Could you have designed a better Warbird?

[Burmese Bandit]

So...all the Sidney Camm, Kurt Tank, Kelly Johnson etc etc etc wannabees out there...


Could you have designed a better Warbird for any side, using only the technology known and in use at the time, staying within reasonable cost parameters, yet making enough of a difference to have been worth producing?

I will start with my idea for a german warbird very similar to the FW 190, staying within the rules I have set out above.

 

[Burmese Bandit]

The warbird I have designed draws upon three of the proven designs of WW II - the La-7, the FW-190, and (I'll bet very few will expect what's coming) the Do335!

First, it will be a twin-prop push-pull design, like the Do 335 ... but with this difference: whereas the Do 335 used two EQUAL engines to pull and push, I will use two engines - one main engine, and one auxiliary engine - the BMW 801 in front, and the Argus 411 in the rear.

Why?

First, it would solve the 335's problem of having to abolish the tail landing gear and introducing a nosewheel configuration - that would have caused training and production problems. An Argus 411 with 485 horsepower, together with a short-radius small four-blade propeller, could easily have been mounted in the tail fuselage behind the pilot, and the arc of the propeller would not extend below the vertical tail.

Furthermore, on the production side, using the Argus 411 as the rear engine would sidestep the 'engine shortage' problem perennially afflicting the Luftwaffe.

In addition, with the 1600 hp of the BMW and the 450-485 hp of the Argus, we have a fighter with a total hp of around 2100 ... in my mind, just about right for the balance of speed, weight and agility needed by fighters.

And, of course, both of these engines were air-cooled. Very important in terms of resistance to battle damage and field maintenance.

I shall continue...

 

[Burmese Bandit]

...to continue:

Since to balance the aircraft with its heavy (700 lbs) rear Argus engine, the nose would need to be moved forward, we will have an airplane resembling the long nosed FW 190 dora 9 - but with a fatter nose for the radial - plus a thick rear fuselage similar to the LaGG-7. A short radius 4 bladed propeller splitting the vertical tail behind will be seen, which of course means that the vertical tail has two sections, an upper and a lower. Since the propeller does not extend lower than the vertical tail, a normal tailwheel landing gear can be used.

The canopy will be a bubble. Either a full bubble that extends back, or the canopy similar to the LaGG-7 or the P-51 B with the Malcolm hood. For reasons of production simplicity simplicity, and in order to have the option of opening the canopy in flight and sticking your head out to get a better look (so essential when landing in bad weather!) I will opt for this solution.

The wings will only be about 25% than the normal FW 190 wings - this will give a wingspan of about 37-38 feet, 4-5 feet wider than the 190. The longer nose and wider wings will reduce the roll rate of this fighter compared to the 190, but not by very much. It should still do quite a creditable roll.

Total weight should be about 10,000 lbs for the fast fighter version, which I will continue to describe...

 

[Burmese Bandit]

...why 10,000 lbs?

The FW 190 with two cannon, 550 rounds of ammo, fuel, oil, pilot, etc, etc, ready to fight and fly, is quoted by many reliable sources as weighing 8500 lbs or near as to make no difference.

Add the 700 lbs of the Argus, add the structural and wing strength wing reinforcements, add the extra fuel the Argus will consume, and we have something like 1,300 lbs. That's 10,000 lbs.

At 2100 hp and 10,000 lbs we have a power loading of 4.8 lbs per hp. That's a very good ratio...

...to be continued...

 

[Burmese Bandit]

Now in an 8500 lbs bird, an extra 500 lbs will most likely make a small but visible difference to its performance and handling. Whereas in a 10,000 lbs bird, another 500 lbs will probably make almost no difference at all...

So, what if we have a slightly higher figure of 10,500 lbs for our hyothetical fighter - what could we do with that extra 500 lbs?

We could put in 150 rounds of ammo and another four 20 mm cannon.

