Could you have designed a better Warbird?

Now a point I want to ask drgondog and other engine experts on this forum:

I am almost sure, though not completely sure, that the total weight of the Merlin and the radiator and the coolant liquid on the P-51 was more than the BMW 801 with its cooling fan and cowl flaps. Who can give me numbers on this?

Weight of Merlin 61, complete:



In addition, you need the weight of oil, coolant and intercooler fluids. Unfortunately, I don't have the weight for the BMW 801.

Ah, half my question answered!

Thank you kindly, Kurfurst!

Now who has the other half.... I need it to think about whether the 700 lb argus was really that much of a "cg problem" (considering the point that the Pony had a radiator behind the wing in about the same position that I plan to put the Argus) plus that 85 gallon tank above.

I hope the very experienced members of this forum can help me!

Burmese Bandit said:

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.

Remember the duct on the P-39 was required for even a liquid cooled Alliason and the ducting should be forward of the engine as much as possible to avoid creating a possible flat plat parasite drag component

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.

Remember for a conventional tail aircraft the empty weight design would start by planning cg at aeordynamic center of the wing and contemplate a +/- travel of ~ 20% forward and aft. Second the forward and aft Cg travel must not be so far forward or aft that equilibrium may not be maintained at CLmax, with or without thrust, and that the farther forward or aft of the the CG (from Ac) the greater the tail control surface required for control. This becomes more severe as the cg to tail arm is decreased.

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?

I have only seen the condition when discussing ducted fans and only in the circumstance where the fans were imbedded in wing design... in your configuration with feather position placing blades in plane with horizontal and vertical stabilizer and aft, I suspect the blades would tend to improve the aeordynamic flow properties but at the same time reduce the effectiveness of the elevator (and rudder) when deflected.

I need to think more on this, but is seems like the possiblity that the elevator starts to look like a 'spoiler' as it deflects and the prop acts as the trailing edge of the airfoil - thereby reducing the 'increased camber' effect of elevator to more of a drag contributor.

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?)

If you use the Mustang as a comparison to evaluate weight tradeoffs then it quickly reduces to BMW 801 and Argus in comparison with Merlin and radiator and cooling system. The 85 gallon tank is light and the fuel is optional depending on the mission profile and disposed of early in any case. The trade off between a cooling system for the Argus and the radiator of the 51 is probably equal. That core is not very heavy.

Then the next comparison is the gun/ammo comparison of 20mm and .50 caliber. One trade off is to reduce fuel capacity

Then the next discussion is comparative drag for both airfoil CDo and parasite drag of the airframes. I am deeply suspicious that the Argus pusher with both addditional weight of engine prop system and questions regarding aft control surface design.Cg is becoming a more serious question

My suspicion is that you won't need to make your ship longer depending on the aft engine placement and the air cooling/heat shield design, and that you could manage the Cg just fine.. the tail size and tail moment arm from the

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.

Click to expand...

The need for a tractor/pusher config is driven by speed objectives not achieved with a single engine. I would question the value of using two engines not matched for reasons of maintenance and commonality of parts?

Some other thoughts from MY world....

Limit stress panels installed with screws - use as many cam lock panels as possible for ease of maintenance. If screws have to be used because of a panel in a stressed area, use screws that can be turned with a Phillips or straight screwdriver. To be real fancy, have screws with an opposite threaded center point on the head so an easy out could be installed if the screw head is stripped out.

Install all quick disconnects on plumbing, control cables and electrical connections that go to the engine. Build a "QEC" (Quick Engine Change) unit that allows the engine mounts and engine to be removed. Design all oil and coolant drains (if liquid cooled) so they drain down and do not flow on to structure. Have "two hand access" to all filters. Install magnetic chip detectors in the low points of the oil systems with easy access so if the engine is "making metal" it could be easily detected.

Have flush "indented" jack points so no jack adapter needs to be used to jack the aircraft. Use disk brakes that have pads that could be removed without removing the entire wheel. Have all axle nuts installed with standard size nuts so special removal tools could be avoided. Lastly, use common greases and lubricants through out the aircraft.

