XP-39 Airplane in wind tunnel

[P-39 Expert]

Get it right....

It's RULE BRITANNIA.

I thought it was "Roll" because of their sea heritage. Good to know.

 

[P-39 Expert]

You may want to rethink that and get off the anti-british track.
"USAAC was generally pleased with the Airacobra, and an initial order for 80 production examples (Bell Model 13) was issued on August 10, 1939 under Contract AC13383. "
"Armament was one 37-mm cannon, two 0.50-inch and two 0.30-inch machine guns, all in the nose."

So the British just moved two of the .30 cal guns from the nose to the wings, and since they were using a cannon over 100lbs lighter than the American cannon, added another 24lb machine gun in each wing. Somehow this lighter weight armament than the US was using ruined the rest of the Production run?



View attachment 540397
P-39C

I think the Army would have wised up and deleted those nose .30s to restore the full 30 rounds for the 37mm cannon. Having the two nose .30's reduced the cannon armament to 15 rounds.

 

[pbehn]

I thought it was "Roll" because of their sea heritage. Good to know.

Its a song.

 

[P-39 Expert]

Potato/poTAHto.

 

[wuzak]

I thought it was "Roll" because of their sea heritage. Good to know.

It is related to their sea heritage. The chorus is:

Rule, Britannia! Britannia, rule the waves!
Britons never, never, never shall be slaves.

 

[Shortround6]

I think the Army would have wised up and deleted those nose .30s to restore the full 30 rounds for the 37mm cannon. Having the two nose .30's reduced the cannon armament to 15 rounds.

There was no "restore" the full 30 rounds. The YP-39s (the model right before the C, there were no As or Bs) that had guns (most were completed without guns and some had the gins added later), had the 37mm with 15 rounds (the 30 round capacity required a different feedway). the two .50 cal guns with 200rpg and two .30 cal guns with 500rpg.
There was no early version of the P-39 with just the 37mm and two .50s unless it was one of the YP-39s without the full armament layout.

lets also remember that the USAAC told Bell (and other companies) what they wanted for guns, the companies might push back and say it won't fit or it will reduce performance by X amount, but the companies did NOT tell the USAAC what the armament should be ( they could offer a certain set up in the sales pitch like Republic and the eight .50s in the P-47B).
Larry Bell pushed for the .30s to be taken out but then his company had lied about the basic airplane could do performance wise and he may have been looking for the last few percent of performance to keep up the numbers.

 

[P-39 Expert]

It is related to their sea heritage. The chorus is:

Rule, Britannia! Britannia, rule the waves!
Britons never, never, never shall be slaves.

I stand corrected. Good to know. Should I go back and correct my original post?

 

[wuzak]

and some had the gins added later

Did they fit a cup holder, or was it fed through a tube?

And did it come with tonic?

 

[P-39 Expert]

There was no "restore" the full 30 rounds. The YP-39s (the model right before the C, there were no As or Bs) that had guns (most were completed without guns and some had the gins added later), had the 37mm with 15 rounds (the 30 round capacity required a different feedway). the two .50 cal guns with 200rpg and two .30 cal guns with 500rpg.
There was no early version of the P-39 with just the 37mm and two .50s unless it was one of the YP-39s without the full armament layout.

lets also remember that the USAAC told Bell (and other companies) what they wanted for guns, the companies might push back and say it won't fit or it will reduce performance by X amount, but the companies did NOT tell the USAAC what the armament should be ( they could offer a certain set up in the sales pitch like Republic and the eight .50s in the P-47B).
Larry Bell pushed for the .30s to be taken out but then his company had lied about the basic airplane could do performance wise and he may have been looking for the last few percent of performance to keep up the numbers.

Absolutely the Army told the contractors what they wanted and the contractor built it. In any event, the 37mm cannon needed 30 rounds. And Bell was no more crooked than any other defense contractor, just smaller and less influential.

 

[Shortround6]

Did they fit a cup holder, or was it fed through a tube?

