Can someone simply explain RPM and Boost?

[NeilWillis]

Really useful link to the PHAK manual downloads. Hours of reading there!

 

As for RPM v Boost - we could talk all week about it, and still not cover it all.

 

Basic principals - more RPM (up to a point) equals more power produced by the engine. As in all things, more RPM also means more wear and tear, and higher fuel consumption (generally) plus higher operating temperatures (though this is also a factor controlled by mixture - lean = hotter and more economical, rich = cooler but higher fuel useage.

 

So to a degree, increasing RPM makes an engine produce more power, but lower revs mean better economy, and more longevity. Exceeding RPM/Time limits will kill an engine quickly.

 

Boost is far more complex as it determines intake manifold pressure, and the factors affecting this are myriad. Altitude, Compressor stage, engine RPM, and mixture all affect the way boost and throttle setting coincide. Basically, the higher you go, the more boost you require to maintain engine power and RPM.

 

The bottom line though is to follow the guidance in your flight manual. Each aircraft is different, so there are no real general rules that can be applied. Some aircraft handle mixture, some handle RPM through automatic regulation, some will vary boost to maintain whatever you set using the throttle. But you have to juggle all 3 controls to maintain power. Altitude change affects all 3, as does aircraft speed. Then there's carb heating, air filtration, intake pre-heating, ram air settings...

 

Enough to fill a large novel!

[Perfesser]

and no matter what advice I follow, or do the training module, or look at videos and do a whole heap of trial and error, I just can't get a landing with out bounce.

I find the high sink rate you get when landing with flaps deployed is the major contributor to that landing bounce.

Try to come in with no flaps, about 120 and then kill power over the threshold and just hold the plane a foot or two off the runway as long as you can with increasing elevator pressure.

[imacken]

I can't thank you enough for all your contributions. However, I am struggling so badly with this Spit, that I am really tearing my hair out!

Although I have been away from flight sims for a while, I have played many in my time, stretching back to Geoff Crammond's Spitfire sim 'Aviator' on the BBC Micro around 1983 - how many of you remember that? - and through Microprose's Gunship and F15 Strike Eagle, etc. and many more since - Falcon 4, etc.!

DCS inspired me to come back to the fold, and for the first few weeks, I loved it whilst learning the intricacies of the A-10C.

Never, and I mean, never, have I experienced anything like this Spitfire module! I have tried so hard to learn, but clearly I am missing something fundamental.

1) I can manage about 50% of take offs OK. Only about 50%, despite the fact I go through the same procedure with throttle, trim, rudder, stick position every time. I dance on the rudder, etc. but so often, the Spit gets in the air and immediately severely banks to the left, and that is it.

2) landing. Well, after probably hundreds of landing attempts, I have NEVER managed to get the Spit down 100% successfully. I have managed a few that I have survived to be able to taxi away from, but in general, I am OK till a few feet above the runway, then no matter what, after I touch down, a wing eventually tips and scrapes the runway. No matter what I try - faster or slower speed (usually around 90mph), dancing on the rudder, approach from a greater/lesser altitude, glide along just above runway, etc., I have never managed a 100% clean landing.

3) trying out the combat section in 'Instant Action'. I have tried this a few times, and not once have I been able to down a Focke-Wulf. Add to that, almost constant, uncontrollable spins, wings falling off, engines overheating and blowing up, despite my attempts lower speed and/or RPM, thrust etc.

I really am struggling to see why I am so bad at handling this plane. It's not for the want of trying, believe me!

[NeilWillis]

Two questions regarding your difficulties...

 

1. Have you updated DCS World to the latest version? There was a tweak of the flight modelling which makes both take off and landing less fraught, and upgrading could be a help.

 

2. Are you taking off with +9 boost pressure? More power = more torque from the prop. The spitfire easily gets airborne with low throttle settings, so +9 is the maximum necessary.

 

The other thing to be aware of is that you will lose rudder authority on landing as soon as the airspeed drops below a critical point, and you'll need some very careful use of differential braking to keep it straight on roll out.

 

Also, jumping on the very first indication of yaw is essential, and applying just the correct amount of rudder to counteract the yaw is a skill that takes a little while to develop.

