Aces High Bulletin Board
General Forums => Aces High General Discussion => Topic started by: beet1e on January 25, 2002, 03:17:08 AM
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I read this board from time to time, and notice posts concerning flight performance of various planes such as rudder drag, but this is piffling stuff compared to some glaring misrepresentations of various flight characteristics.
Am I alone in shaking my head in disbelief at the glide performance of the fighters? I was recently piloting a Spitfire 9, and attacked a B26. I escaped under the belly of the B26, but my radiator was pinged out and my engine quit shortly afterwards. (Stupid for water cooling to be used in fighter aircraft!) I have no idea about the best glide speed for the Spitfire 9, so I trimmed out at about 120-130mph. Well, just as in Warbirds, the glide performance of fighters is ridiculously overmodelled! I was able to glide all the way back to home base, which took about 10-15 minutes! I don’t recall the altitude at the start of that glide, but it wasn’t huge. Assuming still wind conditions, that’s at least 20 miles!!! I don’t have any figures for the wing loading factor of a Spitfire 9, but I do know from my RL flying days that no way could such a glide be possible in real life. In a 22 metre open class sailplane, maybe. But in a high performance plane with high wing loading and low aspect wings? No way.
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AH Spit IX? You can go too the moon and back.
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I've got it in my head that P-51 had a glide ratio of 10:1. I can't remember where I read it though. Anybody have any sources?
PS Aircraft and Vehicles forum is a better place to post this question. There are some pretty smart guys who frequent that forum but never read this one.
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Try to get to the same altitude and just switch engine off. You will glide twice shorter.
For some reason in some cases when your engine dies you can glide forever. I think it is bug?
Fariz
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Yes you really can glide forever in AH.... i dont know anything about aerodynamics and such but could this be an E-retention problem? :confused:
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Heres what I came up with for the Spit 9. I used 50% fuel, and set my airspeed to 170 on auto.. shut the engine off, reduced the prop RPM fully, and waited for it to stabilize. TAS was a little higher than 170, and the speed worked out to 249 ft/sec. The vertical speed was around -1700 fpm, which worked out to 28.333 ft/sec. L/D, which is the same as glide ratio = 249/28 = 8.89:1.
This seems pretty reasonable to me.
At 140 MPH I got closer to 10:1.
That seems pretty good, but my dad's M20E got around 13 with gear and flaps up, and even a cessna 182 can get around 11, so I don't see why a clean fighter like a Spitfire couldn't get similar glide ratios. The 182 has its gear hanging out.
Maybe what happened is that when your engines got shot out, you were going 300 MPH or something. This isn't a fair test. Get it stabilized in a descent with the autopilot on speed, and determine how fast it's moving vs how fast its falling.
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Just ran a glide test at 150 in the P-38, and got 12.8 to one. rate of descent was about 1100 fpm. This was 50% fuel. Did the P-38 have a higher L/D than the spitfire? I'd imagine so because of the higher aspect ratio wings, and the fully feathering prop. Those two things alone would make a decent difference. I wonder if anyone else already ran these tests. I seem to remember something.
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Try out the glide performance in the Typhoon or the F4U. ;) Can you say "Lead Balloon" ?
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So, why do AH planes glide so much better with a dead engine, than with the engine shut down? Or is that just my imagination?
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The props stop, no drag from props. thus u glide longer.
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Good Gliders:
Ta-152
Ki-61
La-7
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Try the P-51 at 175 IAS. The P-51 manual gives a glide of approximately 14.5 statute miles for every 5000 feet of altitude with no wind. That's a ratio of 15.3:1. From 35000 feet, you should be able to glide 100 miles(each sector is 25 miles across). I think you're more likely to find that AH planes tend to not glide well enough rather than glide too well.
(http://www.hitechcreations.com/pyro/p51glide.jpg)
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Great Info Pyro!
I will try it in other planes...
-Mitsu
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I'm waiting for Wulfe, Leph, ammo and some others to storm here calling you whinners, painting your experiences of "anecdotal" colour and asking you for videos and controled tests ;) Cmon Leph, where are your comments??
Back to the topic, in my experience, some planes glide forever while some others go down like stones (109).
