Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Randy1 on November 06, 2015, 12:10:52 PM
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I was just wondering what engine characteristics would make one engine type more suitable than another when designing a WW 2 plane?
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Drag, weight, power, reliability, and availability.
Navy liked radials for flying over water.
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ki61 and ki100 are close to same plane with the difference that ki100 had radial engine vs ki61's inline.
It won quite some in weight and power, but lost some due to higher drag.
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Radiator.. coolant.. holes
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Inline: Pro: Low-drag, low-weight, fuel efficient. Con: Susceptible to damage, liquid cooling, technically complex.
Radial: Pro: Power, reliable, simple to maintain. Con: Draggy, gas guzzler, obstructs forward view.
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I was just wondering what engine characteristics would make one engine type more suitable than another when designing a WW 2 plane?
:airplane: I think the Navy preferred radials to V or in line engines for one reason: Acceleration! Its no secret that horse power for horse power, the radial will out climb the others, and short field performance is much better with a radial than a in line or V engine! You have to remember that during the WW2, there were no "steam" catapults and the radials had the power and acceleration to operate off of short fields, i.e. aircraft carriers!
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"Its no secret that horse power for horse power, the radial will out climb the others"
How does that work? :O
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Really, radials are heavier than inlines? And radials obstruct the view more? But landing seafires they would approach landing in a curve. Gas guzzlers?
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Ta-152 has an inline engine and I believe it hit the highest altitude of the war.
Edit: Earl is talking about climb rate?
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The main reason for the US Navy preferring radials over inline had to do with the drawbacks of liquid cooling - easy to critically damage, thus less likely to return to the ship. Another consideration was having to store coolant aboard the ship - less space for other supplies.
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A Radial engine was actually lighter than its Inline counter-parts. see Ki-100 vs Ki-61 and 190A vs 190D.
American planes just had over sized Radials for the most part.
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So I get to be the first to resort to Wikipedia - which, in this case, makes as much sense as anything else. I hadn't thought about their last point (that people stopped using inline engines by the end of WWII), but I think it's true.
Comparison with inline engines
Pros
Weight: Air-cooled radial engines often weigh less than equivalent liquid-cooled inline engines.
Damage tolerance: Liquid cooling systems are generally more vulnerable to battle damage. Minor shrapnel damage easily results in a loss of coolant and consequent engine seizure, while an air-cooled radial might be largely unaffected by minor damage.
Simplicity: Radials have shorter and stiffer crankshafts, a single bank radial needing only two crankshaft bearings as opposed to the seven required for a liquid-cooled six-cylinder inline engine of similar stiffness.
Reliability:The shorter crankshaft also produces less vibration and hence higher reliability through reduced wear and fatigue.
Smooth running: It is typically easier to achieve smooth running with a radial engine.
Cons
Cooling: While a single bank radial permits all cylinders to be cooled equally, the same is not true for multi-row engines where the rear cylinders can be affected by the heat coming off the front row, and air flow being masked.
Drag: Having the cylinders exposed to the airflow increases drag considerably. The answer was the addition of specially designed cowlings with baffles to force the air between the cylinders. The first effective drag reducing cowling that didn't impair engine cooling was the British Townend ring or "drag ring" which formed a narrow band around the engine covering the cylinder heads, reducing drag. The National Advisory Committee for Aeronautics studied the problem, developing the NACA cowling which further reduced drag and improved cooling. Nearly all aircraft radial engines since have used NACA-type cowlings. Because radial engines are often wider than similar inlines or vees, it is more difficult to design an aircraft to minimize cross sectional area, a major cause of drag, although by the beginning of the Second World War, this disadvantage had largely disappeared as aircraft sizes increased, and multi-row radials increased the power produced in relation to the cross sectional area.
Power: Because each cylinder on a radial engine has its own head, it is impractical to use a multivalve valvetrain on a radial engine. Therefore, almost all radial engines use a two valve pushrod-type valvetrain which may result in less power for a given displacement than multi-valve inline engines. The limitations of the poppet valve were largely overcome by the development of the sleeve valve, but at the cost of increased complexity, maintenance costs and reduced reliability.
Visibility: Pilot visibility may be poorer due to the width of the engine on single-engine aircraft, although tight fitting cowlings helped reduce this factor somewhat. Equivalent inline engines often resulted in overly long noses, which similarly impaired visibility directly forward.
Installation: It is more difficult to ensure adequate cooling air in a buried engine installation or with pusher configurations.
Size: The smallest classes of radial engines, with three and five cylinders are very rough running and unreliable when compared to equivalent four cylinder inline or horizontally opposed engines which later became more popular for light aircraft as a result.
