Piaggio P-119

[Elmas]

It seems that there are some fans of fighters with central placed engine in this Forum...

P-119 was a single prototipe built by Piaggio and completed in 1942.

As in P-39, the long transmission shaft caused vibration and substantially, despite the good pilot view, the mass of the engine close to the CG and all other, it did not represent an advance respect to the Serie 5 Fighters that were going to production in that year, so it was abandoned.

 

[tomo pauk]

Such a fighter with big radial would've been interesting for carrier vessel use, since the cockpit can be 'pushed' well in the front thus allowing for better downward field of view. Elevated thrust line allows for for shorter U/C legs.

 

[gomwolf]

Engine temperature problem was one of major problem of this aircraft. Italians made large cooling intake for its engine, but engine was not cooled enough. Only each side part was cooled sufficiently. Upper part was almost didn't cooled and normally overheated.

Still I cant understand why Piaggio tried that kind of design with air-cooling enigne. Piaggio was a company which produce air-cooling engine. If they wanted to make some good fighter aircraft, they had to find other designer for that.

 

[Elmas]

As Piaggio was a manufacturer of air cooled engines, and just air cooled, it is obvious that they wanted to produce that aircraft with their own engines.

 

[Piper106]

Interesting design, not so much as fighter, but more as ground attack aircraft. The layout allows a large centerline mounted cannon, combined with a ground fire resistant air cooled radial engine, something that is not possible with 'normal' single engine radial powered designs. Tank buster anyone???

As far as the engine cooling problems, there was a lot of that with radial engines in the late 1930s and early 1940s. Given a reasonable amount of time and resources, it is likely the overheating problems with the P.119 could have been trampled into submission, as they were with the Fw 190 and the B-29 to name two examples. Problem is that by 1943 the Italians were short on time and engineering resources. . .

 

[wuzak]

As far as the engine cooling problems, there was a lot of that with radial engines in the late 1930s and early 1940s. Given a reasonable amount of time and resources, it is likely the overheating problems with the P.119 could have been trampled into submission, as they were with the Fw 190 and the B-29 to name two examples. Problem is that by 1943 the Italians were short on time and engineering resources. . .

Perhaps the use of a fan to force cooling air through the engine would have helped.

Like the one on the Fw 190.

 

[Koopernic]

Perhaps the use of a fan to force cooling air through the engine would have helped.

Like the one on the Fw 190.

Forced pressure cooling almost certainly would have helped. One would have more pressure to play with to distribute the airflow with baffles. Besides the BMW 801's geared fan similar fans were later used on the R-4360, a version of the R-2800 on the P-47J and the Bristol Centaurus. Baffles were often used to direct and balance the airflow. On the R-4360 this was supposedly so well done that the rear cylinders row ran cooler than the first.

I imagine you would put the engine on a test stand in its installation and run it up and then probe the airflow around each cylinder with a anemometer, air temperature sensor, pressure sensor, piece of lint, cylinder temperature sensor until you built up a picture of what was going on and then readjust the baffles.

The P-119 intake is missing a boundary layer spliter. I imagine Piaggio understood what was going on and trying to build the installation without one but its a more complex task. I'd be tempted to use two intakes on either side.

Late model Radial engines are really oil cooled rather than air cooled. The fan on the BMW 801 not only forced air to flow over the cylinders but forced air to flow through a serpentine path through the annular oil cooler/tank that was integrated into the cowling ring.

Note the size of the oil cooler on this Sea Fury

There is more too it than just cooling flow. One of the problems on the early R-3350 was too sharp an angle in the exhaust manifolds. This caused the gas to get hotter than necessary. This became critical on the top rear cylinders which had less cool air flow than the rest of the engine and suffered overheating problems and damaged valves on the B-29.

 

[tomo pauk]

Interesting design, not so much as fighter, but more as ground attack aircraft. The layout allows a large centerline mounted cannon, combined with a ground fire resistant air cooled radial engine, something that is not possible with 'normal' single engine radial powered designs. Tank buster anyone???
...

