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Touchy Jug


Igor4U

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Been trying to get a Good Feel for the P-47 over last couple months.    But of all my Aircraft - this one has been the most challenging.

Almost all my other War Birds have detectable cues you can pick up on as you approach and reach Stall AoA - and back off the Pull/Back-Pressure on the Stick before you Depart controlled Flight.   The P-51 Stang took a while to feel out - but I'm Good with her Now.  But the 'Jug' is an entirely different Animal.

 

I really don't detect any cues (Vibration - Buffet - Lack of Turn Rate - etc...) at all before she'll snap off and depart into a Spin - Usually at the most inopportune time.     Besides flying her gently like a Fast Cessna 172 - what's a Feller to do ?  

 

 Any tips would be appreciated.

 

TANKS !

 

Related:

Spin, Spin Spin.....
https://forums.eagle.ru/topic/257010-spin-spin-spin/

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  • 2 weeks later...

Her mass might dampen things a bit.

 

Sounds like you're at high power when this happens? What is your speed on entry?

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"When performing a forced landing, fly the aircraft as far into the crash as possible." - Bob Hoover.

The JF-17 is not better than the F-16; it's different. It's how you fly that counts.

"An average aircraft with a skilled pilot, will out-perform the superior aircraft with an average pilot."

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I got the P-47 earlier this evening and taken her out for some flying...

 

The roll due to torque/spin is quite controllable if you're on the rudder as you add power. Even slamming the throttle from near-idle to max power is controllable with rudder and some aileron.

 

I tested empty, full aux tank (aft CoG), and low speed/high AoA (~100 MPH).

 

Accelerated stall entry is a bit harder to deal with, but unload, power, and anti-spin control inputs can really help get you out even at low altitude. Just don't go trying to bury the airspeed needle below 100 kts and you can get out of most situations from relatively low altitude.

 

She flies really nice! My only question is: does the engine really fail that quickly if you mis-handle it? Specifically low power at relatively high speed. Seems to destroy the engine in seconds.

Motorola 68000 | 1 Mb | Debug port

"When performing a forced landing, fly the aircraft as far into the crash as possible." - Bob Hoover.

The JF-17 is not better than the F-16; it's different. It's how you fly that counts.

"An average aircraft with a skilled pilot, will out-perform the superior aircraft with an average pilot."

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6 hours ago, Tiger-II said:

 

 

She flies really nice! My only question is: does the engine really fail that quickly if you mis-handle it? Specifically low power at relatively high speed. Seems to destroy the engine in seconds.

You need to reduce RPM before reducing throttle, master bearing wont survive long.

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16 hours ago, grafspee said:

You need to reduce RPM before reducing throttle, master bearing wont survive long.

 

Thanks! I saw another post that says this is accurate to the real engine due to it having a single main bearing.

Motorola 68000 | 1 Mb | Debug port

"When performing a forced landing, fly the aircraft as far into the crash as possible." - Bob Hoover.

The JF-17 is not better than the F-16; it's different. It's how you fly that counts.

"An average aircraft with a skilled pilot, will out-perform the superior aircraft with an average pilot."

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21 hours ago, grafspee said:

You need to reduce RPM before reducing throttle, master bearing wont survive long.

 

Is this specific to the Thunderbolt? It should always be "prop on top:" Advance RPM before advancing throttle, reduce throttle before reducing RPM.

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46 minutes ago, Nealius said:

 

Is this specific to the Thunderbolt? It should always be "prop on top:" Advance RPM before advancing throttle, reduce throttle before reducing RPM.

What i meant that you need to do it in steps

Drop MP a little bit then drop rpm a little bit something like that, when you cut throttle to 0 with out reducing rpm at the same time master bearing wont survive.

In our P-47 we have throttle/rpm interconnector, this is super handy in dives when you need to reduce power a lot to not over speed.

Rule stays the same when reducing power always throttle go first then rpm.

But someone posted interesting observation, that when you set your rpm higher then 2900 engine main bearing will be damaged no matter MP is.Mine failed at 3000rpm at 52" in matter of seconds when 3060rpm is max permissible rpm for p-47.Something isn't modeled as should be. Maybe in deed engine is too touchy in this underboost departament. Sure you can avoid it, easy when operating below 2700 rpm but at higher rpm engine should survive as well.


Edited by grafspee

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This does seem way too touchy, because having to reduce throttle AND RPM during landing, and then being expected to put both throttle AND RPM back on for a go-around seems wholly unreasonable to me. No other warbird has issues with prop pitch full, idle throttle. 

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^ That's because they don't have this bearing-related stuff implemented yet :D. Well, A-8 does, but since it adjusts throttle and pitch at the same time, it doesn't count. Seriously though, I think P-47 will be a testbed for a while before these effects get tweaked and introduced in other warbirds as well.