While inline liquid-cooled engines continued to be common in new designs until late in World War II, radial engines dominated afterwards until overtaken by jet engines, with the late-war Hawker Sea Fury and Grumman Bearcat, two of the fastest production piston-engined aircraft ever built, using radial engines.
https://en.wikipedia.org/wiki/Radial_engine
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The points made by Waffen and Oldman cover most of it.
On the durability issue, the Navy preferred radials as they could be flown having lost several cylinders. While the lost cylinders would lose some oil, the remaining cylinders would continue to operate normally allowing pilots to safely return to their carriers over the extended ranges required.
On a side note, the FW 190 was originally designed for in-line engine use but, due to supply's being dedicated to the Bf 109, was converted to radials. To overcome the inefficiencies of associated drag Kurt Tank designed the curved cowl, wrapping over and in front of the "top" portion of the engine while still allowing sufficient cooling. The resulting aerodynamics (speed) combined with the durability of the radial engine allowed the 190 to become Germany's primary bomber interceptor.
Another advantage of the radial was simplicity of design/maintenance.
One last point I seen haven't seen mentioned is gun placement, particularly in V engine designs which, due to engine design, allowed for cowl and center hub gun placements. These aerodynamic and gun placement advantages were exemplified in the 109 series of aircraft.
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A Radial engine was actually lighter than its Inline counter-parts. see Ki-100 vs Ki-61 and 190A vs 190D.
American planes just had over sized Radials for the most part.
The Ha40 engine of the Ki-61 weighs 1,320 lb vs the Ki-100 Kinsei Ha112 engine's 1,202 lb. The Ha40 engine was a Japanese version of the DB 601 engine used in the 109E, so it was getting very long in the tooth by 1945. The power to weight advantage goes to the Ki-100's Ha112 because it is a more developed engine. Against a contemporary 1945 inline engine the Ha114 would have lost, as your other example illustrates: The 190D's Jumo 213 weighs in at 2,072 lb vs the 190A's BMW 801D-2's 2,226 lb. The Jumo delivers 2,022 hp vs the BMW's 1,677 hp. So not only does the inline Jumo engine weigh less it produces more power as well for a much better power to weight ratio. The added weight of the 190D over the 190A is mostly structural since the longer engine shifted the CG forward requiring a lengthening of the rear fuselage to balance it out.
My point about weight and power with regard to radial engines is that they are much easier to scale up into the 3,000-4000 hp range than a complicated inline engine. Big inline engines like the 24 cylinder Napier Sabre that powered the Typhoon and Tempest were plagued by reliability problems. Sure the radial will be heavy, draggy and use more gas, but it will work.
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I mean look at it. Imagine having to work on this beast!
(http://www.passion-aviation.qc.ca/images/moteurs/sabre2.jpg)
If a piston cracks, assuming it doesn't wreck the whole engine you'd still have to pull the engine off the plane. God only knows how many man hours would be needed to change a cylinder lining and piston.
On a radial each cylinder is a separate unit bolted to the crankcase. You'd just pull the pot and piston, inspect the connecting rods and crank for damage and put in a new piston and pot. The work can be done with the engine still on the plane.
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Ta-152 has an inline engine and I believe it hit the highest altitude of the war.
Edit: Earl is talking about climb rate?
:airplane: Climb rate had nothing to do with their decision, it was all about what could accelerate from "zero" to 80 knots in the shortest distance, which is the speed at which the early fighters became airborne. Most of all the "by-winged" early fighters could fly at 60 knots and even they had radial engines. Of course, we must remember that after the carrier turned into the wind, the aircraft had anywhere from a 40 knot to 60 knot headwind, before they started their roll down the carrier.
I have often wondered what the B-17 performance would have been, with the Avro Lancaster engines installed on it! Any comments on that question?
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They tried it. I'm not sure what the performance results were though:
(http://upload.wikimedia.org/wikipedia/commons/thumb/a/a3/XB-38.jpg/800px-XB-38.jpg)
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I don't know about the performance, but that thing is just gorgeous.
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And those are turbo-supercharged Allisons I believe, not the Merlins of a Lancaster.
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Interesting replies. I greatly appreciate the information. It was one of those questions you ponder for a bit then just had to ask.
After reading all the replies I wondered if radial engines had been tried in cars. Do a Google on "radial engine cars." Some real neat images. Too many to post.
