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Best glide speed to use for maximum range?


ekg
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Hello, I'm looking to do some emergency engine failure exercises with the spitfire. Does anyone know what the best glide speeds are in flaps up / flaps down configurations? Is it weight dependent?

 

Looks like speed is 150 mph [when maneuvering]. Not if this is an authentic/accurate POH. On final use glide speeds (105 flaps down 110 flaps up). Looks like the procedure would be flaps up and keeping the speed between 110-160 mph. A bit of a wide range.

http://zenoswarbirdvideos.com/Images/spit/SPIT9MANUAL.pdf


Edited by ekg
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According to the manual, 100-120 mph IAS.

 

What page / section? I tried looking. I saw 120 mph but that was for landing, with power?

 

Is this intended for emergency?

 

Gliding descent

1. Straight gliding descent with retracted undercarriage and flaps is performed at a speed of 100-120 mph IAS; with deployed gear and flaps, 100-110 mph IAS.

2. Avoid overcooling the engine. On lengthy gliding descents, raise the engine RPM to 2400-2500 for 5-6 seconds every 3-4 minutes.

3. Reliable motor acceleration is guaranteed when the coolant temperature is not lower than 60° C and oil temperature is not lower than 20° C.

4. Turning before landing approach must be done at a speed of 150mph IAS. (assuming final approach is started at an altitude of no lower than 500ft)

5. Deploy flaps at a speed no greater than 160mph by pulling the flap deploy handle downwards.

6. Check instruments to ensure that the flaps have indeed deployed successfully.

7. NOTE. In case of pneumatic system malfunction and a loss of pressure (below 120 lb/in²), perform the landing with retracted flaps, setting aside compressed air for the brakes.

8. After flaps deployment, smoothly pull the stick to reduce speed to 100-110 mph IAS, which is the normal gliding speed.


Edited by ekg
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Hello, I'm looking to do some emergency engine failure exercises with the spitfire. Does anyone know what the best glide speeds are in flaps up / flaps down configurations? Is it weight dependent?

 

not sure what the best speed is, but you should glide with flaps up.

Spitfire flaps don't really generate lift.. they just add drag.

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not sure what the best speed is, but you should glide with flaps up.

Spitfire flaps don't really generate lift.. they just add drag.

 

Would you say that it should never be used? For real life (i.e. in a Cessna) the flaps are used to slow down usually when final to the field is established.

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Regardless if flaps create lift or not, they always create drag. Only very few planes (e.g. the Do27) achieve the highest L/D ratio with the flaps partially extended.

 

@ekg You asked about the best glide speed, and this almost always happens with retracted flaps. If you want to glide as far as possible you keep the flaps retracted.

 

The Spitfire PN aren't very clear as they mention that at least 150mph should be maintained when maneuvering. When stretching the glide as much as possible you aren't maneuvering.

 

 

Ah I missed that. OK so I guess the way to fly it would be to maintain 110 and when turning drop the nose to get to 150, probably to not stall the aircraft? Makes it a bit interesting if I want to circle a particular field.

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Do not forget to set prop pitch to coarse. It affected much more than +- 10 mph.

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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I don’t know what is the best l/d is for the Spitfire. But, you could experiment a bit by noting the rate of decent at various speeds, and use the highest speed with the lowest decent rate.

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I've always assumed that best glide speed is about the same as best climb speed. I could be entirely wrong; anyone know?

 

Any function around its extremum varies very slightly, so there will be no fatal mistake if you use the same speed for dead engine gliding, The fatal mistake will be if you choose the wrong correction value trying to take the prop in account... :)

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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Do not forget to set prop pitch to coarse. It affected much more than +- 10 mph.

 

To be clear that's setting the RPM lever to lowest position? So humiliating to ask this. I should know. IIRC coarse grain is for slower flight and fine grain for cruise / performance?

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Nothing wrong at all to ask, but it's the other way round. Lowest RPM (high/coarse pitch) for high speed and highest RPM for low/fine pitch) for high speed.

Basically the same way as in a car, low gear for low speed and high gear for high speed.

 

I believe you meant: highest RPM for low/fine pitch) for lower speeds - instead...


Edited by jcomm
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Can we finally summarize for simplification and close this thread?

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And why would you want to close this thread?

 

"Best glide speed to use for maximum range?"

 

Simple answer and there is no more doubts.

 

There is a saying in my language " Why would you want to split a single hair in 4 quarts? "

 

...if you know what I mean :D

 

Basically the simple table is what we need ;) Then we can close this thread as [sOLVED]

 

Pedro out.