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Mandoble you maroon, I never called you a whiner.
As far as this thread is concerned, some evidence is required. Saying "but this plane glides forver while mine can't!" is ludicrous. All planes are aerodynamically different. Some have very smooth lines, while others have lots of drag.
Mandoble, data is required- whether you like it or not.
-SW
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i dont understand how a p51 with a windmilling propeller has a L/D of 14.5:1. At a weight of 9000 lbs that is saying that it only has 620 lbs of drag at 175 mph. Even if you use the cd0 calculated by using top speed where ther p51 gets a big benefit because of thrust from the radiator this means that the windmilling propeller is adding less than fifty pounds of drag. Kinda hard to swallow.
As a reference a schweitzer sailplane gets a L/D of 22 and it has a massive aspect ratio, is obtaining that L/D at like 60 mph, and doesnt have to worry about propellers.
I see what the chart says buts its just kind of unbelievable.
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Originally posted by AKSWulfe
I never called you a whiner.
As far as I remember, agree with that. In any case, hope my post have not been the trigger for you to ask for some evidences here.
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I won't ask for any evidence, but if they want to get something changed- they will have to provide some evidence.
HTC just doesn't look at things because "they might be wrong", they need to know it's wrong so they can go look for it. Otherwise they waste valuable devel time on trying to find a bug that may or may not exist.
-SW
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Within reason, L:D has almost nothing to do with weight or wing loading. The best glide airspeed simply increases as you add weight internally (not counting external ordinance). Because of the increase of airspeed, and since the aircraft is traveling along the same slope, the vertical speed does increase. You could make a glider that would be absolutely useless for soaring, but that got a 50:1 L:D simply because it's best glide speed was 300 knots. If a draggy old Cessna 172 can get a 9:1 glide ratio, why then couldn't a clean, retractable, with a prop that can go to very low pitch, and laminar flow wings do somewhat better? Pyro posted the chart right from the manufacturer, and that's not good enough?
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That was supposed to be L (Colon) D, but I guess I should have written it L/D since this program knows what I want to say better than I do myself. Gotta love "artificial" intelligence...
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Originally posted by beet1e
I read this board from time to time, and notice posts concerning flight performance of various planes such as rudder drag, but this is piffling stuff compared to some glaring misrepresentations of various flight characteristics.
Am I alone in shaking my head in disbelief at the glide performance of the fighters? I was recently piloting a Spitfire 9, and attacked a B26. I escaped under the belly of the B26, but my radiator was pinged out and my engine quit shortly afterwards. (Stupid for water cooling to be used in fighter aircraft!) I have no idea about the best glide speed for the Spitfire 9, so I trimmed out at about 120-130mph. Well, just as in Warbirds, the glide performance of fighters is ridiculously overmodelled! I was able to glide all the way back to home base, which took about 10-15 minutes! I don’t recall the altitude at the start of that glide, but it wasn’t huge. Assuming still wind conditions, that’s at least 20 miles!!! I don’t have any figures for the wing loading factor of a Spitfire 9, but I do know from my RL flying days that no way could such a glide be possible in real life. In a 22 metre open class sailplane, maybe. But in a high performance plane with high wing loading and low aspect wings? No way.
Actually, what you have described doesn't sound wrong at all. If you were flying at 120mph for about 10 minutes and managed to glide 20 miles, that fits perfectly with what one might expect. For example, if your starting altitude had been 13200ft you glide ratio would have been only 8:1 and at 120mph the descent would have taken you just over 10 minutes. Now that isn't a particularly good glide ratio and is less than you would expect from a clean airframe, and could be due to prop drag. The real Spitfire would have been able to glide that far from under 8000ft, and that also falls within the 120-130mph and 10-15 minute parameters you quoted. So what you have described, actually looks ok to me.
Badboy
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Originally posted by funkedup
I've got it in my head that P-51 had a glide ratio of 10:1. I can't remember where I read it though. Anybody have any sources?
PS Aircraft and Vehicles forum is a better place to post this question. There are some pretty smart guys who frequent that forum but never read this one.