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General characteristics
Crew: 10
Length: 74 ft 0 in (22.56 m)
Wingspan: 103 ft 11 in (31.67 m)
Height: 19 ft 2 in (5.84 m)
Wing area: 1,420 ft² (131.9 m²)
Empty weight: 34,750 lb (15,762 kg)
Loaded weight: 56,000 lb (25,401 kg)
Max. takeoff weight: 64,000 lb (29,030 kg)
Powerplant: 4 × Allison V-1710-97 turbosupercharged liquid-cooled V12 engines, 1,425 hp (1,063 kW) each
Performance
Maximum speed: 327 mph (284 knots, 526 km/h)
Cruise speed: 226 mph (197 knots, 364 km/h)
Range: 3,300 mi (2,870 nmi, 5,310 km)
Service ceiling: 29,600 ft (9,020 m)
The work for this project was handed over to Lockheed’s Vega subsidiary who were already building B-17’s at the time. When the prototype flew it showed improved performance over the standard radial engines. The B-38 was 40mph an hour faster then the standard B-17.
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I love the radiator placement between the engine nacelles.
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I would have suspected a notable increase in fuselage length with the forward weight shift.
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Not on such a big bird. Could probably compensate by moving some internal equipment like oxygen bottles etc. back in the rear fuselage.
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I would have suspected a notable increase in fuselage length with the forward weight shift.
:airplane: The "moment" arm would have more than compensated for the additional weight, by placing a, for example, a 72 inch "plug" between the end of the dosal fin and the bomb bay rear bulk head! I am not sure what the length of travel of the C.G. is on the 17, Columbo could tell us I suppose, but with a plug like I describe, I doubt if it would increase the travel distance enough to make much difference in figuring weight and balance.
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In radial engine the cooling opening itself causes comparatively small drag increase to that of an inline cowling but the drag rises if a vent in opened behind the engine to vent the hot air. If you look at the early 190s they had no vents what so ever except the holes for exhaust stacks. Later on there were cooling louvers added in back of the engine mount to assist cooling the engine accessories. The fan added the forced circulation of air inside the cowling so that the needed venting remained low if you compare it to eg. that of Corsair which had ample venting for the engine.
The cylinder weight is also higher since the heat transfer to air is less efficient than transferring the heat to coolant causing the radial to have more "cooling weight" compared to inline engines.
-C+
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Regardless of cooling drag the wider fuselage required for a radial engine application increases form drag considerably.
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The work for this project was handed over to Lockheed’s Vega subsidiary who were already building B-17’s at the time. When the prototype flew it showed improved performance over the standard radial engines. The B-38 was 40mph an hour faster then the standard B-17.
The XB-38 only showed improvements in its higher speed over the B-17 but at the cost of a lower service ceiling.
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How much lower?
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How much lower?
Wiki puts the XB-38's service ceiling at 29,600 feet, and the B-17G's at 35,600 feet. The XB-38 only flew nine times, between May and June, 1943, before catching fire and crashing.
https://en.wikipedia.org/wiki/Boeing_XB-38_Flying_Fortress#Specifications_.28XB-38.29
https://en.wikipedia.org/wiki/Boeing_B-17_Flying_Fortress#Specifications_.28B-17G.29
- oldman
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Too bad they didn't just go for looks and used the inlines in the 17!
This is my first time seeing one. That thing looks fantastic.
Thanks for posting.
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If they went with inline engines for the 17's, I can only imagine how many more would not have made it home.
But I will admit, she has a nice look. :aok
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A bunch of Griffons instead of the Allisons would have done it. :D
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Regardless of cooling drag the wider fuselage required for a radial engine application increases form drag considerably.
Wider fuselage does not necessarily means increased drag. It was all about the so called cooling drag. In radiators, designers already knew how to use the heat energy that was transferred to the air to not only reduce the drag, but to end up with thrust in some conditions. Only post war radials had a significant improvement to their cooling drag.
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I am not sure what the length of travel of the C.G. is on the 17, Columbo could tell us I suppose
CG limit on the B-17G is from 20% MAC to 32% MAC (Mean Aerodynamic Chord). For the most part I never noticed much difference CG related in the B-17. When doing rides quite often all 9 pax would end up aft of the bomb bay, never noticed much trim change when flying. On the B-24 you notice on the ground because the nose would "bounce" more. Main gear are quite close to the CG, rough brake usage could get the nose bobbing up and down, aft loading just made that worse.
Probably the heaviest I flew the airplanes was the B-24 out of Naples, Fl. Full fuel, 11 SOB, baggage, fresh load of oil (2 gal cans stowed above wing)…around 56000 for takeoff on a warm, muggy Florida afternoon. I got my share of the landing fee out of the runway on takeoff. Video here (http://www.dalefalk.com/Movies/Bombers/i-QG7rfT3)
You guys are worried about the CG on the airplane with the Allisons, Boeing seems to have worked it out without any noticeable differences in the airplane. :devil
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Wider fuselage does not necessarily means increased drag.