And did it come with tonic?

Ah, now we know why the British airacobras performed so poorly. it was the several hundred pound gin dispenser

 

[wuzak]

Absolutely the Army told the contractors what they wanted and the contractor built it. In any event, the 37mm cannon needed 30 rounds. And Bell was no more crooked than any other defense contractor, just smaller and less influential.

Because it couldn't hit the side of a barn from 20 paces?

 

[Shortround6]

Absolutely the Army told the contractors what they wanted and the contractor built it. In any event, the 37mm cannon needed 30 rounds. And Bell was no more crooked than any other defense contractor, just smaller and less influential.

You said they restored the 30 round capacity, they didn't.
Doesn't matter if they needed 30 rounds or not (and 15 rounds would last the 37 M4 about 6 seconds, which is just a bit less than 60 rounds lasts a Hispano or 55-60 rounds lasts an MGFF/M or japanese type 99 mark I)

As to Bell's honesty, I can't think of another company that lied about the performance of a prototype aircraft to the extent that Bell did. Plenty of companies gave optimistic estimates of performance before the prototype flew (some were very optimistic). But Bell at least had few hours of flight testing before the XP-39 was shipped to Langley. There Is strong evidence that the prototype never flew at full power let alone achieved the performance numbers claimed for it. Langley said it wouldn't come close to the numbers from wind tunnel results and yet nearly a year later Bell was still advertising it as a 400mph airplane. Based on the performance estimates and not test results?

BTW, Curtiss had to either refund or accept over 14,000 dollars less in payment when the 2nd XP-46 failed to meet the promised performance figures.

 

[P-39 Expert]

So, those liars at Bell somehow got a second plane into production (P-63) before the end of the war. More lying?

 

[Shortround6]

So, those liars at Bell somehow got a second plane into production (P-63) before the end of the war. More lying?

Imaterial.

The XP-39 never flew 400mph or even 390mph before being sent to Langley, It never climbed to 20,000ft in 5 minutes. There was a potential vibration problem with the driveshaft and they never ran the engine faster than 2600rpm before going to Langley. They used a different diameter drive shaft with different thickness walls after the XP-39 was rebuilt and on every P-39 after that.
Yet they claimed the plane did 390mph and had that fantastic climb rate. If that is telling the truth then I'm a little green man from Mars.
ANd then we have the rather modified plane the British tested at the Bell Factory to get within a few mph of the promised performance. Modifications that were never done to another military P-39 out of thousands built. More TRUTH????

I will let the Performance of the XP-76 off the hook as mere exuberance in the design phase since they didn't keep claiming the same performance after they flew the thing.

 

[wuzak]

I will let the Performance of the XP-76 off the hook as mere exuberance in the design phase since they didn't keep claiming the same performance after they flew the thing.

XP-76/XP-39E or P-63?

 

[Shortround6]

Sorry. XP-77

Planned engine used a supercharger that never materialized (it had a supercharger, just not one that would give 400-500hp at 27,000ft)
It wound up seriously overweight (sound familiar?) even after deleting the 20mm cannon through the prop hub,

 

[fubar57]

XP-76 was a waste any way

 

[P-39 Expert]

XP-76 was a waste any way

Way too heavy at 8900# and never got the 4 blade propeller. Six .50MGs AND a 37mm cannon. AAF should have just put the two stage engine in a P-39 already in production.

 

[Peter Gunn]

Way too heavy at 8900# and never got the 4 blade propeller. Six .50MGs AND a 37mm cannon. AAF should have just put the two stage engine in a P-39 already in production.

I didn't think a two stage supercharger would fit in the existing P-39 airframe.

 

[P-39 Expert]

The P-39E used a P-39D fuselage. The area behind the engine where the second stage went was exactly the same size as the P-63 which had the second stage. The coolant expansion tank was reconfigured and moved forward between the pilot and engine to make room for the second stage. The increase in fuselage length was aft of the bulkhead forming the back of the engine compartment.