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Pigeon_
09-13-2009, 05:33 PM
Is there a list of optimal glide speeds for the planes in IL-2 somewhere?

The_Stealth_Owl
09-13-2009, 05:40 PM
I could probably tell some if you name the planes you want to know about. http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

WTE_Galway
09-13-2009, 05:47 PM
It's going to be very close to or in many cases identical with the best climb speed.

AndyJWest
09-13-2009, 06:05 PM
Originally posted by WTE_Galway:
It's going to be very close to or in many cases identical with the best climb speed.
That is my understanding too. There are really two 'optimal' speeds: one giving the shallowest angle of descent, and the other (a bit slower I think, but probably not much) giving the slowest rate of descent.

If you do lose an engine and have to glide (rather than bailing, which can sometimes be more sensible) you should convert any excess speed you have into height, with a gentle climb, until you approach the best glide speed. If you need to make a turn, keep it gentle. close radiators to minimise drag. Unless you can land on a runway, keep the wheels up and belly-land. Pick a spot clear of obstructions and flat. Landing parallel to, and close by, a river will usually provide flat ground.

na85
09-14-2009, 02:30 AM
Originally posted by AndyJWest:

That is my understanding too. There are really two 'optimal' speeds: one giving the shallowest angle of descent, and the other (a bit slower I think, but probably not much) giving the slowest rate of descent.

I don't think descent angle is something you want to optimize. In an engine failure or no fuel situation what you're looking for is slowest descent rate, regardless of angle, and the slowest descent rate occurs only at L/Dmax (i.e. minimum drag speed)

Pigeon_
09-14-2009, 03:36 AM
Actually, you would want to optimize the descent angle. Your objective is to get as far as you can. It doesn't matter how fast you are dropping towards the ground, as long as you get the greatest range.

Stealth Owl. Couldn't you just point me to the source of that information?

Bremspropeller
09-14-2009, 04:10 AM
I don't think descent angle is something you want to optimize. In an engine failure or no fuel situation what you're looking for is slowest descent rate, regardless of angle, and the slowest descent rate occurs only at L/Dmax (i.e. minimum drag speed)

Not quite:

As you want to make the largest distance with your altitude avaliable (maybe reaching an airfiled..), you're looking for glide-angle in the first place.

L/D-max is the speed of the shallowest glide-angle.
Lmax is the speed of lowest descent-rate.

The first buys you distance to the ground-contact, the latter buys you time to the ground-contact.

Chose wisely.

Tully__
09-14-2009, 05:09 AM
Originally posted by na85:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by AndyJWest:

That is my understanding too. There are really two 'optimal' speeds: one giving the shallowest angle of descent, and the other (a bit slower I think, but probably not much) giving the slowest rate of descent.

I don't think descent angle is something you want to optimize. In an engine failure or no fuel situation what you're looking for is slowest descent rate, regardless of angle, and the slowest descent rate occurs only at L/Dmax (i.e. minimum drag speed) </div></BLOCKQUOTE>

Pigeon and Brems have it right, if you're after the longest distance to touch down you want shallowest angle of glide. Andy's description of the procedure on engine out is pretty good. There's some good stuff on the topic at http://www.av8n.com/how/htm/aoa.html#sec-ias-aoa

Bremspropeller
09-14-2009, 05:25 AM
Superb site, thanks Tully! http://forums.ubi.com/images/smilies/25.gif

RPMcMurphy
09-14-2009, 06:38 AM
The other night I was in a P-51 and out of ammo and there was still one more He111 on target for my airfield at about 500M. I chopped his elevator with my prop. He crashed and I was in glide mode with inop engine about three miles from the airstrip. I trimmed it to about 180 KPH and closed the radiator. I thought I would make it and I kept gear and flaps up as long as I could but I still came up short and landed next to some RR tracks and nosed over but did'nt flip. Too bad you can't dump fuel.

Kettenhunde
09-14-2009, 06:49 AM
Minimum Sink and Best Glide are two different velocities.

Best Glide is at L/Dmax and Minimum Sink at Dmin.

Minimum Sink is mainly used for Gliders and has little application for powered aircraft. If your engine quits, it is an emergency and getting the aircraft safely on the ground is the focus.

