Author Topic: Drag and gliding? (Read 493 times)

BD · « **Reply #15 on:** November 12, 2002, 11:16:25 PM »

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

Pyro · « **Reply #16 on:** November 12, 2002, 11:51:44 PM »

Quote

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.

GRUNHERZ · « **Reply #17 on:** November 12, 2002, 11:53:45 PM »

Ok I'll try that.

Furious · « **Reply #18 on:** November 13, 2002, 01:16:53 AM »

Quote

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 and then explain to me how I am wrong.

F.

funkedup · « **Reply #19 on:** November 13, 2002, 02:54:38 AM »

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.

Rollio · « **Reply #20 on:** November 13, 2002, 03:57:43 AM »

Quote

Originally posted by Furious
Read this link 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.

dtango · « **Reply #21 on:** November 13, 2002, 02:29:43 PM »

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

udet · « **Reply #22 on:** November 13, 2002, 02:44:56 PM »

weight is not a factor in the slope of the glide. However, it increases the velocity for a specified slope.

CMC Airboss · « **Reply #23 on:** November 13, 2002, 05:03:18 PM »

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

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

GRUNHERZ · « **Reply #24 on:** November 13, 2002, 10:24:51 PM »

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?

NOD2000 · « **Reply #25 on:** November 14, 2002, 01:00:15 PM »

accually i have found that the AR234 glides so well it gets hard to land at times

CMC Airboss · « **Reply #26 on:** November 14, 2002, 01:38:58 PM »

Quote

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)

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

Pyro · « **Reply #27 on:** November 14, 2002, 03:24:52 PM »

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.

F4UDOA · « **Reply #28 on:** November 14, 2002, 03:35:11 PM »

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.

dtango · « **Reply #29 on:** November 14, 2002, 05:09:59 PM »

Thanks for clarifying that Pyro. Thought that might be the case.

Tango, XO
412th FS Braunco Mustangs