Yep, Francis Dean quotes a value of 14.92
Badboy
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Originally posted by CJ
Heres what I came up with for the Spit 9. I used 50% fuel, and set my airspeed to 170 on auto.. shut the engine off, reduced the prop RPM fully, and waited for it to stabilize. TAS was a little higher than 170, and the speed worked out to 249 ft/sec. The vertical speed was around -1700 fpm, which worked out to 28.333 ft/sec. L/D, which is the same as glide ratio = 249/28 = 8.89:1.
This seems pretty reasonable to me.
At 140 MPH I got closer to 10:1.
Turns out that the maximum L/D for the Aces High Spitfire occurs at 140mph so that 10:1 ratio is the best you will get under those conditions. In order to improve that to the figure you would expect the airframe to be capable of, you need to fully feather the prop, which isn't possible, but it may be that a fully feathered situation is being modelled when the engine is damaged and the prop is unable to rotate.
Badboy
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Originally posted by Zigrat
i dont understand how a p51 with a windmilling propeller has a L/D of 14.5:1. At a weight of 9000 lbs that is saying that it only has 620 lbs of drag at 175 mph. Even if you use the cd0 calculated by using top speed where ther p51 gets a big benefit because of thrust from the radiator this means that the windmilling propeller is adding less than fifty pounds of drag. Kinda hard to swallow.
As a reference a schweitzer sailplane gets a L/D of 22 and it has a massive aspect ratio, is obtaining that L/D at like 60 mph, and doesnt have to worry about propellers.
I see what the chart says buts its just kind of unbelievable.
Read it and weep. The P-51 may have had too high a wing loading to turn with a Spitfire, but aerodynamically, it is one of the most efficient aircraft of the war. It has one of the lowest drag coefficients, partly due to clean lines, but largely due to its wing cross section's advanced laminar flow shape. The fact is that even though it weighed 10,000 lbs loaded compared to the Spitfire's 7,0000 lbs, it was still faster despite having basically the same engine. Since power was essentially the same, that performance could only come from much lower drag.
One other thing to consider is how much of the P-51's weight came from fuel. The glide chart doesn't specify the fuel load. Perhaps it is assuming all fuel has been dumped? Or perhaps the usual 1/2 full = combat weight?
The P-51 might not have been the best all-round fighter, but neither the Spitfire nor the Bf109G10 could do what it did: fly from Britain to Germany and back at incredible speeds with fuel to spare. The United States has not ever really built lightweight point-defense aircraft unless you count the F-16. The best defense is not a short-ranged, tight-turning dogfighter; nor is it a short-ranged, rapid climbing interceptor.
"The best defense is a good offense"- Mel, the cook on the TV show Alice :D
I am proud to say, the F-15 represents this same strategy. It will never turn with the MiG-29 or Su-27, but it doesn't need to.
Back to the topic of glide slope: The F-16 has a pretty decent glide slope for its wing-loading/aspect ratio. I can't remember the numbers, but I think it is better than 8 : 1 at 170 kts. Back in the 1980s when F-16s used to be based here in Tampa at MacDill AFB, every time one would make a dead stick landing it would make the local news including data on its glide performance.
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Originally posted by Zigrat
i dont understand how a p51 with a windmilling propeller has a L/D of 14.5:1. At a weight of 9000 lbs that is saying that it only has 620 lbs of drag at 175 mph. Even if you use the cd0 calculated by using top speed where ther p51 gets a big benefit because of thrust from the radiator this means that the windmilling propeller is adding less than fifty pounds of drag. Kinda hard to swallow.
As a reference a schweitzer sailplane gets a L/D of 22 and it has a massive aspect ratio, is obtaining that L/D at like 60 mph, and doesnt have to worry about propellers.
I see what the chart says buts its just kind of unbelievable.
The L/D ratio of 14.5 does not include the prop. In Aces High the P-51 has a L/D closer to 14 at 174mph with 50% fuel, but with the prop windmilling it can't do that.
Badboy
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Thanks for all the feedback, guys. I've done some of my own tests, and I think I piped up too soon. I think CJ hit the nail on the head - I was probably at 300mph when I got hit, and gently slowed down to about 130mph. That would have been a good glide.
The planes still FEEL that they're gliding ever so well. Thanks, Pyro, for that P51 glide data.
