Merlin engine in Ace's

[jamdive]

jamdive... while I agree it should be a tachometer it does not act like a tachometer when it still reads RPMS with the engine off. In the P-51 it was a tachometer but in AH it acts as though it is reading prop RPM. Thats just what the evidence shows.

Now if you can show me that an engine like a Merlin will still rotate once it is turned off and therefore give an indication on an RPM gauge then I might side with you but until then I must conclude the RPM gauge is measuring prop RPM.

What do you mean by "when the engine is turned off" ? If the prop is spinning so is the engine, and that gauge in cockpit comes off the engine camshaft. I still don't get the confusion.

[FLS]

If you dive the Spit 14 you can get 4500 RPM.

[BulletVI]

Its a friggin governor.....You being some airframes/powerplant engineer should understand this basic concept.

P/S. stop arguing and go learn something.

Ahem i was tought it to be called a reduction gearbox as to spin the prop at a 3-1 ratio from the engine rpm hence the engine idles at 1000 rpm the prop is doing 3000 rpm at the outer edge.

[jamdive]

Ahem i was tought it to be called a reduction gearbox as to spin the prop at a 3-1 ratio from the engine rpm hence the engine idles at 1000 rpm the prop is doing 3000 rpm at the outer edge.

What does that have to do with changing the engine RPM? Here you go again with more wishy washy rhetoric. Please stay on one subject and not change your conversation objective every time somebody points out the errors in your logic.

[MiloMorai]

Ahem i was tought it to be called a reduction gearbox as to spin the prop at a 3-1 ratio from the engine rpm hence the engine idles at 1000 rpm the prop is doing 3000 rpm at the outer edge.

That not would be a reduction. I take it you failed math miserably. RPM is rpm not matter if is 1 foot or 10ft from the center of rotation.

The Merlin 66 had a 0.477 reduction ratio. An engine turning 3000rpm, the prop would turning at 1431rpm.

Chalenge, please see Item 37, Engine-speed indicator drive.


http://www.airpages.ru/eng/draw/merlin25.shtml

[dtango]

Ahem i was tought it to be called a reduction gearbox as to spin the prop at a 3-1 ratio from the engine rpm hence the engine idles at 1000 rpm the prop is doing 3000 rpm at the outer edge.

Hmmm BulletVI, what you're describing wouldn't be gear reduction but gear addition (as Milo has pointed out).  It's called reduction for a reason.  Think about it for a second.  Here's the equation for propeller tip speed:

Vtip = pi * rotational_speed * propeller_diameter

For a 10ft 9in prop like that on the Spitfire at 3000 rpm tip speed would be 1151 mph.  At sea level the propeller tip would be rotating at mach 1.51.  At little fast don't you think ?   With a 2:1 gear reduction that brings it to a manageable 1500 rpm which equals 576mph (mach .76 at sea level).

[BulletVI]

OOpps yup correct i was basing it on an example from the head not paper oopps

I was thinking of for example a 100 tooth cog rotating at 1000 rpm now to get 2000 rpm you needed a 50 tooth cog connected to the 100 tooth cog which in turn would spin at 2000 rpm as its smaller it has to go twice as fast as the 100 tooth cog to travel the same distance ( bugger )
Slip up on my part was i forgot that prop diameter was  bigger than the engine fly wheel. but from the above picture it shows a small output shaft from the engine thus it needs to an encrease in gear ratio not reduction ( bummer Rookie mistake Sorry )

Blast it i could stab myself for that one

[BulletVI]

Now back to the main topic here guys


Hitech now is the rpm gauge animation out of alinement Or is it an error of some other sort In the rpm gauge of the Spit 1 , 8, 9.
Please look into it

Thankyou BulletVI

[SlapShot]

Hmmm BulletVI, what you're describing wouldn't be gear reduction but gear addition (as Milo has pointed out).  It's called reduction for a reason.  Think about it for a second.  Here's the equation for propeller tip speed:

Vtip = pi * rotational_speed * propeller_diameter

For a 10ft 9in prop like that on the Spitfire at 3000 rpm tip speed would be 1151 mph.  At sea level the propeller tip would be rotating at mach 1.51.  At little fast don't you think ?   With a 2:1 gear reduction that brings it to a manageable 1500 rpm which equals 576mph (mach .76 at sea level).

You are a Saint ... Why you even bother to try and educate this kid is beyond me ... and what you have explained to him is way beyond his grasp.

[Chalenge]

Im still at a loss to understand why the Spitfire gauge reads up to 12000 RPM. I mean there is no way a Merlin of any description ever hit those revs.

[SlapShot]

Im still at a loss to understand why the Spitfire gauge reads up to 12000 RPM. I mean there is no way a Merlin of any description ever hit those revs.

I owned a car that had a speedometer that went to 140 ... it could barely break 100 mph going downhill with a tail wind and in the slip stream of a 45' tractor trailer truck.

[Masherbrum]

I owned a car that had a speedometer that went to 140 ... it could barely break 100 mph going downhill with a tail wind and in the slip stream of a 45' tractor trailer truck.

http://www.youtube.com/watch?v=EbVKWCpNFhY 

[hitech]

Bullet learn what wep is in AH, your saying your getting a max of 2750 I.E. you have never pushed the "p" i.e. wep button when at full throttle to get 3000 rpm and max manifold pressure.Or are you complaining about 1 pixel width adjustment?
Also just like before start learning instead of stating complete bolder dash. And go get a refund on that "degree" of yours.

RPM is engine rpm.

Engine rpm and prop rpm are the same thing except for a gear ratio.

RPM lever does not change the pitch on the props , it only changes a preset on a governor.  The governor changes pitch via opening an oil valve to increase or decrease pitch to maintain a constant rpm.

The RPM will only vary from preset if the prop has hit mechanical stops at min or max pitch.

some multi engine planes can adjust to about 90 degees and hence feather/stop the props. Single engines planes normally do not have a need for this like multi's.

HiTech

[dtango]

You are a Saint ... Why you even bother to try and educate this kid is beyond me ... and what you have explained to him is way beyond his grasp.

LOL Slapshot.  My secret is I don't read everything he posts .

Tango

[dtango]

http://www.youtube.com/watch?v=EbVKWCpNFhY 

LOL, that was exactly what I was thinking.  "It's one louder."