SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
How many furlongs to the hogshead does your car get?
Escort Fighter Performance Comparison
- Thread starter Zipper730
- Start date
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special ed
2nd Lieutenant
- 5,708
- May 13, 2018
I don't have a car. However if I had half of a horse would I have 1/2 horse power?
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
What if it's a quarter horse?
GregP
Major
Up north here, because to the massive temperature difference between the cold of winter and the heat of summer, the pumps have temperature compensation built in, so no real advantage on when you fuel.
Yes, there is. If you fuel in the morning and fill to the brim, you'll weep fuel out of the vent as it warms up. Not much, but some.
Aviation gasoline has a volume correction factor of 1.0000 at 15°C. At -20°C, it is 1.0450. At 30°C, it is 0.9803.
Let's say you fill up at 15°C and your fuel load in the Cessna is 30 gallons, and late afternoon is 30°C. Then you would lose .0197 * 30 gallons, or you would vent out 0.591 gallons. Granted, .6 gallons isn't much, but if you burn 12 gallons per hour, you vented out 3 minutes of fuel. Not much, to be sure, but worth thinking about over time, particularly if your airplane has a more fuel than 30 gallons. If your plane holds 100 gallons and you burn 25 gallons per hour at cruise, you will vent almost 5 minutes of fuel overboard if you plane just sits on the ramp as temperature rises and you are full to the brim in early morning.
If you do that 30 days out of the year, you vented out 2.4 hours of fuel for no reason other than to be full in the early morning. It likely won't make or break your budget, but that's why flying club aircraft are almost always fueled to about 3/4 full only. You can bet the airlines know all about it since they burn huge amount of fuel. They would have no problem filling up if the plane is going to fly soon but, if it going to sit for a couple of hours, they'll fuel accordingly. They also fuel by weight (pounds or kilograms of Jet-A), not by volume, and they fuel according to the route to be flown and the availability of fuel at various stops along the way.
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Howard Gibson
Senior Airman
don4331
Senior Airman
I think (hope) this is a slightly more descriptive picture than W wuzak 's . The Low speed shafts at the e.g. "6 O'clock" position with High speed shafts are at "3 and 9 O'clock, but in a cutaway, the shafts are rotated for better visibility - low speed at bottom, high speed at top.
Farman's patent is for the multi clutch, separate shaft drive - very similar to Volkswagen's DSG transmission.
By releasing the slow speed clutch while applying the high speed one, Farman is able to accelerate the supercharger impeller to faster speed in a controlled manner.
Rolls Royce tried using an over running freewheel (think bicycle rear hub) in Kestrel to allow faster high ratio (it added less length to engine), but impeller running at 20k rpms, caused heat related issues in the freewheel.
The low speed has a single shaft as the load is less. The high speed has two shafts as the load is higher and RR wanted to better balance the load on the impeller shaft. They also expected the engine to spend more time at altitude, in high speed. Class 8 trucks, e.g. Kenworth's, transmission also had dual counter shafts to allow acceleration of 80k lbs without needing an overly larger transmission.
It also allows you to understand why early Griffon Seafire's had issues with the supercharger slipping during takeoff - the single shaft for low speed was designed to hold the load of the crankshaft impeller at constant speed, not that of crankshaft suddenly being accelerated for take off, while impeller needs a moment to catch up.
During normal flight: Crankshaft and Impeller would not be running the same speed - crankshaft would be running a constant 2,700rpm, while impeller would be a constant 15,750rpm in low range (Assuming Griffon 65, 5.84:1 step up gears). At take off, the engine is accelerating from say 1,000 rpms to 2,700 requires the impeller to accelerate from 5,840 to 15,750 (almost 10k rpm increase) with the boost control is fighting the impeller to avoid over boosting. Something had to give.
For the Griffon 101, with 3 speeds, you have a single shaft in "6 O'clock" for LS, another single shaft at "12 O'clock" for MS, and shafts at "3 & 9 O'clock" for FS. And the cool part is - you can do it all in the thickness of a couple gears. With a little juggling of components, no addition length to engine.
The rest of
W
wuzak
post is bang on.- Thread starter
- #107
I've never been able to resolve this, but what PR variant had the 20 IG tank under the pilot?
I can't find anything on that...
Was there a typical rule of thumb for computing landing speed in those days? Postwar, generally landing speeds seemed to be around 1.15-1.2 Vs and later on, that went up to 1.3 Vs.
Correct
You seem to spend your life looking for rules of thumb. By the time the Tempest was put into service things had long since passed using rules of thumb, except maybe for a test pilots first flights, but test pilots stayed alive by not using such guidance.
- Thread starter
- #109
Reluctant Poster
Tech Sergeant
- 1,667
- Dec 6, 2006
I don't believe it was under the pilot. Spitfire Bs and Cs had a 29 gallon tank in the rear fuselage.