In my RL flying days, would you believe I once flew and owned a share in a German 109? Yep, that's absolutely true. It was a Grob 109a motor glider :D I think its wingspan was 15m (54 feet) and THAT thing really could glide for miles. hehe - I used to restart the engine by "bumpstarting" it in the air - unfeather the prop and then accelerate to 95mph (remember to turn on ignition ). The absolute hardest thing for me when converting to Power planes (Cherokee 140) was getting used to the fact that they wont glide very well. I remember during one lesson, my instructor cut the engine and said "pick your field". And I said "oooh, let's see now - how about that one over there?" (about 5 miles away). And he yelled "we'd never get there! it's a Cherokee, not a glider. Your choice of fields is that one, that one or this one" - pointing to various fields almost directly below. And sure enough, we really were coming down like a brick. The later Cherokee Warriors had a bigger wingspan, and an improved wing design. Those old slab wings were OK when fuel was cheap...
While we're on the subject, I attach a pic of my first EVER field capture in Warbirds - in the days when you simply had to land at a closed field. I had been shot and my engine was dead. I was flying a ki84. Rather than bail, I thought I would glide to safety. I must have covered 20 miles! And I saw a field but it was an enemy field. I didn't know it was closed so I landed anyway - got the capture! See how many names you recognise.
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doh! - screwed up prev. post - here is pic
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Originally posted by streakeagle
Back to the topic of glide slope: The F-16 has a pretty decent glide slope for its wing-loading/aspect ratio. I can't remember the numbers, but I think it is better than 8 : 1 at 170 kts. Back in the 1980s when F-16s used to be based here in Tampa at MacDill AFB, every time one would make a dead stick landing it would make the local news including data on its glide performance.
Glide slope for the F-16 (according to my analysis) is about 13.5:1
Badboy
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Pilots wish F-16 had a 13 : 1.
Here is a link to a PDF of an Air Force manual describing flameout procedures (how to glide in deadstick :D).
http://www.fas.org/man/dod-101/sys/ac/docs/16v5.pdf
To make a long story short:
When the engine quits, jettison stores and turn toward the nearest suitable runway. Establish best range speed of 210 KCAS (plus fuel/stores). Trade excess airspeed for altitude.... The gear may be extended when the aimpoint is between 11º and 17º and landing is assured.
If EPU fuel depletion is a factor because of range to the runway, consider a 10º gear-up glide when the best range glide has given you a 1:1 ratio between altitude in thousands of feet and range to the runway (i.e., 20,000' AGL at 20 NM).
1 NM (6076.1 feet) : 1000 feet ===> 6:1 which is close to 10 degrees.
The 11 degree angle is for gear down.
The 17 degree angle is for gear down with airbrake deployed.
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Originally posted by streakeagle
Pilots wish F-16 had a 13 : 1.
The 11 degree angle is for gear down.
The 17 degree angle is for gear down with airbrake deployed.
Yep, but I think those glide angles have been arrived at with the intention of generating the speeds for the correct landing approach, because a little later, it mentions "In a nutshell, if you flame out, regardless of altitude or distance out and the recovery field is below the 7º pitch line, you immediately know you can get there." and 7 degrees is a little better than 8:1 and that would probably include an allowance for the steeper approach and a possible turn required in the landing pattern, all with the gear down and not less than a 5% margin above the stall. Not forgetting that's 7 degrees with the additional drag caused by the need to drive the generator with airflow through the engine, a drag situation similar to the windmilling prop in Aces High. Also, in order to make a statement such as "you immediately know you can get there" that 7 degree glide slope would have to have a comfortable margin of safety. Taking all that into account, and accepting that perhaps the 4.3 degree glide slope suggested by a 13:1 ratio might be a tad optimistic, I still don't think it is far off. All of which is a million miles away from Aces High :)
Badboy
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I just ran some calculations and although Francis Dean quotes a glide ratio of 14.92, the chart that pyro posted suggests something a little better than 15. For example, to glide 115 miles from 40k you would need a max L/D of 15.18, however to glide 14.5 miles from 5k you would need a L/D of 15.32.
However, in order to glide the 20 miles suggested at the start of this thread, and if the L/D was 15.32, then with 7000ft of altitude you would be able to glide 20.3 miles.