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We have the original pilot's handbook for the Spitfire, and there is clearly no published data for maximum gliding range. There is possibly a good reason for that. Bear with me...

 

I don't expect they were used much as gliders, and in an emergency, you either hit the silk, or make the best of a bad deal. I'm just guessing here, but unless you happen to have been carrying the manual into flight every time, tables wouldn't really be a lot of use.

 

There is also no way of telling the weight of the aircraft in order to establish precisely what your glide performance would be - you may have noticed the fuel gauge only measures the total in one of the tanks, and unless you can climb out of the cockpit, unfasten the panels on the wings and count the remaining rounds, another variable is also absent. So what use precisely would a set of graphs be to you when your engine fails?

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What will increase your glide time quite a bit is setting the prop to coarse pitch (lever fully back) so the prop is almost feathered and therefore reducing induced drag, this is assuming that you are in the glide following an engine failure! Every little helps to get you to that airfield in the distance or extra time in the air to look for a safe field and set up your approach to belly land.


Edited by bart

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We have the original pilot's handbook for the Spitfire, and there is clearly no published data for maximum gliding range. There is possibly a good reason for that. Bear with me...

 

I don't expect they were used much as gliders, and in an emergency, you either hit the silk, or make the best of a bad deal. I'm just guessing here, but unless you happen to have been carrying the manual into flight every time, tables wouldn't really be a lot of use.

 

There is also no way of telling the weight of the aircraft in order to establish precisely what your glide performance would be - you may have noticed the fuel gauge only measures the total in one of the tanks, and unless you can climb out of the cockpit, unfasten the panels on the wings and count the remaining rounds, another variable is also absent. So what use precisely would a set of graphs be to you when your engine fails?

 

This ^^

 

------

 

Basically your procedure on engine failure should be:

1. Quickly convert any excess airspeed (anything above around 140 mph) to altitude

2. confirm flaps up and gear up, and coarsen the prop

3. set a nose slightly down attitude for somewhere around 120mph indicated airspeed

4. trim out any forces and slip!

5. look for the nearest flat thing to try and land on (or bail out)

On YouTube: https://www.youtube.com/philstylenz

Storm of War WW2 server website: https://stormofwar.net/

 

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Even today most planes in this low weight category usually have only a single table.

 

True

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I'm just guessing here, but unless you happen to have been carrying the manual into flight every time, tables wouldn't really be a lot of use.

 

Back when I was at my peak of skill, I actually extrapolated the real-life P-38 best climb speed chart (IIRC, the speed went up with mass, up with power, and down with altitude) for the masses and power ratings I was using, and memorized it. I utilized this to great effect in the old sim-games. People often wondered how I got my P-38 to climb so well, and that was the answer.*

 

I didn't always have it exactly spot on; indeed, I tended to habitually climb about 10 MPH slower than the chart recommended (at the mass and power setting I was flying at, that was ~165 MPH instead of ~175, below 10,000 ft). I still don't know if this was an impatient mistake, or if my gut feeling was correct about the lower figure being more effective in the (often erroneous) sim-game. It's also possible that the original chart was wrong (or at least an "overly-gross approximation"), given that the real-life manual it was taken from had multiple errors.

 

I also, of course, had to guess my mass, but I did know my masses for various states (for example, when nearly out of fuel, and when taking off clean with a hundred gallons, and when I'm carrying drop tanks). This allowed me to guess with a reasonable degree of accuracy. "Close enough," while still giving me an advantage over anyone using a single figure for all cases.

 

So, I don't know about real fighter pilots, but given that at least one serious competitive simmer memorized one of these charts, I would assume that at least the more responsible of real fighter pilots, whose lives were on the line, memorized glide speeds as well as climb speeds.

 

 

* Over the thousands of hours I played old IL-2: Pacific Fighters, back in the early 2000s, I only met exactly one Zero pilot (a guy from Japan who went by the handle Sennbei) whom I could not out-climb over the course of five or ten minutes. Unlike all of the others, he kept up with me all the way to ceiling, and our protracted duels thus resulted in draws, with neither of us being able to touch the other. I was quite surprised when I first encountered him, because I'd always assumed that the P-38 out-climbed the Zero. Instead, I then realized, none of the other Zero pilots were climbing at their best climb speeds, the way he and I were. The difference was pretty drastic. I'm not sure if it would be so pronounced in DCS, because the older sim-games had less sophisticated drag models, which may have affected the results.


Edited by Echo38
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