Jump to content

Hawker Tempest turning performance


Recommended Posts

15 hours ago, Bremspropeller said:

paging all the others, too (certaily including @Talon_ ) : Would a +13lbs option make sense for the Tempest on the Normandy map, given that most (all?) Tempest units were supposed to go V-1 hunting? Can't find any evidence for or against the use of the +13lbs setting during that timeframe.

 

Tempests hunting V-1s used Sabre IIA engines (modified to IIB standards at the fields, but not yet with that name) running +11lbs boost at 3700rpm.

  • Thanks 1
Link to post
Share on other sites
15 часов назад, Bremspropeller сказал:

Turning performance Tempest V vs Typhoon from 1943 (+7lbs boost available at this time).

 

Source:

http://www.wwiiaircraftperformance.org/tempest/Tempest-V_Eng-47-1658-C.pdf

 

 

 

Is it correct to compare the Tempest of the 1st production series and the 2nd? We have the 2nd. There's clearly something improved.

Link to post
Share on other sites
1 hour ago, Bremspropeller said:

 

But nothing's been improved that changes the turning-circle/ turn-radius.

Cannons. Hispanos mkV don't protrude the wing. Less resistance.

Do not know how much impact they created in terms of turning.

Link to post
Share on other sites
1 час назад, Bremspropeller сказал:

 

But nothing's been improved that changes the turning-circle/ turn-radius.

Цитата

Turning performance Tempest V vs Typhoon from 1943 (+7lbs boost available at this time).

And boost? We have +9 and +11 in the game. In 1943 - +7lbs boost

Link to post
Share on other sites
54 minutes ago, Bremspropeller said:

The boost-setting doesn't account for instantaneous turn-rates, which are lift-limited.

Boost-settings and RPM-limits will make a difference in sustained turn-performance.

Power setting has a considerable impact on Clmax, so it indeed does impact instantaneous performance to a degree. Question is how much?

Link to post
Share on other sites
15 minutes ago, Floppy_Sock said:

Power setting has a considerable impact on Clmax, so it indeed does impact instantaneous performance to a degree. Question is how much?

In the report mentioned above about the Spitfire they found that power setting is not really increasing Clmax in tight turns. If that was the case and all sim aircraft benefitted from that "mistake", then a plane like the Tempest is probably one of the planes that is helped the most. The Thunderspit had to be toned down, as it was obviously performing excessively well so in the sim. The larger the prop, the higher the power, the more a plane is prone to overperform then.

 

I don't really see a flaw in the Tempest specifically, but MAYBE a universal property that helps all planes in slow speed turns pulling rather impressive AoA.

Edited by ZachariasX
  • Upvote 1
Link to post
Share on other sites
3 minutes ago, ZachariasX said:

In the report mentioned above about the Spitfire they found that power setting is not really increasing Clmax in tight turns. If that was the case and all sim aircraft benefitted from that "mistake", then a plane like the Tempest is probably one of the planes that is helped the most. The Thunderspit had to be toned down, as it was obviously performing excessively well so in the sim. The larger the prop, the higher the power, the more a plane is prone to overperform then.

 

I don't really see a flaw in the Tempest specifically, but MAYBE a universal property that helps all planes in slow speed turns pulling rather impressive AoA.

Indeed. The reason I say how much is because it’s really hard to deduce how much the stall warning behavior designed into the spit wing effects clmax while turning. The claim  in the report above is that the buffet specifically lowers Clmax. So this is possibly unique to the spitfire wing. I’ve spent a bit of time going through the literature on the impact of slipstream on Clmax. Unfortunately I’ve yet to find much which supports the report.  Most I’ve found show a strict, considerable increase in Clmax with power on. 

  • Thanks 1
Link to post
Share on other sites
2 minutes ago, Floppy_Sock said:

Most I’ve found show a strict, considerable increase in Clmax with power on.

 

Yeah, but does that include speeds above the rather academic power-on stall?

The delta v between free air flow and the propwash is reduced at corner-speed, compared to the power-on stall condition.

I'd expect a noticeable decrease in thrust-induced Cl_max increse at corner.

Link to post
Share on other sites
3 minutes ago, Bremspropeller said:

 

Yeah, but does that include speeds above the rather academic power-on stall?