Minimum sink is still a good thing to know for a proficient pilot but is generally not even listed in most POH's as the focus is being able to cover the largest distance on the ground in order to reach a safe landing point.

In an engine out situation for example, it is good to make any required large turns at minimum sink if you are proficient. It is just another things to place in your bag of tricks.

All the best,

Crumpp

Kettenhunde
09-14-2009, 06:52 AM
I trimmed it to about 180 KPH and closed the radiator.


Open your propeller to minimum rpm too if you can. Most POH L/D ratio's assume minimum rpm on the propeller in a glide. A constant speed propeller can create tons of drag and the VDM hydraulic-electric propeller will operate with engine out in emergency mode.

All the best,

Crumpp

Viper2005_
09-14-2009, 08:34 AM
Originally posted by Bremspropeller:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I don't think descent angle is something you want to optimize. In an engine failure or no fuel situation what you're looking for is slowest descent rate, regardless of angle, and the slowest descent rate occurs only at L/Dmax (i.e. minimum drag speed)

Not quite:

As you want to make the largest distance with your altitude avaliable (maybe reaching an airfiled..), you're looking for glide-angle in the first place.

L/D-max is the speed of the shallowest glide-angle.
Lmax is the speed of lowest descent-rate.

The first buys you distance to the ground-contact, the latter buys you time to the ground-contact.

Chose wisely. </div></BLOCKQUOTE>

There is an analogy between Vy and L/D max on the one hand, and Vx and (L^3/D^2) (otherwise known as minimum sink) on the other.

Aircraft in IL2 glide extremely, if not suspiciously well if you fly them correctly.

Best glide speed for most of the fighters seems to be roughly 260 km/h IAS, which is coincidentally about the best climb speed as well.

When the engine quits, you should zoom climb to convert any excess speed to height as efficiently as possible. At the same time you should clean the aeroplane up as best you can:

1) Prop pitch setting to minimum rpm. If you can feather the prop(s) then do so.

2) Radiator closed.

3) Trim all axes.

4) Dump all external* stores.

Never glide with flaps.

A stationary prop always produces less drag than a windmilling one, so if you have spare height it is worth slowing down almost to the stall to stop the prop, and then re-accelerating to best glide. At low altitudes the height lost in the manoeuvre is likely to exceed the performance benefit. Obviously if you stop the prop then it will be much harder to get the engine started again, so this manoeuvre should be viewed with circumspection. IRL I'd only bother if I absolutely knew the engine was dead and I was at medium altitude (>3000 feet or so).

There is no such thing as the best glide speed IRL. There is an alpha which gives (L/D)max, and this will translate into a "best glide speed" which will vary as a function of weight. However, the small-print of this concept is that even if you had an alpha gauge in the cockpit, flying at the alpha which maximises (L/D) will only maximise the distance that your aeroplane travels over the ground if the air is still.

IRL the air is never still, so the best speed to glide at will depend not only upon the aircraft's weight, but also the conditions.

If the air is sinking, or you are trying to penetrate a headwind then you need to fly faster to minimise the pain.

If the air is rising, or you are flying downwind, you'll do better to fly more slowly to maximise the benefit. In the limit if the air is rising faster than your aircraft's minimum sink rate then you should fly at the speed for minimum sink rate and circle to gain height.

This may sound fanciful for a WWII fighter, but you'd be surprised how fast the air can move under certain conditions. It's not unknown for thermals to exceed 1000 fpm on a good summer day, and if there is a large fire or a thunderstorm then this can be exceeded, potentially by an order of magnitude. I mention this because it is generally considered inadvisable to land close to the people you have just bombed; bomber pilots keen on starting fire storms take note!

BTW, minimum sink is not Dmin. Dmin is at (L/D)max because at constant weight L is fixed, so maximisation of the L/D ratio requires minimisation of the drag force. Minimum sink rate is achieved at the speed which minimises drag power, which is the product of the drag force and the velocity. This is why sink rate is minimised when you maximise (L^3/D^2); I will leave the rigorous mathematical proof to others.

