How fast do dive bombers dive?

[Greyman]

Because at that given RPM you are not going to build up speed to exceed Vne or Vmax.

I don't think that's how it works, but my knowledge of engines and propellers isn't the greatest so I'll leave it to the more knowledgeable folks.

Interestingly, with regards to the pilot's notes, the Barracuda I, II (Merlin 30 32) are as you describe, but the Barracuda II III (Merlin 32) notes give no mention of RPM, but say the dive should be entered with not less than +6lb./sq.in. boost to avoid gaining excess speed.

This indicates to me that the reason for the 2,000 rpm is due to a propeller damage/overspeeding issue: the smaller pitch range on the 3-bladed prop compared to the 4-bladed, 32 degree prop.

All this aside - in reading A&AEE dive bombing tests with the Barracuda II (merlin 32) the aircraft could be dived to 300 IAS with brakes deployed, 2000 rpm and 0lb boost.

A telling bit in the 'conclusions' of the report:

The limiting diving speed was reached in a near-vertical dive (entry being effected by a firm push force on the control column) after diving through 4000-5000 feet, and hence, if a steep diving technique is to be employed operationally, the height at which the dive is entered must not be more than 5000 feet approximately above the required pull-out height. This may limit the operational role of the aircraft.

This doesn't seem like an aircraft that can set a certain RPM and stop accelerating straight down.

 

[FLYBOYJ]

I don't think that's how it works, but my knowledge of engines and propellers isn't the greatest so I'll leave it to the more knowledgeable folks.

I've been flying for 20 years and am also a flight instructor. I've been working in the aviation business for 35 years. I think I know a little something about this stuff!

Interestingly, with regards to the pilot's notes, the Barracuda I, II (Merlin 30 32) are as you describe, but the Barracuda II III (Merlin 32) notes give no mention of RPM, but say the dive should be entered with not less than +6lb./sq.in. boost to avoid gaining excess speed.

And boost and RPM are used in conjunction with each other when flying a high performance aircraft with a constant speed propeller.

This indicates to me that the reason for the 2,000 rpm is due to a propeller damage/overspeeding issue: the smaller pitch range on the 3-bladed prop compared to the 4-bladed, 32 degree prop.

No it indicates that you are not going to over speed the engine or over boost it. You are also keeping the propeller at a pitch that will limit efficiency, slowing the aircraft down and preventing you from reaching Vne at a given dive altitude.

All this aside - in reading A&AEE dive bombing tests with the Barracuda II (merlin 32) the aircraft could be dived to 300 IAS with brakes deployed, 2000 rpm and 0lb boost.

A telling bit in the 'conclusions' of the report:

The limiting diving speed was reached in a near-vertical dive (entry being effected by a firm push force on the control column) after diving through 4000-5000 feet, and hence, if a steep diving technique is to be employed operationally, the height at which the dive is entered must not be more than 5000 feet approximately above the required pull-out height. This may limit the operational role of the aircraft.

This doesn't seem like an aircraft that can set a certain RPM and stop accelerating straight down.

No, but this is the technique developed to dive the aircraft at speeds that won't wreck the engine or airframe when diving from 5000'.

 

[Greyman]

I still have issues with some of what you're saying - but overall it doesn't matter as it appears I was misreading you.

I thought you were saying that setting an aircraft's prop speed to 'X' would stop it from accelerating past a certain speed in a vertical dive.

 

[stan reid]

I believe the ultimate dive bomber, the Japanese Ohka, had a maximum dive speed of around 650 mph.

 

[FLYBOYJ]

I still have issues with some of what you're saying - but overall it doesn't matter as it appears I was misreading you.

I thought you were saying that setting an aircraft's prop speed to 'X' would stop it from accelerating past a certain speed in a vertical dive.

It would to a point at a certain altitude because the propeller is not operating at it max efficiency. 5000' is mentioned in this discussion. I think it's obvious if you dive a barracuda from 30,000' and keep the prop in low pitch, it's lack of efficiency will be overcome by mother gravity.

 

[RCAFson]

I don't think that's how it works, but my knowledge of engines and propellers isn't the greatest so I'll leave it to the more knowledgeable folks.

Interestingly, with regards to the pilot's notes, the Barracuda I, II (Merlin 30 32) are as you describe, but the Barracuda II III (Merlin 32) notes give no mention of RPM, but say the dive should be entered with not less than +6lb./sq.in. boost to avoid gaining excess speed.

This indicates to me that the reason for the 2,000 rpm is due to a propeller damage/overspeeding issue: the smaller pitch range on the 3-bladed prop compared to the 4-bladed, 32 degree prop.

