Aces High Bulletin Board
General Forums => Aces High General Discussion => Topic started by: Rollio on November 12, 2002, 12:13:56 AM
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OK, something is really bugging me. Why is it that certain planes glide soooooo much better than others?
Case in point Hurricane IIC versus La-7. Emptied guns, 25% fuel 3k of alt, Engines turned off. The Hurricane will glide at a rate of roughly -3.9k feet/second. The La-7 glides at around -1.2k feet/second. That's a difference of a factor of 3. Looking at the specs, both planes have roughly the same weight (slight edge to the La-7). However the hurricane also has a 20% longer wing (40' versus 32'), which should theoretically help it's glide slope. And then there is drag. Sure the hurricane had a fat wing, but so fat as to induce enough drag to create this kind of disparity, espescially considering the difference between it's clean inline engine fuse to the hog nose radial of the la-7?
My thinking is that HTC, in their lust to get the top speed stats accurate to the books, fudged the drag values, and thus probably botched engine thrust as well.
Another case in point is the Me-262. This is the BEST glider in the game. Under the same conditions it will glide at a rate of -0.9k feet/second. This is phenomenal for a 7 ton, swept wing, *jet*, don't you think? However it also might explain the ridiculously slow rates of decceleration the thing has (climb 8k feet from the deck vertical anyone?).
Anyway, I'm looking for a few of the experts to set me straight. I accept that this is all conjecture on my part and I could be completely wrong. Anyway I leave this topic open for further discussion.
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Don't know about your measurement (-3.9k ft/sec?) but planes do glide way too well.
ra
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Did you change the prop pitch on the Hurri by reducing the RPM's? Prop drag might be affecting your result.
I did constant velocity glide tests of the P-51D, F4U1-D, and the La-7 awhile back. The La-7 for whatever reason seems to go to a min prop drag configuration when you shut off the engine. In the P-51D and F4U1-D you have to reduce RPM with engine off to change the prop pitch for min drag.
All that being said this only reduces the prop drag. There's not assurance that it's an apples to apples comparison in engine off glides since we can't eliminate prop drag out of the equation or make sure they are equal prop drag values between both a/c.
Tango, XO
412th FS Braunco Mustangs
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RL Pilots flying the Fw-190 stated it would "drop like as stone" when the engine was dead, making ditches extremly dangerous.
I'm happy that I can sail home in my AH Fw-190, but I usually still have so much excess speed while gliding that I overshoot the Runway on a regular basis... :)
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I glide my 190 home quite alot... wtg AH :D
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In AH you will most likely overshoot the runway on a deadstick landing, even with flaps and gear down and sideslipping - you will actually slow down much faster with the engine on, and not just at idle. Most fighhters will just stick to around 200mph for some reason...
I think this is one of the worst aspects and most obvious errors of the AH FM, and certainly leads me to doubt all the AH FM apologists whenever some FM error is found in a plane. If HTC cant get gliding right, and all other flying is just powered gliding, then what else arent they doing right?
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Every airframe has a best L/D value that is it's optimal glide ratio achieved at a certain speed. The best L/D is typically *not* achieved by holding a minimal "glide angle" just above the stalling spped of the aircraft.
Even though the so-called glide angle may be greater (measured in minus ft/min on the VVI), the overal L/D could be better because a higher speed means the aircraft is traveling forward faster (and technically generating more lift than at near stall speed).
Whether AH accurately models best L/D for each airframe is another question, but if you want to extend your unpowered glide (further distance, not necessarily longer time), suppress your instinct to pull back to reduce glide angle and nose down a bit to get to a more efficient gliding speed.
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Rollio, keep in mind that the LA-7 has a metal fuselage, while the Hurricanes, being much older, are metal airframes covered in canvas, and canvas has a MUCH greater drag factor than smooth metal, which helps to explain why the Hurri loses speed so quickly with the engine off, and also why the Hurri II is so slow even when the engine puts out very decent horsepower.
You might have also noticed that Hurricanes seem to have incredible durability to enemy fire, occasionally sustaining 15 or 20 .50 cal hits in a tracking shot without taking any real damage. Bullets that pass through canvas without hitting any frame struts won't really hurt the plane. At the same time, this type of construction makes the Hurri very fragile to high-G manuevers. Try pulling hard while going 400 mph in a dive and you'll rip the wings off easily.
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You experts are welcome to produce some historical glide ratio figures which contradict the results in AH.
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Uhmm.. IF someone would just post the POH for the aircraft, or a Drag curve you can clearly see what the speed in knots/Mph is for each plane at a specified Max gross weight.
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The weight of an aircraft is not a factor in how far it can glide.
F.
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Really? That doesnt seem to make sense. One would think that a plane with a wing area of 400 square feet and a weight of 2,000 pounds would glide farther than a plane with a wing area of 400 square feet and a weight of 18,000 pounds.
