Extra 400

What a gorgeous looking engine.You must be proud!

Flyingfish wrote:

Before I get nailed again

Haha! I guess when you expose yourself in a public forum this is a risk we all take. Fortunately Prob90 in this forum it will be well-meant nailing.

I personally dislike the oil filter setup with the outlet at the bottom: difficult not to make a mess at the time of filter change. I wonder if there is not an adapter you could use to install it upside down on the firewall or a different position like these Airwolf kits..

Flyingfish wrote:

I checked the chart, and it looks like this is a lot more than what the turbocharged engine should deliver at the same MP of 29.5 inches.
So I do expect this to be a very powerful engine, guessing 375+ HP at full power (39.5 inches) . Am I correct ?
If I can get the cooling right, take-off and climb should be quite interesting.

Obviously you have a powerful beast, but it is normal that you get more power than the TC charts for same MP since the turbocharger exhaust backpressure will mean you need at least a couple more inches MP than NA to make the same hp.

Flyingfish wrote:

Frankly I think they over did it: since the POH restricts the pilot from using all of the available MP over FL200, there is no benefit from making so much pressure.

You will definitely see that benefit (unless POH-limited) on ISA+20C days, not so rare any more nowadays.

Flyingfish wrote:

Spaghetti all’ olio minérale

Flyingfish wrote:

the engine is IAT limited, so on an ISA+20 day there would be this limitation before the turbo runs out of spare pressure, no?

It depends on the efficiency of the turbo and the intercooler. What is your experience? Is the IAT limitation an AFM limitation? What is it?

Flyingfish wrote:

The back pressure will cost some power, any idea how much?

Flyingfish wrote:

 2 inches is about right

I did learn to map all this a long time ago…but I am afraid only the basic ideas remain in my brain….It is not that easy to figure it out depending on conditions, you need to factor, amongst other things:

-Type of turbocharger (on my airplane the first versions produced so much backpressure at altitude that a different, larger turbocharger with less backpressure was implemented for better temperature control)
-Type and current operating mode of wastegate control (ie on my engine it is always regulating for 37.5" UDP, maybe yours is only looking for 2" above MP (slope type controller) ?)
-Ambient conditions and power setting (ie backpressure will be higher the harder the turbo has to work to maintain the required inlet air conditions)
-Intercooler efficiency and pressure drop through it (ie if air pressure drops a lot through it then the turbo needs to work harder for the same MP)

Think of it in terms of pressure through the gas piping on the engine, and bear in mind the pressure drop in the turbine and the compressor are similar.

For your example, at low altitude, the numbers are probably easier, so I’ll bite. At SL for 29.5" MP , assuming say 2" drop (a reasonable number if your turbo controller is of the “slope” type, higher if not, like mine) across intercooler and throttle body, that means you need about 29.5+2=31.5" compressor outlet pressure . We can assume at high power and SL the pressure drop through the air filter and associated ducts will be say 0.3" depending on your ducting and filter. That means your compressor inlet pressure will be around 29.92-0.3=29.62" . Pressure increase through the compressor will be about 31.5-29.62=1.88" and we can assume turbine pressure drop will be similar, so the back pressure on the exhaust will be similar or about 2" , and will be regulated by the wastegate to spin the turbine just right for about 31.5". At those low backpressure values you can assume the effect of backpressure is equivalent or a bit less than a similar decrease in MP. So 29.5" MP without turbo or intercooler in the test cell at SL is roughly equivalent to 31-31.5" with turbo and intercooler on the aircraft at SL.

Antonio wrote:

fibreglass sleeving…It is somewhat conductive and provides a minor measure of shielding. If you are really interested then there are also full EMI shielding versions available.

I came up with this on a different project and realized my mistake here: I don’t know what I must have been thinking: fibreglass sleeving is a good insulator, not conductive. You need the EMI type of sleeving if that is what you are after.

The pure fibreglass does not need it, but the EMI type may need separate insulation for your uninsulated JPI terminals if they are to live inside the sleeving, as they are conductive.

Most aircratf installations, however, work well without such extreme measures.

Flyingfish wrote:

The limitation of IAT is self inflicted

I seem to recall you posted about it, yes. Can you direct us to your post on it?

I think this IAT limit is very conservative.

In general, if you are cruising LOP, peak ICP’s (internal cylinder pressures) are so much lower (vs ROP) that a higher IAT does not pose such a high detonation risk.

A different matter is if you are operating slightly ROP for max power in climb (or F1 racing) when ICP’s will indeed be high

some widely known visualization of ICP vs crank angle

from this old and well known article here

So if you are ROP yes you have to be more careful about MP and IAT, but LOP cruise should not need to be so conservative, at least from detonation concerns. Also intercooler efficiency with high-altitude , low-density air is not as high as down low.

Of course you know this but for the same MP, your CDT (compressor discharge) will be higher as you climb, since compressor pressure ratio climbs form 1.1 at SL to over 2.5 at FL200 for say 32"MP. This means you will have little over ambient CDT at SL vs over 100C at FL200 on an ISA+10/+20 day , so aiming for 55C IAT with an intercooler efficiency of 40% is no easy feat, as you have found out. On warm days my typical data for 31" MP is CDT/IAT of 100C/50C (OAT -9C) at FL170 and 110C/72C (OAT -10C) at FL200. I think redoing a cleaning of the internals in my intercooler would improve those numbers a bit. On my 210 the intercooler is an aftermarket mod, though, but as you see efficiency is better lower down than higher up.