Two NEW CANNON in the nose cowling, two ORIGINAL cannonin the wing roots, AND TWO MORE in a slightly bulged belly in a reverse nose cowling under the bottom of the plane.

(The russians showed that it was entirely possible to put 20 mm guns in the fat nose cowling or radial engined fighters with the LaGG 7. I see no reason why we should not be able to take this one step further, and put two more in the belly in a reverse nose cowling position.)

I have done a weight estimate, and 4 more 20 mm cannons and 150 rounds more 20 mm ammo seem to be quite plausible for a weight budget of 500 lbs.

Very well then - we have our 2100 hp fighter with push/pull engines with six centerline 20 mm cannon weighing in at 10,500 lbs and with a wing loading similar too, or just slightly higher than, the FW 190.

What sort of performance and handling and, perhaps, other advantages - or disadvantages - could we reasonably expect from our hypothetical fighter?

to be continued...

 

[Burmese Bandit]

First, though, a word on armament...

550 rounds plus 150 rounds is 700 rounds. There are six cannon, therefore there will be about 115 rounds a cannon. That will mean a fire time of around ten seconds if you fire all six cannon at once, or twenty seconds if you fire three and three. Yes, this could be a limitation on the fighter's capabilities. I shall discuss more on this later..

but to continue...

 

[Burmese Bandit]

...to continue our performance expectations on our "FW 335" (heh) or as I would prefer it now to be called, the "Burmese 190" (someone kick that conceited ass BB please!) (OK I'll be serious now) what type of performance could we reasonably expect from this FW 190/Do 335/LaGG-7 hybrid?

Well, I think that the increase in level speed would be modest - about the same as the Dora-9, say about 420 mph max. That's still a 30 mph increase over the FW 190 A mid series. Let's be conservative and call it 415 mph.

The increase in climb, due to the increased hp and greater wingspan wing, would be slightly better, IMHO.

It is in the DIVE that I expect a much greater performance boost - and of course a faster dive also makes for a faster zoom climb out of the dive. Our new Burmese 190 should dive almost as fast as a P-47. It has the same hp, it has slightly less weight but has slightly less drag, so it should perform very, very well in the dive.

Note that with two engines rotating propellers in opposite directions, this plane should be easier to fly - especially in situations where from flying in a gentle cruise you have to suddenly pour on the power. If done badly in an ordinary FW 190 the sudden increase in torque could snap roll the aircraft. While the auxiliary engine of the Burmese 190 will not cancel out the torque completely (as is the case in the 335) it should reduce the torque to a fairly manageable level so that a sudden increase in power would not tend to throw the plane into a snap roll followed by a spin.

The longer nose, and the concomitant forward movement of the cockpit, also means that the pilot can now see around the nose - very, very useful for taxi-ing, for landing in poor weather, and for ground attack.

And of course, the big rear engine gives you a very, very solid defense, even against cannon shells, from a rear attack.

To be continued...

 

[drgondog]

...to continue:

The wings will only be about 25% than the normal FW 190 wings - this will give a wingspan of about 37-38 feet, 4-5 feet wider than the 190. The longer nose and wider wings will reduce the roll rate of this fighter compared to the 190, but not by very much. It should still do quite a creditable roll.

Total weight should be about 10,000 lbs for the fast fighter version, which I will continue to describe...

Adding the structure to transmit and distribute torque from the second engine as well as the additional weight of the structure to sustain structural integrity to support a large mass near the tail in high G pull out, plus the engine weight itself plus the proposed armament and ammo, and still keep the weight in the P-51D range?

The long fat nose proposed, combined with a tail dragger design, will certainly make it tougher to taxi than the 335 design. The increased longitudinal moment of Intertia with significant masses fore and aft will introduce possible stability and control issues in pitch and might force larger horizontal stabilzer area (and weight and drag).

What is your airfoil choice? If you go laminar flow like the 51 you can keep drag lower than other type airfoils but that has disadvantages also.