*Whilst you don't want to land with bombs in a bomb-bay either, it may be useful to carry them for part of the descent because the extra weight increases your gliding speed at the optimum gliding alpha and imposes no drag penalty. This will therefore help you penetrate into the wind. If you are gliding downwind then you should dump as much weight as possible within reason so that you descend more slowly and can derive more benefit from the wind.

RAF_OldBuzzard
09-14-2009, 08:48 AM
Originally posted by Kettenhunde:
Minimum Sink and Best Glide are two different velocities. ...

This is very true. Minimum sink is going to be slower the L/D Max. In a sailplane you fly at minimum sink while in a thermal, and L/D Max when searching for thermals and when in the landing pattern.


...In an engine out situation for example, it is good to make any required large turns at minimum sink if you are proficient. It is just another things to place in your bag of tricks. ...

That would be a good way to kill yourself.

You would want to fly at L/D max NOT minimum sink. Minimum sink is WAY too close to stall speed.

A good 'rule of thumb' to use for L/D Max is 1.25 x stall speed.

Kettenhunde
09-14-2009, 09:03 AM
That would be a good way to kill yourself.



Yes it is if you don't know what you are doing.

Hence the warning:


it is good to make any required large turns at minimum sink if you are proficient.

That is why most POH's don't even list minimum sink speed.

I would not recommend using it to turn unless you are capable of maintain a coordinated turn and familiar with the aircraft handling in slow flight.

If you are a proficient pilot minimum sink is a good way to safely extend your time aloft in order to complete a turn. If you have not practiced it do not attempt it because the margins of safety are small.

Take the airplane up to a safe altitude and practice.

Playing an ostrich sticking your head in the sand by not becoming proficient with all emergency maneuvers simply limits your options when you need them most.

Kettenhunde
09-14-2009, 09:06 AM
Middle of the page starting with the phrase, "You also need to know something that is not published in most POH's: the minimum sink speed."

http://books.google.com/books?...Sink%20speed&f=false (http://books.google.com/books?id=XO8CLGeHjrgC&pg=PA25&lpg=PA25&dq=Best+Glide+vs+Minimum+Sink+speed&source=bl&ots=arihlWmd4m&sig=L51fDU6lSHY-S2woC8G8Jfhpamo&hl=en&ei=hVuuSt6DHZGtlAeJyKHWBg&sa=X&oi=book_result&ct=result&resnum=4#v=onepage&q=Best%20Glide%20vs%20Minimum%20Sink%20speed&f=false)

Kettenhunde
09-14-2009, 09:24 AM
BTW,

These airplanes are not sail-planes and that experience does not translate well for off airstrip landings, most of the WWII Fighters touchdown at ~80-90 (+) mph.

The landing spot selection is much more critical and your selection is narrower than aircraft that land at slower velocities. Your chances of surviving a forced landing are much less than a sailplane due to size of the forces involved.

M_Gunz
09-14-2009, 10:07 AM
I was up once and commented on how many houses were down there. The pilot I was with said he told his instructor; there's
lots of houses and things down there, what do you do if you have to make a forced landing at night and want to miss them?
And the instructor said turn on your landing lights and if you don't like what you see then turn em off!

Kettenhunde
09-15-2009, 06:27 AM
There is no such thing as the best glide speed IRL.

I just caught this.

There is a best glide speed in real life. It is found at L/Dmax and is an extremely important speed to know for the airplane you are operating in real life. In fact, the first thing you do in any engine out emergency is get the airplane to best glide speed.


In your troubleshooting to figure out why the engine quit, don't dally around the cockpit oblivious to your piloting duties. Nail the best-glide speed. It should be on the emergency checklist. Look it up in your pilot's operating handbook and remember it.

http://www.aopa.org/pilot/features/inflight9902.html

Because of the shape of curve in that portion we have some tolerance in the air in our speed selection too. That is good because Vbg does change with weight. The IAS selected by the manufacturer will put us within the tolerances no matter what our weight if it is within CG limits.

Your logic appears to be that because it changes with weight and the shape of the curve, it does not exist?