I'd go for a full fighter-bomber. The aircraft can be pretty compact - not as big as Il-2 or Ju-87 - that would meant it will be a tough proposal for an enemy fighter pilot looking for an easy kill, while also being a threat for enemy bombers/attack A/C. Soviets can install 23 mm and then 37mm as the main gun, Americans the variation of the 1.1in, 37mm AA or 40mm AA, British can go with 2pdr HV and, S class etc, Germans have a choice between different 30 and 37mm, and they can also try bomber-busting with such cannons.

But then, the plain vanilla P-39 with Class "S" cannon would've been a threat to Axis tanks, while being a problem to their fighters at low level.

 

[Elmas]

Some airplane designs seem to be at first sight very innovative and clever, like the "pushers", but when properly tested, their limits clearly appear.

First of all the position of the engine itself: certainly the weight of the engine very close to the Cg adds manouverabilty, but in some cases, like a sharp exit from a dive (Laws of Phisics always apply: Angular momentum, Momentum of Inertia and so on.... Laws that are not always completely considered by "armchair Pilots"...) the lack of weight in the nose tends to raise the nose itself "capsizing" the aeroplane, with obvious catastrophic results. So, why add manouverability if all this manouverability can't be fully exploited, not only, but it can be very dangerous?

This, with the very low reliability of the worn out Allisons, was the bitter complaint of the Italian Pilots that flew P-39s.

Since the first flights, P-119 was found extremely difficult to "balance", and so discarded from possible fighter duties and relegated, to "assault", as generally happens with botched fighters.

Secondly, in the event of an emergency landing, the pilot would have been at seriously risk: Ambronsini test engineer, Ing. A. Colombo, while performing a test flight with SS.4

an airplane with an engine behind as well, was forced to land; and it became a fatal accident because the plane crashed against a tree: the engine was projected forward in the cockpit, crushing the Pilot.

So, while the cooling problems could have been sorted out, as it has been said, the basic design flaws of the design could not, despite the "pretty" appearance of the airplane.

 

[Shortround6]

The problems of having the engine behind the pilot in a crash had been well appreciated in WW I where quite a number of planes were pushers. Not to mention that most WW I aircraft were pretty flimsy to begin with.
The front engined SE5A was considered to rather safe in crash.

because the plane was sturdier than some others AND because of the distance between the engine and pilot meant there was some room for the fuselage to "crush" before the engine landed in the pilots lap. unlike the Sopwith Dolphin

 

[tomo pauk]

Seems like there was no instance of P-39 or P-63 'launching' their engines and crushing the pilots in what would be otherwise an minor incident. As for the CoG being dangerously too much behind, the P-63 was not known for such problems, ie. it can be avoided in A/C with such powerplant layout.
Problem with P-39, at least with P-39C -> P-39D, stemmed much from added protection and radios behind the CoG, while in the same time nose got lighter due to deletion of LMGs, thus pushing the CoG too much behind. But again, we don't seem to hear from Soviet pilots about the CoG problems on their P-39s.

 

[swampyankee]

The devil's in the details...

Usually, non-standard configurations are non-standard simply because they're not as good. The P-39 and P-63 had trouble finding volume where they could put enough fuel -- one wants to put fuel tanks as close to the center of gravity as possible, and these Bell aircraft put the engine there -- and they also tended to have their c/g shift rearwards as the guns were fired. Now, this is a problem with all conventional aircraft with nose-mounted guns but the mid-placement of the engines means that the nose-mounted guns and ammunition are farther from the c/g, increasing the size of the c/g shift. The mid-engine also requires larger vertical and horizontal tail surfaces to get the required tail volume.

As an aside, engine cooling system design is hard. North American did an absolutely brilliant design of it with the P-51, but (slightly jingoistically, and cheering for my people in the US world of aero), American engineers did this better for air-cooled engines than anybody else.

 

[Shortround6]

The P-39 fuselage/engine bay was a pretty substantial structure. It had to be (as would parts of the P-119) in order to keep the propeller/gear box aligned with the engine. A problem that some pushers like the SS4 don't have.

Some Soviet pilots were used to planes with somewhat wonky CG issues. The Mig-1&3 being somewhat notorious in this regard and the comment that ex I-16 pilots had less trouble with the Migs (or perhaps the statement that pilots who could fly the I016 had little trouble with Migs) lends some doubt as to the I-16s stability or lack of.