The two engines to boost your speed performance, in radial engine design is pretty much going to boost your fuel consumption -----> driving larger fuel cells/capacity depending on your Cruise and Range criteria ----> driving more weight, less climb performance, slightly lower horizontal speed, longer take off run, heavier landing gear.

Because you need more fuel you have to think continuously about keeping the fuel tanks around the empty cg - otherwaise, for eaxample, draining a fwd or aft located tank will screw up your cg and play hob with static margin and stability in different flight profiles.

There was a reason the 335 would have made a poor fighter against other fighters except for speed... which required the maximum Hp available.

I'm not saying a really competent airframe design team couldn't make your concept work but I have mentioned a couple of things that would cause me to ask - "How do we solve this" and "what is the objective of this design over single engine"

 

[Burmese Bandit]

Excellent points drgondog - I shall try to respond to each of them!

"...Adding the structure to transmit and distribute torque from the second engine as well as the additional weight of the structure to sustain structural integrity to support a large mass near the tail in high G pull out, plus the engine weight itself plus the proposed armament and ammo, and still keep the weight in the P-51D range?..."

The mass (of the rear Argus) would actually be much nearer the center of the "Burmese 190" than to the tail. I realise this is difficult to envisage without a diagram - I intend to put up a sketch within a week. For the moment let's say that the rear engine looks lie a P-39 installation, but one in which the engine and the pilots cockpit are moved further forward. I of course freely and humbly admit I am no engineer - but neither am I a total ignoramus either. I think all that I proposed above could be done within the 10,500 lbs limit.

"...The long fat nose proposed, combined with a tail dragger design, will certainly make it tougher to taxi than the 335 design. The increased longitudinal moment of Intertia with significant masses fore and aft will introduce possible stability and control issues in pitch and might force larger horizontal stabilzer area (and weight and drag). ..."

The problem with taxi-ing vision with the 190 and the P-47 was more wing than nose. Sitting on the ground at a high angle of attack caused the wing to block all vision forward, which was why the 190 usually had a crewman on the wing to call out directions to the pilot when taxi-ing. Moving the cockpit forward would not solve the nose problem, but it would solve the wing problem...the pilot could stick his head out of the cockpit and see, not over the nose, but around it.

Now about two engines consuming more fuel - there's a way around that. I shall come to that in a later post.

The most important point... the CG shifting as fuel is consumed...I intend to keep the wings free of all armament (which is why my proposed six cannons have a centerline configuration) and keep all the fuel IN THE WINGS.

 

[Burmese Bandit]

...but before I go on into an explanation of how I would solve the rest of the problems that drgondog has so saliently pointed out above, I would like to explain WHY I chose this concept.

The main reason is that this fighter could have been built using, in the main, OFF THE SHELF PARTS already in production at the time. The landing gear and the tailwheel for the 190 could have been used (we know that the fighter bomber version of the FW 190 routinely took off at 10,800 lbs (4900 kg) : so, too, much of the airframe forward of the cockpit. I suspect even the wings of the FW 190 could have been used, too, with 2-ft wing root extensions to each wing (similar to the wing root extensions that were used to build the P-47 N).

Remember that in my first post I said the goal of the design was to build a better warbird at a reasonable cost and in a reasonable timeframe. This was the reason why I propose this design.

To be continued....

 

[Burmese Bandit]

And now to reply to the very intelligent question drgondog posed..

"..."what is the objective of this design over single engine" ..." ?

The objectives are these:

To have TWIN ENGINE reliability - yes, yes, I know that if the main engine
was destroyed, the 450/485 hp of the Argus might not have been enough to keep the Burmese 190 flying...but it would be quite possible to keep the plane in a shallow dive, and if your main engine failed at, say, 3000 feet it should be possible to extend your shallow dive at a 25:1 to cover a distance of 75000 feet - that's 15 miles. Let's be conservative and say 10. If your main engine is damaged over enemy territory, that's 10 miles nearer to your own lines.