All the best,

Crumpp

Viper2005_
09-15-2009, 07:42 AM
Originally posted by Kettenhunde:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> There is no such thing as the best glide speed IRL.

I just caught this.

There is a best glide speed in real life. It is found at L/Dmax and is an extremely important speed to know for the airplane you are operating in real life. In fact, the first thing you do in any engine out emergency is get the airplane to best glide speed.


In your troubleshooting to figure out why the engine quit, don't dally around the cockpit oblivious to your piloting duties. Nail the best-glide speed. It should be on the emergency checklist. Look it up in your pilot's operating handbook and remember it.

http://www.aopa.org/pilot/features/inflight9902.html

Because of the shape of curve in that portion we have some tolerance in the air in our speed selection too. That is good because Vbg does change with weight. The IAS selected by the manufacturer will put us within the tolerances no matter what our weight if it is within CG limits.

Your logic appears to be that because it changes with weight and the shape of the curve, it does not exist?

All the best,

Crumpp </div></BLOCKQUOTE>

It is a simple fact that aerodynamics cares far more about alpha than Q. Nail the correct alpha and the speed will take care of itself. There is not one magic speed lying around in the POH which will magically deliver optimum performance.

Why GA aeroplanes don't generally have alpha gauges is a question which has long perplexed me especially given the litigious nature of the country in which so many of them are manufactured, as this would undoubtedly make low speed flying much safer.

In any case however, even given an alpha gauge, I don't think that it is productive to get too hung up on the idea of "nailing" the still-air best glide point.

For a start, you aren't going to land successfully in a field at the limit of your gliding range because if you are on the edge of the performance envelope you have no margin left for approach control, so there isn't an absolutely urgent need to instantly get to best glide.

In any case, the best glide speed merely maximises horizontal travel through the air mass for a given descent through the air mass. Unless you intend to land on a cloud, this isn't actually the be all and end all.

What you want to do initially is buy yourself some time to troubleshoot the problem, and to plan against the possibility that your trouble shooting fails.

That means you don't want to stall, and you don't want to descend at VNE either. Best glide speed is going to be in the correct neighbourhood, but actually whilst you're troubleshooting and field-picking, something a bit closer to minimum sink is probably more appropriate, provided that you are sufficiently calm and competent that flying a bit slower isn't going to cause you to commit suicide via stall/spin.

If you are flying at reasonable altitude over a relatively isotropic landscape then you'll increase your options by turning down-wind and gliding somewhat more slowly than the book "best glide". This also naturally positions you approximately on a downwind leg into whatever field you pick.

If you're flying at low altitude then you should have a escape route already planned to enable instant action, or a will made out.

Of course, the faster your aeroplane the less important the outside environment becomes. A 10 knot wind has much more effect on a 100 knot glide than a 200 knot glide. And if you've got lots of kinetic energy then an engine failure at low level is likely to be less immediately scary, though the high approach speed and rate of descent which will follow would strongly advocate abandoning the aeroplane at the top of the zoom unless a very good alternative presents itself...

But the guiding principle that alpha and common sense are far more important than KIAS when dealing with engine failures remains.

Kettenhunde
09-15-2009, 11:38 AM
It is a simple fact that aerodynamics cares far more about alpha than Q.

I would say the wing or airfoil cares more about AoA and that AoA has a definitive relationship to Q.

Vbg occurs at a specific angle of attack. It occurs at a specific coefficient of lift that is fixed by the design.

That coefficient of lift is fixed to a specific coefficient of drag.

None of that has anything to do with the fact Vbg exists and is a very important number for a pilot to know. To say it does not exist in real pilotage is not correct at all.

Not everything though is about angle of attack and that is even aircraft equipped with an AoA indicator still retain an airspeed indicator.

RAF_OldBuzzard
09-15-2009, 11:43 AM
Originally posted by Kettenhunde:... Yes it is if you don't know what you are doing....

People that DO know what they are doing WOULDN'T do that, because they know tht it isn't safe.

Having more than a 'few' hours in various Sailplanes, and having owned a Cessna 140, I believe that I DO know what I'm doing, and I'd no sooner make an engine off approach at min sink speed in my 140 than I would in a Grob G-103.

