Improve That Design: How Aircraft Could Have Been Made Better

[Zipper730]

I think it was all theoretical, did anyone ever do serious dive bombing in four engined ww2 bombers and evaluate the difference to something like a He177?

What would intrinsically stop a 4 engined plane from dive-bombing? The only issue would be structural limits and, I can't see why two huge engines or four large engines would make a difference if the bomber weighs around the same amount.

 

[pbehn]

What would intrinsically stop a 4 engined plane from dive-bombing? The only issue would be structural limits and, I can't see why two huge engines or four large engines would make a difference if the bomber weighs around the same amount.

It is way above my pay grade in the subject but it is about the slowing effect of two big props against four smaller ones, then the spread of the loads on pull out from the dive, you need massively strong wings to withstand the forces of the engine weight so far from the fuselage/wing root.

 

[Thumpalumpacus]

What would intrinsically stop a 4 engined plane from dive-bombing? The only issue would be structural limits and, I can't see why two huge engines or four large engines would make a difference if the bomber weighs around the same amount.

The weight itself. When we talk about a "3-G pullout" or "6-G turn" what is really being said is that for a short period of time, the aircraft functionally weighs that much more in that part of the envelope. So a big 4-engined bomber (two or four props, I don't think it's very different) weighing 60,000 lbs at the bottom of a dive requiring a 2-G pullout functionally weighs, for a few brief moments, 120,000 lbs -- meaning that the airframe must be designed for the stresses of that weight if you want it to do that maneuver.

The bitch about that with heavy bombers pulling higher Gs is that all the reinforcement you put on it to resist those strains also add a lot of weight when you're pulling Gs. And with wider spans and longer lengths, you get more leverage at high-Gs at the ends of the wings, or the tailplane. I think it's called "moment"? I'm still learning this stuff, hopefully someone can chime in with detail and fix what I've gotten wrong.

 

[Zipper730]

It is way above my pay grade in the subject but it is about the slowing effect of two big props against four smaller ones, then the spread of the loads on pull out from the dive, you need massively strong wings to withstand the forces of the engine weight so far from the fuselage/wing root.

With the He 177, I remember the drag difference was around 3%. If you're supposed to do 500 km/h, that would shave off around 15 km/h of top-speed, which isn't trivial.

As for the structural loads, i was told that the engine pods counter wing bending, which increases with g-load. I figure that would be beneficial not counterproductive. Admittedly, that knowledge comes from commercial aviation.

The bitch about that with heavy bombers pulling higher Gs is that all the reinforcement you put on it to resist those strains also add a lot of weight when you're pulling Gs. And with wider spans and longer lengths, you get more leverage at high-Gs at the ends of the wings, or the tailplane. I think it's called "moment"? I'm still learning this stuff, hopefully someone can chime in with detail and fix what I've gotten wrong.

G-loads are a force of acceleration, in this case centrifugal as a result of changing direction. To do so requires excess lift, which has to be present to pull off the maneuver. That said, it's a structural issue for sure, and strength/weight and thrust/weight favor the small (volume favors the large).

 

[XBe02Drvr]

The bitch about that with heavy bombers pulling higher Gs is that all the reinforcement you put on it to resist those strains also add a lot of weight when you're pulling Gs. And with wider spans and longer lengths, you get more leverage at high-Gs at the ends of the wings, or the tailplane. I think it's called "moment"? I'm still learning this stuff, hopefully someone can chime in with detail and fix what I've gotten wrong.

Well said. Another factor to consider is with a high aspect ratio long wing full of heavy fuel and engines your inertial moment is going to be so great as to interfere with rolling maneuvers. Why does this matter? Look at how dive bombing (as opposed to glide bombing) is actually done. Positioning for the run in requires the pilot to keep the target in sight as he judges angles and spacing, resulting in a roll-in to the final dive, not the gentle forward bunt into the dive that armchair heavy dive bomber designers imagine. Dive bombers have shorter, lower aspect wings and weight concentrated near the CG for a reason.

 

[Thumpalumpacus]

G-loads are a force of acceleration, in this case centrifugal as a result of changing direction.

Yeah, that's what I was getting at.