The delta v between free air flow and the propwash is reduced at corner-speed, compared to the power-on stall condition.

I'd expect a noticeable decrease in thrust-induced Cl_max increse at corner.

Depends on the publication. 
 

I am waiting for my university library to get me a few publications from the RAC from the late 30s on this subject specifically. 

  • Like 1
  • Thanks 2
Link to post
Share on other sites
7 hours ago, Bremspropeller said:

Another point worth asking is at which power-settings the turn-performance is measured. I haven't ever read a test-report that specificly mentions this.

I'd suggest they're testing at either fast cruise or MCP.

 

There likely exists an optimum. High power settings, especially at low speeds almost always destabilizes the aircraft. This is not modeled in game. So in theory, there's a happy medium between the added lift due to the slipstream of the propeller and the reduction in longitudinal stability of the aircraft. 

 

See the US Navy's test pilot school's flight manual found here: http://www.usntpsalumni.com/Resources/Documents/USNTPS_FTM_103.pdf in section 4.2.1.9 from which I quote:

 

Quote

Direct and indirect propeller effects on static longitudinal stability are generally significant. For “conventional” propeller airplanes (propeller ahead of CG), the combined effects are usually destabilizing.

 

DCS actually captures this quite well - it always makes me smile when people hop in the 109 in DCS and act all confused when they're trying to maneuver at slow speeds at 1.9 ata and the plane wants to pitch up like crazy..

 

Tangent aside, I did a really really rough test in the Tempest, maybe someone else can confirm:

 

At sea level, took the plane down to about 110 IAS, throttled back to zero. Was able to hold the plane level until 95-98 IAS at sea level. After that, could not prevent a nonzero sink rate.  With some rough numbers this returns a Clmax power off of 1.65 +- 0.5 

 

On the same map, started on the airfield, trimmed nose high as much as I could, applied full power and full stick back to see when the plane would lift off. Yes I understand that this is a terrible comparison but it's an easy way to get a "rough" estimate of power on lift coefficient. If anything, it should return a higher Cl due to ground effect.  However, the plane lifts off right at 95 mph.  I think I had about 40% fuel in both cases. This seems quite concerning.

 

Could it be possible that @ZachariasX's assumption might be right and that this trend is uniform across all aircraft in this sim?

 

 

 

 

Edited by Floppy_Sock
  • Like 4
  • Upvote 1
Link to post
Share on other sites

A ballpark estimate of the Tempest Clmax on aircraft level:

 

The Tempest wing profile is designed for low drag and not very well suited for high lift: Small nose radius, almost symmetrical and maximum thickness far back.

 

The site airfoiltools.com lists the 2D (infinite span) Clmax as around 1.2 for the Tempest profile. As a comparison, the popular NACA 230 used on the Fw-190 etc. lands at a Clmax of around 1.5 to 1.6. Note that the NACA 230 series has a bit of a “LE flap” down tilt at the nose which helps at high aoa which the Tempest profile lacks. While a Re of 1 M as used in airfoiltools is in on the low side you still get the idea how they compare.

 

But the 2D (infinite span) values do not account for 3D effects like a limited span and that lift goes to zero at tips and that the wing area in fuselage does not contribute as much as the wing. Usually, aircraft using the NACA 230 series profile therefore end up at an aircraft Clmax of around 1.35 power off or idling even if the 2D Clmax is around 1.5 to 1.6.

 

So a rough ballpark estimate for the Tempest would be Clmax=1.35*1.2/1.5= 1.1

 

If you are seeing Clmax in glide power off conditions for the Tempest substantially higher than that in-game then that sounds strange.

Edited by Holtzauge
  • Thanks 1
  • Upvote 1
Link to post
Share on other sites
24 minutes ago, Holtzauge said:

So a rough ballpark estimate for the Tempest would be Clmax=1.35*1.2/1.5= 1.1

 

If you are seeing Clmax in glide power off conditions for the Tempest substantially higher than that in-game then that sounds strange.

This makes sense. I look at it from this angle:

1.jpg.90e8ffc6726444208a74c29590687d11.jpg

 

If I use 85 mph as Vmin, then I get monstrous Clmax for 5'300 kg weight and 28.1 m2 wing, using the standard formulae.

