Along with every real-world diagram I've ever seen.
Why a Rear Engine For the P-39?
- Thread starter MIflyer
- Start date
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Hello XBe02Drvr,
In section 6.1.6 of the document in the link I posted, the author describes a real world test of flying an aircraft with CoG far enough aft so that the Stabilizer was providing lift. He did this with a Cessna 172 loaded with CoG at the aft limit.
I am wondering now what a diagram for the rather common Cessna 172 looks like. I had found a diagram of a Cessna earlier but with the CoG limits ahead of CoL. I did not save it, so I don't know what model Cessna it was and if they differ that much between models.
- Ivan.
Hello Ivan,
I don't have a C172 manual handy, but from memory, they made some major changes with the 1968 model year that changed how it handled, especially around the stall and around aft CG loading.
The major changes were to replace the 6 cylinder 145 HP Continental engine with a 4 cylinder 150 HP Lycoming, and to add a couple of features that the Robertson STOL company had been modifying 172s with to improve their short field performance. This entailed "cuffing" the leading edge of the wing to give it a less pointy, more bulbous, rounded profile, which helped delay airflow separation at high AOA, and changes to the stab profile and elevator area that improved pitch authority under forward CG high AOA conditions.
In my experience, '67 and earlier 172s flew marginally faster on less HP, but had a sharper stall break and were more difficult to get a "greaser" landing with. Just when you were deep in a protracted flare "feeling" for the runway with your mains, stall horn blaring, the tail would quit flying, the nose would drop, and you'd plop in from an altitude of 12 inches. Later models had an "easy chair" stall behaviour and almost landed themselves, besides making short field/soft field takeoffs and landings much less stressful.
C182s underwent similar changes at about that time, which stopped them from bending firewalls in hard landings.
You might try googling POHs for various years and models of Cessnas if it's something you want to pursue.
Cheers,
Wes
I was surprised by Eric Brown's glowing words about the P-39 in one of his volumes of Wings of the Weird and Wonderful. He used it as a hack and described it as a very pleasant plane to fly. Of course, he was in England and not flying in combat. Chuck Yeager, I believe, also liked the P-39. My father was a Liaison Pilot and crew chief on both 39s and 38s in North Africa (my father was the most untalented mechanic I have ever known so I don't know how he made it work) but he told me of a P-39 doing the so called nose and tail tumble over an airfield (I think in Africa) and he always believed it was sabotage. The pilot bailed out but his chute didn't open and he landed on the edge of the field (my father never forgot about that). Of course the debate over the Alison and the lack of turbocharging is well known. However, I think the decision to put the engine behind the pilot was based on an attempt to have the center of gravity and the most mass in a central location. I believe this is mentioned in Ray Wagner's history of U.S. military aircraft. The P-39 was certainly not an outstanding success but I think it was better than some other planes being used by the by the allies at the start of the war in 1939. There were still worse planes in active service in January of 1942. If you want me to track down some references about the design I will look through some books.
Welcome aboard, Oldparts! Join the armchair society of oldpharts where we have fun dissecting every aspect of aviation history.
Eric and Chuck and the P-39: an F1 car is fun to drive, IF you have the skill to handle it. If not, it's an unholy terror. Ditto P-39.
Your father as mechanic and Liason Pilot?? Huh? You mean one of those L-4 drivers that hopped from base to base and did parts runs? Well there's your answer right there. Everybody knows pilots don't make good mechanics and vice versa. Just ask anybody who only does one and not the other! Did he go through flight training, then wash out near the end, or lose combat pilot status for some other reason, or did he get trained in the prewar CPT and then not qualify for a commission and get sent to mechanic school? People who weren't military pilot rated, but had the training, were sometimes pressed into service as Grasshopper pilots in a pinch. One of them even scored a "kill" of a Storch with an M1911 from his L-4.
Cheers,
Wes
Eric and Chuck and the P-39: an F1 car is fun to drive, IF you have the skill to handle it. If not, it's an unholy terror. Ditto P-39.
Your father as mechanic and Liason Pilot?? Huh? You mean one of those L-4 drivers that hopped from base to base and did parts runs? Well there's your answer right there. Everybody knows pilots don't make good mechanics and vice versa. Just ask anybody who only does one and not the other! Did he go through flight training, then wash out near the end, or lose combat pilot status for some other reason, or did he get trained in the prewar CPT and then not qualify for a commission and get sent to mechanic school? People who weren't military pilot rated, but had the training, were sometimes pressed into service as Grasshopper pilots in a pinch. One of them even scored a "kill" of a Storch with an M1911 from his L-4.
Cheers,
Wes
wuzak
Captain
While that may be part of it, it really was all about the big cannon.
That big, heavy, almost useless in air-to-air combat 37mm cannon.
The USAAC/F loved it. It was supposed to be in the P-38. Two were in the XP-54 (needed a special tilting nose to be able to shoot the 37mm guns at the same target as the 0.50" mgs) and the XP-67 was to have 6 (!