To have REAR PROTECTION. I have mentioned this already.

And ... this is where I think I can (partly) get around the problem of fuel consumption...

 

[Burmese Bandit]

.... to be able to cruise on the MAIN ENGINE, and to shut down the rear engine on long cruises...

Since the rear engine is embedded in the rear fuselage anyway, and since the four bladed short radius rear propeller can be neatly masked by the vertical and horizontal tails in the 'feathered' position, unlike conventional twin engined aircraft there will be little drag penalty with one engine stopped. I would expect cruise speed with the main engine only operating to be lower, but not dramatically lower, than cruise speeds with both engines operating.

 

[Burmese Bandit]

Other objectives of the twin design, which are the ability to carry very heavy armament and an increase in level speed and climb, and a dramatic increase in dive speed, have already been explained.

Whew. Let me rest for a bit now.... will be back.

 

[kool kitty89]

One of the advantages of the Do 335's engine arrangement is that each engine cancelled the other's torque. (at similar settings) This works because the props rotate in opposite directions and the engines have the same performance and same type of propeller. This elliminates the need to trim the aircraft to counter torque. (except with an engine out)

When you introduce 2 very different engines with very different performance characteristics. This creates the opposite situation than above, with countering torque being more problematic than with a single engine.
Assuming they still counter rotate, the Argus engine will counter some of the torque of the BWM radial, but changes in power settings and altitude will result in torque changes necessitating trim changes (or pilot imput) to counter it.
The difference will be particularly noticable at altitude as the Argus engine was designed for relatively low altitude operation. (there would be a particularly noticable jump at the BMW's supercharger gear change altitude)

To minimize this effect, you'd have to develop a version of the As 411 with a 2-speed supercharger with altitude power curves matched as closely as possible to the BMW 801, and would have to be further developed to follow later developments of the 801.


You also may run into problems designing a satisfactory cooling ducting arrangement for the As 411 that also minimizes drag.

 

[drgondog]

Excellent points drgondog - I shall try to respond to each of them!

"...Adding the structure to transmit and distribute torque from the second engine as well as the additional weight of the structure to sustain structural integrity to support a large mass near the tail in high G pull out, plus the engine weight itself plus the proposed armament and ammo, and still keep the weight in the P-51D range?..."

The mass (of the rear Argus) would actually be much nearer the center of the "Burmese 190" than to the tail. I realise this is difficult to envisage without a diagram - I intend to put up a sketch within a week. For the moment let's say that the rear engine looks lie a P-39 installation, but one in which the engine and the pilots cockpit are moved further forward. I of course freely and humbly admit I am no engineer - but neither am I a total ignoramus either. I think all that I proposed above could be done within the 10,500 lbs limit.

No need for diagram-it would be feasible. Staring with this preliminary design concept, a desire for heavy amament in forward fuse, variable pitch prop with feathering mechanism, all fuel in the wings and your second engine right behind pilot.. here are some questions.

If 10500 Gross takeoff is your target max for this two engine bird and a proposed wingspan of ~ 37 feet, then a nice aircraft for rule of thumb would be a P-51D for comparison purposes.

You could start with initial premise that for a similar Aspect ratio that a relatively thick laminar flow wing could obtain 180-200 gallons of fuel particularly with no guns/ammo in wing and keep control of fuel contribution to static and dynamic margins. If you change the wing say to a Spit wing you will have less volume available for fuel cells... ditto Fw 190.

You will however introduce potential cg issues as you expend your 20mm ammo unless all the ammo is essentially near the cg.

This airframe Must be longer by definition to incorporate a 'main' engine' front and a pusher engine aft of cockpit, as well as a drive shaft, heat barrier, shaft bearing hangers and structure, prop/gears for variable speed and four props aft of the cockpit. The fuselage must, by incorporation of these features, have more width as you noted and probably be cylindrical in shape to minimze the volume, weight of the surrounding airframe... and raises question of cooling strategy for aft engine.

