10 out of 10 onto the carrier without an arrestor hook with only minor damage (?) it made for an eye opening preliminary trial
Like wonder what the success rate would be with an arrestor hook?

 

[Engineman]

Unfortunately, the terrible loss of Glorious and her two light escorts with 1500 Souls, is an awful and probably avoidable saga in the history of British Naval Operations.
The truth remains obfuscated, despite UK Parliamentary debate as recently as 1999.

Eng

 

[RCAFson]

Based on discussions like this, just wondering if there is any practical way to fit more than 97 imperial gallons of fuel in the Hurricane while remaining a useful fighter? Just on gross size - bigger and thicker wings than Mustang (224 imperial gallons or about 150 without rear tank?) - seems like it should be possible, particularly once you get stressed-skin wings?

Particularly wondering if the radiator was moved/deleted (Hercules!) could a tank be fitted under the pilot, or does the steel tube construction take up too much space? The wheels get in the way too. https://ww2aircraft.net/forum/attachments/1730592675350-png.804041/

Or is there a reason not to have a bigger tank in front of the pilot? Spitfire seemed to fit a lot more in there.

Cutaways:
Hawker-Hurricane-cutaway | HistoryNet
https://conceptbunny.com/wp-content/uploads/2019/04/hawker-hurricane.gif

The Hurricane IIB had 12 x .303BMGs and this was achieved by fitting two more .303BMGs outboard in each wing. It seems likely that these extra gun bays could have been converted to wing tanks instead with a capacity of 10-15IG per wing.