Drag and gliding?

[Rollio]

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.

[ra]

Don't know about your measurement (-3.9k ft/sec?) but planes do glide way too well.  

ra

[dtango]

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

[robsan]

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...

[iceydee]

I glide my 190 home quite alot... wtg AH

[GRUNHERZ]

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?

[Samiam]

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.

[Ecliptik]

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.

[funkedup]

You experts are welcome to produce some historical glide ratio figures which contradict the results in AH.

[jbroey3]

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.

[Furious]

The weight of an aircraft is not a factor in how far it can glide.


F.

[Urchin]

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.

[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.

[Pyro]

Hey Rollio,

Check out this thread.

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.

[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 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.