 

Can it be that this stall speed is actually a steady-state flight configuration at considerable power, as opposed to full idle and holding the aircraft straight as it slows down, noting the moment where it drops over the left wing?

 

I have a real trouble making sense from this speed declaration in the manual. You know, the Merlin Spit stops flying slightly below that speed as well, meaning you can come in below 100 mph and set it down around that speed. The aircraft feels very handy at that speed. Apart from the sink rate you can get, it is not far from the optics you get from a potent GA aircraft.

 

3.jpg.36450ddd5aae5c91997454dbf70df89b.jpg

It is obvious from the manual that the Spit flies happily at 110 mph, and I can tell you it does, there is not even nose up at all noticeable. She always just goes straight where you point her, unless for the last momen where you flair her out on landing.

 

The Tempest on the other hand is said to be a whole different animal. Tha manual even says so:

2.jpg.6364db2982a7f1758ff2e7c3a3acc804.jpg

 

The manual wants you to come in WAY FASTER than in the Spit, in the Spit IX, you'd come in at 110 mph for primary approach and drop flaps and gear. In the Tempest, they ask for 170 mph!

 

There was supposedly this joke that a Tempest would land faster than a Spitfire would cruise. Looking at 85 mph stall speed, this is odd. On the other hand, using 1.1 as Clmax, I hear what they are saying. Looking in the Tempests PN, it tells me that below 300 km/h things will get problematic when goofing around in the Tempest. In the sim, that is where I outturn most others.

 

What we do know however, is that the Tempest indeed does fly at 120 mph:

4.jpg.a55906b7479889e2b02f86536aaf6622.jpg

 

If you can make a gliding apporaoch at 130 mph, it better still stays airborne at 120 mph, devoid of any safety margin whatsoever. That we indeed reach the ultimate limit around 120 mph in glide is, that we are told to not turn anymore at that speed. Notice that in the approach instructions, you still have more power on when pasing the inner marker than your Mooney could ever give you. That is why you can still go in your final approach at 110 mph. You take back that throttle, she will sit down right away.

 

I would say that in effect, the Tempest had to be calibrated to roughly 115 mph glide speed, as 85 mph is obviously only attainable through engine assisted increase of Clmax.

 

This would then give us indeed a Clmax of ~1.1. (Phew, I'd have hated getting 1.4 or so there..)

 

Then again.. as said above. I think all aircraft in the sim suffer through varying degrees from this systematic mistake, depending on their layout and what "stall speed" actually means as flight configuration in the manual. The at times very high Clmax allow for incredible high AoA flying in low speed turns. Something that you do not see in warbird flights, like ever.

 

Furthermore, it appears that in turns, you have to apply a glide Clmax instead of a power on Clmax.

 

I also want to put on a disclaimer on this for me not openly requesting FM overhauls, as that would mean they had to rebalance all affected aircraft completely. They better do this when there's time for such.

 

  • Upvote 3
Link to post
Share on other sites

Glad to see the experts pitching in. I will just add one more piece to the jigsaw.  I know a Sea Fury is not a Tempest, but it is a pretty good approximation in some respects. 

 

There was a fatal accident involving a Sea Fury in a botched landing in 2001: no peculiar icing or anything.

https://assets.publishing.service.gov.uk/media/5422f66440f0b61342000577/dft_avsafety_pdf_500974.pdf

 

My understanding is that the Sea Fury wing is the same as the Tempest's with a section cut out of the middle span, giving it an area of 26m^2 compared to the Tempest's 27.8m^2, but made of the same airfoils.

 

In the accident report the weight of the plane was given as ~4,500kg and the stall speed, power off in landing configuration as ~87 kt, = 161kph

Assuming that this is corrected speed, (he report gives no source) that means a F&G down CLmax of 1.39

 

Tempest in game specs data at minimum operating weight, F&G down, 4,585kg, minimum stall is 128kph = CLmax 2.09  (F&G up = 1.52)  Way higher than for any other single seater. Edit - so there may be a generic problem in the FM affecting all planes, but I doubt that is the only issue here. 

