Compressor Discharge Temperature

[JohnL]

I am trying to understand the CDT gauge's value on a Rocket installation. The airplane has a TSIO-520-NB engine with dual intercoolers.

My understanding is that this CDT measurement is of induction air temp after the turbo but before the intercoolers. Is that correct?

I don't seem to have an induction air temp gauge post intercoolers, so CDT doesn't really tell me much unless I can calculate the delta T through the intercooler.

 

The Rocket POH supplement does not list a CDT limit in the power plant limitations section, like in the M20K POH. Does this mean CDT is not required equipment post Rocket conversion?.

 

I just added an Insight engine monitor that is certified to be the primary TIT gauge.  Does this mean I can remove the TIT/CDT gauge?

 

 

[Awful_Charlie]

I've got the CDT, as well as the OAT and IAT probes on my JPI.  There's nothing in any of the Bravo POH about any limits or guidelines, probably as none of these (well, apart from the OAT) are standard equipment.  Anyway, you are correct that CDT is the outlet from the turbo, and if you had an IAT you could see what the intercooler is doing for you.  FWIW, I see CDT's up to 120 C when in the climb at high power and up high (say 34" and FL200), with IAT's up to around 55 C.

 

When I slapped in the probes, I put the OAT for the JPI onto the outlet end of the air filter - this way I can see if the alternate air has cut in, and interestingly it show that just opening the alternate air manually in flight makes no difference, probably due to the big duct behind the prop being a substantially higher pressure than the alternate air behind the oil cooler.  On the single occasion the air filter has iced up though, it jumped upwards about 15C

[jlunseth]

I went through this with my 231. CDT is what you say, the temp after the turbo but before the inter cooler. It is a redline limit in a nonintercooled aircraft, the purpose is to prevent detonation because the induction air is too hot. The inter cooler cools the air so much that the limit temp is never reached, or even approached, so the original equipment CDT gauge becomes irrelevant.

[chrisk]

Hey John, 

It's a great question.  My guess is that it is not worth much.   Fundamentally you want to know the inlet temp limits for the engine and  the temp of the air at this point.  If the CDT is below this temp, you are fine.  If CDT is above this, it depends on the conditions and the efficiency of the inter cooler.  Maybe Rocket has a supplement for the POH.  I'd send them an email.

[David Brown]

Being able to keep track of the CDT and IAT is a valuable thing. Intercooler efficiency can be tracked and you can tell when it is time to clean out the core of the intercooler.

 

I would want both.