All this aside - in reading A&AEE dive bombing tests with the Barracuda II (merlin 32) the aircraft could be dived to 300 IAS with brakes deployed, 2000 rpm and 0lb boost.

A telling bit in the 'conclusions' of the report:

The limiting diving speed was reached in a near-vertical dive (entry being effected by a firm push force on the control column) after diving through 4000-5000 feet, and hence, if a steep diving technique is to be employed operationally, the height at which the dive is entered must not be more than 5000 feet approximately above the required pull-out height. This may limit the operational role of the aircraft.

This doesn't seem like an aircraft that can set a certain RPM and stop accelerating straight down.

Do you know the aircraft weight and bomb load for that test?

Here's the exact wording of the paragraph from the Feb 1945 Pilot's Notes:

49. Diving

(i) The dive should be entered smoothly at not less than +6 Lb./sq.in. boost. This will avoid any tendency for the carburettor to cut momentarily due to the effect of negative g. The throttle lever may be retracted during the dive to avoid gaining excessive speed.

 

[GrauGeist]

I believe the ultimate dive bomber, the Japanese Ohka, had a maximum dive speed of around 650 mph.

The MXY7 may have had a high speed in it's final dive, but even then, it had terrible accuracy.

And technically speaking, the Ohka wasn't a "dive bomber" but rather a flying bomb...

 

[Greyman]

Do you know the aircraft weight and bomb load for that test?

Here's the exact wording of the paragraph from the Feb 1945 Pilot's Notes:

Good catch on the Pilot's Notes, different meaning if read correctly.

Condition of the Barracuda during the dive was 13,900 lb, 4x 500 lb GP bombs loaded.

It would to a point at a certain altitude because the propeller is not operating at it max efficiency. 5000' is mentioned in this discussion. I think it's obvious if you dive a barracuda from 30,000' and keep the prop in low pitch, it's lack of efficiency will be overcome by mother gravity.

That I'm prepared to believe. It was the image of a Barracuda diving straight down--not accelerating--at 260 IAS that had my eyebrow raised.

 

[FLYBOYJ]

That I'm prepared to believe. It was the image of a Barracuda diving straight down--not accelerating--at 260 IAS that had my eyebrow raised.

The picture is reality if started from 5000' as the pilot's notes say.

 

[Greyman]

No, the 5000 foot figure is mentioned (in the A&AEE conclusions) because beyond that, the Barracuda will exceed the limiting dive speed, not stop accelerating and coast down at 260 IAS.

 

[FLYBOYJ]

No, the 5000 foot figure is mentioned (in the A&AEE conclusions) because beyond that, the Barracuda will exceed the limiting dive speed, not stop accelerating and coast down at 260 IAS.

Exactly but it's also mentioned in the pilot's notes for the same reason, remember you're looking at "a picture." The numbers paint something a bit different.

 

[stona]

Can you name any dive bomber attack on a carrier that was stopped by AA? NO WW2 AA system had the capability to defeat a determined DB attack, even with considerably larger numbers of defending ships than were present when Illustrious was attacked.

RN carriers survived air attacks in the Mediterranean. It really depends how you qualify 'determined'.

In operations off Crete the light cruiser HMS Fiji survived thirteen hours of more or less continuous air attack before finally sustaining two hits which proved fatal. This may have been due to the fact that she had run out of ammunition and was reduced to firing practice (solid) shot at the incoming aircraft before ceasing fire altogether. Ordinary Seaman Leonard Michaels, a survivor, said with typical understatement that his 'emboldened the attacking aircraft.'

HMS Kipling was attacked 83 times in roughly five hours but survived. HMS Kandahar survived 22 attacks in four hours and forty five minutes but survived. Not carriers and obviously smaller and harder to hit, but they survived what I would call determined attack.

Cheers

Steve

 

[Juha]

There are several cases of ships surviving when attacked by numerous DBs, one happened on June 5 1942 during the Battle of Midway. 58 SBDs from Enterprise and Hornet attacked lonely DD Tanikaze which zigzagged furiously and fired "a large volume of small caliber and anti-aircraft fire." She suffered damage, bomb fragments from near-misses caused explosion in after turret (6 KIA) but shot down one of Enterprise's SBDs (2 KIA). She survived most probably because of skillfull manoeuvring but probably partly because of that "a large volume of small caliber and anti-aircraft fire."

 

[RCAFson]

RN carriers survived air attacks in the Mediterranean. It really depends how you qualify 'determined'.