 

 

Edited by unreasonable
  • Like 1
Link to post
Share on other sites

I think @unreasonablehas posted the reason we see deviations from stated stall speeds in manuals and in-game before: At low speeds many aircraft IRL had a large position error so that the real stall speed is way higher than that indicated to the pilot which of course is what they would publish in a manual. In Il-2 we have no position error so WYSIWYG.

 

Taking the Spitfire as an example, we know that the aircraft Clmax idling is 1.36 from RAE trailing pitot measurements which are very accurate (The NACA 1.2 value is wrong due to calibration errors*). As I recall it the Spitfire had a very large position error evident in a calibration chart unreasonable posted a while back and if you used the uncalibrated cockpit IAS speed then you would get an unreasonable Clmax (no pun intended!).

 

Assuming that the Tempest weight 5221 Kg in the Il-2 tech specs is connected to the 150 Km/h stall speed figure this gives a Clmax of 1.73 which is simply too high especially seeing that the Fw-190 Clmax calculated the same way gives 1.58 and the Spitfire Mk9 gives 1.52.

 

So like @ZachariasX was saying, redoing all aircraft is probably not what anyone is asking for but it certainly looks like the Tempest needs to be toned down in this respect in relation to the other aircraft.

 

* Ref: RAE technical report 1106 by M B Morgan

Link to post
Share on other sites

The more I read about "stall speed", the less I am sure that I understand what actually happens with the respective aircraft at that speed.

 

You know, with a GA aircraft, you give maybe 50% margin over stall speed for a ladning approach. With a C172, you do maybe 65 kias for approach and at 44 kias (all up) it stops flying at max weight, they say.

 

Now, what do they say about our dear warbirds? The Tempest supposedly stopps flying at 85 mph, yet they ask you to come in for landing at 170 mph or so, a mighty 100% margin on top of whatever is stall speed! Why? Why not 50%?

 

The SpitfireIX's stated stall speed is ~95 mph all up or ~85 mph all down. They ask you to come for landing at 110 mph! that gives you 30% margin!

 

Now, they are not alone with that. As you posted @unreasonable, the Sea Fury is said to stop flying at 87 kias. How do you land that aircraft? There's Mikael Carlson, someone always worth listening to. He flew Duxfords Sea Fury I reserved time on that aircraft last year, I planned to go flying this Summer. But there was COVID19 and they had to crash that plane. For anyone still not believing that these aircraft are dangerous rides, think agan!  Mikael had this to say about stalling and landing:

 

Clean stall at idle power: 65 kias

All down stall, idle power: 60 kias

Acellerated stall, 4 g, at "around" 200 kias.

 

You know, for a 5 ton aircraft, with a 26 m2 wing, 65 kias stall speed clean gives an outlandish Clmax of about 2.9.

BUT, 4 g at 200 kias gives me 1.23. This is something we can work with.

 

It is of note that the Sea Fury gives you ample warning when it will depart when the wing starts to "burble", as oposed to the Tempest, of which I have read that it gives little warning. The Sea Fury will drop the left wing that is pushed down by torque of the engine.

 

Now, how about landing her? 170 (!) kias they say to come in and drop flaps first stage. That is mighty fast if indeed 65 kias would be "stall". What is going on there? What is the Fury doing at 65 kias? You bring her in over the threshold at 100 kias, i.e. at the same speed you bring in the Tempest V. The Fury becomes directionally unstable at lower speeds, hence the desire to do wheel landings (one of which led to the accident unreasonable posted) instead of doing three pointers.

 

That it is indeed imperative to maintain a good airspeed in order to make her going where you want to is also documented in the sad demise of that particular Sea Fury. They stated that they brought her down at 150 mph. This is very consistent to what you'd have to do in the Tempest. Now, a Spitfire can be brought down relatively safe in a small field. Not so the Tempest or the Fury. On paper, we have identical stall speeds, yet in reality, it just doesn't work that way.

 

Those low stall speed numbers are just not what we thing they are. The 4 g test gives a theoretical stall speed of ~110 mph, something that reall points where I envision the Tempests performance. These numbers are not supposed to be exact, but for the sake of the argument, they give me a plausible range of what should be.