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58 minutes ago, Art-J said:

^ That's because they don't have this bearing-related stuff implemented yet :D. Well, A-8 does, but since it adjusts throttle and pitch at the same time, it doesn't count. Seriously though, I think P-47 will be a testbed for a while before these effects get tweaked and introduced in other warbirds as well.

It's only for radials, V12 are immune to that.

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6 hours ago, Nealius said:

This does seem way too touchy, because having to reduce throttle AND RPM during landing, and then being expected to put both throttle AND RPM back on for a go-around seems wholly unreasonable to me. No other warbird has issues with prop pitch full, idle throttle. 

I'm not sure about this.

When you're flying reasonably slow (ca. 150 mph) pulling the throttle to idle with RPM level at max (or better, at the specified 2550 rpm) shouldn't be an issue - the prop RPM will drop anyway.

Every manual tells you to set RPM to 2550 prior to landing (usually upon entering the landing pattern) along with all other landing checks.

landing.png

I've been following this instruction on every landing and never had any issue (unless the engine was already damaged)


Edited by PL_Harpoon
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Very important thing is to set 2550rpm while you fly power on at speed, setting 2550 at low speed or low throttle may not be exactly 2550 when you back on power.

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"Engine controls - interconnected"

 

Link throttle and prop for landing?? Am I understanding this correctly?

Motorola 68000 | 1 Mb | Debug port

"When performing a forced landing, fly the aircraft as far into the crash as possible." - Bob Hoover.

The JF-17 is not better than the F-16; it's different. It's how you fly that counts.

"An average aircraft with a skilled pilot, will out-perform the superior aircraft with an average pilot."

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@grafspee Where were you seeing the 3060 max permissible RPM from? The P-47C/D manuals I've got (AAF Manual no 50-6) list the redline at 2700 rpm, while the P-47N (AAF Manual 51-127-4) only goes up to 2800 RPM.

 

They're pilot training manuals rather than engine vendor specs, so they certainly don't tell the whole story, but I am interested where I could find those numbers.

 

Thank you,

 

Harry Voyager

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1 hour ago, Voyager said:

@grafspee Where were you seeing the 3060 max permissible RPM from? The P-47C/D manuals I've got (AAF Manual no 50-6) list the redline at 2700 rpm, while the P-47N (AAF Manual 51-127-4) only goes up to 2800 RPM.

 

They're pilot training manuals rather than engine vendor specs, so they certainly don't tell the whole story, but I am interested where I could find those numbers.

 

Thank you,

 

Harry Voyager

Search for engine chart at the end of manual, then you will find this 3060 rpm limit among turbo rpm limit and other limits.

3060 is not operational range of the engine.

Same is in P-51 max rpm 3000rpm. But max dive rpm speed is 3250rpm, it is even mentioned in emergency procedures that you can utilize this limit in case of gavernor fail.

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4 hours ago, grafspee said:

Search for engine chart at the end of manual, then you will find this 3060 rpm limit among turbo rpm limit and other limits.

3060 is not operational range of the engine.

Same is in P-51 max rpm 3000rpm. But max dive rpm speed is 3250rpm, it is even mentioned in emergency procedures that you can utilize this limit in case of gavernor fail.

Ah, found it. Thank you. Interestingly, the P-47B, C and D models pre-25 appear to have has a 3050 RPM limit, so not much on a change between the engine versions. 

 

I wonder how that interacts with the throttle recommendations for diving? 

 

I also wonder what mach speed the tips are at at that RPM? I recall that there was a big drag spike when the prop tips start hitting the transonic region, which leads me to wonder if that could counter the flight speed acceleration on the prop RPM? Have to think about how to analyze and test that. 

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I calculated that at 3060rpm assumed 0.45 gear reduction ~ 640mph at tip of the blade..

In dive where your rpm is going above 2700 you can only reduce throttle to avoid overspeeding the engine, prop handle wont change a thing in that situation (prop pitch already reached max pitch angle it cant go farther.). So you cant test  how fast you will dive with or w/o engine overspeed.

One thing interested is that Curtis electric prop pitch span is between 22 to 45 degrees, for example prop from P-51 hydromantic Hamilton has range 26 to 65 degrees and personally i didn't experience any prop overspeed in P-51


Edited by grafspee

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Is that 640 mph at the tip with the aircraft at a standstill? 

 

From what I recall, the top speed in motion becomes a combination of the rotation and aircraft velocity. 

 

I think I need a whiteboard to draw what I'm thinking the forces are... I'll try that tonight when I'm back at my decktop. 

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