Reluctant Poster
Tech Sergeant
- 1,667
- Dec 6, 2006
A detailed discussion of PR Spifires was posted in this forum a few years back
The Story of the Photographic Reconnaissance Spitfire
The story of the Spitfire as a photographic reconnaissance aeroplane starts at the end of 1939, by which time operational experience with Blenheims and Lysanders used on photographic missions had shown that an aeroplane capable of flying much faster and higher was needed. A special flight...
ww2aircraft.net
- Thread starter
- #112
- Thread starter
- #113
That's not exactly right. The P-38's specs were classified as being an interceptor because of the fact that Lt. Saville and Kelsey wanted to circumvent requirements that the USAAF had placed into effect which limited the total load of guns & ammo to 500 lb. (they wanted 1000 lb. as a starting point), they felt that two engines would probably be needed to carry such an armament load with decent performance (particularly since they figured at least 1500 hp would be needed and, given they wanted inlines, and none produced that power, that kind of made it a necessity), and pursuit aircraft were restricted to 2 engines (unless they had multiple crew like the YFM-1).
Since Lieutenants cannot override Majors, Colonels, and Generals, they sidestepped it by classifying the plane as an interceptor (a designation which might have existed in other countries, but did not appear to formally exist here), which allowed them to draw up their own specifications around a new category. With names having power, and being careful in never mentioning the term "pursuit" when referring to their design (they procured the XP-39 probably as an insurance policy in case they couldn't slip the two-engined designs passed the top-brass), they ultimately got their wish.
The aircraft was basically intended to be a fighter with high-altitude performance and heavier armament.
Ironically, due to Kelsey. He figured they were needed, but there was (at best) little interest in using them for anything other than ferry missions at best.
The USN was using them on the PV's to extend their range over water and, at the risk of his career, he put nothing in writing and managed to get everything in place. His superiors were not impressed at first, but ultimately let it go (there was a need for a photo-reconnaissance aircraft, which the USAAC lacked).
I think you made a typo there, the -7's critical altitude was lower than the -3.
- Thread starter
- #114
Regarding the Hawker Tempest, I remember some mention of problems being present with the wing-mounted radiators on the Mk.I and the Sabre IV engine having a tendency to consume excessive oil at higher RPM levels. Does anybody have anything as to why that's the case?
S Shortround6 W wuzak
S Shortround6 W wuzak
Shortround6
Major General
I may be wrong but somewhere one of the few differences between the X-608 (later P-38) and the X-609 (later P-39) proposals or requirements (and they changed over the years) was that the X-608 was supposed to haven an endurance of 2 hours as opposed to the X-609's endurance of 1 hour.
Now between 1936 and 1939 the desired speeds at both 20,000ft and sea level changed and there may have been other changes.
The 1000lbs of armament was a goal as they hadn't actually selected the gun/s and numbers yet. The 37mm was the front runner but there was a 23mm and perhaps a 25mm. Not sure if the Navy 28mm (1.1in ) was any more than a pipe dream. The 1000lb weight may include the bracing, brackets, ammo boxes etc in addition to the gun and ammo weight.
The "endurance" may have been at high speed (max cruise) rather than most economical and if so a single engine plane was going to need around 100 gallons (600lbs) more fuel for 2 hours of endurance vs one hour. An extra 600lbs of fuel (or even 500lbs) in a 5-6000lb plane (XP-39 was supposed to be well under 6000lbs when still on paper).
In some of these requirements there were minimum speeds listed, desired speeds listed, and the companies replies might give a "guarantee" which if the actual completed airplane didn't meet the company had to pay penalties. (Curtiss XP-46 failed bad enough that the government got back over $14,000.)
There was certainly a lot of room for changes and for short descriptions to leave a lot out.
But the basic difference between the X-608 and the X-609 seems to be the change in endurance since both planes were supposed to meet the same speed and climb goals the Bell 3 was supposed to carry a much heavier armament than the P-36/P-37. Perhaps the X-608 was supposed to carry more armament but by the the time the XP-39 was on paper the high armament was a given.
Bell has started with an even earlier design that this.
With the reduction gear on the engine and four (?) machine guns above the extension shaft in 1936.
Then they moved the reduction gear to just behind the prop and fitted the cannon (with that pan magazine) and finally they moved the engine even further back and put the cockpit between the guns and the engine.
Drawing says four .50cal guns or two .50cal and one 25mm.
It doesn't matter if they called it a pursuit or an interceptor, if they wanted plane that could fly at 1.75-2 hours at max continuous or close to it (and some of these 1930s specifications were rather unrealistic) you were going to have trouble with a single engine plane.
Sydney Cotton put a 20G tank under the pilots seat but the aircraft was a stripped out fighter, the 29G rear fuselage tank was in the first production PR model.
ThomasP
Senior Master Sergeant
I could be wrong, but it does not look like a 20 Impgal fuel tank would fit under the seat. The control runs would interfere?
The above photo is from the SpitfireSite.com
The above photo is from the SpitfireSite.com
- Thread starter
- #119
Zipper, Sydney Cotton fell out of favour with the RAF soon after his Cotton specials started flying, I've as yet not been able to find a drawing of the under seat or rear tank, I assume and I have no proof that the 29G tank could also be the same the Malta MkV's used, there's lots of info on the 42G lower 33G upper and 33G lower 33G upper tanks but that's it, I've also found info on the leading edge tanks that say they were 57G but most sources claim 66G, I've been meaning to find a definitive book on the PR Spit's. As for an escort Spit, easy to get to Germany once the MkVII VIII and IX Spits get into service.
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