Interchangeable control surfaces - no left or right ailerons or elevators. One piece horizontal and vertical stabilizer that is bolted to the tail and can be removed in one piece. If the aerodynamics work - a symmetrical outer wing panel so that to is common left to right...

Structure - common hardware, avoid specially made bolts and pins. Design the structure in bolted "segments" so heavily damaged portions of the airframe could be unbolted and changed out rather than undertaking timely airframe repairs.


All these wonder aerodynamics and performance wants won't mean a thing if the aircraft cannot be easily maintained.

My 2 cents - avoid the stock market!

Lindberg chose a single engine AC to fly the Atlantic because with two engines you are twice as likely to have an engine failure. The remaining engine would not allow the completion of the mission.

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.

Click to expand...

The P-39 had the radiator and oil cooler mounted directly below engine, but the intake for the cooling ducting was located at the wing roots. The scoop directly behind the cocpit canopy of the P-39 is for the carburetor.
Putting the cooling air intake on the top of the fuselage would require a fairly larger scoop and long ducting running to the bottom of the engine. (it being an inverted V-12)
The simplest configuration would be to add a belly scoop, possibly similar in apearance to the P-51's. Though that would likely result in the loss of the ability to carry external stores under fuselage.

My perfect aircraft fighter design ends up as a Grumman Bearcat or Hawker Sea Fury.

Put the most powerful engine around the smallest lightest airframe and give it some cannon...teardrop canopy and some toughness so it can take a good beating...plenty of agility...radial engine so it can lose a few cylinders and still come home.

Not sure about your twin design. Why have 2 engines when 1 can do? Making something more expensive and doubling your logistics as you need spares and training for two different engines.

Ah, many have taken the time to reply!

I shall try to reply to all, starting with a new face...the scottish basket

Simple reason - availability. In a perfect world I would have a single powerful engine of 2500 hp driving counterotaing props in front. But this is 1941, (see premise at beginning of thread)that engine is still three or so years away, and the war won't wait for me!

Have to leave now. Will be back with looooong post!

Have to attend to some business now, but a quick reply to

Flyboy J: the BMW was designed by the Bavarians as an integral unit, with cowl and fan integrated. Most probably it was already a quick change unit!

I have sources such as Wiki on the weight of the BMW but I don't completely trust them. Could someone help me on this...weight of BMW with cooling fan? I suspect it would be less than the total merlin 61 which at nearly 1200kg is about 2620 lbs.

I need to know this before I can finalise my reply to drgondog's very incisive and helpful posts.

Burmese Bandit said:

Flyboy J: the BMW was designed by the Bavarians as an integral unit, with cowl and fan integrated. Most probably it was already a quick change unit.

Click to expand...

But did they have quick change cables and plumbing? Did they use screws or cam locks around panels? Did plugs and fittings had to be safety wired? Many WW2 aircraft had "QECs" but just because they used the term didn't mean they were maintenance friendly.

Kurfürst said:

Weight of Merlin 61, complete:


In addition, you need the weight of oil, coolant and intercooler fluids. Unfortunately, I don't have the weight for the BMW 801.

Click to expand...

wikipedia claims the BMW 801 dry weight is 1,055 kg (2325 lbs), or about the same weight as the PW R2800 (2360 lbs).

The 2-stage models of the R-2800 (ie Helcat and Corsair) were somewhat heavier at ~2,500 lbs. (the -10 was 2480 lbs)

http://www.enginehistory.org/ModDesig/SecI.pdf

The single stage (turbocharger sperate) of the P-40B/C/D (the -21, and 59/63) weighed 2,265 lbs. The 2800 hp -57C engine of the P-47M/N (and XP-47J) weighed 2315 lbs. (all dry)

Also the single stage 2-speed supercharged R-2800-39/41/43 of the B-26 weighed 2300 lbs. (and had somewhat poorer altitude performance than the BMW 801D)

sounds like your designing an epic bomber destroyer Burma.

