will the P-47 have an optional dorsal fin?

[ZachariasX]

1 hour ago, Bremspropeller said:

Those fins are mostly about improving stability in the pattern (when slow), not necessarily during combat (when fast).

Those fins made it harder to signifiacantly yaw the aircraft. Once they got the bubble canopy, you could yaw them too easily past specified loads. The fin helps you not doing that. Especially when nervous. 

[Legioneod]

1 minute ago, ZachariasX said:

Those fins made it harder to signifiacantly yaw the aircraft. Once they got the bubble canopy, you could yaw them too easily past specified loads. The fin helps you not doing that. Especially when nervous. 

I already have happy feet when trying to get a gun solution, I don't need it to be any harder, plus I like the look of the dorsal fin.

[Bremspropeller]

It's more about additional damping than about restricting yaw angles per sé.

 

Were there any maneuvering/ yaw restrictions on bubbletop P-47s (or P-51s for that matter) without the fin?

Edited August 23, 2018 by Bremspropeller

[Legioneod]

30 minutes ago, Bremspropeller said:

It's more about additional damping than about restricting yaw angles per sé.

 

Were there any maneuvering/ yaw restrictions on bubbletop P-47s (or P-51s for that matter) without the fin?

Ive read that slow rolls were restricted in the P-51 for the most part, it was discovered that it could induce a snap roll and was one of the reasons for the dorsal being added.

 

The only maneuver that was restricted in the P-47 was a snap roll and sometimes a split s, though neither of these were due to a lack of dorsal fin as far as Im aware.

[Rjel]

3 hours ago, Poochnboo said:

Yeah, Gambit. I think calling the early models Mustangs "razorbacks" is a gamer/flight simmer thing. Never heard a Mustang pilot call it that. I also hate, "Stang." Another gamer term that real pilots never used. 

Oh, and I also don't understand why the dorsal fin, or fin strake, is so important to some people. I'm just glad we're getting a Thunderbolt. 

Thank you!!! I've railed against those clicky modernistic terms for a long time too. I can handle T-Bolt even though I don't know that that was a WWII term or if it is just an extension of T-Bird as in Thunderbird. 'Stang just seems like a lazy way of saying North American P-51 Mustang, the fighter that won the war, the greatest fighter ever built, better than anything else anywhere in the world..... sorry. I got carried away.

[Poochnboo]

By the way, not to bore everybody, but that picture of Tarheel Hal reminded me of a great day I had at an airshow years ago. I was allowed to sit in that airplane! It was at the Alliance Airshow in Dallas Texas. I saw that beautiful Jug and of course ran right over. I was talking to the pilot and I suppose that he could see that I wasn't the usual, "Uh...is that a World War Two airplane?" type of airshow viewer. 

He says, "Climb up on the wing and I'll show you the cockpit. Just step on the tire and pull yourself up with the gunbarrel."

As if he had to tell me that. I'd done it a million times in my mind! 

So I'm standing on the left side of the cockpit and he's on the right. Were talking and I say, "I've read that it was pretty roomy compared to other cockpits. It looks it."

"Yeah, it is," he says. "Go ahead, get in!"

Uh....what!? Hell yeah... over the side I go and I'm sitting in a real life Republic P-47D Thunderbolt! You can't imgaine how many times I'd been there in my head.

He decides to let me see what it felt like with the canopy closed. He slid it shut. It was in the middle of August. In Texas!. Sweat started running down my back immediately. Can't imagine what it must have been like in the South Pacific. 

My Brother-In Law, Victor, took a picture of me sitting there with a big ^*&% eating grin on my face. I don't know what the hell happened to it because I've searched for it a dozen times.

Oh well..hope that didn't go on too long. But can't wait for this models release. Maybe a skinner will do Tarheel Hal!

Edited August 23, 2018 by Poochnboo

[Legioneod]

34 minutes ago, Rjel said:

'Stang just seems like a lazy way of saying North American P-51 Mustang, the fighter that won the war, the greatest fighter ever built, better than anything else anywhere in the world..... sorry. I got carried away.

We all know you meant P-47 Thunderbolt, it's ok to get confused sometimes.