In operations off Crete the light cruiser HMS Fiji survived thirteen hours of more or less continuous air attack before finally sustaining two hits which proved fatal. This may have been due to the fact that she had run out of ammunition and was reduced to firing practice (solid) shot at the incoming aircraft before ceasing fire altogether. Ordinary Seaman Leonard Michaels, a survivor, said with typical understatement that his 'emboldened the attacking aircraft.'

HMS Kipling was attacked 83 times in roughly five hours but survived. HMS Kandahar survived 22 attacks in four hours and forty five minutes but survived. Not carriers and obviously smaller and harder to hit, but they survived what I would call determined attack.

Cheers

Steve

IOW, there are no (AFAIK) examples of carriers defeating DB attacks with AA. Certainly, there are lots of examples of ships evading being hit by manoeuvre or because the bombs simply missed as did the vast majority of those aimed at Illustrious. Fliegerkorps X had been formed with the specific intention of sinking an RN carrier with heavy AP bombs. In their initial attack on Illustrious they achieved a measure of surprise but subsequent attacks were much less successful.

 

[stona]

Actually the attack on Illustrious was disrupted by the FAA's Fulmars. The final attacking formation was intercepted and only one Ju 87 of this group achieved a hit. This bomb struck about 6 metres forward of the after lift and penetrated to the hangar deck before exploding on the ammunition lift. Most of the Ju87s, but not all, were dropping 500Kg armour piercing bombs with delay fuses. Some accounts say that the second and third attacks dropped 1000Kg bombs. I don't recall what delay the Germans had decided on for shipping attacks of this type. The British varied between 0.1 and 0.3 seconds depending on the weight of the bomb and altitude from which it was dropped.

Illustrious sustained six direct hits and several near misses in less than seven minutes. The attack was brilliantly executed by 40 Ju 87s commanded by experienced men who knew exactly how to go about dividing and defeating the fleets anti aircraft defences.

A subsequent attack (around 16.00) by 15 Ju 87s escorted by Bf 110s was foiled not because the British had ample warning but because the FAA Fulmars were in a position to disrupt it as the fortuitously returned, refuelled and rearmed, from Malta at the right time. Luck plays a part in war as in everything else. One further hit was sustained, tragically exploding on the hangar deck where a temporary sick bay had been rigged, killing 30 men instantly. Bad luck has a role too.

As for surprise Cunningham knew that the Luftwaffe was present on Sicilian airfields as evidenced by intelligence reports of 9th January, the day before the attack. The Luftwaffe was brilliant at rapid redeployments and Fligerkorps X had 96 Ju 87s ready for action (from Comiso and Catania) on the 8th January, just three days after their deployment.
He also had roughly one hours warning of an impending German attack from intercepted Luftwaffe radio traffic. What neither he, nor his intelligence officer, knew was just how professional and ferocious this attack would be, particularly compared to the somewhat half hearted efforts of the Italians. In this aspect Cunningham, Boyd and the rest of the RN were taken completely by surprise.

Cheers

Steve

 

[RCAFson]

Cunningham also had to expect that the Luftwaffe would attack the convoy that he was escorting through to Malta.

 

[ohogain]

Which dive bombers were vertical dive bombers and which ones weren't?

From reading above, the Stuka and the Helldivers were vertical dive bombers. What about Henschel Hs 123? Heinkel He 50? Heinkel He 66/Aichi D1A? etc.

 

[Wildcat]

A-31 Vengeance was.

 

[Shortround6]

There may be a bit of confusion (or not?) as in the plane may be pointed straight down ( axis of plane is 90 degrees to surface of the earth) but the flight path may not be 90 degrees. The wings are still trying to provide "lift" or a force 90 degrees (or close) to the axis of the plane which would force the actual flight path "forward" (as in the direction of the canopy?).

Once you get around 80 degrees it gets rather academic or good for winning bar bets. A 80.54 degree dive will have the plane dropping 6 feet for every 1 foot of forward travel. a 59.97 degree dive drops 1.73 feet for every foot of forward travel and a 45 degree dive is 1 foot fot 1 foot. Even a 10 foot drop for each foot of forward travel is still only an 84.29 degree dive.

 

[BiffF15]

Shortround6,

Your understanding of dive angles is good. Remember, that the aircraft can be "trimmed" to an airspeed, and if the speed in a pure vertical dive (90') is held constant the aircraft will go "straight" down. However, in WW2 they didn't have a Heads Up Display to help them determine straight down. However, they did the math and figured out that if you are steep (greater dive angle than planned), fast (higher airspeed than planned) and press below your pickle altitude then your accuracy goes up. The pure vertical dive removes / reduces the dive angle variable from the equation.

Cheers,
Biff