Burmese Bandit,

Wth all the trouble of your proposed design, just replacing the BMW engine with a 2-stage R-2800 model would seem a lot less trouble. (the Centaurus would be somewhat more difficult due to size differences)

You'd have 2,000 hp in the early part of the war, somewhat less than your proposed combo, but much more power at altitude with an engine only moderately heavier than the historical one (compensated by a shorter nose or longer rear fuselage). The dimentiuons were very similar to the BMW engine as well, and a tight cowling with large spinner and cooling fan would of course be used to minimize drag. (actually done with the R-2800 on the XP-47J) Overall modifications would be relatively small. (probably similar to the changes made to the Dora)

You wouldn't have the problems of using 2 different engine types and the complexity of the mid mounted engine with extension shaft driving a pusher propeller.


The disadvantage would be the need of a larger propeller and taller langing gear. though depending on the propeller used the gear maybe able to stay the same, but requiring 3-point take-off and landing -which was already common for the Fw 190 iirc)

Without your other changes you'd end up with an a/c of the Bearcat or Tempest/Sea-Fury type.

With your wing changes, a longer span and area (not as extreme as the Ta 152) could be a good idea, as could carrying fuel in the inboard wings. (just outboard of the cannon) However I'd keep the original fuelelage fuel tanks and have moderately sized fuel tanks in the wings. (max internal fuel capacity of around 200 US gallons, ~250 gallons if you want a long range fighter, so 33-58 gallons in each wing)

To improve foreward visibility and peripheral vision on the ground, raise the coucpit slightly and use a taller canopy. (similar to the change from the "birdcage" to the hooded canopy Corsair) Possibly raise the rear fuselage as well to improve streamlining with the larger canopy and reduce the necessary size of the vertical stabilizer for adequate stability.

I think a low drag airfoil of 15% at the root is reasonable, tapering to 9% at the tip. (same as with the actual 109's wing) Use a fairly broad wing with a moderate taper (similar to the 190's) but increase span to 42-45 ft and area to 240-250 ft. (the longer span and resulting higher aspect ratio will also improve the lift to drag ratio and coeficient of lift -though using the low-lift/low-drag airfoil will reduce the latter)

I'm not so keen on the lower nose guns (it's getting kind of bulky, and possibly interfere with external stores on the belly), I think the 2 upper 20 mm and wing root 20 mm are good, keeping the 250 rpg at the wing roots and another 200 rpg for the upper nose guns (if possible). Then add provisions for on cannon outside the propeller arc in each wing for added guns for bomber killing missions. (another pair of 20 mm guns, or a pair of MK 108's which can't be synchronized, and thus have to be mounted here and there's no possibility for a motorkanone placement with a radial engine)

I think this could result in an aircraft in the 10,500 lb range. (it would seem reasonable for ~800-1000 mi range and a top speed around 440 mph)

First of all, I would like to thank drgondog, FlyboyJ, koolkitty89, Watanabe, Daveparl, The Basket, Kurfurst, MikeGadzik....wait....yes, that's all for now. Unless someone new posts while I'm typing this looong reply. Which is quite possible...

Thank you, all of you, for taking the time and for your insights. And here, I think I should make a small apology, for I believe I was not QUITE clear on what I was trying to do.

I said " 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?"

One of the key phrases in that premise was "...for any SIDE." This meant that if you were, say, designing for the Allied side, you couldn't use a DB series engine to put into your super spitfire, or a BMW engine to put into an improved uber Hurricane. And in the same way...you couldn't use an R-2800 to put into the "uber 190" that the Germans were going to be using! And of course the allied side couldn't use the "minegeschloss" shell technology for their cannons....etc etc etc...

(I believe this answers your post, koolkitty89....but thank you nonetheless. Your points are, as always, very good.)

And I would humbly like to be clear on another point in the premise..."....using only the technology known and in use AT THE TIME..." This means that your design can't use revolver cannon for a plane that's going to have to be ready to fight in 1944 at the latest, or use the Griffon for a plane that's going to fight in the Battle of Britain, or use the R-4360 for a bomber that's going to bomb Germany in 1943.... I think we all get the picture? And of course no use of such things as titanium components for engines and airframes before 1945!

