(P-47) Entry conditions of the power on Split-S?

[69th_chuter]

So, OK, with your confidence in induced drag being enough to overcome open throttle looping through straight down one would have a definite margin before things started to get out of hand.  But you'd have to have be very quick to have the stick well hauled in at start.  As a pilot I've found motors can be very much more impressively "powerful" going down than horizontal - lol.

 

 

[Voyager]

So just inferring from Greg's Airplanes and Automobiles recent video on P-47 match numbers: 

 

 

I'm thinking it's a combination of factors. First being, at 15,000 feet, it looks like the Max dive speed is higher than its highest likely critical match number, so if you aren't careful, or the weather is colder(?) than you were expecting, you can get stuck in the dive for several thousand feet and be in trouble. Further, it seems like the assumed max stick force and max G force they used was probably lower than what we have in game, and it sounds like the manual writers may have believed the aircraft had a lower critical match number than it seems like turned up in late war testing. 

 

All of this adds up to a goodly pile of reasons to recommend against doing a full power split S, and why it may still be in the performance envelope of the plane. 

 

Incidentally, it is striking that the speed of aileron reversal seems to be about where people are reporting that the ailerons come off in game. I'm wondering if the wings are being modeled as rigid objects in game, and that lack of springiness is causing the forces to concentrate on the aileron and pushing them past their failure threshold? 

[Legioneod]

1 hour ago, Voyager said:

So just inferring from Greg's Airplanes and Automobiles recent video on P-47 match numbers: 

 

 

I'm thinking it's a combination of factors. First being, at 15,000 feet, it looks like the Max dive speed is higher than its highest likely critical match number, so if you aren't careful, or the weather is colder(?) than you were expecting, you can get stuck in the dive for several thousand feet and be in trouble. Further, it seems like the assumed max stick force and max G force they used was probably lower than what we have in game, and it sounds like the manual writers may have believed the aircraft had a lower critical match number than it seems like turned up in late war testing. 

 

All of this adds up to a goodly pile of reasons to recommend against doing a full power split S, and why it may still be in the performance envelope of the plane. 

 

Incidentally, it is striking that the speed of aileron reversal seems to be about where people are reporting that the ailerons come off in game. I'm wondering if the wings are being modeled as rigid objects in game, and that lack of springiness is causing the forces to concentrate on the aileron and pushing them past their failure threshold? 

 

The jug was found to dive at speeds upwards of 600 mph which is above it's critical mach number so I'm sure there is a real danger  of getting stuck in the dive like you said.

 

As for the ailerons coming off it should never happen at the speeds the P-47 can attain, even at 600 mph it didn't lose ailerons but it did lock up and suffer from reversals.

I think ailerons coming off is just a result of previous damage models for dives, it needs to change and be updated to represent a more accurate model.

[Bremspropeller]

8 hours ago, Legioneod said:

I'm thinking it's a combination of factors. First being, at 15,000 feet, it looks like the Max dive speed is higher than its highest likely critical match number, so if you aren't careful, or the weather is colder(?) than you were expecting, you can get stuck in the dive for several thousand feet and be in trouble. Further, it seems like the assumed max stick force and max G force they used was probably lower than what we have in game, and it sounds like the manual writers may have believed the aircraft had a lower critical match number than it seems like turned up in late war testing. 

 

The temperature is a very important factor, good point!

I also think they're very conservative in their numbers - probably assuming a cruise-trimed airplane and thus a higher stick-force.

 

10 hours ago, Voyager said:

Incidentally, it is striking that the speed of aileron reversal seems to be about where people are reporting that the ailerons come off in game. I'm wondering if the wings are being modeled as rigid objects in game, and that lack of springiness is causing the forces to concentrate on the aileron and pushing them past their failure threshold? 

 

I think this is just a limitation of the game to enforce dive-speed limits.

While structural failure when disobeying limitations might be ok for some russian airframes (there, flutter MIGHT be an issue*), it's very much out of place for many other airplanes.

 

___

* It wasn't on most western (including german) fighters**. It also usually (well, pretty much always) takes off the entire wing - nut just the aileron.

** Well, the 109 had a couple of issues, but that's another story.

[CisTer-dB-]

On 11/20/2018 at 7:50 PM, CUJO_1970 said:

 

Yes, and the physics also tell us that potential energy turns in to kinetic energy that quickly carries us into compressibility - a double edged sword for the Thunderbolt. This is what was borne out by pretty much every P-47 dive test, ever - and it's really why the P-47 was not considered a remarkable aircraft tactically with regard to diving.

 

The physics advantage of the P-47 and it's heavy weight will be not so much the dive as the zoom climb following the dive. 

 

As far as how that will translate in the sim - we can see something similar in dives and zooms with combats between heavier and more powerful FW-190 against lighter Yak-1/7 and in the sim the advantage is not much at all.

 

 

 

 

Are you saying that he have a physic advantage on descent because of it's heavy masses?