 

I can quite safely say that tail draggers are the hardest modules to take off and land in, and I can also safely say that the Spitfire, with it's narrow track landing gear is the hardest tail dragger of them all.

 

It might be worth investing some time in the TF-51D to get to grips with an easier module first - it is free and part of the basic DCS World package, and perfecting that would make the step to the Spitfire more managable.

 

Above all, persistence, and practice will help you build the necessary muscle memory to crack it.

[Holbeach]

@ imacken.

 

I had the same trouble as you, until I hit these, 3 in a row, landings.

 

 

 

I hope these will inspire you to keep at it, it's well worth the satisfaction when it starts to come together.

 

Good luck..

[imacken]

Two questions regarding your difficulties...

 

1. Have you updated DCS World to the latest version? There was a tweak of the flight modelling which makes both take off and landing less fraught, and upgrading could be a help.

 

2. Are you taking off with +9 boost pressure? More power = more torque from the prop. The spitfire easily gets airborne with low throttle settings, so +9 is the maximum necessary.

 

The other thing to be aware of is that you will lose rudder authority on landing as soon as the airspeed drops below a critical point, and you'll need some very careful use of differential braking to keep it straight on roll out.

 

Also, jumping on the very first indication of yaw is essential, and applying just the correct amount of rudder to counteract the yaw is a skill that takes a little while to develop.

 

I can quite safely say that tail draggers are the hardest modules to take off and land in, and I can also safely say that the Spitfire, with it's narrow track landing gear is the hardest tail dragger of them all.

 

It might be worth investing some time in the TF-51D to get to grips with an easier module first - it is free and part of the basic DCS World package, and perfecting that would make the step to the Spitfire more manageable.

 

Above all, persistence, and practice will help you build the necessary muscle memory to crack it.

1) I'm on 1.5.6.1938

2) usually take off with +8

3) I have tried the TF-51D, and I can take off and land OK with it. So, weird.

What is the cause of the Spit's huge lunge to the left just after take off? Not enough boost? What is the best way to counteract it?

Thanks again.

[imacken]

@ imacken.

 

I had the same trouble as you, until I hit these, 3 in a row, landings.

 

 

 

I hope these will inspire you to keep at it, it's well worth the satisfaction when it starts to come together.

 

Good luck..

 

I am not at all jealous!!!!

[DD_Fenrir]

1) ... the Spit gets in the air and immediately severely banks to the left, and that is it.!

 

Get the tail up during the takeoff run. Can't stress this enough. The veer left flip over and crash is a full on stall; you're leaving the runway in ground effect; it's an aerodynamic effect both a blessing and a curse. Gives you a lift boost if you're low level (within about a wingspan of your aircraft in altitude) but once you leave that zone it disappears.

 

What's happening is you are lifting off whilst in that zone at an airspeed not high enough to sustain the lift as soon as you climb out of it; result = stall!

 

My advice is to lift the tail and keep her on the main wheels on the takeoff roll till you get to 100mph IAS, then lift off very slowly and make sure you climb through that GE boundary slowly and with more airspeed.

 

I humbly submit my video for your reference:

 

2) landing. Well, after probably hundreds of landing attempts, I have NEVER managed to get the Spit down 100% successfully. I have managed a few that I have survived to be able to taxi away from, but in general, I am OK till a few feet above the runway, then no matter what, after I touch down, a wing eventually tips and scrapes the runway. No matter what I try - faster or slower speed (usually around 90mph), dancing on the rudder, approach from a greater/lesser altitude, glide along just above runway, etc., I have never managed a 100% clean landing.

 

1st step is always adopt the curve approach - with the lack of rudder air load at the moment the Spits rudder is super sensitive and easily over controlled. Get used to making a curved approach in zero wind conditions without using the rudder and concentrate on getting lined up using ailerons alone. This will help mitigate any sideslip and hence side load on landing which can contribute to a wing down.

 

But by far the most important 2nd step as I've said before and in the video, the 1st person camera lens is different than other flight sims and if you come here from others it can lead to a false impression of height at the round-out (the point at which you flare) and you end up doing so far too high off the runway; this leads to excessive sink on touch down and leads to the wing-down behaviour. Concentrate on consciously waiting a little longer before pulling the aircraft into the three-point attitude and do so slowly and deliberately; with that sensitive elevator it's easy to over-rotate. Become completely familiar of where the horizon intersects the cockpit cowling when the aircraft is sat on the ground in the tail down attitude and find the reference points that tell you so until you know instinctively what a good attitude is. And remember too much flare is worse than too little - you can touch down mains slightly first without drama, but touchdown tailwheel first and you're opening the door to a world of trouble!

