Saucey12

altitude and air breathing engines..

Recommended Posts

Hey guys this is a question for those of you who are experienced with air breathing props.  At what altitude (generally) does it begin to be hard to start one?  I have been flying Cessnas and the DC-3 into some high altitude terrain and pushing the limits.  I always decrease the mixture accordingly but when I land at an airport of 7000+ MSL I cant get the engine restarted after I kill it.  Any pointers ? Or have I just reached the limits for those type of engines?  

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

Generally speaking, things are going to start being affected to a point where it actually matters when you get above 5,000 feet. Of course you need to tweak the mixture accordingly for all altitudes, but if you didn't, most aerolane engines would let you know by running rough or spluttering etc. Having said that, you need to be careful, because in addition to fueling the engine, the fuel actually has the effect of cooling the engine a bit before it ignites, so running too lean can cause overheating.

Some more modern aircraft automatically adjust the fuel/air mixture when at altitude for starting (for example, some of the flashier Mooney GA aircraft do that), and if you are in an aircraft which simulates that, you might not need to lean off the mixture at all when starting up and doing so might actually prevent it starting. Of course another problem with more realistically simulated engines is that if you are cranking it several times and messing about with the mixture settings, you could flood it or vapour lock it, in which case then it is never gonna start until you clear the flooding or vapour lock, even when you have the mixture lever in the right place for starting.

So it is worth finding out of your particular add-on simulates any fancy engine conditions such as that, and that may indeed be the case with a fancier older aeroplane simulation. In such a case, you might not be able to start it with a simple Control+E, it may need you to go a bit more realistic. For example, the Aerosoft PBY Catalina simulates a lot of intricate engine behaviour and can certainly be tricky to start in hot and high conditions. Like with the Catalina, on something with a big-arse radial engine and an electric starter (for example a B-17), where you prime the engine with fuel, then crank the starters and then mesh it to get the props turning to fire the engine, over-priming or pressing the starter for too long before meshing could make the mixture too rich for it to fire up and you can be sure that something like A2A's Accusim'd Flying Fortress will do that. Starting might be even trickier to get right at altitude if you had a Coffman shotgun starter lol, although as far as I'm aware, not many FS aeroplanes simulate that in anything other than a basic way by playing a big bang sound and kicking out a big cloud of smoke (I think the Flying Stations Hawker Sea Fury is one that simulates that a bit more realistically), which is a shame because lots of aeroplanes really did have those shotgun starters and it would be kind of fun to go all 'Flight of the Phoenix' with one. The F4U Corsair was another aeroplane which used Coffman starter cartidges too, so if you get a realistically simulated one of those, that'd be kind of fun. A Coffman starter will require you to prime the engine correctly, and that will be critical (as a rough guide, 2 to 3 pumps of the primer lever is usually about right) and then fire the starter, then play with the mixture to get it to start fuel ignition. The Coffman starter itself is quite a crude method, even though it does work, whereby a blank shotgun cartridge literally blasts a piston crown downwards to get the engine turning, then the ignition hopefully fires your correct mixture, so you've only got a couple of seconds to get the mixture right before the engine will stop rotating, because of that, you might need to be pretty fast on sliding that mixture lever in or out in order to find the sweet spot.

An easy thing to try when starting an aeroplane up at altitude in your sim, is to make the weather a lot colder. Obviously air pressure is reduced at altitude, but at somewhere like Mexico City airport, the ambient temperature might still be quite high even up at altitude, and the higher the temp, the thinner the air, so coupled with the air being thinner anyway because of the pressure altitude, the combination of high temp and thin air might make it impossible/difficult to have the engine fire up, since there might not be enough air pressure.

Another thing that you can try, is to switch the fuel tank selector to a single tank. Doing so might give you more fuel pressure from using a single fuel line, but more pertinently for your situation, it could potentially reduce the chances of a vapour lock (this is where the fuel turns into a gas in the fuel line and then that vapour blocks the system up). Theoretically for something like a Cessna, one should always be flying it with both tanks selected, however, there is a caveat to this which is mentioned in old C172's operating handbooks, and that is with an older Cessna (and I mean really old, i.e. something built in the early 70s which has not had its fuel system modified to alleviate the problem) it states that above 5,000 feet you should switch to feeding from a single tank to reduce the possibility of a vapour lock.

You could also try cranking with/without the fuel pump going. On a high wing design, gravity will of course help to feed the engines with fuel, whereas on a low wing design, the fuel pump may very well be a necessity, but you might actually reduce the fuel pressure without the pumps on, and doing that might give the reduced air pressure a chance to hit the right mixture if the fuel pressure is reduced by not having the fuel pump on.

Of course a lot of this will depend on how realistic your simlated aeroplane is, for example, the shiny new Just Flight PA-28 Piper Cherokee Arrow III does indeed simulate vapour locking of the fuel on start up, and I would assume more realistic Cessnas, such as those from A2A with all that Accusim malarkey would also do it, so you might also want to check if your aeroplane simulates vapour locks, because if it does, you will need to clear it to get the engine to fire up.

Share this post


Link to post
Share on other sites
8 hours ago, Chock said:

Generally speaking, things are going to start being affected to a point where it actually matters when you get above 5,000 feet. Of course you need to tweak the mixture accordingly for all altitudes, but if you didn't, most aerolane engines would let you know by running rough or spluttering etc. Having said that, you need to be careful, because in addition to fueling the engine, the fuel actually has the effect of cooling the engine a bit before it ignites, so running too lean can cause overheating.