Not only does minimum sink put you too close to stall speed for comfort, it also limits your options for an off field landing. Flying at L/D max extends your range which could make all of the difference in the word.

Do a bit of research and read the story of the "Gimli Glider". Flying at best L/D (well as best as they could get to it) rather than minimum sink made the difference between life and death for the passenfers and crew.

Viper2005_
09-15-2009, 12:12 PM
I think that the point Kettenhunde is making is that if you are turning then by definition you can't be travelling in the direction you want to go.

Maximising distance travelled in the the wrong direction is clearly pointless.

Instead you just want to minimise the altitude lost in the turn. For shallow bank angles this will be achieved by slowing down.

For steeper bank angles alpha will have to increase during the turn, which will bring you closer to the minimum sink alpha anyway.

It is not immediately obvious by inspection how to optimise bank angle (and thus Q) in the turn, but it does seem reasonable to suggest that you want to be closer to the minimum sink alpha when turning than when flying straight.

I don't recall anybody in this thread suggesting that one should stay at the minimum sink alpha for long.

However, as for minimum sink being close to the stall, the faster your aeroplane the less important this is likely to be since windshear is a fixed quantity in absolute terms, whilst minimum sink is likely to always be some multiple of stall speed; the safety margin in absolute terms (ie knots) will therefore tend to be larger for faster aeroplanes.

***

Kettenhunde, Vbg does not exist in the sense that it is not a fixed quantity that you can look up. The value quoted in the POH will be "about right", but the point I'm trying to make is that it is not necessary to religiously nail this book value, which is likely to be representative for a different weight than you're flying at in any case.

OTOH, with an alpha gauge, it would be perfectly possible to just say "fly at 11 units of alpha" and this would be correct for all loadings.

But this still only optimises the motion of the aeroplane relative to the air, which is not ideal given that the air is likely to be moving in relation to the ground.

For this reason, even if you are flying alpha then the optimum strategy is probably not to simply park the aeroplane at L/D max.

Best performance relative to the ground is a function of the relative motion between the ground and the air mass.

In the seconds immediately following an engine failure at a sensible altitude, the pilot needs to buy time for troubleshooting.

This means not stalling and not descending too fast. The best glide speed is a good compromise because it's not too close to the stall and gives a reasonably low sink rate. But until you've decided where you want to go, there is no good reason to look for (L/D)max - the best place to land might be behind you!

As such, it is not sensible to devote a large amount of effort to nailing the speed. Get the speed into the right ballpark and make a plan. Clean the aircraft up, provided that this will not deplete electrical, pneumatic or hydraulic resources better used later in the approach.

Then by all means attempt to optimise your flightpath by tuning the speed.

But IMO trying to nail the speed given in the POH down to the last knot is a waste of precious capacity, not least because you're going to want some margin to modify your L/D in both directions for approach control, and therefore a field which genuinely requires you to perfectly nail (L/D)max isn't actually safely reachable in the first place.

Kettenhunde
09-15-2009, 05:53 PM
Vbg .....is not a fixed quantity that you can look up.

I agree that it changes based upon weight. Due to the shape of the curve, IAS is close enough and works well which is why it is listed in the POH as a fixed quantity a pilot can look up to commit to memory.


the safety margin in absolute terms (ie knots) will therefore tend to be larger for faster aeroplanes.


Depends on the airplane, Viper.


OTOH, with an alpha gauge, it would be perfectly possible to just say "fly at 11 units of alpha" and this would be correct for all loadings.


I agree and an AoA indicator is great tool to have on the panel.

I was thinking about installing this one:

http://www.aircraftspruce.com/.../aoaprofessional.php (http://www.aircraftspruce.com/catalog/inpages/aoaprofessional.php)

On my aircraft.


Instead you just want to minimise the altitude lost in the turn.

Exactly, thank you for explaining it to RAF_OldBuzzard. It is just another tool in the tool bag for a proficient pilot. There is no need to fear it.

All the best,

Crumpp

WTE_Galway
09-15-2009, 06:49 PM
Naturally we all get drummed into us in basic training "engine failure on take off never try and turn back to the airfield" but the situation is different with enough altitude.