 

Good luck, I hope these tips help and most importantly keep persevering!

[Holbeach]

1) I'm on 1.5.6.1938

2) usually take off with +8

3) I have tried the TF-51D, and I can take off and land OK with it. So, weird.

What is the cause of the Spit's huge lunge to the left just after take off? Not enough boost? What is the best way to counteract it?

Thanks again.

 

Posted from another thread.

 

Set 3000 rpm before moving, do not advance rpm when moving.

Pitch trim 0 deg

Rudder trim full right

Advance throttle 4 lb

Let go brake

Advance throttle 8/9 lb

Stick neutral.

Do not use aileron unless there is a crosswind

Do not use brakes

Counter initial left swing with very slight right rudder ( do not use aileron )

A swing will start to develop to the right

Before this happens start a slight left rudder to counter the swing ( do not use aileron ) by this time direction is easily controlled by rudder (do not use aileron or brakes)

Slight aft stick will achieve a clean lift off.

Raise gear will give nose up

Re trim pitch and rudder

Climb out at 180 mph and 12lb 2850 rpm.

 

 

It never fails..

[imacken]

OK guys, I've mastered(?) the take off. My problem was too much pulling back on the stick, or not releasing it fast enough, which caused me to lift off with not enough speed. All sorted now, I just keep the stick in neutral position until speed picks up, then I push it slightly forward so as not to get too much lift.

As for landing, I can get the plane on the ground reasonably softly, but still there is always a wing scraping on the runway until speed drops enough for the Spit to right itself and then I can taxi or take off again. Still got work to do to make that all OK!

[NeilWillis]

I lift the tail as soon as I have enough airspeed, and let the speed build until it is safe to unstick. Do that with the minimum back pressure needed to get airborne, then maintain level flight until 140 MPH before retracting gear and climbing out.

 

Landing is best carried out at around 100 MPH, very gently settling it down with the slip ball centred. As the speed drops in the flare, you should feel the tail wheel touch down first followed by the mains. Allow the speed to decay and pull full back on the stick to pin down the tail wheel. Once it is on the ground, lots of rudder pedal dancing to keep it straight, and when you feel the rudder is losing authority, start tapping the differential brakes to maintain a straight course along the runway until you stop.

 

It does take practice, but you'll build that all important muscle memory, and things will get easier over time.

[Rogue Trooper]

Landing is the nightmare in these WWII aircraft, A long shallow approach is required for the noob (including me). The advice given above is superb.

 

 

As for take off, In DCS you got a real long run way for take off... ease off the power, what's your rush?

Take off gentle like, less power more runway and a touch of pedal. Take your time to feel her needs.

[The Black Swan]

Let me have a try at explaining it.

Think of rowing a boat. The end of the oar is the propeller blade, and the water is the air.

The force with which you pull the oar is your manifold pressure or throttle.

The rpm control is the speed at which you Row, except it governs how fast you row by changing the angle that the oar enters the water.

At a certain power setting, you pull the oar through the water at a certain angle let's say at its widest. As you increase your rpm's setting, you turn the oar so that it more cuts through the water instead of paddling through it. You keep using the same amount of force with your muscles, but you're able to do it faster since you're not moving as much water with each stroke.

 

Obviously, there are limits to how fast you can row as well as limits to how much in either direction you can angle your oar.

Thus, adjusting your manifold pressure or rpm setting far enough, will cause a change in the other ones setting

 

If you set your rowing speed (RPM) at a certain rate, and then increase your strength (MP) you will slowly turn your oar to its widest in order to maintain the same rowing rate.

But if you keep adding strength, you will eventually have to start rowing at a faster rate.

(this is why changing your throttle enough will change your RPM as well)

 

Hope this helps.

 

Let me know how I did guys! :)

[acdelta57]

Let me have a try at explaining it.

Think of rowing a boat. The end of the oar is the propeller blade, and the water is the air.