To do so requires excess lift, which has to be present to pull off the maneuver. That said, it's a structural issue for sure, and strength/weight and thrust/weight favor the small (volume favors the large).

Yep. Big wings are required to swing a big plane through the sky. Those same big wings come with the penalty of having to be robust enough to carry the airplane that nominally weighs thirty tons through a turn that makes the plane think it's sixty tons.

As others have noted above, He-177s used much more a glide profile for attack. I bet wing-loading at pullout would be too much for steeper attacks.

 

[Thumpalumpacus]

Well said. Another factor to consider is with a high aspect ratio long wing full of heavy fuel and engines your inertial moment is going to be so great as to interfere with rolling maneuvers. Why does this matter? Look at how dive bombing (as opposed to glide bombing) is actually done. Positioning for the run in requires the pilot to keep the target in sight as he judges angles and spacing, resulting in a roll-in to the final dive, not the gentle forward bunt into the dive that armchair heavy dive bomber designers imagine. Dive bombers have shorter, lower aspect wings and weight concentrated near the CG for a reason.

That really makes sense to a layman like me. I hadn't considered that aspect at all.

 

[Zipper730]

As others have noted above, He-177s used much more a glide profile for attack.

In practice, I'm not sure if the aircraft ever used dive-bombing attacks. That said, the aircraft was able to pull a normal rated g-load of 4.0 (4.8 if you used a safety factor of 1.5) with an ultimate load of 7.2 (the Germans, for reasons I'm not clear, used a safety factor of 1.8)

I bet wing-loading at pullout would be too much for steeper attacks.

Wing loading is the ratio of weight to wing area. You're talking about g-load, or structural loads, but I know what you mean.

 

[Thumpalumpacus]

Wing loading is the ratio of weight to wing area. You're talking about g-load, or structural loads, but I know what you mean.

As the functional weight increases due to g-loading, so does the wing loading.

 

[pbehn]

In practice, I'm not sure if the aircraft ever used dive-bombing attacks. That said, the aircraft was able to pull a normal rated g-load of 4.0 (4.8 if you used a safety factor of 1.5) with an ultimate load of 7.2 (the Germans, for reasons I'm not clear, used a safety factor of 1.8)
Wing loading is the ratio of weight to wing area. You're talking about g-load, or structural loads, but I know what you mean.

I think you just stumbled upon the difference between a pound weight and a kilogramme.

 

[Zipper730]

Regarding the V-3420

I always wondered if the XP-54 wouldn't have faired better with the V-3420 and ditching the "turret" in the nose. It certainly looked cool!

I'm curious when the V-3420 was first available. The first plane that flew with it off the bat might have been the P-75, which first flew 11/17/43. That said, the XB-19 was fitted with it at some point in 1943. I'm not sure if anybody has anything on that.

(The following members P pbehn , S Shortround6 , W wuzak might have something here).

Regarding the Blackburn Firebrand

If there's any pre-jet era FAA aircraft that desperately needed intervention it's the Blackburn Firebrand.

It definitely could have used quite a number of refinements. From what I understand, it was designed as a single-seat, high-performance fighter to defend naval bases, but also could be carrier suitable, with a considerable endurance demanded.

"In test pilot and naval aviator Captain Eric Brown's opinion the aircraft was "short of performance, sadly lacking in manoeuvrability, especially in rate of roll".[12] The position of the cockpit even with the trailing edge of the wing gave the pilot a very poor view over the nose, inhibited his ability to view his target and to land his aircraft aboard a carrier, sufficient for Brown to call it "a disaster as a deck-landing aircraft".[13]"

Why the poor over the nose visibility to start with?

Regarding the B-26

The NACA M6 airfoil was rather close.

While I'm not sure why the NACA M6 wouldn't have been usable on the B-26, I think it would have been a good fit, and with mods, it could have probably been refined into something similar to the RAF 34.

I remember another member ( Greg Boeser ?) who appeared to have suggested the use of fowler flaps. I'm mixed on that. On one hand, it would have lowered increased the wing-area, but on the other hand -- it might have made the wing weaker (requiring additional beefening).

