Mach Limit/Critical mach? Gunsight position?

[James DeSouza]

I watched a video about dive performance that talked about mach limits and critical/compressibility mach.  I am wondering what the mach limits on the mosquito are, as i can't find them.  Also what happens when the mosquito exceeds these limits, does it lock up due to compressibility or does it break to pieces since it is made of posicle sticks?

 

Also another question that I forgot I was curious until I posted this.  Does anyone know what the rationale for them putting the gunsight between the pilot and copilot was?  Since the pilot is the only person that can aim the guns it doesn't make sense for it to be anywhere but right in front of him.

Edited March 1, 2023 by James DeSouza
Another question.

[grafspee]

A lot things i british cockipt lay out does not make sense. For example why gear and flaps handle is located to the right so pilot to operate those need to switch hands on stick.

[Shibbyland]

Was the video about dive performance to do with the mosquito? 
 

I wouldn’t have thought Mach number would be relevant to the mosquito. 
 

Mach number is a ratio of aircraft speed to the local speed of sound where Mach 1 would see the aircraft meeting the sound barrier. That being said, as the aircraft approaches the sound barrier, the airflow over the wing (or perhaps another part of the aircraft) is travelling faster than the speed of the aircraft itself and that air may break the sound barrier before the rest of the aircraft does. The speed at which this occurs is called Mcrit and for something like a commercial airliner might occur at around about Mach 0.84 give or take.

In terms of the speed of sound itself, in standard atmospheric conditions at sea level, it sits at around about 660kts (760mph) and decreases with altitude (decreasing temperature). 
 

So what does this all mean for the Mosquito? The mosquitos wing isn’t designed for high speed flight and its “never exceed speed” sits at about 425mph (I think), that would be Mach 0.55. That’s a long way off running into any of the difficulties of high speed flight. But let’s say the pilot put it into a dive and just held it there from high altitude, busted through the never exceed speed and didn’t do anything about it. I’d be speculating as to what would happen to the aircraft precisely but at the very least the aircraft would wind up being over stressed in some way. Whether it would break up or not, I’m not sure, pull enough G above it’s max speed and yea eventually something will snap.

 

 But let’s take it further, let’s say somehow it didn’t break up and the aircraft held together in that dive well above Vne. It’s probably still going to be difficult for it to run into compressibility issues as the faster the aircraft goes, the more drag it will experience and it will tend to slow down. For those aircraft that do manage to approach Mach 1 that aren’t designed for it, you can get weird stuff like control reversal where youll try to roll right but the aircraft will roll left. This can occur because the force through the ailerons actually twists the wing around the spar.

I hope this information is what you were looking for. Long story short, if you’re in the mosquito anywhere near Mach 1, you’ve got bigger problems than compressibility.

 

Edited March 17, 2023 by Shibbyland

[Ala13_ManOWar]

425 mph can be any Mach Number at any altitude. He's asking for Mach limit (structural Mach limit), if known.

[Ala13_ManOWar]

By the way, no Mach number but here are absolute speed limits (in knots) from Mosquito Pilot's Notes, easily converted since data is given,

null

 

[Shibbyland]

So I tried to do a bit more research into WW2 aircraft approaching Mach 1 and didn’t find anything on the Mosquito.

There’s quite a bit of info about the P-38 tho and that aircraft has a similar max speed to the mosquito. That being said, it’s still nowhere near Mach 1.
 

Turns out P-38 pilots did run into compressibility issues at high altitude in dives. So having looked at that, I suppose it is likely that a mosquito in a dive could run into similar issues. For interests sake, for the P-38 the documents give a critical Mach number of 0.66 and beyond this pilots experience difficulty with the elevator.

 

[Jel]

Am 16.3.2023 um 11:26 schrieb grafspee:

A lot things i british cockipt lay out does not make sense. For example why gear and flaps handle is located to the right so pilot to operate those need to switch hands on stick.

what bothers me more is having the VSI directly behind the sight. You can´t really see anything unless you lean to the left as pilot - making long flights tricky to maintain altitude or to adjust your trim.

[razo+r]

15 minutes ago, Jel said:

what bothers me more is having the VSI directly behind the sight. You can´t really see anything unless you lean to the left as pilot - making long flights tricky to maintain altitude or to adjust your trim.

If you lean right there is a gap between the sight and lamp where you can see part of the needle of the VSI. 

Besides, you can also use the altimeter, which you can see without obstruction, to see if you fly level. 