There is a question of aerodynamics relative to elevator and rudder deflection effectiveness with a feathered pros acting as an 'additional and separate' airfoil aft of those control surfaces... almost like a short coupled canard?

Conceptually they would operate as separate airfoils when local angle of
attack on the tail surfaces changed - and probably opposite in direction - an interesting problem both in aero and contribution to stability - particularly in pitch axis.

"...The long fat nose proposed, combined with a tail dragger design, will certainly make it tougher to taxi than the 335 design. The increased longitudinal moment of Intertia with significant masses fore and aft will introduce possible stability and control issues in pitch and might force larger horizontal stabilzer area (and weight and drag). ..."

The problem with taxi-ing vision with the 190 and the P-47 was more wing than nose. Sitting on the ground at a high angle of attack caused the wing to block all vision forward, which was why the 190 usually had a crewman on the wing to call out directions to the pilot when taxi-ing. Moving the cockpit forward would not solve the nose problem, but it would solve the wing problem...the pilot could stick his head out of the cockpit and see, not over the nose, but around it.

We would tend to disagree here. I have never flown the 190 or the 47 but I have flown (and taxiied) the Mustang. The nose on the Mustang which would be closer analogue to your proposed long nose IS a problem. The wing is not even noticeable. Conceptually and in reality the leading edge of a Mustang is well below the vision plane to the horizon and for some significant angle below the horizon. Needed same crewchiew/armorer sitting on wing along taxi way for similar reasons - but at the end of the day it is doable as was well proven. Tricycle better for ground handling, however

Now about two engines consuming more fuel - there's a way around that. I shall come to that in a later post.

The most important point... the CG shifting as fuel is consumed...I intend to keep the wings free of all armament (which is why my proposed six cannons have a centerline configuration) and keep all the fuel IN THE WINGS.

So let's pause and make sure my comments, even if incorrect, are at least clearly conveying my thoughts.

1. New engine and drive shaft and propeller combination as well as additional structure and heat shield behind the cockpit adds minimal ~ 600-800 pounds?

2. Heavy six x 20mm combination in nose adds another 150-200 pounds over a six x .50 combo in a P-51D, including the additional structure to absorb recoil.

3. 20mm ammo ~ 900 rounds compared to 1800 .50 about the same? but must focus on location close to cg.

So, compare weights and balances to the Mustang. Mustang has one significant variable to cg location - the 85 gallon fuse tank aft of cockpit and cg - not as much weight as your engine/prop combo - and designed for normal cg when fuel consumed. The aft engine stays in your fighter - so,

a. Your wing probably needs to move back to get the aerodynamic center backwards toward the aft engine - or the forward engine need to move forward to compensate the moment arms about the Cg. Maybe you can move the cockpit forward to get the pilot weight to contribute.

Forward movement of cockpit/pilot a probable better choice than extending nose for primary engine as the latter adds weight for more airframe structure and raises longitudinal moment of intertia. Ballast is terrible idea and to be avoided

b. While a Mustang sheds the weight of the fuselage tank fuel, your fighter keeps 600-800 pounds of the engine combo. That will be a climb and cruise penalty in every condition vs Mustang - all things being equal...

c. You have much better firepower but pay another permanent weight penalty with the 6 x 20mm cannon.

d. Unclear what extra weight is incurred in channeling cooling air to the aft engine or what effect to parasite drag.

e. Difficult to conceive of many off the shelf major components other than landing gear and engines.

f. There is no reason why it should not have a decent roll rate - at least as good as the Mustang.

In the comparison of the Mustang vs your design - you have to ask yourself what could be carved out of a P-51D to compensate for say 600 plus extra pounds of steel alone for your extra engine, remembering that the P-51H as a near new design only carved about six hundred out of the D airframe - so when you start with a 37 foot wing and EXTEND the fuselage to compensate for the aft weight w/o adding ballast... where are you going to sacrifice structural integrity?