And finally, another constraint in the premise is "...reasonable cost parameters." This means no Rolls-Royce hand-built "R" engines for a 1,000 - 5,000 plane production run.

Yep, that's right. If you've read Anthony Williams "The Foresight War" and others like it in the WW 2.1 genre, those are the design limitations set up for the hypothetical designer who has arrived back into 1939 or 1940 WITH the hindsight of the 21st century, but WITHOUT its advances in technology. Take the bricks that were available at the time, with the labour available at that time, and see if you could have built a better house than the architects of that time!

And now, that having been said, let's continue...

Having digested the thoughts and excellent suggestions and criticisms of all you kind posters, I have decided to do what Watanabe so shrewdly pointed out - change my design to be an epic....bomber destroyer and ground attack aircraft.

There are many reasons. Oh, I could still have built a fighter within the 10,500 lbs self-imposed limit, by giving up the two belly 20 mm and doing other design changes, but I have chosen not to...because...

I have ANOTHER design coming - an "uber 109" - which uses a single DB 605 engine and is light, maneuverable, and yet carries eight MG 131 HMGs and has an airframe which I believe is superior to the 109 in drag reduction. It's actually a much less technologically ambitious design than this one, yet it has design characteristics which have not, AFAIK, have been seen before. The goal is a plane with the maneuverability of the Me 109 F with an armament heavier than the G and a speed higher than both. Oh, yes, and affordable and buildable by the technology of the time too.

So, I've decided that my uber 190 is going to fill the heavy end of the spectrum because it's ideally suited to do so, by virtue of its high hp from its two engines, and my next project, the uber 109 referred to above, will fill the light fighter end of the spectrum, so that both could work together in tandem. Against the hordes of Stormoviks. Against the hordes of B-17s and 24s.

(In passing - why don't I design uber spitfires and ponies and jugs or even a better Stormovik? I will. Later. I just loved the challenge of designing from the Axis end first.)

Enough already. Let's get back to designing the uber 190

I have arrived at the conclusion: actually the uber 190 is a Burmese FW 47.

Why?

Let's look at the P-47. Big 2300 lb radial in front. 600 lb turbosupercharger in the back. Total output 2300 hp. Fat belly carrying chin air scoop for the intercooler and pipes for said turbo. Said belly still capable of carrying centerline stores. Tail dragger. Two waste gate air outlets in rear fuselage for discharge of hot turbo gases.

Now, the Burmese uber 190...

Big 2300 lb 1700 hp (1942 version) BMW in front. 700 lb 485 hp Argus in back. Total output 2185 hp. Fat belly carrying chin air scoop for Argus and two 20 mm belly cannon. Said belly still capable of carrying centerline stores. Tail dragger. Two air outlets in rear fuselage for discharge of exhaust gases and cooling air for the Argus.

The slight extra weight of the Argus and firewall against the turbo is counter balanced by the weight of the top and belly 20 cannon in the nose of the uber 190. Thus we have a good cg balance.

A two-part vertical tail, reminiscent of the 335, at the back of the uber 190 will be a crucial difference in side view. Said tail will not be lower than belly - unlike the 335 - as radius of 4 blade Argus rear pusher propeller is smaller.

Same teardrop canopy for both designs.

A shorter, 37 foot 240 sq foot wing for the uber 190. Takeoff weight for bomber destroyer version, 12000 lbs. This will give a wing loading of 50 lbs per square foot. At 2185 hp (yes, I know the later versions of the Argus developed 700 hp as used in the Si 204, but for the time being I'll stick with the 485 hp Argus) this will give a power loading of just under 5.5 lbs per hp - about the same as the early Spits.

Regarding the ammo supply and the fuel, I intend to reverse the 47 design, and put the ammo where the 47 has its fuel and the fuel in the wings. Why? I intend for the outer fuel tanks to be used up first, and the inner later...in this way the outer wings will be fairly light when combat begins, as the outer tanks will have had their fuel used up in the climb to combat height and the cruise to the battle area, and thus the uber 190 will enter combat with a better roll capacity.

