Take Off

[Holbeach]

The most important speed after T/O is the 'Safety Speed', which at full load and boost reduced to 12lb is,

200 mph or 225 mph at 18lb.

Maintain this until boost starts to drop, 170 mph can then be maintained for best rate.

This only applies if you're interested in any kind of realism.

..

Edited May 5 by Holbeach

[Slippa]

Patience, time and practice, practice, practice 

and post tracks of Mossies thundering towards thresholds, people here can help then.

[Terry Dactil]

On 5/5/2025 at 5:06 PM, Holbeach said:

The most important speed after T/O is the 'Safety Speed', which at full load and boost reduced to 12lb is,

200 mph or 225 mph at 18lb.

Maintain this until boost starts to drop, 170 mph can then be maintained for best rate.

This only applies if you're interested in any kind of realism.

Where did you get that from? 

It's a myth that the Mosquito has a very high takeoff safety speed. Its Vmca (minimum control speed airborne) is 140 ~150 mph depending on weight temperature altitude and other stuff like bank angle. Sure, it's like any other twin and would get very exciting with an engine failure  between lift-off and Vmca.

Some more info from ChatGPT:...

Geoffrey de Havilland, the legendary British aircraft designer and pioneer behind the de Havilland Mosquito, played a unique and bold role in supporting his aircraft's reputation during World War II—not just in the design office, but on the front lines of perception and morale.

A persistent myth among some operational RAF crews was that the Mosquito had a dangerously high take-off safety speed, and that the aircraft was extremely difficult—or even impossible—to control if an engine failed on take-off. This belief posed a serious problem: not only could it undermine confidence in the aircraft, but it might also affect performance and mission readiness if pilots hesitated or overcompensated due to fear.

To directly combat this, Geoffrey de Havilland himself visited squadrons flying the Mosquito, bringing with him not just technical data, but a dramatic and personal demonstration. On at least a few occasions, he would personally take off in a Mosquito and deliberately cut one engine during the take-off roll—the very scenario pilots feared. Even more impressively, he would then proceed to fly the aircraft on one engine, performing aerobatics such as loops and rolls, to prove that the aircraft could be safely handled even under such adverse conditions.

This hands-on approach served several purposes:

• It dramatically boosted pilot morale and confidence in the Mosquito’s handling characteristics.

• It dispelled misinformation about the aircraft’s safety and performance.

• It reflected de Havilland’s personal courage and belief in his design—a powerful endorsement for frontline airmen.

 De Havilland’s willingness to prove its mettle in such a public and daring fashion became part of the lore surrounding the aircraft.

 

[Holbeach]

On 5/9/2025 at 5:22 AM, Terry Dactil said:

Where did you get that from? 

.

To directly combat this, Geoffrey de Havilland himself visited squadrons flying the Mosquito, bringing with him not just technical data, but a dramatic and personal demonstration. On at least a few occasions, he would personally take off in a Mosquito and deliberately cut one engine during the take-off roll—the very scenario pilots feared. Even more impressively, he would then proceed to fly the aircraft on one engine, performing aerobatics such as loops and rolls, to prove that the aircraft could be safely handled even under such adverse conditions.

 

 

Hello.

The speeds are from the MkVI manual, almost word for word and please note they are at full load, ( 22,000lb.).

G de H did not T/O on one engine and perform loops and rolls with full tanks and 4 500lb bombs hanging on..

At half tanks and no weapons, about 17,000lb, T/O boost can be 9lb, which will give a safety speed of 178 mph.

Also note Safety Speed has a margin added.

..

Edited May 10 by Holbeach
Typo

[Terry Dactil]

2 hours ago, Holbeach said:

Hello.

The speeds are from the MkVI manual, almost word for word and please note they are at full load, ( 22,500lb.).

G de H did not T/O on one engine and perform loops and rolls with full tanks and 4 500lb bombs hanging on..

At half tanks and no weapons, about 17,000lb, T/O boost can be 9lb, which will give a safety speed of 178 mph.

Also note Safety Speed has a margin added.

..

Thanks for your explanation Holbeach, what you say is correct.

I managed to find a great site for aviation manuals  Avialog: Aviation Library and downloaded the Pilots Notes for our Mosquito. It looks like your reference.

 

Since I have been happily flying the Mosquito on one engine at max power by staying above 150 mph, I think adding 65 mph and calling it a

'Safety Speed' is a bit excessive.  I would call it a 'Feel Good Speed' 

All this is understandable since Vmca in performance calculations was not official in WW2.

ChatGPT has some interesting stuff on this subject ...

The concept of Vmca (Minimum Control Speed Airborne) as a formalized element in takeoff performance calculations did not exist in its modern regulatory form during the development and operational service of the de Havilland Mosquito in the 1940s.

Key Points:

• Vmca as a defined regulatory term became standardized in post-WWII civil aviation regulations, particularly with the introduction of FAR Part 23 and Part 25 by the U.S. Federal Aviation Administration (FAA) in the 1950s and later by ICAO and EASA equivalents.

• During WWII, aircraft performance calculations—including for multi-engine aircraft like the Mosquito—were based on empirical testing and operational experience, rather than a codified set of performance speeds like V1, Vr, V2, or Vmca.

• The Mosquito, being a military aircraft, was not subject to civil certification standards. Its performance charts and procedures included speeds for safety, single-engine climb, and control, but these were not labeled using modern terminology like Vmca.