 

Now, if the aircraft's flying qualities become questionable at 110 mph, then coming in at 200 mph makes more sense.

 

18 minutes ago, Holtzauge said:

but it certainly looks like the Tempest needs to be toned down in this respect in relation to the other aircraft.

It looks to me that several other aircraft need to be toned down as well. It would depend on the documentations "what kind of stall" actually was achieved when giving said numbers.

 

EDIT: I might add that there might be a lot of things going on at edges of the enveloppe, things that our lifting line theory has a hard time approximating. The Zebra videos give testament to this peculiarity present in all sims. So I am not really sure if the Tempest is"set right" wouldn't make it under par regarding many other planes that also overperform at low speeds.

Edited by ZachariasX
Link to post
Share on other sites
1 hour ago, ZachariasX said:

It looks to me that several other aircraft need to be toned down as well. It would depend on the documentations "what kind of stall" actually was achieved when giving said numbers.

 

EDIT: I might add that there might be a lot of things going on at edges of the enveloppe, things that our lifting line theory has a hard time approximating. The Zebra videos give testament to this peculiarity present in all sims. So I am not really sure if the Tempest is"set right" wouldn't make it under par regarding many other planes that also overperform at low speeds.

 

For sure it may affect other aircraft as well but if we can't get all tuned then the next important thing is to get the relative performance right (even if the mean is off for all) and right now it looks like the Tempest with a Clmax of 1.73 on aircraft level places it in a "class" of its own compared to the around 1.5 of the Fw-190, Me-109 and Spitfire.

 

The IRL power off Clmax for the Me-109 and Spitfire is around 1.4 and 1.36 respectively. If we in-game have 1.56 and 1.52 that is slightly more than 10% better. So reducing the in-game Tempest 1.73 by 10 % gives 1.56 compared to the Me-109 at 1.4 and Spitfire at 1.36. How on earth does that compute?

 

I would make an IRL estimate of the Tempest's Clmax at circa 1.1. Increasing that by 10 % yields 1.21 which seems a more reasonable in-game Clmax if the Spitfire is at 1.52 and the Me-109 at 1.56 in-game.

 

And yes, the low speed modeling with full power on can be funky sometimes: I especially enjoy @Monostripezebra's videos of Il-2's helicoptering onto Stalingrad roofs etc. ;)

Edited by Holtzauge
  • Thanks 1
Link to post
Share on other sites
19 minutes ago, Holtzauge said:

 

The IRL power off Clmax for the Me-109 and Spitfire is around 1.4 and 1.36 respectively. If we in-game have 1.56 and 1.52 that is slightly more than 10% better. So reducing the in-game Tempest 1.73 by 10 % gives 1.56 compared to the Me-109 at 1.4 and Spitfire at 1.36. How on earth does that compute?

 

 

Using the tech specs numbers we have Spitfires at 1.33-1.34, and the 109s at 1.38-1.40 : that is very close to the IRL numbers. The "NuTempest" is 1.52

Link to post
Share on other sites
30 minutes ago, unreasonable said:

 

Using the tech specs numbers we have Spitfires at 1.33-1.34, and the 109s at 1.38-1.40 : that is very close to the IRL numbers. The "NuTempest" is 1.52

 

Yes that was what I remembered as well from earlier calculations but take the stall speed of the Spitfire Mk9 143 Km/h and the weight 3359 from the tech specs:

 

3359*9.81=0.5*1.225*39.7**2*Cl*22.48 gives me a Cl of 1.52?

Link to post
Share on other sites
39 minutes ago, Holtzauge said:

 

Yes that was what I remembered as well from earlier calculations but take the stall speed of the Spitfire Mk9 143 Km/h and the weight 3359 from the tech specs:

 

3359*9.81=0.5*1.225*39.7**2*Cl*22.48 gives me a Cl of 1.52?

 

That is because you are using the "standard weight". The way I interpret the tech specs is that the lowest speed in each pair is at the "minimum operating weight" - ie 10% fuel and no ammo, which would represent the state of the plane at the end of a sortie, (2977kg for the Spit IX) while the higher speed is with the maximum take off weight. 

 

For the majority of aircraft, when you calculate the CLmax for these pairs, you get two values within about 0.01 of one another, so I am confident that this is the right way to do it.

