Hello XBe02Drvr.
You're right. A major drawback of the "big engine, small airfame" approach is lack of room for growth and evolution. Couple that to an unorthodox layout, and you've doubled your problems. I can't see much fuctional difference between a 109 tail and the approach Bell used except the 109 version might have added more usable keel area aft for stability.
We are getting quite a bit off the original topic here.
I never stated that the Airacobra was a good design. Interesting? Yes. Good? Not so much.
It had a lot of designed in flaws that were hard to work around.
I like it because I think it looks cool and not because I think it was a particularly good aeroplane.
My original response to Swampyankee was that the long nose and short tail was not necessarily a consequence of the engine location.
I wasn't advocating for lengthening the tail so much as I was proposing how it could easily be done if necessary AND how it could be done with less consequence than with a tail dragger design.
I was also commenting that the relatively long nose was also not necessarily a consequence of the engine location but because of other factors.
The problem was all the "growth" that came along after metal was cut. Cockpit armor, self sealing tanks, more and heavier radio equipment, a battery capable of repeated engine starts without a GPU, wing guns and ammo, and (the biggie!) removal of the turbocharger system. The net effect of all these tended towards increased aft moment. Not a good thing. In a borderline tailheavy aircraft, increasing aft moment DOES affect everything else.
So what about the cooling system? You could put the coolant and oil radiators up front like the P-40, but this entails a lot of drag and unwanted additional keel area forward, plus with all the additional plumbing, turning the cockpit into an oven, and guaranteeing a scalded pilot if a single bullet finds its way under the cockpit floor.
I am in general agreement with you here about the no room for stretch. I do not see how removal of the Turbocharger would make the aeroplane more tail heavy or adversely affect anything other than performance at altitude.
Regarding the cooling system:
I wasn't suggesting something along the lines of the P-40 which would destroy aerodynamics. I was thinking their buried setup might still work move a bit further forward by where the nose wheel was.
If you think about it, the P-51 and just about every other fighter that had the coolant radiators or oil coolers somewhere other than right next tot he engine had to have some substantial plumbing between the engine and Radiators. I am thinking of Hurricanes, Ki 61, Yak fighters et al. Others managed to deal with the issue of remote radiators without great difficulty.
Your assumption about cannon armament non-negotiable is right on, but I don't know if it was internal or external. USAAC WAS very fond of their 37MM. An upright V-12 is an awkward customer when it comes to a hub-mounted cannon (the DB was inverted), so if you're stuck with an Allison, you've got to figure out somewhere else to put it.
Move the wing FORWARD to match CofG??? Tell me that's a typo! If anything it needs to move aft to get the lift behind and near where the CofG is.
An upright V-12 isn't really the problem with mounting a motor cannon. The Hispano Suiza and Klimov engines both had motor cannon.
As I understand it, the issue is more because the space between the cylinder banks has to be have enough room and there needs to be room behind the engine block itself for the cannon. Of course the engine reduction gear has to have enough offset for the cannon bore to clear the engine block as well.
With the Allison, there was a really convoluted intake manifold in the way. With the Merlin, there was the supercharger. The Daimler Benz and JuMo engines got around the supercharger issue by offsetting their superchargers to the side.
Forward? Oops! The problem here is that the CoG of the Airacobra moves around quite a lot depending on the amount of disposable loads remaining. Perhaps we really needed a variable sweep setup like F-111 or MiG 23?
What I was trying to point out is CofG isn't a fixed point but a range of points and that range has to be positioned forward of the CofL an appropriate distance to give the aircraft a slightly nose heavy condition throughout it's CofG range.
I believe what we are really getting at here is to properly locate the heavy equipment and variable loads in a manner that allows only for minimal changes with lighter pieces of equipment. In other words, it helps to plan for the inevitable growth very early in the design. Nose heavy will be addressed shortly.
Stabilizer with no down load? What are you smoking, man?? We're talking circa 1940 here, and fly-by-wire computer enhanced active stability (F-16, F-18, A120) is still a half century away. For any conventional planform aircraft (ignoring canards, flying wings, and tail-less curiosities) stability requires an inherent nose-down balance matched by an equivalent down load generated by the tail to achieve stable steady-state flight.
With a conventional layout, the forward CoG limit is limited by the amount of down force that the tail surfaces can apply to offset pitch down moment.
As the CoG moves aft, the aircraft stability gradual decreases.
When the CoG moves behind the CoL, the tail surfaces will need to provide lift instead of downforce.
There is nothing inherently wrong with that except for the reduction in stability.
As the CoG moves further aft, at some point stability will become nil and this is the aircraft "Neutral Point".
As the CoG moves even further aft, there gets to be a situation in which the tail surfaces which are providing lift will stall before the wing will.
When this happens, the whole world blows up because the aircraft will continue to pitch up and increase the Angle of Attack and load on the wing and likely cause a structural failure.
Regarding the conventional versus canard versus something like Langley's Aerodrome. They all follow the same basic rules.
The aeroplane will fly most efficiently if forward and aft horizontal surfaces are providing lift. Stability may be poor in certain load conditions but life gets really bad if the aft surface stalls and results in the aircraft pitching up.
As for the 1900, it's been 27 years since I last flew one, and 23 since I last flew anything, and my 1900 manual went away years ago, so I don't remember picayune details like that. In any case figuring CG vs MAC was a ground school exercise we did twice a year in recurrent. In practice we used a pre-computed "cheat sheet" where we entered the weights in various parts of the plane which gave us a moment number which we plotted on a graph opposite the GTOW and if the dot fell in the cross-hatched area, we were good to go. You'd be surprised how quickly you can pull that off when you're being yelled at by the Ramp Supervisor, the Captain's got the right engine turning already, the last little old lady is hobbling across the ramp to your door, there's a DC-9 idling at the edge of the ramp waiting for your spot, and Ground Control is advising you have two minutes remaining on your clearance void time!
My apologies. I didn't know your history. I know nothing about the Beech 1900 and was trying to get a data point to understand better.
- Ivan.