 

[pbehn]

look at it Interesting facts about the Blackburn Firebrand

 

[pbehn]

With the He 177, I remember the drag difference was around 3%. If you're supposed to do 500 km/h, that would shave off around 15 km/h of top-speed, which isn't trivial.

As for the structural loads, i was told that the engine pods counter wing bending, which increases with g-load. I figure that would be beneficial not counterproductive. Admittedly, that knowledge comes from commercial aviation.

G-loads are a force of acceleration, in this case centrifugal as a result of changing direction. To do so requires excess lift, which has to be present to pull off the maneuver. That said, it's a structural issue for sure, and strength/weight and thrust/weight favor the small (volume favors the large).

Wiki says this from Heinkel He 177 Greif - Wikipedia In the section on engines.
"A four-engine version would have been possible with engines like the Daimler-Benz DB 601 but the four-engine layout would impose higher propeller drag to the detriment of performance in dive bombing. "


The ins and outs of what propeller drag is and what it means are way above what I know or even want to know.

 

[MiTasol]

look at it Interesting facts about the Blackburn FirebrandView attachment 625425

Too bad the author did such sloppy research and writes so poorly. Could have been a much better article if the many mistakes like after equipping the aircraft with a Centaurus VII inline position engine had been edited by someone who knows that the Centaurus is a radial and left out the redundant word position.

 

[pbehn]

Too bad the author did such sloppy research and writes so poorly. Could have been a much better article if the many mistakes like after equipping the aircraft with a Centaurus VII inline position engine had been edited by someone who knows that the Centaurus is a radial and left out the redundant word position.

I was just looking at the pictures, it has the canopy of a Reno racer.

 

[XBe02Drvr]

Why the poor over the nose visibility to start with?

Are you asking why that visibility Is considered poor, or why did they build it that way? The first part of that question is obvious. Put yourself in that little cubbyhole almost back in the tail with your eyes only inches above the fuselage top and that big round engine sticking away out in front. Nuff said.

As for why they designed it that way, think of CG and fixed vs variable loads. Which would you rather have sitting on the CG, fuel or pilot? Got it?

 

[Thumpalumpacus]

look at it Interesting facts about the Blackburn FirebrandView attachment 625425

This needs an "oh s**t" likey-button.

 

[Shortround6]

Why the poor over the nose visibility to start with?

Engine and placement of the main fuel tank.
Changing to the radial did not help.

 

[Conslaw]

Regarding the V-3420

I'm curious when the V-3420 was first available. The first plane that flew with it off the bat might have been the P-75, which first flew 11/17/43. That said, the XB-19 was fitted with it at some point in 1943. I'm not sure if anybody has anything on that.
.

Well, it depends on what you mean by "available". The V-3420 was never set up for mass production It had commonality with the V-1710, but if you stole V-1710 production for the V-3420, you wouldn't have had as many P-38s, P-40s, P-39s, P-63s. There was only one plant building V-1710s (Indianapolis). Setting up a large bomber engine plant was a huge undertaking, witness the big R-3350 engine plant in Chicago.

 

[Zipper730]

Re: He 177 Grief

"A four-engine version would have been possible with engines like the Daimler-Benz DB 601 but the four-engine layout would impose higher propeller drag to the detriment of performance in dive bombing."

Hang on, I thought the drag was the installation (carburetor intake, radiator, oil-cooler) not the propeller? Is a larger propeller similar in effect to a wing with higher aspect ratio?

Regardless, I would have figured that higher drag would be beneficial in the dive phase as it acts like a brake a little bit. I'd have figured the problem would be during the cruise phase.

Re: Blackburn Firebrand

Engine and placement of the main fuel tank.

I guess it would have been preferable to put more fuel in the wings to avoid this?

Re: V-3420

Well, it depends on what you mean by "available".

I figure used in an aircraft for a starting point.

The V-3420 was never set up for mass production It had commonality with the V-1710, but if you stole V-1710 production for the V-3420, you wouldn't have had as many P-38s, P-40s, P-39s, P-63s.

I would have figured they'd have just built another factory to be honest.

I'm kind of tired, but I'd almost swear I was told once by somebody online that the original idea was to simply use 2 x V-1710 blocks, and it started out as an X-cylinder engine, but for one reason, it ended up as a W.

Why was this?