The Chief pilot at my old school had a neat trick, he used to mark the furtherest point you could reach at L/Dmax on the strut of a Cessna or wing of a Piper with a small piece of plastic tape. Anything on the ground inboard of the tape you could reach deadstick ... anything outboard of the tape forget it. The trick worked up to a reasonable altitude very reliably.

RPMcMurphy
09-15-2009, 07:46 PM
Pretty neat idea. I had a soaring instructor pull a fast one on me. He said we were going to go to a 2000 ft release fly a ways out and try some left and right 360s to check my ability to hold a constant speed.
On take off, and to my complete suprize, he pulled the release just as we passed 200 ft AGL. "Okay what now?" He asked.
I turned into the wind and then tear-dropped back to the grass strip and set her down nicley in the oposite direction. After we finally got set up and ready for take-off again, I was just about to waggle the rudder to signal the tow plane to go ahead when he said "Wait a minute."
Then, he unbuckled his straps, opened the canopy and got.
"Go ahead and take her up yourself to 2000 ft."
He said. I was kind of shocked. I was'nt expecting him to say that because that was then my first ever solo flight. I took the glider up and had a good time.

Wurkeri
09-15-2009, 11:08 PM
Originally posted by Pigeon_:
Is there a list of optimal glide speeds for the planes in IL-2 somewhere?

As Viper notes, there is no single optimal glide speed in game because the weight varies and there is no direct way to find out the optimal AoA or read it while in flight.

However, you can make a sort of device to get all this information using the devicelink and UDPGraph and see all this real time while in flight.

The optimal AoA and weight information can be found from the modded side of the world (details elsewhere) or you can test them yourself (time consuming alternative). Once you know these, just add the needed to the functions to the UDPGraph: The real time AoA can be calculated from the devicelink pitch and variometer data and optimal AoA using the polar or alternatively directly the speed using the weight (IAS or TAS, what ever you see most practical). Naturally you can add function for the minimum sink as well if you want.

Then just place the UDPGraph to the side of the screen and adjust glide angle in flight until your AoA (or speed) matches the wanted AoA (or speed) be it the best glide or minimum sink or what ever you see desirable.

M_Gunz
09-16-2009, 03:48 AM
You know that our VSI's lag and even the movement of The Ball includes type of fluid used in IL2?
You know that those devicelink readouts are to drive home-pit displays? Not absolute game data?

Of course in steady conditions you can probably trust the reading except, ummmm, fast dives and climbs?

Wurkeri
09-16-2009, 04:55 AM
Originally posted by M_Gunz:
You know that our VSI's lag and even the movement of The Ball includes type of fluid used in IL2?
You know that those devicelink readouts are to drive home-pit displays? Not absolute game data?

Of course in steady conditions you can probably trust the reading except, ummmm, fast dives and climbs?

Yes, there is lag in the variometer readings, however it's pretty much neglible once the plane settles to steady flying condition, be it steady glide, fast dive, climb or what ever.

But test it yourself; setup devicelink and UDPGraph, take a plane, get some altitude and test various glide speeds. You can set the UDPGraph to show directly the glide angle or ratio which makes easy to find right ballpark.

Note that you can calculate glide angle also from the speed, altitude and time variables so you don't have to depend on variometer readings. Then just crosscheck if the results are sound.

Kettenhunde
09-16-2009, 05:42 AM
there is no single optimal glide speed in game

I don't know about your game but IRL the tolerance in this realm of flight is ~5%. That is pretty wide.

The first action in an engine out in an aircraft with jettisonable stores is to jettison the stores so I canít figure what the use for Best Glide while loaded would be. Maybe it has some game application that does not apply to actual airplanes?

M_Gunz
09-16-2009, 02:23 PM
Originally posted by Wurkeri:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by M_Gunz:
You know that our VSI's lag and even the movement of The Ball includes type of fluid used in IL2?
You know that those devicelink readouts are to drive home-pit displays? Not absolute game data?

Of course in steady conditions you can probably trust the reading except, ummmm, fast dives and climbs?

Yes, there is lag in the variometer readings, however it's pretty much neglible once the plane settles to steady flying condition, be it steady glide, fast dive, climb or what ever.