[Rjel]

30 minutes ago, Legioneod said:

We all know you meant P-47 Thunderbolt, it's ok to get confused sometimes.

Well second best then.

[MiloMorai]

3 hours ago, Bremspropeller said:

It's more about additional damping than about restricting yaw angles per sé.

 

Were there any maneuvering/ yaw restrictions on bubbletop P-47s (or P-51s for that matter) without the fin?

 

The P-51B/C had some yaw instability.

 

2 hours ago, Legioneod said:

We all know you meant P-47 Thunderbolt, it's ok to get confused sometimes.

 

Nope, the P-51 brought the fight to the Luftwaffe well into German while the P-47 could barely make it to the German border.

 

If one wants to get into a P-47/P-51 discussion on that, a new thread should be stated.

[Rjel]

31 minutes ago, MiloMorai said:

 

The P-51B/C had some yaw instability.

 

 

Nope, the P-51 brought the fight to the Luftwaffe well into German while the P-47 could barely make it to the German border.

 

If one wants to get into a P-47/P-51 discussion on that, a new thread should be stated.

I think it was meant as a joke. Therefore, I hereby state that any thread started should clearly start what was stated. 

[MiloMorai]

or use a ?

[Legioneod]

53 minutes ago, MiloMorai said:

 

The P-51B/C had some yaw instability.

 

 

Nope, the P-51 brought the fight to the Luftwaffe well into German while the P-47 could barely make it to the German border.

 

If one wants to get into a P-47/P-51 discussion on that, a new thread should be stated.

In terms of actual contribution to the war effort the P-47 did more. It's a similar situation with the B-17 vs B-24. Another thread should be started, I'm curious to see what people say.

[ZachariasX]

8 hours ago, Bremspropeller said:

It's more about additional damping than about restricting yaw angles per sé.

 

Were there any maneuvering/ yaw restrictions on bubbletop P-47s (or P-51s for that matter) without the fin?

It would oscillate once you give yaw input? I can‘t really think of an aircraft that does that. That is news to me.

 

On the other hand, most aircraft are very restricted in tolerating sideways loads. American aircraft were built with larger tolerances, British aircraft were not even *cleared* for any sideways loads whatsoever (although they surely could absorb them). You can see this as the planes are not being cleared for flick rolls or any maneuver that combines vertical and horizontal loads.

 

For instance, you are not supposed to flick roll a Tiger Moth, but the Bücker is cleared for that. But both aircraft are built rather similarish. My take is really that this is related to preferences on the side of the designers rather than a whish from pilots that supposeldy were complaining about a yaw unstability. Also I have never read about a pilot complaining about the aircraft without the fins.

 

But if anyone has solid info on this, I‘d be happy to learn about that.

[303_Bies]

Destructive load factor required in US fighters was 12, for British 11.

Load factor of the undercarriage in US fighters was 6g, for British 4g.

In US fighters the engine mount structure was resistant to lateral load of 2g, for British there was no such requirement at all.

etc.

That's one of the reasons why Mustang was havier but more durable than Spitfire.

[BornToBattle]

Looks-wise definitely I’m for flying without it. I think it mucks up the lines on the Jug. However, as suggested I suppose once the base model is up and running they can introduce a few different variants as they have with other aircraft (the 109 leaps to mind). I’m also not a fan of the Razorbacks at all but for those that are, hey, why not introduce that variant which as time goes on, I’m quite sure they will.

 

I’m just so anxious to see the thing for the first time in the sim as it’s my favorite for WW2. Oh, and zipping around in the P-38 in the Pacific wouldn’t hurt either, or pretending I’m the “Iceman” in my Zero, or taking up my B-24 as a pilot with some amazing nose art and then switxhing to play bombardier in order to help achieve the mission goal on the western front or getting white knuckles dive bombing shipping not to then mention the eventual carrier landing in my Dauntless somewhere in open waters and then there’s yadda, yadda, yadda along with with a nice electric bill for running my PC’s 1200 watt power supply 24/7 for months on end and the inevitable expensive and somewhat embarrassing divorce proceedings that follow as “Irreconcilable Differences” has been crossed out and “IL2” written over top of it and I’m reduced to playing Namco’s Air Combat on PlayStation while on lunch break at work since the wench cleaned me out and I’m living in a ‘84 Ford Tempo...but I digress...