) of the 37mm cannon.Anyway, the only practical way to have a gun firing through the hub of an aircraft equipped with a V-1710 was with a remote drive. Such a remote drive featured in other proposed layouts by Bell and Curtiss, usually with smaller cannon (20-25mm) and with front engines. The 37mm needed more space, however.
I don't know all of the details. My dad was a good athlete and played organized community baseball and softball into his 60's. I think he was dyslexia. He was in flight school. He had worked at a CC camp and joined the Army Air Corps (as I think it was known then) in 1939. He did wash out of flight school (my guess is primary) when he ground looped a plane (I think at PT-19). Yes, he flew little piper cub like aircraft. But I don't think they were made by Piper -- I think they were Taylorcraft but I could be wrong. I do have some pictures from Camp (or Fort Polk). I think he was also in the big 1939 maneuvers. I have a scan of his DD214 but they are hard to read.. He told me he had about 250 hours of flight time. He never flew after getting out of the service but work in a cotton mill where my mom's father had worked and where I worked part time my last couple of years in high school. My dad was discharged in 1944 because of malaria and a very large melanoma. He lived to be 82 but died from renal cell cancer which evidently runs in my family and melanoma and renal cell cancers appear to be related. I went to flight school in the Army in 1968. I did about 80 hours in rotary wing at Fort Wolters. I did not wash out but got recycled and resigned. Since I was only about 6 weeks from finishing basic flight school; the Army was not happy. Advanced infantry training back at Fort Charles but I ended up at Fort Benning and became a Scout Dog Handler. In Vietnam, I lost a dog to illness (leukemia) and ended up with one of the first Super Dogs trained by psychologist at NC State (where I had flunked out a few semesters before). I retired after 36 years of university teaching last May. I read history, especially now technical history of WW2. I also fly the new version of IL-2.
I had a next door neighbor who flew TBM's off of the Shamrock Bay. I live in Eastern NC and there are all sorts of old WW2 pilots around here but they are disappearing fast. My brother is a retired Air Force officer (he did 13 years in the Navy but got out and went back into the Air Force 2 years later). He lives near Wright Patterson. My older sister lived near Dayton after college so I started going to the Air Force Museum around 1962. I think they had fewer than 20 planes and all were outside.
Thanks for the warm welcome. I will say that my mechanical skills are almost as bad as my fathers. My brother builds is own furniture, can plumb, lay tile, fix anything. But his military career was unexciting except for dong a CAT shot. He was on a nuclear surface warfare tender and they need a qualified reactor operator for a nuclear refuel in the Mediterranean and he went off a carrier in something like a E-6. I guess he was beside the pilot and only the two of the were flying. He told me that pilot told him the classic line about if you hear me say eject you won't hear be say it again.
My other neighbor (when I lived beside the gentleman who flew TBM's) graduated from Annapolis in 1948 (I think) but took his commission in the Air Force. He was flying in Korea (ground support) and got hit on his first mission but made it make to the base and crashed on landing. He broke his back. Where I live now, my neighbor flew F6F photo reconnaissance and early Navy Jets. He is also unfortunately deceased. One reason there are so many old pilots around here is that when the Air Force became an independent service, most pilots keep their commissions in the Army. Kinston NC which is near me was one of the training bases set up to train pilots for the Air Force. My daughter in law's grandfather (a B-29 pilot who didn't go over seas) ran that training base for part of the time. I wish I had more of chance to know him. A newspaper article reported that he had 36,000 hours of flight time. However, he had just died when I read that because it seemed impossible. He was in his early 90's when I met him I just filled up a large brief case of aviation books and he was a happy man. He did ask me once about the guy who ran our university bookstore. He had been one of the trainees at Kinston. I knew the guy and remember talking to him about flying. He had been a medium bomber pilot around 1950 or so and had flown B-25s. His transition from the B-25 was to the B-47. That had to be a big leap.
I only regret that I didn't do interviews and tape some of these guys. Twenty years ago (I was almost 50), I almost took up flying again but instead started buying sports bikes. I even go my amateur racing license but never raced. I was slow!
I had a next door neighbor who flew TBM's off of the Shamrock Bay. I live in Eastern NC and there are all sorts of old WW2 pilots around here but they are disappearing fast. My brother is a retired Air Force officer (he did 13 years in the Navy but got out and went back into the Air Force 2 years later). He lives near Wright Patterson. My older sister lived near Dayton after college so I started going to the Air Force Museum around 1962. I think they had fewer than 20 planes and all were outside.
Thanks for the warm welcome. I will say that my mechanical skills are almost as bad as my fathers. My brother builds is own furniture, can plumb, lay tile, fix anything. But his military career was unexciting except for dong a CAT shot. He was on a nuclear surface warfare tender and they need a qualified reactor operator for a nuclear refuel in the Mediterranean and he went off a carrier in something like a E-6. I guess he was beside the pilot and only the two of the were flying. He told me that pilot told him the classic line about if you hear me say eject you won't hear be say it again.