Yes it most certainly does. Two aircraft otherwise identical the one with the wider fuselage will produce more drag.
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Yes it most certainly does. Two aircraft otherwise identical the one with the wider fuselage will produce more drag.
Not simply because the fuselage is wider. A bigger plane tends to have more drag because it has a larger wet area overall, not because its front is wider.
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The wider the fuselage the more mass of air is displaced when that fuselage moves through the air. That takes energy. Think of it like a boat moving through water and it becomes more obvious. The air needs to be pushed aside and then back again as the aircraft moves through it.
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Or think of it like this:
(http://static.sportskeeda.com/wp-content/uploads/2014/01/football-vs-soccer-ball-2069030.jpg)
Same approximate wetted area the wider shape produce more drag.
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Doesn't that depend on how you throw it?
I think one of you is arguing about shape and the other about size.
One of you is saying that given the same airplane made bigger the increase in drag that comes from the increase in frontal area is less than the increase that comes from drag due to the increase in wetted area.
The other of you is saying a blunt shaped fuselage has more drag than a pointy shaped one.
I would chime in and say that with WW2 fighters the biggest drag reduction benefit available from a liquid cooled inline engine would come from the reduction in cooling drag for the same horsepower, not from benefits in frontal area reduction or wetted surface reduction.
What I would like to know is if this is because of the state of aerodynamics/technology at the time that enabled the design of low or negative drag cooling systems for liquid cooled but was unable to produce the same for aircooled or if it is some kind of theoretical limitation having to do with the air flow requirements of air cooling, especially at higher altitudes.
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CG limit on the B-17G is from 20% MAC to 32% MAC (Mean Aerodynamic Chord). For the most part I never noticed much difference CG related in the B-17. When doing rides quite often all 9 pax would end up aft of the bomb bay, never noticed much trim change when flying. On the B-24 you notice on the ground because the nose would "bounce" more. Main gear are quite close to the CG, rough brake usage could get the nose bobbing up and down, aft loading just made that worse.
Probably the heaviest I flew the airplanes was the B-24 out of Naples, Fl. Full fuel, 11 SOB, baggage, fresh load of oil (2 gal cans stowed above wing)…around 56000 for takeoff on a warm, muggy Florida afternoon. I got my share of the landing fee out of the runway on takeoff. Video here (http://www.dalefalk.com/Movies/Bombers/i-QG7rfT3)
You guys are worried about the CG on the airplane with the Allisons, Boeing seems to have worked it out without any noticeable differences in the airplane. :devil
:airplane: Great video's!
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Premb... I'm simply saying you can't move air molecules without spending energy. That's what drag is: Moving air molecules. The wider the fuselage the more air molecules need to be moved.
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Waaaait....I thought drag was when you put on girlie things.
But seriously, I wasn't saying you were wrong just that it seemed like you two were talking past each other, (something virtually unheard of on this bbs.)
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The wider the fuselage the more mass of air is displaced when that fuselage moves through the air. That takes energy. Think of it like a boat moving through water and it becomes more obvious. The air needs to be pushed aside and then back again as the aircraft moves through it.
This is not how drag works. Common misconception, one of great many in hydrodynamics/aerodynamics.
The energy that goes into moving the air out of the way is small. In addition, if the flow is laminar on the large scales, you get this energy back. In order to lose energy, you have to leave something in the flow behind you in the form of vortices (mostly, a turbulent wake). The later is determined by small scales where the Reynolds number is low.
The effect of accelerating a bulk airflow out of the way (large frontal area) is a small resistance to acceleration, but has no effect on steady state flow, that is the drag.
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What you are saying is nonsense. We've hijacked this thread long enough and I'm not going to get into a major aerodynamics debate with you. I'll just end by pointing out that if you want something to go fast in air or water you'd better make it slender and pointy. And the less power you have the more important it becomes. There's a reason these guys aren't sitting two abreast.
(https://upload.wikimedia.org/wikipedia/commons/e/e6/DMURC_mens_8%2B_at_BUCS_Regatta_2010.png)
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This is not a hijack, we are still on topic, as everyone will easily point out that one difference between radials and inlines is the frontal crossection area. The "frontal area means drag" often comes up in such debates and I wanted to point out that frontal area has little to do (directly) with drag. Surprising maybe, but this is physics. It is the big hole in the center, the edges of the rim around this hole, and labyrinth of airflow through the engine that makes the difference - also known as "cooling drag".