The force with which you pull the oar is your manifold pressure or throttle.

The rpm control is the speed at which you Row, except it governs how fast you row by changing the angle that the oar enters the water.

At a certain power setting, you pull the oar through the water at a certain angle let's say at its widest. As you increase your rpm's setting, you turn the oar so that it more cuts through the water instead of paddling through it. You keep using the same amount of force with your muscles, but you're able to do it faster since you're not moving as much water with each stroke.

 

Obviously, there are limits to how fast you can row as well as limits to how much in either direction you can angle your oar.

Thus, adjusting your manifold pressure or rpm setting far enough, will cause a change in the other ones setting

 

If you set your rowing speed (RPM) at a certain rate, and then increase your strength (MP) you will slowly turn your oar to its widest in order to maintain the same rowing rate.

But if you keep adding strength, you will eventually have to start rowing at a faster rate.

(this is why changing your throttle enough will change your RPM as well)

 

Hope this helps.

 

Let me know how I did guys! :)

 

 

Lol while I know what your getting at it still took me a few re-reads. But I must say, this is the best explanation I've read and also the first time I've ever heard of the boat and paddle reference. Nicely done

[r4y30n]

One minor note about boost as indicated in the Spit, many assume that it references how much pressure the supercharger is adding to the outside air in real time, this is not the case. 0 boost is only really 0 boost (engine pressure = outside pressure) at sea level. When cruising at, say, 20,000 ft then 0 boost really means you have sea level pressure in the engine, quite a lot more than ambient!

 

 

Sent from my iPhone using Tapatalk

[imacken]

I'm still struggling with landing after a more than a week now!

I can make a nice soft landing, but always, when the speed drops on the ground, the plane shoots off to the left, wing tip scrapes the ground and I go off into the grass until it rights itself intact.

I have tried dancing on the rudder, but the movement is so quick and severe that I can't catch it!

Anything obvious I can do to solve this? Sorry to keep asking. I am trying!

[dburne]

Anything obvious I can do to solve this? Sorry to keep asking. I am trying!

 

Yep - Ease some braking in after touchdown...

To do properly you should have touched down three point right at stall, then full back on the elevator and gentle on the braking. She will roll straight ahead and slow to a stop fairly quickly.

Edited March 11, 2017 by dburne

[imacken]

Thanks for all your advice, guys.

I'm taking a break from the Spit as my head can't take it. I can land with scraping of wing on runway, but never perfect.

So, I bought the Mustang, and fortunately, some sanity has been restored! I can take off and land with no problem at all on the Mustang, so it seems I've got some kind of mental block with the Spit!

[Art-J]

One minor note about boost as indicated in the Spit, many assume that it references how much pressure the supercharger is adding to the outside air in real time, this is not the case. 0 boost is only really 0 boost (engine pressure = outside pressure) at sea level. When cruising at, say, 20,000 ft then 0 boost really means you have sea level pressure in the engine, quite a lot more than ambient!

 

 

 

Something doesn't add up here. "Many assume" so, because I've yet to find a source stating otherwise. Looking at Your example, I can't quite imagine how simple aneroids in boost regulator and gauge, located at 20k ft altitude, would "know" what sea level pressure for reference datum is.

[Quijano72]

Just a minor update on a quite useful link:

www.faa.gov

[=475FG= Dawger]

Old thread but the explanation is quite simple. 
 

Propellors used to be called air screws

This leads to the simplest explanation 

In a fixed pitch propellor aircraft, you cannot change the blade angle of the propellor, so your airscrew has only one pitch. Pitch is a term directly from hardware terminology. Thread pitch refers to the distance between threads on a screw. 
 

The larger the pitch, the fewer the thread count for a given length screw or bolt. 
 

A large pitch screw travels further for each revolution compared to smaller pitch. 
 

However, a large pitch screw requires much more force to rotate than smaller pitch. 
 

In a variable pitch propellor (constant speed or not), the propellor control sets your pitch. 
 

The throttle controls manifold pressure, which is the equivalent of the torque applied to the screwdriver. 
 

Too much torque on a large pitch screw ( slow rpm) and you will twist the screw head right off. 
 

Thats the relationship between manifold pressure and propellor RPM that you need to understand