F4F dive speed

[TimRas]

AFAIK, the F4F was one of the few planes of WW2, that was not red-lined in dives. The reason was that the drag of the airframe was so big that the plane reached its terminal dive velocity before its structural or Mach limits. This velocity was around 500mph. But in AH2 the F4F can dive around 600 mph TAS no problem. This speed (Mach 0.8) seems to be the limit for all prop planes in AH2. Is this because the transonic drag rise is modelled using the same curve for all planes?

In RL there seems to have been significant differences. Below is drag curves for XP-51 and XF2A-2 (Brewster Buffalo):


Curves for terminal dive speed for P-47, P-39N and XF2A-2:


The document:A simple method for estimating terminal velocity including effect of compressibility on drag

[F4UDOA]

The limitation on most Structural limitation diagrams list the limits in IAS not TAS.

So not only do you need to know the IAS to TAS conversion depending on altitude but you need the IAS to CAS error to start with. Also gross weight changes the restriction as weight.

For instance you must add 8 knots to 410KNOTS IAS to get the correct speed.

[ra]

What's the dive brake mentioned in the F4U chart?

[CMC Airboss]

Originally posted by ra
What's the dive brake mentioned in the F4U chart?

The F4U landing gear extension system had a setting that would enable only the main wheels to be extended (this setting would lock-out the tailwheel to prevent damage).  The main gear was essentially used as a dive brake through extension prior to the dive.   There is a very commonly shown film clip from WW2 that shows an F4U dive bombing a Japanese island with napalm with it's gear extended.  



From the Corsair I-IV Pilot's Notes (published by Royal Air Ministry)

Para 7

(i) On early aircraft the undercarriage control is a spring-loaded knob situated below the left-hand side of the instrument panel. To raise the undercarriage, pull out the knob, release the safety catch, and move to UP. To lower the u/c, pull out the knob, and move to DOWN when the safety catch will be automatically engaged. After setting the control to UP or DOWN ensure that the pin on the knob engages with the hole in the quadrant. The main wheels are used as dive brakes and may be lowered or raise independantly of the tailwheel by the control on the left of the u/c indicator.

NB. on later aircraft the dive brake control is combined with the u/c control.

Para 44 Flying Limitations

(iii) Dive Bombing

Maximum speed (u/c up)... ... ... ... 375 Knots IAS

Maximum speed for lowering u/c (dive brakes)... 250 KIAS

Maximum speed u/c down ... ... ... ... ... 350 KIAS

MiG

[F4UDOA]

Airboss,

Do you have the entire copy of the Pilots notes you posted? I have 4 F4U pilots manuals but all USN.

The retriction on extending the break was raised and use of the break was unlimited on later F4U-1 models and later.

[Jester]

Airboss,

Think you are mistaken about the pic you are showing. Napalm is generaly "Flown On" in a very shallow flight path to spread it over a wider area. "Dive Bombing" with it would decrease it's effectiveness.

I think if memory serves correctly the reason the F4U's in your pic still have their wheels down is because the contact with the enemy was that close. The aircraft took off, dropped their loads & returned to the field to rearm all without pulling their gear up to speed the process up.

[Widewing]

Originally posted by Jester
Airboss,

I think if memory serves correctly the reason the F4U's in your pic still have their wheels down is because the contact with the enemy was that close. The aircraft took off, dropped their loads & returned to the field to rearm all without pulling their gear up to speed the process up.

I've heard that too. But, it's still bogus. This stems from some not-so-brilliant people seeing film and assuming for why the gear was down. I've heard narrators state this as the reason for the gear being down. When taking off from ship or land base, the first thing you do is clean up the airplane. Airspeed is critical and unneeded drag is bad for one's health.

Note also that the F4U in the photo has the tailwheel up, doors closed.

My regards,

Widewing

[hawker238]

Originally posted by Jester
Airboss,

Think you are mistaken about the pic you are showing. Napalm is generaly "Flown On" in a very shallow flight path to spread it over a wider area. "Dive Bombing" with it would decrease it's effectiveness.

I think if memory serves correctly the reason the F4U's in your pic still have their wheels down is because the contact with the enemy was that close. The aircraft took off, dropped their loads & returned to the field to rearm all without pulling their gear up to speed the process up.

Maybe in this case direct accuracy of the napalm on the cave entrance in order to oxygen-starve the area was more important than a general sweep?

[Jester]

Originally posted by Widewing
I've heard that too. But, it's still bogus. This stems from some not-so-brilliant people seeing film and assuming for why the gear was down. I've heard narrators state this as the reason for the gear being down. When taking off from ship or land base, the first thing you do is clean up the airplane. Airspeed is critical and unneeded drag is bad for one's health.

Note also that the F4U in the photo has the tailwheel up, doors closed.

My regards,

Widewing

Where I heard it from was a interview from one of the Marine pilots that was actually flying one of the Corsairs doing this. I will see if I can track it down.

[RedBeard]

Originally posted by F4UDOA
Airboss,

Do you have the entire copy of the Pilots notes you posted? I have 4 F4U pilots manuals but all USN.

The retriction on extending the break was raised and use of the break was unlimited on later F4U-1 models and later.

My manual (Aviation Publications) says basically the same thing, but has different restrictions on the speed.  It supposedly covers the F4U-1D, F3A-1D, FG-1D, and British Corsair I, II, and III.

[Arlo]

Originally posted by Jester
Where I heard it from was a interview from one of the Marine pilots that was actually flying one of the Corsairs doing this. I will see if I can track it down.

WW's right, Jest. Main LG was the divebrake on the F4U. The pic does show the tailwheel up, as well. Zeno's has the training film for the F4U and goes into it in detail. I can't see any such comment in an interview being more than some tongue-in-cheek leg-pulling. Ya take off, ya raise gear ... even if ya don't leave the pattern. How close a fight is that?

One additional comment ...

The F4U also had an emergency system that pneumatically blew the gear down for emergencies. Once actuated, the gear could not be raised. Blackburn tells of a pilot on escort duty that reached down and mistakenly actuated it by mistake instead of turning on his oxygen (the knobs were identical and next to each other). Subsequently he was shot down by the Zekes trailing the formation when he fell out of it. Pilots in the formation requested they cover him but they were ordered to stay with the buffs.

[Red Tail 444]

I always thought only the doors opened, and the gear assembly remained up while deploying dive brakes....

[rshubert]

Originally posted by Red Tail 444
I always thought only the doors opened, and the gear assembly remained up while deploying dive brakes....

IIRC, the door is firmly connected to the gear leg on the corsair.