 

From tech specs:

Note 2: flight performance ranges are given for possible aircraft mass ranges. [ie how I calculate CLmax]
Note 3: maximum speeds, climb rates and turn times are given for standard aircraft mass. [Everything else].

 

edit: if you use the standard weight with the mean of the speed range (143-163kph) you get 1.325 -  or better use the mean of the max and min operating weights and the mean speed and you get 1.343  - but I prefer to do the ends of each range method.

Edited by unreasonable
  • Thanks 1
  • Upvote 1
Link to post
Share on other sites

That rings a bell @unreasonable so thanks for reminding me how to connect weights and stall speeds in Il-2! :good:

 

So to compare apples with apples, using the number you posted above, the Tempest with a Clmax of 1.52 on aircraft level still places it in a "class" of its own compared to the 1.4 for the Me-109 and 1.36 for the Spitfire.

 

For the Fw-190 A3 I get 1.37 which is very reasonable seeing that the 2D Clmax for the NACA 230-series is 1.5 according to airfoiltools.com.

 

Using the airfoiltools.com 2D Clmax number for the Tempest profile which is 1.2, a first order approximation of the Tempest Clmax on aircraft level would then be:

 

Clmax=1.37*1.2/1.5=1.1 which is way lower than the 1.52 we have in-game today.

 

 

 

 

Edited by Holtzauge
  • Upvote 1
Link to post
Share on other sites

Yes the Tempest is definitely an outlier.  The 109s, for instance, get most of their extra CLmax compared to the Spitfires from their higher critical AoA - ie their AoA/CLmax polar graph which IIRC I posted earlier in this thread [see note 1] is almost the same slope as the Spit's, but extends further to the right. The Tempest has a lower critical AoA than the Spitfires.

 

1.1 gives an implied stall speed range of 176-205kph (109-127mph) using the weights on this method. Given the issues of speed measurement I could believe this, but if the number was dialed back to ~1.3ish  it would then be in a similar group with most of the other non-slatted types.

 

(Note1:  Heroically plotted with one data point per plane and an assumed origin at zero - I have an economics MSc so I am allowed to do that ;) )

Link to post
Share on other sites
1 hour ago, Holtzauge said:

I would make an IRL estimate of the Tempest's Clmax at circa 1.1. Increasing that by 10 % yields 1.21 which seems a more reasonable in-game Clmax if the Spitfire is at 1.52 and the Me-109 at 1.56 in-game.

Just as ballpark assumptions, my take away lessons are these:

 

The Tempest (and the Sea Fury) have a Clmax of ~1.1 when flown as gliders.

They both have a practical Clmax of about 1.25 in power turns, maybe only a 15% increase.

 

If a speed of 85 mph can be reached as the PN states, then a Clmax of ~1.45 must be reached in a power on, straight flight, meaning I get ~1/3rd increase due to propwash in best conditions.

 

IIRC, there has been a flight test with the Hellcat, where the Clmax power on / power off was something like 1.4 and 1.9, in relative terms an equal increase. But please, correct me on this.

 

It is of note that as soon as you actually have considerable flight speed, the propeller slipstream becomes progressively less effective. Has anyone done tests with accellerated stalls to see if the sim FM also compensates propwash for airspeed? One would have for instance to try a 200 kias turn in the Tempest and see when it flicks out. It should be around 4 g as well.

 

Now, if the game FM does not compensate power on / power off Clmax in relation to airspeed, then we would be hurting the Tempest by clipping it to "real" values, when competition gets slow speed power on Clmax.

 

I mean, I'd be really weary to touch the Tempest FM withput exactly knowing what is going on. I mean, the Tempest is only correct if I can hit 85 mph flight as well as having a "glider Clmax" of ~1.1.

 

 

  • Upvote 1
Link to post
Share on other sites
17 minutes ago, ZachariasX said:

 

 

I mean, I'd be really weary to touch the Tempest FM withput exactly knowing what is going on. I mean, the Tempest is only correct if I can hit 85 mph flight as well as having a "glider Clmax" of ~1.1.

 

 

 

No - the  "85" mph from the PNs is IAS.  We know that you have to add to that to get from RL IAS to game IAS, which is = CAS. Problem is 1) we do not know how much, and 2) Clmax calculation is very sensitive to change in V.