[Legioneod]

21 minutes ago, BornToBattle said:

Looks-wise definitely I’m for flying without it. I think it mucks up the lines on the Jug. However, as suggested I suppose once the base model is up and running they can introduce a few different variants as they have with other aircraft (the 109 leaps to mind). I’m also not a fan of the Razorbacks at all but for those that are, hey, why not introduce that variant which as time goes on, I’m quite sure they will.

 

I’m just so anxious to see the thing for the first time in the sim as it’s my favorite for WW2. Oh, and zipping around in the P-38 in the Pacific wouldn’t hurt either, or pretending I’m the “Iceman” in my Zero, or taking up my B-24 as a pilot with some amazing nose art and then switxhing to play bombardier in order to help achieve the mission goal on the western front or getting white knuckles dive bombing shipping not to then mention the eventual carrier landing in my Dauntless somewhere in open waters and then there’s yadda, yadda, yadda along with with a nice electric bill for running my PC’s 1200 watt power supply 24/7 for months on end and the inevitable expensive and somewhat embarrassing divorce proceedings that follow as “Irreconcilable Differences” has been crossed out and “IL2” written over top of it and I’m reduced to playing Namco’s Air Combat on PlayStation while on lunch break at work since the wench cleaned me out and I’m living in a ‘84 Ford Tempo...but I digress...

Sounds like you got the next year or so all planned out, good thinkin, most people can't see that far ahead.

 

The Razorback is by far my favorite of the P-47s, the D-22 specifically. The cockpit just looks so cool with that thick piece of armored glass right in front of you. Another reason I like the Razorbacks is because they had different turbos which resulted in different critical altitudes, the D-22 was around 25k ft iirc, it had the same performance as the later blocks, just at a lower altitude.

 

Not sure if this is a D-22 but the cockpit would look similar.

[69th_chuter]

18 hours ago, Poochnboo said:

By the way, not to bore everybody, but that picture of Tarheel Hal reminded me of a great day I had at an airshow years ago. I was allowed to sit in that airplane! It was at the Alliance Airshow in Dallas Texas. I saw that beautiful Jug and of course ran right over. I was talking to the pilot and I suppose that he could see that I wasn't the usual, "Uh...is that a World War Two airplane?" type of airshow viewer. 

He says, "Climb up on the wing and I'll show you the cockpit. Just step on the tire and pull yourself up with the gunbarrel."

As if he had to tell me that. I'd done it a million times in my mind! 

So I'm standing on the left side of the cockpit and he's on the right. Were talking and I say, "I've read that it was pretty roomy compared to other cockpits. It looks it."

"Yeah, it is," he says. "Go ahead, get in!"

Uh....what!? Hell yeah... over the side I go and I'm sitting in a real life Republic P-47D Thunderbolt! You can't imgaine how many times I'd been there in my head.

He decides to let me see what it felt like with the canopy closed. He slid it shut. It was in the middle of August. In Texas!. Sweat started running down my back immediately. Can't imagine what it must have been like in the South Pacific. 

My Brother-In Law, Victor, took a picture of me sitting there with a big ^*&% eating grin on my face. I don't know what the hell happened to it because I've searched for it a dozen times.

Oh well..hope that didn't go on too long. But can't wait for this models release. Maybe a skinner will do Tarheel Hal!

 

 

That cockpit is up there, like sitting on top of the wing on a bar stool!

[Talon_]

6 hours ago, Legioneod said:

Sounds like you got the next year or so all planned out, good thinkin, most people can't see that far ahead.

 

The Razorback is by far my favorite of the P-47s, the D-22 specifically. The cockpit just looks so cool with that thick piece of armored glass right in front of you. Another reason I like the Razorbacks is because they had different turbos which resulted in different critical altitudes, the D-22 was around 25k ft iirc, it had the same performance as the later blocks, just at a lower altitude.

 

Not sure if this is a D-22 but the cockpit would look similar.

 

P-47G-10-CU, identical to P-51D-5-RE but built by Curtiss.

[Bremspropeller]

13 hours ago, ZachariasX said:

It would oscillate once you give yaw input? I can‘t really think of an aircraft that does that. That is news to me.

