Jump to content
zelil

IAS vs Ground speed

Recommended Posts

When watching WW2 pilots or aviation experts talk about the level flight top speed of and aircraft is it in reference to IAS or 

ground speed? The reason I would like to know is I can never even get close to those numbers even with AI handling complex engine management. 

example the P47 is supposed to have a top speed of 375mph but I can only make it go 275 even with boost on. Any info would be nice. I have no idea at what Altitudes any of these speed  tests took place.

Share this post


Link to post
Share on other sites
6 minutes ago, zelil said:

When watching WW2 pilots or aviation experts talk about the level flight top speed of and aircraft is it in reference to IAS or 

ground speed? The reason I would like to know is I can never even get close to those numbers even with AI handling complex engine management. 

example the P47 is supposed to have a top speed of 375mph but I can only make it go 275 even with boost on. Any info would be nice. I have no idea at what Altitudes any of these speed  tests took place.

 

Aircraft performance figures should only ever be given as true airspeed (TAS) - the speed the aircraft is moving through the air. Ground speed will only be the same as true airspeed if there is no wind. Measuring TAS accurately isn't simple.

 

As for the P-47 in-game, neither the cockpit instrument nor the on-screen display show TAS. They show indicated airspeed (IAS) , which should approximate to TAS at sea level under standard conditions, but will show progressively lower as pressure drops with altitude. As an approximation, adding 2% of your IAS (or more accurately in the real word, calibrated airspeed, CAS) for every 1000 ft of altitude above sea level should give a ball-park figure for TAS.

  • Upvote 2

Share this post


Link to post
Share on other sites

You can see the difference pretty good in the Me262, which shows above 400km/h TAS both, IAS and TAS. You can see how the difference gets more, the higher you climb.

Share this post


Link to post
Share on other sites

The real answer to your question is basically if the speed is not stated you can never know what they are using. 

Share this post


Link to post
Share on other sites

Go to apps on your phone, and download E6B pathfinder flight computer.

 

(Many other flight computer apps are available)

 

Put the relevant info in and voila, you'll get your TAS.

 

Really useful for plotting legs and doing blind navigation flying, remember first using it with the dangerdogz, doing an operation Jericho mission in hsfx6 1946, where we flew mosquitos tree top height across the channel all the way to target in blind visibility (heavy snow) using legs created on an earlier veversion of this app and a stopwatch.

 

Very satisfying indeed.

 

Oh, and top speed of an plane will always be TAS at a givern altitude which will be fairly high.

 

Edited by DD_fruitbat

Share this post


Link to post
Share on other sites
10 hours ago, zelil said:

When watching WW2 pilots or aviation experts talk about the level flight top speed of and aircraft is it in reference to IAS or 

ground speed? The reason I would like to know is I can never even get close to those numbers even with AI handling complex engine management. 

example the P47 is supposed to have a top speed of 375mph but I can only make it go 275 even with boost on. Any info would be nice. I have no idea at what Altitudes any of these speed  tests took place.

One thing with the P-47 is that you should be running it with cowl flaps fully closed except when you are are below about 200 MPH. Having the outlet flaps open even just a little bit causes a lot of drag, and you really don't need them for cooling as long as you keep your speed up. Also, you need to use the Turbo to get the most out of the engine, and with boost even at low alts I think you need the turbo engaged to get max speed. Make sure the turbo is set so the red light is blinking on the dash. The Jug really is just slow on the deck and doesn't start to come into its own until around 15000 feet or so.

  • Like 1

Share this post


Link to post
Share on other sites
16 hours ago, DD_fruitbat said:

Go to apps on your phone, and download E6B pathfinder flight computer.

 

(Many other flight computer apps are available)

 

Put the relevant info in and voila, you'll get your TAS.

 

Really useful for plotting legs and doing blind navigation flying, remember first using it with the dangerdogz, doing an operation Jericho mission in hsfx6 1946, where we flew mosquitos tree top height across the channel all the way to target in blind visibility (heavy snow) using legs created on an earlier veversion of this app and a stopwatch.

 

Very satisfying indeed.

 

Oh, and top speed of an plane will always be TAS at a givern altitude which will be fairly high.

 


First thing that popped into my head when reading about  your Mosquito sortie:

Image result for flight of the intruder

Edited by novicebutdeadly

Share this post


Link to post
Share on other sites
18 hours ago, RedKestrel said:

One thing with the P-47 is that you should be running it with cowl flaps fully closed except when you are are below about 200 MPH. Having the outlet flaps open even just a little bit causes a lot of drag, and you really don't need them for cooling as long as you keep your speed up. Also, you need to use the Turbo to get the most out of the engine, and with boost even at low alts I think you need the turbo engaged to get max speed. Make sure the turbo is set so the red light is blinking on the dash. The Jug really is just slow on the deck and doesn't start to come into its own until around 15000 feet or so.