Just saying :)
Badboy
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badboy,
i have a drag polar of the f-16c. its best l/d is 10 at mach .5 at 20,000 ft.
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Originally posted by Zigrat
badboy,
i have a drag polar of the f-16c. its best l/d is 10 at mach .5 at 20,000 ft.
Thanks, but that's much lower than I expected, so I'm disappointed, it also means that Falcon4 is way off :)
Is that drag polar something you can share? You have any thrust data for the F100-220?
Badz
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Engine-out tests at Edwards AFB resulted in a gear-down best range glide between 10º and 11º flight path angle which could be steepened to 17º flight path angle with the speed brakes; thus the 11º - 17º window for lowering the gear.
Regardless of actual flight path angles involved, lowering the gear will increase the flight path angle 3.5 - 4º.
After re-reading the procedure, I agree 10 degrees is the optimum glide angle with gear up and EPU windmilling. The 7 degree slope makes sense: 11 - 4 = 7 degree glide slope.
As far as being a "million miles away from Aces High", the key to the discussion here was establishing a ball park figure for glide slope for Aces High aircraft. The laws of physics didn't change since WWII the last time I checked. The F-16 represents a worst case for a high wing loaded high performance fighter compared to WWII fighters. Using its performance as a lower boundary is valid for comparison. Ironically, my original estimate based on vague memories of news stories was correct at 8:1. If an F-16 can manage 8:1, surely something like a P-51 with long straight wings (much higher aspect ratio than the F-16's 40 degree delta) can manage the gliding ability observed in Aces High (of course Pyro was the man and provided a chart of the real thing).
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Originally posted by Fariz
Try to get to the same altitude and just switch engine off. You will glide twice shorter.
For some reason in some cases when your engine dies you can glide forever. I think it is bug?
Fariz
i think so. Whenever your engine dies, rpm is at zero, and prop drag disappears completly. This is why you glide way longer with a dead engine, no prop drag anymore.
I used this little bug when i did some glide tests a while back, i started from a field in 5k and right before the edge of the mountain i pushed the stick forward. This way i rammed my prop into the ground, the engine died, i ran over the edge and was a clean glider now.
niklas
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Great tactic.. Now I just gotta find a mountian at 35K and see if i can break M 1.0... once i lose the prop..
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Originally posted by streakeagle
The quote about being safe with the 7 degree line probably includes the range bonus that comes from having a speed significantly higher than 210 knots optimum glide range speed during flameout (probably 400 to 500 knots). Per the procedure, this speed will be traded for additional altitude which will permit recovery at the optimal 10 degree angle.
I disagree, if they meant that you could only make it if your airspeed was high enough to begin with, I assume they would have said so. If there was a speed below which you couldn't make it, I'm sure they would have qualified it. The fact that they say you know you can get there, regardless of other factors, providing you have a 7º glide slope, implies that the 7º already includes a safety margin and it also implies that you could make it regardless of the airspeed you had at the time. Particularly since flameout due to compressor stagnation stalls, for example, are more likely to occur at high angles of attack and low speeds, and are also covered by that statement.
If the information from Zigrat's F-16 drag polar is correct (Isn't the genuine F-16 drag polar classified?) then a L/D of 10 gives a glide slope of only 5.7º. Now I know that L/D is not constant, and may be slightly lower at the speeds and altitudes we are considering, but this could be the source of the safety margin for the 7º glide slope, a margin of 1.3º equivalent to the difference between the 8:1 and 10:1 glide slope.