But test it yourself; setup devicelink and UDPGraph, take a plane, get some altitude and test various glide speeds. You can set the UDPGraph to show directly the glide angle or ratio which makes easy to find right ballpark.

Note that you can calculate glide angle also from the speed, altitude and time variables so you don't have to depend on variometer readings. Then just crosscheck if the results are sound. </div></BLOCKQUOTE>

When I was doing devicelink checks, I used altimeter data which does seem solid in response. At every turn there are
obstacles in how close or how well the data can be used, it's amazing what's been done.

AndyJWest
09-16-2009, 03:52 PM
M_Gunz wrote:
You know that those devicelink readouts are to drive home-pit displays? Not absolute game data?

I've done quite a bit of experimentation with DeviceLink, while working on a prototype autopilot/instrument panel application (never finished, and probably never will be). From what I can tell, much of the data is pretty close to that used in-game, and things like VSI lag are probably handled by the individual cockpit display software for each aircraft, rather than at the stage DeviceLink is acquiring them. One would need to see the IL-2 source code to be sure about this, and I haven't (and nor do I want to, unless it is officially released by the legitimate copyright owners...)

The DeviceLink data is quite adequate to enable my autopilot to hold altitude to within a metre or so, for instance, and this is in spite of my iffy algorithms.

M_Gunz
09-16-2009, 06:10 PM
I go by my own email exchanges with Oleg long ago. And there was info dropped in many threads the last 7+ years.

UDPSpeed which I ran first has external gauges. Set one up and see, the needle points to the devicelink data value.
I can buy simpit panels with gauges and readouts or separate gauges, switches, whatever and they all display the
data given directly.

Oleg Maddox has realistic instrument lag built-in, devicelink values only reflect what your instrument panel shows.
You can IL2 in a Window and set up the UDPSpeed gauges below and viola, the same. Gauges you can glance down at.

AndyJWest
09-16-2009, 06:25 PM
I'm going by memory here, as I've not got my AP software installed on this PC (I must do this soon...), so you may be right - as I said, the data seemed mostly good enough to do what I wanted, and maybe the lag isn't significant there - in fact it could account for some of the problems I had getting it to stabilise rapidly, though I think this is mostly due to 'inertia' effects, pitch/yaw coupling and the like - basically, I treated the problem as if I was looking at data from a real aircraft, and programmed accordingly, though I was very much making it up as I went along.

My app had its own gauges, which would presumably show the same data since it is all coming from DeviceLink.

M_Gunz
09-16-2009, 08:32 PM
When IAS is below takeoff speed, have it ignore the Ball and VSI and just watch the wings and the horizon and use the rudder
to keep the wings level instead of the ailerons. I know of one AI that does not handle back side of the curve flying already.

Wurkeri
09-16-2009, 10:34 PM
Gunz,
You don't need to speculate. Just do those test glides as suggested above and crosscheck variometer values against altitude/time variable. Simple test takes less than 15 minutes.

M_Gunz
09-17-2009, 02:30 AM
Speculate? About what?

The VSI needle lags only with changes beyond gentle. The Ball is very sensitive to negative G too.
If you fly a gentle path then sure, no lag. Does that prove there is no VSI lag or something?

Wurkeri
09-17-2009, 04:00 AM
Originally posted by M_Gunz:
Speculate? About what?

The VSI needle lags only with changes beyond gentle. The Ball is very sensitive to negative G too.
If you fly a gentle path then sure, no lag. Does that prove there is no VSI lag or something?

The point is very simple: There is lag, no one denies it, however, you can easily test how large the error caused by the lag is, so you don't need to doubt if the variometer gives good enough values at steady conditions (dive, glide or climb). Simple test takes no time and after that you have something concrete instead hazy doubts.

If a simple test is too much, then you can just take one of those spreadsheets on dive tests I posted to you. Take any steady part of the dive or climb and crosscheck variometer value against altitude and time variable.

My own finding is that once the plane has settled to the dive or climb, the variometer reading error is less than 1% depending somewhat on Autopilot settings. Your mileage might vary but walk before you talk.