Regarding armament...I intend to keep ammo at average levels, at only 800 20 mm cannon shells, but I intend to add an extra pair of 20 mm in the wing roots to get a total of EIGHT 20 mm cannon! Two in the upper nose, two in the belly, two in each wing root! This will give a total of only nine seconds firing time if you fire all eight at once (MG 151/20 with electrical synchronization fires at 700 rpm less 10% or so), but it will give 36 seconds if you fire them two at a time. The electrical firing system of the German 20 mm shells should make this two position firing switch easy to make.

I believe all this can be done within the new 12000 lb limit.

I believe that, apart from the possible control problems arising from the rear propeller acting as a close coupled canard, and the problem of matching the power curves of the Argus and the BMW as closely as possible, this design is quite plausible. (Of course, I would greatly appreciate the input and criticisms of the many, many people far more talented than me on this forum! )

Well...suppose we COULD build such a monster...what sort of performance could we expect from it? And how could we use it tactically?

I believe performance will be very similar to, again, the P-47, with the exception of performance at high altitudes. On the deck and at mid levels they should be almost performance twins. My shorter span wing and slightly less hp will penalise the climb versus the Jug slightly, but better the dive. And it should roll better in theory and even better at half fuel in actual combat. Of course, the FW control system should make it an excellent 'transitioner' too - rolling first one way, and then suddenly another.

How should and would it be used tactically?

It should be used in the 'dive-shoot-dive and run like hell' against high flying bombers. Against them it should climb into a height superior to the bomber stream - say 8000 meters, about 27000 feet - and move to a position dead astern. Then dive through the escorts, using the tremendous dive speed possible with high hp and heavy weight, and fire one long burst as it closes into the bombers. With eight guns that's 80-90 cannon shells per second. A four second burst will throw about 330 shells at the target bomber. Pilot Arnauld Average of the Luftwaffe will hit with about 3% - that's 10 shells, grouped close together, Pilot Edgar Experten will hit with 20 or even 30 shells. Bottom line, Arnauld severely damages B-17, Edgar chalks up one more viermot kill.

Then DIVE and TWIST and RUN because now they'll have two or even four angry ponies on their tail each! With the P-47's diving speed or even better, and the superb transitioning ability inheirited from the 190 design, I think there's a fair chance of escape. Remember the ponies can't chase them too far because they might be leaving the bomber stream open to a secondary attack. Climbing back after chasing too far is time and fuel consuming.

One good pass, then dive and run. That's the way to use them. They must never fight the ponies and jugs and 38s...except in a head-on attack situation. Then, if they have any ammo left, they should not run away but attack. With eight guns, two engines, armour, the chances are on their side.

Against the Stormoviks. the opposite should be done...they should hang back, stay at a higher altitude beyond the effective range of the rear gunner, and fire the guns two at a time. The Stormovik can neither run, evade, nor fight back effectively. Its armour is its only hope. But with 36 seconds of fire available, sooner or later even the flying tank will go down. If enemy fighters should suddenly appear and break through the escort, shallow dive and run if they are behind, attack if they are in front.

Whew. That's QUITE a lot. I shall rest now...

It takes about 4 years from first flight to the aircraft earning its keep in terms of numbers and shooting down enemy.

So if your aircraft wants to be fully operational in 1942...you is looking first flight in 1938...would anyone want your design in '38?

Your aircraft seems to big and complex. I would go for a twin in the P-38 mode or a big single engine fighter like the P-47.

It appears you have designed a very lethal bomber destroyer. Basically a flying cannon with two engines

I could see it working but the chance of doing serious damage on 1 pass (which is probably what they would get) is not that high. The plane would be expensive to produce and mince if caught by fighters. Would you work it in cooperation with fighter escort like the Me410 and Ju88 bomber destroyers or rely on its speed to get it out of there?

What do you think about the 1943 style head on attack?