 

[Jel]

vor 56 Minuten schrieb razo+r:

If you lean right there is a gap between the sight and lamp where you can see part of the needle of the VSI. 

Besides, you can also use the altimeter, which you can see without obstruction, to see if you fly level. 

 

My point was you have to lean - left or right - in order to see the VSI. Yes it does work and yes you can work around that but having to lean in order to see a vital instrument is not as convenient as one might expect

Or maybe we expect too much ?

Edited March 20, 2023 by Jel

[razo+r]

37 minutes ago, Jel said:

judging your climb/descrent rate on the altimeter of course is possible - just not precise  That´s what the VSI is for.

Normally, in a climb, you adjust your pitch to maintain the best climb speed. The result will be a variable climb rate. Yes of course you could use climb rate for a climb but that is really rarely done.

In a descent, yeah I can see the use of a VSI.

37 minutes ago, Jel said:

Also you might know the altimeter of the Moss is quite wobbly when your nose moves.

And the VSI is lagging behind. So? Both instruments have their inaccuracies.

37 minutes ago, Jel said:

My point was you have to lean - left or right - in order to see the VSI. Yes it does work and yes you can work around that but having to lean in order to see a vital instrument is not as convenient as one might expect

Or maybe we expect too much ?

A VSI is not a vital instrument. By todays standard, it's not even mandatory to have it installed in an aircraft, at least not for VFR. It's nice to have but it's not required to have it.

Edited March 20, 2023 by razo+r

[Bozon]

On 3/16/2023 at 12:26 PM, grafspee said:

A lot things i british cockipt lay out does not make sense. For example why gear and flaps handle is located to the right so pilot to operate those need to switch hands on stick.

LoL, the mosquito cockpit design took a lot of thought and effort to make it this nonsensical - I mean, if they just randomly placed things here and there, some items may have ended up in a logical position.

On a more serious note - the mosquito cockpit design looks like a hybrid between a fighter and a bomber - don’t forget it started out designed primarily as a bomber. Bombers classically have 2 pilots where the captain sits on the left, co-pilot on the right, and many levers and knobs are placed between the pilots so both could reach them - engine controls, gears, flaps, trims.

In the mosquito it looks like they started to arrange it like a classic bomber, then suddenly realized that the guy on the starboard side is not a pilot - so they moved some of the controls to the left wall as typical in fighters. This is how we ended up with the throttle quadrant to the left, but the flaps and undercarriage levers on the right, bomber style. Elevator trim on the left, but ailerons and rudder trim on the right.

Rockets were an afterthought, given to some engineer to place where the installation will be easiest, and this is how we ended up with the arming switch installed aft of the throttles (nowhere near the bombs arming panel), the volley select switch on the dashboard, and the firing trigger inside the throttle grip.

Put together it is all a very lovely mess.

[Shibbyland]

It's pretty typical De Havilland I think haha.

The Chipmunk (although not all have the same panel) has it's RPM gauge and altimeter right next to each other and if it's the original instrumentation they look very similar with the white and green numbering.

Cruising at 2000ft with 2100rpm set it's easy to mix them up sometimes and find yourself pitching down on the RPM gauge. 

[grafspee]

On 3/20/2023 at 3:02 PM, Bozon said:

LoL, the mosquito cockpit design took a lot of thought and effort to make it this nonsensical - I mean, if they just randomly placed things here and there, some items may have ended up in a logical position.

On a more serious note - the mosquito cockpit design looks like a hybrid between a fighter and a bomber - don’t forget it started out designed primarily as a bomber. Bombers classically have 2 pilots where the captain sits on the left, co-pilot on the right, and many levers and knobs are placed between the pilots so both could reach them - engine controls, gears, flaps, trims.

In the mosquito it looks like they started to arrange it like a classic bomber, then suddenly realized that the guy on the starboard side is not a pilot - so they moved some of the controls to the left wall as typical in fighters. This is how we ended up with the throttle quadrant to the left, but the flaps and undercarriage levers on the right, bomber style. Elevator trim on the left, but ailerons and rudder trim on the right.

Rockets were an afterthought, given to some engineer to place where the installation will be easiest, and this is how we ended up with the arming switch installed aft of the throttles (nowhere near the bombs arming panel), the volley select switch on the dashboard, and the firing trigger inside the throttle grip.

Put together it is all a very lovely mess.

Mosquito was designed initially as bomber, but in Spitfire gear handle is at the same spot, right side of cockpit, so pilot has to switch hands just right after lift off to retract landing gear.