Here and experiments 

In a vacuum chamber. A feather's drop accelerates at the same rate of 1 tonne of lead or 1000 tonne metrics if you want, same speed and distance cover on drop in a vacuum chamber free of any air. That should prove to you that the  masses or weight, heavy or low is irrelavent.

 

Now in a real word we leave and outside of the vacuum chamber you have to deal with air resistance. What you need is best aerodynamics, powerful engine, to name a few. 

 

I hope you find this useful   

 

Check this out 

 

 

Edited November 26, 2018 by ATAG_dB

[Bremspropeller]

5 minutes ago, ATAG_dB said:

Are you saying that he have a physic advantage on descent because of it's masses?

 

A heavier mass will resist acceleration (mass is for all intents and porposes just another term for inertia) initially. It will also resist deceleration for the same reason.

What's important in a dive isn't really mass, but weight (Fw = m*g), which equals a thrust-component, whenever going downhill. The steeper the dive, the more pronounced the additional thrust-component.

 

8 minutes ago, ATAG_dB said:

Check this out 

 

A very similar experiment was performed by David Scott on Apollo 15, when on the Moon.

He dropped a falcon-feather and a hammer - ultimately proving good ole Gallileo right...

[CisTer-dB-]

23 minutes ago, Bremspropeller said:

 

A heavier mass will resist acceleration (mass is for all intents and porposes just another term for inertia) initially. It will also resist deceleration for the same reason.

What's important in a dive isn't really mass, but weight (Fw = m*g), which equals a thrust-component, whenever going downhill. The steeper the dive, the more pronounced the additional thrust-component.

 

 

A very similar experiment was performed by David Scott on Apollo 15, when on the Moon.

He dropped a falcon-feather and a hammer - ultimately proving good ole Gallileo right...

Yes but not better then an aerodynamic one. You can drop two thing the same masses one a save and then other one is shape like a tear drop, what you drop faster?

You can outdive thing with a better a aerodynamic design way lighter aircraft, or a powerful engine, and better control authority (See aerodynamic)

 

If you what the test you understand that the only factor here is the drag . All everything on earth will accelerate at 9.8 m/s²    the only thing that affect that equation is air drag 

 

o7

Edited November 26, 2018 by ATAG_dB

[Bremspropeller]

3 minutes ago, ATAG_dB said:

Yes but not better then an aerodynamic one. You can drop two thing the same masses one a save and then other one is shape like a tear drop, what you drop faster?

You can outdive thing with a better a aerodynamic design way lighter aircraft, or a powerful engine, and better control authority (See aerodynamic)

 

If you what the test you understand that the only factor here is the drag   

 

Your idea is too simplistic.

 

What matters is where combined thrust and weight equal drag.

[CisTer-dB-]

2 minutes ago, Bremspropeller said:

 

Your idea is too simplistic.

 

What matters is where combined thrust and weight equal drag.

Oh you are right and on the case of the P47 its the combined major factor would be her big power. I think we're on the same page but your heavy weight statement that from experience have in most case little relevance in the complete picture   

[HR_Zunzun]

I think this chart is quite relevant for the discussion. It is found at the end of one of the p47 pilot  
manuals (british version)

 

https://www.dropbox.com/s/b5127tsicww7pfo/Screenshot_2018-12-01-01-52-41~2.png?dl=0

It shows that split-s (basically a half roll into the dive if I am not mistaken) can be done at different  
altitudes depending of the speed, providing that constant 4g are applied. If I am interpreting the chart
correctly a maximum of 400mph ias at 15000ft half roll into the dive can be used as long as  
constant 4g are applied. Recovery is at 2000ft. Doesn't says if power on or off but I think only  
makes sense the later.

[Ehret]

Lets compare some specs from the sim and what the Earth surface acceleration (9.8m/s2) can do with some mass:

K4 standard weight: 3361kg

P-47D standard weight: 6504kg

Thunderbolt is 3000kg heavier than the K4 or has twice the weight, roughly.

The K4' engine can output 1800hp at 4900m. The P-47' can output 2600hp up to 7000m.

 

Falling 1t on distance of 1m in 1s has power equivalent of 13.1 hp.

 

If you descend at 30m/s from 5km the Jug's frame will get*: 

6.504 * 13.1 * 30 = 2556.072 hp plus 2600 hp from engine = 5156.072 hp

 

At the same 30m/s from 5km K4' frame will get*:

3.361 * 13.1 * 30 = 1320.873 hp plus 1800 hp from engine = 3120.873 hp

 

It's easy to see that 5156/3120 is bigger than the 2600/1800 so the Thunderbolt effective power in 30m/s descend at 5km alt had increased relatively to the K4' by 14.4%. ((5156/3120)/(2600/1800))

Of course there is more to that but it shows that the gravity does work to an advantage of heavier planes with big engines. In the sim you can keep the K4 at bay if you descend hard enough in the Thunderbolt.

 

edit: to clarify - * this is total power at that very specific point in altitude and time. It doesn't tell what the final result of the dive will be.