Some more modern aircraft automatically adjust the fuel/air mixture when at altitude for starting (for example, some of the flashier Mooney GA aircraft do that), and if you are in an aircraft which simulates that, you might not need to lean off the mixture at all when starting up and doing so might actually prevent it starting. Of course another problem with more realistically simulated engines is that if you are cranking it several times and messing about with the mixture settings, you could flood it or vapour lock it, in which case then it is never gonna start until you clear the flooding or vapour lock, even when you have the mixture lever in the right place for starting.

So it is worth finding out of your particular add-on simulates any fancy engine conditions such as that, and that may indeed be the case with a fancier older aeroplane simulation. In such a case, you might not be able to start it with a simple Control+E, it may need you to go a bit more realistic. For example, the Aerosoft PBY Catalina simulates a lot of intricate engine behaviour and can certainly be tricky to start in hot and high conditions. Like with the Catalina, on something with a big-arse radial engine and an electric starter (for example a B-17), where you prime the engine with fuel, then crank the starters and then mesh it to get the props turning to fire the engine, over-priming or pressing the starter for too long before meshing could make the mixture too rich for it to fire up and you can be sure that something like A2A's Accusim'd Flying Fortress will do that. Starting might be even trickier to get right at altitude if you had a Coffman shotgun starter lol, although as far as I'm aware, not many FS aeroplanes simulate that in anything other than a basic way by playing a big bang sound and kicking out a big cloud of smoke (I think the Flying Stations Hawker Sea Fury is one that simulates that a bit more realistically), which is a shame because lots of aeroplanes really did have those shotgun starters and it would be kind of fun to go all 'Flight of the Phoenix' with one. The F4U Corsair was another aeroplane which used Coffman starter cartidges too, so if you get a realistically simulated one of those, that'd be kind of fun. A Coffman starter will require you to prime the engine correctly, and that will be critical (as a rough guide, 2 to 3 pumps of the primer lever is usually about right) and then fire the starter, then play with the mixture to get it to start fuel ignition. The Coffman starter itself is quite a crude method, even though it does work, whereby a blank shotgun cartridge literally blasts a piston crown downwards to get the engine turning, then the ignition hopefully fires your correct mixture, so you've only got a couple of seconds to get the mixture right before the engine will stop rotating, because of that, you might need to be pretty fast on sliding that mixture lever in or out in order to find the sweet spot.

An easy thing to try when starting an aeroplane up at altitude in your sim, is to make the weather a lot colder. Obviously air pressure is reduced at altitude, but at somewhere like Mexico City airport, the ambient temperature might still be quite high even up at altitude, and the higher the temp, the thinner the air, so coupled with the air being thinner anyway because of the pressure altitude, the combination of high temp and thin air might make it impossible/difficult to have the engine fire up, since there might not be enough air pressure.

Another thing that you can try, is to switch the fuel tank selector to a single tank. Doing so might give you more fuel pressure from using a single fuel line, but more pertinently for your situation, it could potentially reduce the chances of a vapour lock (this is where the fuel turns into a gas in the fuel line and then that vapour blocks the system up). Theoretically for something like a Cessna, one should always be flying it with both tanks selected, however, there is a caveat to this which is mentioned in old C172's operating handbooks, and that is with an older Cessna (and I mean really old, i.e. something built in the early 70s which has not had its fuel system modified to alleviate the problem) it states that above 5,000 feet you should switch to feeding from a single tank to reduce the possibility of a vapour lock.

You could also try cranking with/without the fuel pump going. On a high wing design, gravity will of course help to feed the engines with fuel, whereas on a low wing design, the fuel pump may very well be a necessity, but you might actually reduce the fuel pressure without the pumps on, and doing that might give the reduced air pressure a chance to hit the right mixture if the fuel pressure is reduced by not having the fuel pump on.

Of course a lot of this will depend on how realistic your simlated aeroplane is, for example, the shiny new Just Flight PA-28 Piper Cherokee Arrow III does indeed simulate vapour locking of the fuel on start up, and I would assume more realistic Cessnas, such as those from A2A with all that Accusim malarkey would also do it, so you might also want to check if your aeroplane simulates vapour locks, because if it does, you will need to clear it to get the engine to fire up.

Thats all great info sir I appreciate it!

I will try a few of those things you mentioned. I must say I do not have any add on programs whatsoever.  I finally got a new desktop and got the FSX steam version a few days ago.  I have not played around with it all in almost a decade back when I had FS9.  I am interested in getting addon programs but I also do not want to download a bunch of junk.  Can you give me recommendations as to which sources to go to for all of that?  I really would just like some very general add ons that improve scenery, weather, atc, and good aircraft add ons.  I know there is a lot of specific stuff out there for certain locales and aircraft (and I will get to that also) but for now I am just looking for some good functioning blanket programs that would work well.  

Thanks, 
Jason

Share this post


Link to post
Share on other sites

A2A Cessna 172 is a good one. For weather, I have ActiveSky 2016, and that's also a good one. Scenery ultimately depends on where you want to fly, so you're going to have to be specific about that. FSDreamteam and Flightbeam are some good scenery developers, but if you don't fly commercial, their airports won't do you any good.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now