• However, the underlying concept of a minimum speed at which directional control could be maintained after engine failure was understood by test pilots and engineers. They considered factors like asymmetric thrust, rudder authority, and yaw tendencies in both design and flight test programs.

Summary:

Vmca as a formal part of takeoff performance calculations was introduced in the postwar era, particularly with the advent of civil aviation regulations in the 1950s. For the de Havilland Mosquito, such a parameter was likely considered in practice but not named or standardized as "Vmca" in the way we know it today.

 

[Holbeach]

5 hours ago, Terry Dactil said:

Thanks for your explanation Holbeach, what you say is correct.

I managed to find a great site for aviation manuals  Avialog: Aviation Library and downloaded the Pilots Notes for our Mosquito. It looks like your reference.

 

 

 

Yes it's a great site. I've been using it for many years. It did go bad once when it went payware for a while, but the owner recently returned it to freeware, I'm glad to say.

If you were a 20 YO, on your first flight as pilot, at night with a full load and you still havn't worked out how to read the fuel guages and your crapping yourself but don't want to show it,

you might be glad of those few extra MPH when an engine stops.

I tend to fly by the manua,l except when I don't.

..

[Terry Dactil]

Yeah. It's understandable now. 

My aviation career was after WW2 and performance calculations were greatly improved and more precise. In particular I used (and taught) that the Take-off Safety Speed (V2) was the greater of 1.1 times Vmca or 1.2 times the stall speed. I guess if I was also carrying bombs that would be nowhere fast enough to keep me happy. 

 

 

Edited May 9 by Terry Dactil

[rob10]

On 5/9/2025 at 12:22 AM, Terry Dactil said:

Where did you get that from? 

Some more info from ChatGPT:...

In fairness, ChatGPT is a TERRIBLE reference.  It makes stuff up if it's not sure/doesn't have actual info.  I would not trust any info you get from it.  It might accidentally get something right, but the number of posts in the ED forums alone where it has provide plainly wrong information is mind blowing.

[Terry Dactil]

1 hour ago, rob10 said:

In fairness, ChatGPT is a TERRIBLE reference.  It makes stuff up if it's not sure/doesn't have actual info.  I would not trust any info you get from it.  It might accidentally get something right, but the number of posts in the ED forums alone where it has provide plainly wrong information is mind blowing.

Agreed that's a fair comment if you ask it about  something disputed and there are many different opinions on the internet. However, asking for stuff from official historic documents like aircraft pilot manuals and performance regulations is a pretty safe bet to be correct.

What errors did it make in this thread?

[Bozon]

On 5/9/2025 at 1:36 PM, Terry Dactil said:

Thanks for your explanation Holbeach, what you say is correct.

I managed to find a great site for aviation manuals  Avialog: Aviation Library and downloaded the Pilots Notes for our Mosquito. It looks like your reference.

 

Since I have been happily flying the Mosquito on one engine at max power by staying above 150 mph, I think adding 65 mph and calling it a

'Safety Speed' is a bit excessive.  I would call it a 'Feel Good Speed' 

All this is understandable since Vmca in performance calculations was not official in WW2.

ChatGPT has some interesting stuff on this subject ...

The concept of Vmca (Minimum Control Speed Airborne) as a formalized element in takeoff performance calculations did not exist in its modern regulatory form during the development and operational service of the de Havilland Mosquito in the 1940s.

Key Points:

• Vmca as a defined regulatory term became standardized in post-WWII civil aviation regulations, particularly with the introduction of FAR Part 23 and Part 25 by the U.S. Federal Aviation Administration (FAA) in the 1950s and later by ICAO and EASA equivalents.

• During WWII, aircraft performance calculations—including for multi-engine aircraft like the Mosquito—were based on empirical testing and operational experience, rather than a codified set of performance speeds like V1, Vr, V2, or Vmca.

• The Mosquito, being a military aircraft, was not subject to civil certification standards. Its performance charts and procedures included speeds for safety, single-engine climb, and control, but these were not labeled using modern terminology like Vmca.

• However, the underlying concept of a minimum speed at which directional control could be maintained after engine failure was understood by test pilots and engineers. They considered factors like asymmetric thrust, rudder authority, and yaw tendencies in both design and flight test programs.

Summary:

Vmca as a formal part of takeoff performance calculations was introduced in the postwar era, particularly with the advent of civil aviation regulations in the 1950s. For the de Havilland Mosquito, such a parameter was likely considered in practice but not named or standardized as "Vmca" in the way we know it today.

 

I suspect the one-engine safety speeds in that manual excerpt are with the dead engine un-feathered (and probably being the port side engine). I don’t have the manual to check the context right now. With a feathered engine you can fly significantly slower.

Safety speeds with an un-feathered engine is what you want to achieve asap after takeoff, when there will not be sufficient time and altitude to loose till feathering is achieved (if it works at all). Once feathered, speed can be reduced (1-engine climb).

What I do with the Mosquito is to climb very flat after lift-off and with a high boost to accelerate - when I hit “safety speed” (190–200) I use it to “zoom” and let it drop to best-climb speed, which would be around 160 mph or so. At that point should an engine crap out I can maintain control by reducing boost and shallow diving to increase the speed back to safety - which should be achievable by (at least) the altitude I zoomed up from (and while the dead prop is being feathered).

(Edited for better phrasing)

Edited May 15 by Bozon