 

No, the damping of the yaw-oscillation mode is incresed by the fillet/ strake.

Any aircraft has a short-coupled yaw-oscillation (like in pitch), when excited.

 

The additional damping is achieved by a larger side-area and the strake acts like a vortex-generator (as in a LERX), producing a steeper moment-curve at the same sideslip-angle.

The steeper-curve sets in at a definate beta-angle (just like vortex-lift becoming significant on a delta-wing at a certain AoA).

Edited August 24, 2018 by Bremspropeller

[ZachariasX]

58 minutes ago, Bremspropeller said:

 

No, the damping of the yaw-oscillation mode is incresed by the fillet/ strake.

Any aircraft has a short-coupled yaw-oscillation (like in pitch), when excited.

 

The additional damping is achieved by a larger side-area and the strake acts like a vortex-generator (as in a LERX), producing a steeper moment-curve at the same sideslip-angle.

The steeper-curve sets in at a definate beta-angle (just like vortex-lift becoming significant on a delta-wing at a certain AoA).

What you are saying is a good explanation for why it is harder to yaw the plane by deflecting the same sized rudder.

 

The pendulum motion along the yaw axis is something I‘m sceptical about. In real aircraft, depressing the rudder just makes the nose point to a direction and it is never (I can‘t think of any glider or GA aircraft that would do so) swinging left and right until it found its angle. Or very, very little. As long as the aircraft is not unstable in yaw like the Dr.I that you constantly have to keep from veering of course, it will simply not oscillate like that. (The Dr.I doesn’t oscillate. It just departs to flying crabwise. But it doesn’t swing left snd right.) There might be other oscillations like a duch roll, but no yaw swing.

 

If cutting down the fuselage produces such light rudder controls letting you fully deflect them with ease at cruise speed or faster, a designer might reconsider that as the sideways load might get past specs.

 

The aircraft is not meant to be flown hands off anyway, and certainly not so with full fuel load. You, as designer, expect the pilot to consantly control an aircraft like the P51. In this sense the neutral to unstable configuration is even desired. It improves agility. Unless of course the airframe would potentially end up in a flight configuration that damages the airframe.

[MiloMorai]

Some of the early jets tended to 'snake' at higher speeds. Increasing fin area helped to decrease the 'snaking'.

[ZachariasX]

9 hours ago, MiloMorai said:

Some of the early jets tended to 'snake' at higher speeds. Increasing fin area helped to decrease the 'snaking'.

Wasn‘t that in fact „Dutch Rolling“? Reading again what @Bremspropeller wrote, I went through my library again.

 

The „snaking“ as I know it comes from:

• large propeller (usually in RC models, but P47 etc do have such)
• strong static yaw stability
• low dynamic stability (eg. heavy weight, weight far out)
• tail heavy (longer arm for torque force of the prop)

 

@Bremspropeller was obviously right with his assessment of dynamic instability that may well lead to dutch rolling if it is not corrected in a perfect way on the controls. All criteria fit to both P47 and P51 when you cut down the fuselage and put more weight in the tail.

 

It is of note that this dynamic instability requires a constant torque force, here by the large and heavy propeller.

 

AFAIK jets used to have dutch roll induced by uneven lift generation of the swept wings, as when yawing, one wing gets more lift than the other. If you compensate that in a delayed fashion (it is very hard to do it right) then the plane will keep on doing it.

 

It is thus very plausible that the designers mended more than just the concern about the airframes integrity.

 

[-TBC-AeroAce]

Most modern airliners suffer from Dutch roll hence why they all have computer yaw dampers. 

[Dakpilot]

Even a basic light twin such as a King Air has a yaw damper

 

Cheers Dakpilot

[ZachariasX]

Yes , there are the strakes on the underside of aircraft, like the Learjet as well.

 

16 minutes ago, Dakpilot said:

Even a basic light twin such as a King Air has a yaw damper

 

Cheers Dakpilot

But that one is a toggle that engages sort of an „auto rudder“ function, right? You toggle that after takeoff, as it makes the pedals very hard to depress. Do you still use rudder in cruise flight after engaging the yaw damper in the King Air? Unfortunately, I only have experience in very light aircraft and never made it to light aircraft as the King Air...