My other neighbor (when I lived beside the gentleman who flew TBM's) graduated from Annapolis in 1948 (I think) but took his commission in the Air Force. He was flying in Korea (ground support) and got hit on his first mission but made it make to the base and crashed on landing. He broke his back. Where I live now, my neighbor flew F6F photo reconnaissance and early Navy Jets. He is also unfortunately deceased. One reason there are so many old pilots around here is that when the Air Force became an independent service, most pilots keep their commissions in the Army. Kinston NC which is near me was one of the training bases set up to train pilots for the Air Force. My daughter in law's grandfather (a B-29 pilot who didn't go over seas) ran that training base for part of the time. I wish I had more of chance to know him. A newspaper article reported that he had 36,000 hours of flight time. However, he had just died when I read that because it seemed impossible. He was in his early 90's when I met him I just filled up a large brief case of aviation books and he was a happy man. He did ask me once about the guy who ran our university bookstore. He had been one of the trainees at Kinston. I knew the guy and remember talking to him about flying. He had been a medium bomber pilot around 1950 or so and had flown B-25s. His transition from the B-25 was to the B-47. That had to be a big leap.
I only regret that I didn't do interviews and tape some of these guys. Twenty years ago (I was almost 50), I almost took up flying again but instead started buying sports bikes. I even go my amateur racing license but never raced. I was slow!
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While that may be part of it, it really was all about the big cannon.
That big, heavy, almost useless in air-to-air combat 37mm cannon.
The USAAC/F loved it. It was supposed to be in the P-38. Two were in the XP-54 (needed a special tilting nose to be able to shoot the 37mm guns at the same target as the 0.50" mgs) and the XP-67 was to have 6 (!
Anyway, the only practical way to have a gun firing through the hub of an aircraft equipped with a V-1710 was with a remote drive. Such a remote drive featured in other proposed layouts by Bell and Curtiss, usually with smaller cannon (20-25mm) and with front engines. The 37mm needed more space, however.
daveT
Senior Airman
Back to the original question of why rear engine for the P-39. Robert Woods does make the case why inline engines are much better than radial engines, no argument there. In summery: His reasons for the rear engine include: streamlining the fuselage; increased speed requirements, the 37 mm gun, retractable nose wheel, increase vision for the pilot.
Did I miss any of his main points?
Did I miss any of his main points?
daveT
Senior Airman
The author also states that it was planned that the 37 mm cannon could be replaced by 20 mm depending on the need.
Was this ever done?
Was this ever done?
wuzak
Captain
Yes, the P-400 version had the 20mm Hispano.
The P-400 (a P-39 built for the Brits but they didn't want) had the 20mm HS cannon. According to Wagner, these were called the Model 14 my Bell and the P-400 by USAAF. Wagner reports 675 were built and the U.S. ended up with 179. The P-400s were used a lot on Guadalcanal.
While that may be part of it, it really was all about the big cannon.
That big, heavy, almost useless in air-to-air combat 37mm cannon.
The USAAC/F loved it. It was supposed to be in the P-38. Two were in the XP-54 (needed a special tilting nose to be able to shoot the 37mm guns at the same target as the 0.50" mgs) and the XP-67 was to have 6 (!
Anyway, the only practical way to have a gun firing through the hub of an aircraft equipped with a V-1710 was with a remote drive. Such a remote drive featured in other proposed layouts by Bell and Curtiss, usually with smaller cannon (20-25mm) and with front engines. The 37mm needed more space, however.
The XP-40 did have a belly-radiator, it didn't work so they moves it up to the nose...
Wait... I didn't think the A-320 was designed to be unstable, merely used FBW to reduce weight...
I won't argue with you since the reference to the center of gravity is in Flying Guns of WW2 and not a book on aircraft design and development. I guess the real mystery is why anyone thought the M4 (T-9) was a good choice for a motor cannon. But the P-39 was designed as a point interceptor and if you could hit a bomber with one of those rounds then it was pretty big round. I consider John Browning a brilliant designer and although the M4 was a Browning design, I doubt he was much involved in the work on the M4 (Browning died in 1926). I will note that I just read that the M4 became a favorite weapon of the little boats in the Pacific. As far as the mass of the plane being close to the center of gravity, I do believe it makes sense in theory but it apparently actually caused more problems as fuel and ammunition were expended.
The first aviation books I ever bought were Green's four Volumes on Fighters. I lost them lending them to a relative when I went into the service. However, I recently picked up all four volumes for a reasonable price off of Amazon. I decided to check out Green's entry on the P-39. He states that, and I paraphrase, that to the Bell team the location behind the pilot offered (1) superior maneuverability (located near the CG), facilitated installation of heavy nose armament, better pilot visibility, and permitted the use of tricycle gear. The first gun considered as a motor cannon was (according to Green and Anthony Williams) was a 25mm Madsen (Williams) but Green just states that a 25mm was considered. It has been years since I have read any of Green's books and don't know how it is considered by more modern researchers. I do think he rates the Airacobra too highly.