All the wing does it provide lift, and the less the plane weighs the more lift can go towards "lifting" the plane.
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Furious is wrong.
A simple proof is to glide a plane with no fuel or ammo and then glide the same plane with a full load of fuel and ammo. Assuming balance remains the same. The only relevant change is weight. The loaded plane will glide a LOT worse then the empty one. Try it with Lancaster with a full bomb and fuel load, and an empty lancaster. The result will be very different.
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Hey Rollio,
Check out this thread. (http://www.hitechcreations.com/forums/showthread.php?s=&threadid=43937&highlight=glide+ratio)
It makes the most sense to quantify your results as a glide ratio at a given speed to give some digestible data on the subject. I admit that the glide feels long to me, but as I posted in the aforementioned thread, it's really on the short side, at least for the P-51. If I've really messed up on this on a particular plane, the glide ratio will show that better than any other test.
I think a lot of it is the perception of time when comparing real aircraft to this sim. A 700 fpm climb in a Cessna feels quicker to me than a 3000 fpm climb in AH. I was talking to HT about this when he was describing how awesome his plane climbed(it climbs around 2000 fpm) and how different that feels from a plane in AH that climbs at 2000 fpm. I also notice this when it comes to landing and I think that's where a lot of this comes into play. A typical approach from me has me on final at 300 mph and 3000 feet trying to make a series of break turns to slow down. When using the approach prescibed by the flight manual, it feels absolutely geriatric and I doubt anybody makes textbook approaches and landings more than a few times. It's not that you can't, it's just that most people don't want to. If you doubt me, I'll post the protocol and let you try it a few times and see how it differs from your normal routine.
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Hi Pyro:
I dont have any RL piloting experience but I'm curious why the planes slow down much less on final if the engine is off than if its idling or at part throttle, even if I am doing full flaps, gear down and violently sideslipping. I do have RC experience and although I know well enough that its not directly comporable, the heavy 1/5 - 1/4 scale warbird models have trouble making it back to the strip and often stall out on final, they dont overshoot the runway like happends in AH despite my attempts to sideslip etc.
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As a Real Life (tm) glider pilot with over 350 hours in several different types of gliders, I can state with authority that the weight of a given aircraft does not affect its gliding ratio or distance.
(An important distinction needs to be made here. The best speed for minimum sink is not necessarily the same as the best speed for your best glide ratio. Best L/D speed is usually somewhat higher than that for minimum sink.)
In other words, the same plane will have the same glide ratio at different weights, as long as it is flown at its best glide speed, and that speed changes with its weight. The sink rate will increase with higher weights, however.
What DOES change is that as the best glide speed goes up with an increase in weight, and since the speed has increased, the sink rate will also increase. However, the increase in the sink rate is offset by the higher speed over the ground, resulting in a glide of the same distance from a given height.
Much more information on gliding theory is available at the web site for the Soaring Society of America. http://www.ssa.org
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Originally posted by GRUNHERZ
Hi Pyro:
I dont have any RL piloting experience but I'm curious why the planes slow down much less on final if the engine is off than if its idling or at part throttle, even if I am doing full flaps, gear down and violently sideslipping.
I don't recall how it works at the moment, but if what you say is correct, then the prop is automatically changing to the optimum pitch. On twin-engined planes this would be fully feathered, but on single-engined planes it still makes a large difference even though they don't have fully feathering props. You can test this out for yourself by pulling your engine to idle and then manually adjusting the propeller.
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Ok I'll try that.
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Originally posted by Rollio
Furious is wrong.
A simple proof is to glide a plane with no fuel or ammo and then glide the same plane with a full load of fuel and ammo. Assuming balance remains the same. The only relevant change is weight. The loaded plane will glide a LOT worse then the empty one. Try it with Lancaster with a full bomb and fuel load, and an empty lancaster. The result will be very different.
Read this link (http://142.26.194.131/aerodynamics1/Performance/Page3.html) and then explain to me how I am wrong.
F.
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F. that is correct. Those pages are excellent. A lot of the issues in the Aircraft forum would disappear if people would read those pages and extend them to situations in the game.
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Originally posted by Furious
Read this link (http://142.26.194.131/aerodynamics1/Performance/Page3.html) and then explain to me how I am wrong.
F.
In the real world drag increases as speed increases due to various effects, for example you churn larger wing tip vortices. Thus as weight increases your maximum glide range and sink rate will get worse. The drag effect of windmilling a propeller will also get a lot worse at higher speed.
Still, I've yet to hear an explanation as to why the 262 glides so well and takes so long to lose speed in general. I still don't understand what is causing the massive discrepancy in sink rate between the various planes either.
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Totally agreed Funked.
Rollio:
1) What do you expect the th 262 glide ratio to be?