The F-16 Documents suggest that 7º is possible, while Zigrat's F-16 drag polar suggests that something in the order of 5.7º may even be possible, but in practice it seems pilots count on much less. I'm sure the reason would be that they need to maintain a considerable margin in order to execute maneuvers in the landing pattern and so on. I found this interesting account, that suggests that in practice F-16 pilots expect far less. Notice the rule of thumb:
"Tigre 83 was on what would normally be considered a low threat cross-country sortie; if there is such a thing in a single-engine fighter! Twenty-five nautical miles west of El Paso International, the tone of the sortie took on a drastic change when his aircraft suffered catastrophic engine failure and flamed out. This all occurred at 18,000 feet above ground level and 550 knots true airspeed. Every F-16 pilot knows that the rule of thumb for simulated flameout (SFO) landings is to be at an altitude (thousands) equal to your distance from the intended landing. If you do the math in this problem, it is obvious that any delays in turning back would have resulted in a completely different outcome. Even with Maj Overturf's immediate execution of the critical action procedures, this SFO would require all of his piloting skills to safely recover his crippled F-16 to a heavily populated area. In fact, had this occurred a mere 30 seconds later, the Air Force inventory would be short one F-16C. It's situations like this that help reinforce the single-engine mentality of always being aware of the closest piece of concrete."
After all that, what surprises me the most about this is that most WWII aircraft, actually look less aerodynamically efficient than the F-16, but they all appear to have a far better L/D ratio and can glide much farther. Amazing.
Badboy
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What is the reason for the great difference in glide ratio you get when you shut off your engine vs. when your engine dies from combat damage or no fuel? When your engine dies from combat damage the plane seems to glide twice as well as when you shut off your engine deliberately.
Also, why is the Tempest such a lousy glider compared to other planes?
ra
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Originally posted by streakeagle
As far as being a "million miles away from Aces High", the key to the discussion here was establishing a ball park figure for glide slope for Aces High aircraft.
Nope, the glide slope for the aircraft in Aces High are already known. For most of the US fighters their glide slopes can be found in Francis Dean's book and none of them are below 12, and the P-51 chart posted by Pyro indicates a L/D greater than 15. Those values are for the airframe only, and most of the confusions seems to have been caused by the effect of the windmilling prop.
The laws of physics didn't change since WWII the last time I checked. The F-16 represents a worst case for a high wing loaded high performance fighter compared to WWII fighters. Using its performance as a lower boundary is valid for comparison.
On the contrary, I think the differences in the wing configurations between the F-16 and typical WWII fighters make such comparisons entirely invalid. I'm just surprised that a fighter that looks as good as the F-16 has an aerodynamic efficiency even worse than the Jug :)
But as I type this, the thought occurs to me that in WWII thrust limitations demanded the higher L/D ratios, but when you look at the engines available today, even aircraft with all the aerodynamic properties of a brick are viable, so long as they hit high mach numbers, who cares if they glide worth a damn :)
Badz
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teh drag polar i used was out of "aerodynamics for engineers" by bertin and smith. i do not know if it is accurate, but they reference a 1976 report called "the f-16 air combat fighter" by general dynamics so ???
but i dont have the original document so i dont know. they were simply using it for an example problem they worked in the book so the numbers could be just for illustrative purposes.
a big factor you have to look at carefully in jet aircraft polars is whether they are with the engine installed or without. most of the time teh polars are without the engine, since the engine deck includes installation drag in it.
as for the fact that glide performance is significantly worse than modern fighters, i really wouldnt be that surprised. most fighters have delts wingsnowadays, which really arent optimized for subsonic l/d :)
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Originally posted by ra
What is the reason for the great difference in glide ratio you get when you shut off your engine vs. when your engine dies from combat damage or no fuel? When your engine dies from combat damage the plane seems to glide twice as well as when you shut off your engine deliberately.
Also, why is the Tempest such a lousy glider compared to other planes?
ra
The difference appears to be entirely due to prop drag. When you shut off the engine the prop continues windmilling and creates additional drag beyond that of just the airframe. You can verify that this is so by partially feathering the prop in flight. You can do this by adjusting the rpm when the engine is off. You will notice that with the rpm turned down as low as possible, the prop drag will be much lower and you can thus glide much farther. That can be very handy when you need to glide as far as possible in the arena. Unfortunately you can't feather it all the way back to zero, that only seems to happen when the engine is damaged, possibly due to the loss of engine oil pressure needed by the prop governor, thus allowing the prop to weather vane and consequently reducing the prop drag to zero.
I flew the Tempest for the first time yesterday, it has amazing acceleration and speed, which appears to be entirely due to its ability to generate thrust. If that's true, it would also imply more prop drag when the prop was windmilling, so that could be the reason why it doesn't glide as well.
Badboy