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It is also relevant that a boat travels in the boundary between 2 fluids and the major limitation on a conventional hulls top speed is simply the length of the thing. The shell benefits from a long length with a low wetted surface, hence the narrowness.
From my limited reading on aerodynamics I have realized that intuition changes with experience and that what Bozon is saying is accurate. The first time I read about supersonic aerodynamics it was a real expansion of intuition.
I'd like to know what the apogee of air cooled engine cooling design was, I read that it wasn't until 1949 that things were really improved on the design side (not counting the original NACA cowl.) And if there are inherent limitations with aircooled engines such that they will always suffer greater cooling drag than you get with a radiator.
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Aerodynamics and hydrodynamics are closely related. The two biggest differences are compressibility and cavitation. A conventional boat hull suffers all the same drag penalties as an aircraft fuselage (subsonic) including boundary layer drag.
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Liquid cooled engines were able to harness the Meredith Effect and actually produce thrust. For example, the P-51 produced around 1000 pounds of thrust from it's Merlin engine. The radiator produced an additional 375 pounds of thrust. So this dramatically offset the cooling drag. While most WW2 aircraft used about 10% of their engine power for cooling, the P-51 only needed to use about 2%.
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Aerodynamics and hydrodynamics are closely related. The two biggest differences are compressibility and cavitation. A conventional boat hull suffers all the same drag penalties as an aircraft fuselage (subsonic) including boundary layer drag.
Yes, I am not disagreeing with you however a boat hull has the added complication of traveling within the boundary between two fluids, air and water; I didn't mean boundary layer drag. What is boundary layer drag? I know what a boundary layer is broadly speaking. Would this just be a more specific way of describing wetted surface drag? E.G. when the VariEze gets bugs on its canard the laminar flow is destroyed so the boundary layer drag goes up?
Anyway, I don't really think there is any disagreement here I think you are being misinterpreted as saying that the larger fuselage crossection of a radial powered airplane is a significant factor when compared to cooling drag when comparing the drag between a radial vs water cooled airplane that flew in WW2. But I don't think you mean that.
I think if there is a disagreement it would be that what Bozon is saying and I'm believing is that the increase in drag that would come with an increase in fuselage crossection would come mostly if not all from increased wetted area all along the fuselage and not so much from the increase in frontal area. This is assuming that the design of the fuselage does not create vortices that scale with an increase in dimensions.
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Scoopless mustangs will eventually be dominating reno.
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What you are saying is nonsense. We've hijacked this thread long enough and I'm not going to get into a major aerodynamics debate with you. I'll just end by pointing out that if you want something to go fast in air or water you'd better make it slender and pointy. And the less power you have the more important it becomes. There's a reason these guys aren't sitting two abreast.
(https://upload.wikimedia.org/wikipedia/commons/e/e6/DMURC_mens_8%2B_at_BUCS_Regatta_2010.png)
Waffen simply put, the shape (both front and back) is much more important then the frontal area. It is about how you divide the air and put it back the way it was with out imparting any movement (energy/drag) to the air.
HiTech
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For sure Hitech, but my point was about two otherwise identical aircraft. This discussion has spilled over into general aerodynamics with people discussing all kinds of different points.
Yes it most certainly does. Two aircraft otherwise identical the one with the wider fuselage will produce more drag.
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Waffen simply put, the shape (both front and back) is much more important then the frontal area. It is about how you divide the air and put it back the way it was with out imparting any movement (energy/drag) to the air.
HiTech
:airplane: this is a "for what it is worth" comment! I was told once by a P&W engineer that the shape of the leading edge of the cowling has a lot to do with cooling and cutting drag. When pressed, he said the shape of the "cuff" is everything when trying to reach a compromise between effective cooling and reducing drag! I don't really know, but after he told me that, I started looking at the "cuff" on different aircraft and there are a difference in them!
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You can compare the Mustang and FW190 drag in the middle of the chart. The FW has more total drag but the percentage of total drag from the power plant is lower and the actual total profile drag figure is about .5 lower for the power plant. Maybe it's a D model.
(https://www.mediafire.com/convkey/ced5/u7ugf1vhwa7gvlj6g.jpg) (https://www.mediafire.com/view/?u7ugf1vhwa7gvlj)
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MP499 was an A3 variant.
http://www.iwm.org.uk/collections/item/object/205126940
-C+
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MP499 was an A3 variant.
http://www.iwm.org.uk/collections/item/object/205126940
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Thanks. :aok
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That chart does not take into account the thrust the radiator produces to offset the drag from the P-51's power plant.