[Bremspropeller]

I'm not talking about duch-roll per sé, but it is a major concern, of course.

Dutch roll is a combined effect of yaw- and roll-stability and is basicly the opposite of a divergent spiral-mode.

In dutch-roll, roll-stability is much larger than yaw-stability, so the coupled yaw-response lags behind the roll-response, leading to a yaw-excitement about 90° out of phase (behind) the initial roll upset.

 

I'm talking about an excitement in yaw (e.g. a quick step on the rudder and then quickly going neutral again).*

The aircraft will start a short-coupled oscillation. The osciallation is normally damped within one or two swings. In fact, there is a certification-criteria that has to be met.

But if you take stability (e.g. fuselage side-area aft of the CoG) away, the damping is decreased and the oscillation gets more agressive. That could be in different ways - either the amplidude or just the duration it takes to dampen the osciallation. Or both.

 

A yaw damper is an artificial means of increasing yaw-stability.

If you want to see scary stories about dutch-roll, look for the 707. The 707 (and 727 IIRC) suffer from severe flight-limitations if the YD is MEL'd.

In fact, there was a relatively recent crash of a KC-135 in Kyrgystan due to a less than optimal recovery from dutch-roll.

 

____

* To be more clear here:

You hit the rudder very quickly and then go neutral. Just a quick step. That's an excitement like a gust would do.

The airplane will swing around the yaw axis (there will be a response in roll too, but let's focus on yaw here) and quickly dampen the upset. It's NOT about depressing the pedal and the aircraft swinging into and around it's sideslip angle, although this would happen at large rudder-inputs, resulting in an overswing and the resulting damping around the correspondant sideslip-angle.**

If you excite in pitch, there is a similar induced swing that is quickly dampened. That's the "short period" mode. The "long period" mode in pitch is about how long the airplane takes to seek and find it's trimmed airspeed.

 

** This is mostly due to the high beta-rate (angular speed around the yaw-axis) picked up during the yaw-motion, overshooting the intended sideslip angle and then swinging around that angle with the damped oscillation.

 

14 hours ago, ZachariasX said:

The aircraft is not meant to be flown hands off anyway, and certainly not so with full fuel load. You, as designer, expect the pilot to consantly control an aircraft like the P51. In this sense the neutral to unstable configuration is even desired. It improves agility. Unless of course the airframe would potentially end up in a flight configuration that damages the airframe.

 

That is not quite true. The 51 and most other american warbirds can be trimmed around all axes.

Unless there is a perturbation, the airplane will be flying straight and level if trimmed for the current airspeed.

The trim-effectivity and stability will be effected by the shift of CoG. The more forward, the more stablbe the airplane is in pitch and yaw.

 

A P-51 could be flown "hands off" - not for 8 hours straight, but the airplane was stable enough (once the 85gal tank was used up enough) to be reasonably comfortable to fly.

 

 

Weren't there also simple A/Ps (like wing-levelers) in many late-war US airplanes? I'd have to did it up...

 

 

[Talon_]

42 minutes ago, Bremspropeller said:

Weren't there also simple A/Ps (like wing-levelers) in many late-war US airplanes? I'd have to did it up...

 

 

P-47N manual discusses autopilot operation

[ZachariasX]

39 minutes ago, Bremspropeller said:

A P-51 could be flown "hands off" - not for 8 hours straight, but the airplane was stable enough

No aerobatics with rear fuel tank as well as no blind flying. That's what I meant. It could be trimmed out, absolutely.

[Bremspropeller]

They did do blind-flying with the tank, though.

War is hell...

[Poochnboo]

With the weather in England, there was no way they could put a ban on no blind flying with that tank full. 

12 hours ago, ZachariasX said:

No aerobatics with rear fuel tank as well as no blind flying.

 

[-TBC-AeroAce]

7 hours ago, Poochnboo said:

With the weather in England, there was no way they could put a ban on no blind flying with that tank full. 

 

 

Meaning they put a ban on blind flying? Double negative bro.

Edited August 26, 2018 by AeroAce

[Poochnboo]

With the weather in England, there was no way they could put a ban on blind flying with that tank full. 

Corrected.