Edited December 1, 2018 by Ehret

[Bremspropeller]

8 hours ago, HR_Zunzun said:

I think this chart is quite relevant for the discussion. It is found at the end of one of the p47 pilot  
manuals (british version)

 

https://www.dropbox.com/s/b5127tsicww7pfo/Screenshot_2018-12-01-01-52-41~2.png?dl=0

It shows that split-s (basically a half roll into the dive if I am not mistaken) can be done at different  
altitudes depending of the speed, providing that constant 4g are applied. If I am interpreting the chart
correctly a maximum of 400mph ias at 15000ft half roll into the dive can be used as long as  
constant 4g are applied. Recovery is at 2000ft. Doesn't says if power on or off but I think only  
makes sense the later.

 

Great find!

 

2000ft isn't too much terrain-clearance at all when you're flying on a QNH setting - there are some many areas in Germany (or continental Europe or the US if ou're trying out the chart in training) where 2000MSL will put you into the flank of a mountain. So you'd adjust that chart for real life conditions if you're one of those pilots destined to become old.

 

Would be interesting to know on where the trim is set to be. If you're trimmed for 400mph then the pullout-force will also be much higher than when trimmed to 150mph.

[Rattlesnake]

7 hours ago, Ehret said:

Lets compare some specs from the sim and what the Earth surface acceleration (9.8m/s2) can do with some mass:

K4 standard weight: 3361kg

P-47D standard weight: 6504kg

Thunderbolt is 3000kg heavier than the K4 or has twice the weight, roughly.

The K4' engine can output 1800hp at 4900m. The P-47' can output 2600hp up to 7000m.

 

Falling 1t on distance of 1m in 1s has power equivalent of 13.1 hp.

 

If you descend at 30m/s from 5km the Jug's frame will get: 

6.504 * 13.1 * 30 = 2556.072 hp plus 2600 hp from engine = 5156.072 hp

 

At the same 30m/s from 5km K4' frame will get:

3.361 * 13.1 * 30 = 1320.873 hp plus 1800 hp from engine = 3120.873 hp

 

It's easy to see that 5156/3120 is bigger than the 2600/1800 so the Thunderbolt effective power in 30m/s descend at 5km alt had increased relatively to the K4' by 14.4%. ((5156/3120)/(2600/1800))

Of course there is more to that but it shows that the gravity does work to an advantage of heavier planes with big engines. In the sim you can keep the K4 at bay if you descend hard enough in the Thunderbolt.

Correct me if I’m wrong here: Isn’t the relevant thing in both dive acceleration and energy retention the ratio of the weight of the airplane to its total drag, plus engine power? Ballistic coefficient one might say?

[Ehret]

18 hours ago, CMBailey said:

Correct me if I’m wrong here: Isn’t the relevant thing in both dive acceleration and energy retention the ratio of the weight of the airplane to its total drag, plus engine power? Ballistic coefficient one might say?

 

Yes but I meant only to show there is a difference in a total power and engines power is included, already. What the end result will be exactly - I'm not sure. It only means that at this specific moment the Thunderbolt achieves relatively more of it than lighter planes when descending. From historic remarks by pilots it seems that indeed the P-47 had advantages in diving. It could be one of reasons why.

Edited December 2, 2018 by Ehret

[Voyager]

On 11/30/2018 at 8:18 PM, HR_Zunzun said:

I think this chart is quite relevant for the discussion. It is found at the end of one of the p47 pilot  
manuals (british version)

 

https://www.dropbox.com/s/b5127tsicww7pfo/Screenshot_2018-12-01-01-52-41~2.png?dl=0

It shows that split-s (basically a half roll into the dive if I am not mistaken) can be done at different  
altitudes depending of the speed, providing that constant 4g are applied. If I am interpreting the chart
correctly a maximum of 400mph ias at 15000ft half roll into the dive can be used as long as  
constant 4g are applied. Recovery is at 2000ft. Doesn't says if power on or off but I think only  
makes sense the later.

 

Thank you. Knowing that those are 4g turns clears up the last question I'd had. Most of the games that have had the 'bolt allowed a 6-9g pull out, which would significantly tighten the S, and did not have mach tuck when you started hitting match 0.8, both of which make such a maneuver much more possible. 

[Bremspropeller]

That chart is just there to get the idea around that the airplane will pick up speed quickly when the nose it pointed at the ground and that recovering from a self-inflicted stupid attitude might become critical really fast.

 

Pulling 6-9g in a Split-S isn't really wise - you would not want to black out there or risk a high-speed stall.

[Voyager]

This is a bit of necro, but finally got around to doing testing in Il-2, now that I've got Bodenplatte. Starting from around 200 IAS I lose right around 4-5 kft doing a split-S with either power off, or 41" max continuous. I'm not really able to get the plane to pull enough g's to risk blackout, as the plane really wants to go into an accelerated stall. It's frankly, rather terrifying just how fast the altimeter starts to unwind once the nose is down...

 

Does make me wonder the viability of doing altitude pre-charged fast passes in the aircraft, but I'll need to do comparative tests on the 109K-4 1.98 and Fw-190A-8 to see what they cruise at at lower altitudes.