DA62 RACC system performance

[TotalHavoc]

Good Morning all,

I'll start out by saying I don't own a DA-62, although I do dream a lot. I was wondering if anyone could explain the reduction in performance when using the optional RACC unit. According the the supplement literature, cruise is reduced 10 knots when the system is on. This seems like a pretty big hit when systems in other planes (Cirrus or Bonanza) the books show a loss of a few knots during cruise.

Thanks

[CFIDave]

I found NO decrease in climb or cruise performance with the factory air conditioning ON vs. OFF -- in either the DA42-VI or DA62.

The RACC dedicated alternator puts very little load on the left engine. Turning RACC ON increases the load at idle (you can easily see this on the G1000) by only 1-2%.

If anything, having RACC installed makes your plane faster. That's because the extra 70 lb RACC weight located aft of the rear baggage compartment helps balance out the cast-iron block Austro engines that otherwise make the plane nose-heavy. The aft weight of the RACC unit makes the horizontal stabilizer work less hard to hold down the tail, thus reducing induced drag in flight.

[VickersPilot]

A few points regarding RACC (for now, I speak academically, CFIDave perhaps speaks practically above).

First the aircraft can be optimised to manage heat with easy gains:

The RACC sufficiency is the ratio of [Required BTUs] to [Available BTUs]. Since one can't increase the [Available BTUs], the key is to reduce the [Required BTUs]. I have personally used Kevin Duggan's JetShades and can attest they significantly reduce the greenhouse effect in an aircraft cabin. They also improve thermal stability - removing (reflecting away) the asymmetric solar gain means the aircraft cooling or heat can be evenly distributed. In summary, using JetShades will significantly reduce the [Required BTUs] and more importantly equalises the cooling or heat in the cabin.

Then we refer to the RACC supplement:
http://support.diamond-air.at/fileadmin ... S07-r1.pdf

A few abstracts:
- Takeoff Ground Roll +60m, Takeoff Distance +100m
- Time, Fuel, Distance in Climb +6%
- Rate of Climb -70ftpm
- Cruise - 10kts

Given the above are from the AFM Supplement, one assumes that is worst case (max load on AC). So reducing the load on the AC should in theory, perhaps not in practise, reduce the performance penalties. Further, you're only likely to use the AC at full load with temperatures that are well above ISA, so if one suffers the performance penalty, it's likely to be combined with a hot weather (density alt) penalty.

[CFIDave]

I also have JetShades for my DA62, which almost makes the under-sized (IMHO inadequate capacity) RACC air conditioning handle summertime heat and humidity on the ground. JetShades do help keep the interior cooler -- highly recommended.

[ultraturtle]

Concur with all of the above. JetShades are the best.

I operate the RACC system only at its maximum output (fan at the highest setting, temperature at its lowest), and have observed the same performance as Dave - zero difference in cruise speed between the system turned off and operating at max blast.