P-63 used a different wing and more importantly moved the engine and cockpit in relation to the wing

Note leading edge of door compared to leading edge of wing, not that they even used the same door.

Yes the problem/s can be avoided but there seem to be quite a few problems that while being able to be fixed can also be avoided by using a different layp\out.

 

[Piper106]

I imagine you would put the engine on a test stand in its installation and run it up and then probe the airflow around each cylinder with a anemometer, air temperature sensor, pressure sensor, piece of lint, cylinder temperature sensor until you built up a picture of what was going on and then readjust the baffles. .

Koopernic hit the nail on the head. You figure out which cylinders are running the hottest, and readjust the cylinder baffles to even out the temperature of the cylinders. Might even need to cut some slots into the fuselage (ala the Fw 190) or increase the size of the air exit opening to increase the total airflow through the engine. Another trick would be to use the energy in the exhaust gas pulses to pull cooling air through the engine compartment as was done on the Convair 240 / 340 / 440 airliners. Getting engine cooling right might take three or four tries, if not more. Each try takes time, something that was increasingly short for the Italians by late 1942 early 1943..

As an aside, engine cooling system design is hard. ... but (slightly jingoistically, and cheering for my people in the US world of aero), American engineers did this better for air-cooled engines than anybody else.

And even the US wasn't perfect. As I hinted at in my earlier post, while American engineers, technicians, and mechanics eventually got B-29 engine cooling 'right', it took many months, and a good size chunk of the 'textbook' on that subject was 'written in blood'. .

 

[Graeme]

The front engined SE5A was considered to rather safe in crash.

Unless you try this...

 

[swampyankee]

Unless you try this...

View attachment 472660View attachment 472661

Wow!

A pilot more useful to the enemy than his own side!

 

[johnbr]

View attachment 472690

 

[Koopernic]

Wow!

A pilot more useful to the enemy than his own side!

The military eventually pioneered psychometrics such as IQ tests. It's very effective at finding people with ability that may not have been identified (too little schooling, too young at school) and also the opposit person.

 

[Shortround6]

I would note that fans are not magic. The P119 has a basic problem in that the air going to the bottom cylinders has a short path and little or no change in direction until it hits the front of the engine.

The air going to the upper cylinders has several more feet to travel and two changes of direction. This will affect the mass airflow going over the cylinders. Most planes with fans (at least the tractor engine ones) had an equal amount of air entering the fan all the way around the fan and had pretty much an equal amount of air leaving the fan/entering the cooling baffles at all points in the circle. That will not be the case here without some work on the baffles/ducts leading to the fan (assuming the fan is just a few inches in front of the cylinders.

Careful baffling and adjustments to the ducts could help even out the airflow, like tighter more restrictive baffles on the bottom cylinders to raise the pressure drop through them making it easier for the air to go through the looser baffles at the top of the engine.
This was certainly known to the Italians as cooling in-line 6s and V-12s call for some pretty fancy airflow to get the same airflow past each cylinder. It just takes time, which they did not have.
Going against the plane from a engineering point of view is the remote shaft and remote reduction gear, certainly not impossible but 'new".
Please remember that Allison had a history of building reduction gears and remote gearboxes (including right angle drives) for other engine makers (like Packard) and dirigibles and were probably the best company in the US to undertake a project like the P-39. Also note they got it slightly wrong and the XP-39 had to be fitted with a new drive shaft in order to safely use full power. The first was considered too light if
if the engine started misfiring at high rpm, causing an out of the ordinary vibration pattern.
The engine used in the P119 was also one of the first Italian engines to use a 2 speed supercharger. I am not sure they ever got one on a production engine in WW II. Not extra hard but one more thing to sort out on an experimental airplane.

 

[tomo pauk]

The contemporary booklet about Italian ww2 A/C notes the Piaggio P.XV 45RC engine as capable for making 1475 Cv at 4500 m, single speed S/C. (pdf, pg. 16) - ie. altitude power in-between the BMW 801C and 801D. Italian Wikipedia lists only two-speed variants, and it is indeed questionable how much of any P.XV engines were produced at all.
Installing the P.XV 45RC engine on the Fiat G.55 or Re.2005 airframe would've probably been much easier than going out with new layout in the same time.