 

Just to add - the F6F trials numbers often give a clean stall power on vs power off, with a typical difference of 2mph. That works out as a difference in CLmax of only about 0.05

 

Edited by unreasonable
Link to post
Share on other sites

@unreasonable: For sure, it may be a bit higher than my ballpark estimate of 1.1 but if you look at the Tempest's wing profile in this link you can see that it looks terrible from a Clmax perspective (the small nose radius, minimal camber and thickness so far back so no surprise that the Clmax is only 1.2) and one can only guess why they choose that profile. Most likely Sydney Camm was covering his bets given the problems Hawker had had with the high speed performance of the Typhoon.

 

@ZachariasX: I agree with your rationale about the Clmax being higher with power on on the Tempest but then so should the Spitfire, Fw-190 and Me-109 Clmax be: So if the power on for the Tempest is 15% higher at 1.25 than the power off 1.1 then a first order approximation for the Spitfire and Me-109 would also be about the same 15% higher with power on.

  • Upvote 1
Link to post
Share on other sites
2 minutes ago, unreasonable said:

No - the  "85" mph from the PNs is IAS.  We know that you have to add to that to get from RL IAS to game IAS, which is = CAS. Problem is 1) we do not know how much, and 2) Clmax calculation is very sensitive to change in V.

That is why I said I used these figures as ballparks. I didn't intend to create exact numbers, plausible ones should do. I even added 10 mph  to IAS by using your spreadsheet ;) Thanks for that, it is useful for sanity checking assumptions.

Link to post
Share on other sites

I took your 85mph to be the stall speed F&G up from the PN (page 22) - but it is indeed the same for F&G down plus 10mph!  However, recall the RAE's PEC graph for these low speeds: errors approaching 20mph. 

 

Glad you still like my little calculator though: being useful in one's old age is one of life's few remaining pleasures.... 

  • Like 1
Link to post
Share on other sites

Position-errors can be huge.

 

IIRC during my C210 checkout (two people, low fuel, fully configured) I saw below 50mph on the ASI and we weren't even into the stall-horn yet!

That was at below approach power (we were delaying as ther ewas a Challenger blocking the RWY) and in a slow glide.

 

Link to post
Share on other sites
14 minutes ago, Bremspropeller said:

Position-errors can be huge.

 

IIRC during my C210 checkout (two people, low fuel, fully configured) I saw below 50mph on the ASI and we weren't even into the stall-horn yet!

That was at below approach power (we were delaying as ther ewas a Challenger blocking the RWY) and in a slow glide.

Yes, but huge errors is not what goes into the PN. They could tell if they landed at 85 or at 120 mph. Any kid can tell that difference by using eyeball 1.0. In the PN, you might find slight errors. Huge errors is what you have as base to make life-saving decisions in real time all the way until you turned off the engine on the right parking spot. This is why simple ways to sanity check your input can be handy.

Link to post
Share on other sites

I took our Temoest for a really quick check on accellerated stalls. I set 400 km/h and then did a quick, tight turn to see when it flicks out. It is not easy as speed drops quickly, but it seems that our tempest has indeed a Clmax of about 1.4, something that makes it hit the speed in the PN. By no means it performs as Mikael Carlson describes the Sea Fury with 4 g max at 380 km/h. I can go almost to 6 g at 400 km/h. It appears to me that the power setting has no influence. I must test a bit more  thoroughly. But enough for a plausible (to me at least) current working hypothesis of what we have.

 

We have a Clmax that might represent an all up situation, but is being skewed by the power on situation when obtaining that figure for the PN. Using that as a "glider Clmax" will clearly make the plane way better at slow speed.

 

Thus, every aircraft in the sim that has clean stall speed derived in a power on steady state will have inherited an excessive Clmax. This excessive Clmax should only apply in that steady state slow flight. In maneuvers Clmax is lower than that.

Link to post
Share on other sites

Can you tell the difference using eyeball 1.0 in the dark, or very poor weather, in an instrument approach?  No, you cannot.  The PNs had to say what the pilot would see on their instruments. I do not believe anything else makes sense.