Well depends whats slow for you I guess. The Jug can go 580kph on the deck, 360mph. Which is a tad faster than a Bf 109 G-14. Many just don't setup the plane correctly.
For top speed on the deck you need
1. Closed Outlets
2. Closed Oil rads
3. Intercooler (labeled as inlets) at 50%, which is the "flush" state.

4. Mixture at Auto rich, at 85%

5. Full Turbo

6. RPM at 83% which is around 2800RPM I believe.

7. of course full throttle.

8. Water injection

 

In that setting you can run away from G-14s and Fw 190 A-8s when flying between 2-3k. (they run in their "super charger gap)

 
 

Edited by DerSheriff

Share this post


Link to post
Share on other sites
3 hours ago, DerSheriff said:


Well depends whats slow for you I guess. The Jug can go 580kph on the deck, 360mph. Which is a tad faster than a Bf 109 G-14. Many just don't setup the plane correctly.
For top speed on the deck you need
1. Closed Outlets
2. Closed Oil rads
3. Intercooler (labeled as inlets) at 50%, which is the "flush" state.

4. Mixture at Auto rich, at 85%

5. Full Turbo

6. RPM at 83% which is around 2800RPM I believe.

7. of course full throttle.

8. Water injection

 

In that setting you can run away from G-14s and Fw 190 A-8s when flying between 2-3k. (they run in their "super charger gap)

 
 

Thanks for the tips! I think the fastest I've ever gotten on the deck is about 345 mph, but I forgot about the lower RPM to deal with the inefficient prop governor. I've always found that the 190A-8s just stay out ahead of me and the 109s pull away from me. The tech specs show the P-47 only getting 346 mph (557 km/h) on the deck and that's what I usually get, and the G-14 is shown as getting 576 km/h at emergency settings and the A-8 is shown as getting 558 km/h. I suspect that those specs don't take into account setting the RPM to 2800 for the greater top speed. How does the G-14 do for overheating? Does it lose a lot of top speed when running emergency due to the radiator deployment? The P-47's virtue for me is that running it 'clean' with rads  closed doesn't tend to cause overheats at all as long as you stay fast. 

The supercharger gap is great info. I knew it in the back of my mind but I never seem to apply it in a fight lol.

 

Share this post


Link to post
Share on other sites
6 minutes ago, RedKestrel said:

 The tech specs show the P-47 only getting 346 mph (557 km/h) on the deck and that's what I usually get, and the G-14 is shown as getting 576 km/h at emergency settings and the A-8 is shown as getting 558 km/h.
 


The listed specs for the P-47 are with 50% oil rad (rather than 0%), full RPM and 64" of manifold pressure. You can gain more speed like Sheriff says if you close the oil, decrease RPM, and if you go 100% throttle and 100% turbo you will overboost the engine to just a bit over 67" at sea level, all of this combined give the extra speed.

The A-8's speed of 558 km/h is for 1.42 ata, using it's extra boost to 1.58 ata it goes up to 581 km/h if you adjust the stabilizer for full nose down trim.

  • Thanks 1

Share this post


Link to post
Share on other sites
13 minutes ago, -=PHX=-SuperEtendard said:


The listed specs for the P-47 are with 50% oil rad (rather than 0%), full RPM and 64" of manifold pressure. You can gain more speed like Sheriff says if you close the oil, decrease RPM, and if you go 100% throttle and 100% turbo you will overboost the engine to just a bit over 67" at sea level, all of this combined give the extra speed.

The A-8's speed of 558 km/h is for 1.42 ata, using it's extra boost to 1.58 ata it goes up to 581 km/h if you adjust the stabilizer for full nose down trim.

But you get 10min of max on 109s and A8 while on P-47 less then 5min, and on top they get to their max speed faster then P-47 do as it takes him almost all its max time to reach high speeds close to what 109s and a8 do in no time and then just keep it for mutch longer time.

Share this post


Link to post
Share on other sites
15 hours ago, 77.CountZero said:

But you get 10min of max on 109s and A8 while on P-47 less then 5min, and on top they get to their max speed faster then P-47 do as it takes him almost all its max time to reach high speeds close to what 109s and a8 do in no time and then just keep it for mutch longer time.


true but most chases dont take that long. On most servers you are back to your airfield in 5mins. A little dive helps with the acceleration. and you can extent away a bit. and later to run away at a lower throttle setting until you are safe.

Edited by DerSheriff

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...