2) Regarding the discreprancy between prop planes, have you tried reducing the RPM to change prop pitch on the aircraft in question? As I said earlier (and also evident in the link Pyro provided) windmilling prop drag is a factor. For whatever reason I've found that the La-7 seemed to have it's prop in min drag configuration at engine shutoff as opposed to other aircraft where you have to manually reduce RPM and change prop pitch.
Tango, XO
412th FS Braunco Mustangs
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weight is not a factor in the slope of the glide. However, it increases the velocity for a specified slope.
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Does everyone remember how slick and slippery the aircraft were in Beta AH versions before the prop drag was added? From a "feel" perspective, prop drag seems to have the most overall affect to an aircraft's overall drag. Thats one explanation that I can think of when it comes to the Me 262's glide performance in AH. The fan blades don't seem to be modeled the same as props so an idle throttle position does not seem to have any influence on drag. I'm not saying that it should, either. Without a propeller and its effect on the modeled airplane's drag, the Me 262 has a great advantage.
One other thing that I notice about the Me 262 (after working on the real airplane at Paine Field in WA), is that there is no apparent extra drag or lift effect change for the full span leading edge slats in the AH aircraft (where they would normally deploy at slow speeds). One slat section is installed in this photo for reference (http://www.avphoto.com/stormbird/hangerview-sm.jpg)
On another note regarding the La-7 in AH: From 10,000 feet, this airplane will glide for 25 miles (one sector) with no engine power at best climb speed. I've done this many times after running out of fuel. That gives it roughly a 13:1 glide ratio. During emrgency procedures practice, when the T-34's propeller control is pulled all the way back in its normal operating range, I get glide ratios that match the book value of 10:1. We can pull the prop back to a 600 RPM (low drag) beta condition for real emergencies. This improves the glide ratio to about 13:1. The La-7 doesn't feel all that different from what I've experienced in an airplane - at least until you add flaps and gear in the T-34. LOL, then the glide resembles a space shuttle approach.
MiG
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Airboss can you tell us in more detail what happends to a gliding T34 with low drag prop setting when you lower the gear and flaps. Does it then slow down quickly?
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accually i have found that the AR234 glides so well it gets hard to land at times
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Originally posted by GRUNHERZ
Airboss can you tell us in more detail what happends to a gliding T34 with low drag prop setting when you lower the gear and flaps. Does it then slow down quickly?
Grun, For the T-34B - throwing the gear down during a simulated engine-out glide (with the prop at the 600 RPM beta setting), causes a slight nose-down force and an immediate, but small reduction in airspeed. The pilot has to compensate for this loss by lowering the nose even further to maintain best glide speed of about 85 knots. This increases the sink rate and decreases the glide ratio. Dropping the flaps to the full down position puts so much drag on the airplane that the pilot has to practically dive to maintain best glide speed.
Unless I was in jeopardy of drastically overshooting my emergency landing spot, I would NEVER use a gear down and full flaps config in an engine-out condition. In fact, it requires nearly full throttle at max RPM (Prop control full forward low pitch, high power) to arrest the descent and hold level flight in the T-34B in this configuration. The full down flaps add a lot more drag than the gear. On a go around for an aborted landing, raising the flaps is the very next a pilot does after going to full power so that the airplane has some climbing ability. The only airplane in AH that approximates the feel of the -34 in this condition is a fully loaded F4U-1 with those big flaps and low "thrust" to weight.
(Here is one of the airplanes)
(http://www.avphoto.com/arlington2k/t34-sm.JPG)
for ref:
Max gross: 3045 lbs
Engine pwr: 225 hp
Unfortunately, we're grounded pending the compliance with a wing spar inspection Airworthiness Directive and don't know if the Navy is going to shell out the cash.
MiG
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It turns out that the La-5 and La-7 currently have fully feathering props in the game. Planes with fully feathering props will automatically feather when the engine is shut down which explains why you're seeing that different behavior and why it's gliding better than it should.
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Sorry I missed this thread. It should have been in the A/C and Vehicals section and it would have gotten more attention.
Anyway one thing I noticed about Pyro's mention about climb rate feel in AH and climb rate feel in a real A/C is this.
In a real light A/C the engine noise is overwhelming. In fact the sound of the engine RPM is all your aware of. So you have a feeling not only in the seat of your pants but in your ears that the aircraft is working like a bastard to lift you up. In AH the sound is more of a hum so unless your in WEP you don't have the feeling of a strain of the A/C making it "feel" like your not going anywhere.
If you change your sound settings (for me) it really makes you climb sensation increase with a more strained engine sound. Like the difference between WEP and no WEP.
BTW. My stick time is 16 hours in small A/C logged and 1 hour at Air Combat USA.
Also I have La-7 glide data somewhere. I need to find it.
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Thanks for clarifying that Pyro. Thought that might be the case.
Tango, XO
412th FS Braunco Mustangs