Aircraft performing below book numbers

terbang wrote:

and many antennas all over

I’ve read somewhere that it should be about 0.5 knots loss in cruise speed per antenna installed on the outside.

Socata give some numbers in their POH and they are of the order of 0.5kt for a large VHF antenna.

Dan wrote:

I’m sure that @Mooney_Driver can sing a song about the matter

True. As said before, we got fooled into getting a 3 blade prop after the prop strike we had.

First results would suggest a 3 way punishment: HIGHER noise value on paper (because nobody ever tested it beyond saying it’s Chapter 10 compliant), 5 kts slower and 7 kgs heavier, making need for ballast in the cargo hold when flying alone for CG reasons.

Also what we found out only after installation: This combination of prop with Powerflow Exhaust means we are restricted flying any time below 22* to RPM > 2350 RPM or below 1800 RPM. There are NO cruise control tables for this setup so we are on page 1 of a blank paper to find out as we are flying.

The Ups? It is actually much quieter from the outside (but that does not get reckognized as there are no measurement values) and take off performance is impressive.

Is it also quieter/smoother from the inside?

aart wrote:

Is it also quieter/smoother from the inside?

I could not feel any difference at the time but quite frankly I also did not pay too much attention during the test flight. And I have not had time to fly since.

aart wrote:

Is it also quieter/smoother from the inside?

I found 3B to be noisy inside cockpit than 2B, I still think it’s some harmonics in my ear?
Mrs who can hear better than me did not notice any difference…

Cobalt wrote:

Look no further. I flew a M20J (2010) ages ago; it initially had a two-blade prop; then was converted to three blades to get an enhanced noise certificate when it became fashionable to severely restruct operations on weekends if you did not have one. Lost around 5-7 kts cruise speed in the process with no other changes made to the aircraft.

Reading this, I am glad no one made the effort to certify another prop than the stock Sensenich on the DR253. That prop is well adapted to the airframe and provides a nice sound :) Besides, if “book number” is the 250km/h Robin advertised in the 1960’s, I don’t make it either. Or perhaps at altitude and with full throttle, no thank you. I prefer a more relaxed 60-65% power, which allows to lean aggressively, and still make 120-125kt TAS. Sufficient for me! (I also have a bunch of antennas installed)

Thinking of which, the DR253 is in a curious situation, which comes with (mainly) disadvantages and (some, like here) advantages: the aircraft is not “orphaned” like earlier Robins are, and the DR300/400 STCs are not available either. But I digress. This is a topic for an entire new thread.

etn wrote:

Reading this, I am glad no one made the effort to certify another prop than the stock Sensenich on the DR253.

There is nothing wrong with certifying another prop, but if you do, do it properly. And if you’re a European importer, then you make sure that you get noise certification done properly not just “within Chapter 10”. Oh yea, and make sure you get some information what the darn thing will do to your performance and WnB.

That is prior to selling any STC.