 

Anyway, the issue is what is "huge". For the CLmax calculation, errors in speed will always be more critical due to the squaring. 10% speed error means 21% out in CLmax.  

Take 85mph literally as CAS and you are getting a Tempest CLmax of 1.85 

 

Link to post
Share on other sites
17 minutes ago, unreasonable said:

The PNs had to say what the pilot would see on their instruments. I do not believe anything else makes sense.

You think they would put in 85 knowing the plane goes 120? I mean if values are significantly off then there is usually a table detailing the error.

 

 If the gauge gave a completely arbitary value, it would be sad if all literature under the sun gave completely false values for some of the most profilic flight performance aspects.

 

We are really talking about a factory calibration here. If you wanted to certify an aircraft today and state a stall speed that is 40% off, I doubt you‘d get far.

 

Yes, there is an error to pitot instruments, but within reason.

Link to post
Share on other sites
33 minutes ago, ZachariasX said:

You think they would put in 85 knowing the plane goes 120? I mean if values are significantly off then there is usually a table detailing the error.

 

They do give a position error correction table in the Pilot's Notes. However, the stall speeds are outside its range because the corrections are primarily intended for navigation, where extreme speeds aren't very useful. We don't know what happens to the errors below 120 mph IAS.

 

The errors for an in-game Tempest with reduced CLmax would be around 15 - 25 mph, not 35 mph, so it's somewhat subtle.

 

33 minutes ago, ZachariasX said:

 If the gauge gave a completely arbitary value, it would be sad if all literature under the sun gave completely false values for some of the most profilic flight performance aspects.

 

The pilot doesn't care about the true numerical value of the stall speed. The pilot only needs to know where he is relative to aircraft limits. The stall speeds could be given on a completely arbitrary scale without any real harm.

 

Airspeed measurement errors only become a problem if you are interested in performance calculations. From countless test reports, we know that the errors are often large at very low speeds.

Edited by Mitthrawnuruodo
  • Upvote 1
Link to post
Share on other sites
26 minutes ago, ZachariasX said:

You think they would put in 85 knowing the plane goes 120?

 

Yes, because it's the only gauge to tell airspeed. Speed-perception is about angular speed, so it only really makes a difference approaching other than usually-shaped/ aspect ratio runways.

 

Again, not sure about your technique, but the last time I'm checking the ASI is usually above/ just before crossing the fence. After that, it's power-off, fly her down to the runway and flare.

All eyes outside. The ASI could be reading Mach 3 and I wouldn't notice.

Link to post
Share on other sites
5 minutes ago, ZachariasX said:

You think they would put in 85 knowing the plane goes 120? I mean if values are significantly off then there is usually a table detailing the error.

 

 If the gauge gave a completely arbitary value, it would be sad if all literature under the sun gave completely false values for some of the most profilic flight performance aspects.

 

We are really talking about a factory calibration here. If you wanted to certify an aircraft today and state a stall speed that is 40% off, I doubt you‘d get far.

 

Yes, there is an error to pitot instruments, but within reason.

 

The RAE measured this for the 109 they tested. It has been posted before: +27% CAS vs IAS.

 

The errors are not arbitrary, but presumably difficult to calibrate out at high AoA. Anyway, in a sense the error does not matter for a pilot when it comes to stalling - all he needs to know is the IAS his instrument will show.   The PEC is only relevant to a pilot for navigation purposes at normal transit speeds which is why the PEC correction tables almost never go down that far.  So the numbers are not "false": but they are IAS, not CAS which we need for CLmax.   In the game, no plane stalls at a speed as low as noted in PNs, AFAIK.

 

I am not saying that the Tempest error must be proportionately as large, but an 85mph stall speed is simply inconsistent with the data about the airfoil. Note that in the game now the  lowest clean stall speed is 93mph, not 85mph, which is about what it was on original release. 

 

To get to Holtzauge's 1.10 (plausible if the airfoil data is correct) you would need 110mph - so +30%   I find that surprisingly high, given the 109's exceptionally high critical AoA, but for the Tempest a 20% increase on the original 85mph gets you 101mph and into the 1.30 zone where it would be comparable with the main range of non-slatted fighters.

 

  

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...