The thing that nags me the most is the contemplation of the longitudinal moment of intertia (large for fighter) when you place such large masses as engines fore and aft of cg, as well as the question about how the airplane responds with an 'airfoil' behind the trailing edge of elevator and rudders?

There is a reason the DO 335 would have been nice against bombers but probably never in a manuevering fight with fighters.

this is interesting, and comments are speculative on my part.

 

[Burmese Bandit]

Ah, drgondog, I am so glad you added your comments!

Yep, some points did nag me during the thought concept phase of this design...

1. The cooling and airflow for the Argus behind. My thought was a duct behind the cockpit in the mode of the P-39. However, I confess I have not give as much thought to this as to other parts of the design.

2. The cg shift as the ammo is used up had occurred to me too. At present I am still thinking about it...still, my proposed location for the ammo, in the nose behind the BMW 801, is not too far from the cg.

3. I confess that the 'airfoil' behind the tail and rudder is completely uncharted territory for me, and I suspect, for many on this forum too. Perhaps someone - I am sure there must be one or more than one, it's one of the reasons why I joined this forum - could give us some insights?

4. I totally agree that forward movement of the cockpit is a better idea than simply extending the nose.

5. Hmmm....perhaps my design will come in overweight (what else is new?)

6. The engine symmetry point about the Argus and the BMW is an excellent point. I shall think deeply about this.

Will be back! And the original point of this thread was not to say so much that "THIS could have been done" as to promote discussion, thought, and enlightenment.

I see that this is beginning to happen...and I am very, very glad.

 

[Burmese Bandit]

A point: one of the factors in my choice of the V-12 cylinder air cooled Argus was not just availability, but the "taper" from front to back from the fat BMW to the relatively slimmer Argus, so that a low drag airframe boatailing smoothly from front to back could be built.

Just for clarification!

 

[MikeGazdik]

I would have developed a wing form, similar to the Mustang, for the Messerschmitt. Just smaller in scale to be near the same wing area. I would have left the armament in the nose of the Messerschmitt though. Just used the North American wing to utilize bigger fuel cells, and better main gear, and an overall stronger wing.

Not sure if I would keep it laminar flowing. I just like the structure of the P-51 wing. Two main spars, fuel in between, main gear stows away just ahead of the front spar.

 

[Burmese Bandit]

At present we're discussing the design of an improved 190 here Mike - I'm going to get around to my thoughts on an improved liquid cooled inline later.

However, in passing I would like to note that one of the problems with having an inline V-12 is that what you gain in small frontal area, you lose in having little space to mount weapons on the cowl or in the Vee between the cylinders. This was why Willy could never mount anything bigger than 13 mm HMGs on the cowl of the 109. (Yes, one of the K models mounted two 15 mm guns, but the bumps on the fuselage were so huge I shudder to think of what they would have done to the drag)

 

[kool kitty89]

The Do 335 was powered by a liquid cooled (inverted) V-12 and had cowl mounted 20 mm cannons. (granted the larger DB 603 rather than the Bf 109's DB 601/605) But it has more to do with the nose design than the engine size. (the Bf 109 having a relatively small nose, and it may not have even been able to mount guns the size of the .50 Browning)

Also note the 15 mm cowl guns on the Bf 109K is a mistake, this was never a planned armament. (the Bf 109's nose was too small to practically fit them there, plus I don't think production of the 15mm MG 151 went into le late war period)


There is a significant advantage to the V-12 though, the engine cannon mounting to fire through the spinner allows a centraly mounted (possibly large) unsynchronized gun (important as some significant weapons couldn't be synchronized). This is the only way the MK 108 could be mounted on the centerline of a fighter with a nose mounted tractor angine. (granted the engine layout had to permit it, not feasible on the V-1710 or Merlin due to supercharger placement, but possible on the Jumo 210, 211, 213, DB 601, 605, 603, the Hispano-Suiza 12Y -and subsequent Russian derivatives)