Prop strike yesterday (and propeller specific noise level)

Ibra wrote:

The difference between 3 blades vs 2 blades is very minimal when you cruise LOP at 125KIAS near 55% power…not everybody flies Mooney for speed, it’s can be flown as 4 seater ULM with 140-150KTAS burning less than 25LPH at 8kft then in/out of tight strips, that is where 3 blades shines

Provided you have performance figures for this. The “C” POH has no such information, at 7500 ft the lowest power they indicate is 66% for 2400 RPM. At 10’000 ft there is a 54% figure at 8 GPH. It gives a TAS of 146mph which translates into 126 kt indeed.

Ibra wrote:

At 75% cruise in M20J, on clean props we lost 5kts with 3 blades vs 2 blades

Is that a fixed factor vs the POH figures or simply the top speed?

Ibra wrote:

That was an actual loss after one prop strike and moving from 2 to 3

I understood that much, but throughout the whole performance range or just at top speeds? I am trying to compile a revised cruise control table and update the flight model in the flight plan system. This implies to have correct cruise figures or I might as well forget it. Just to give you an idea, this is what I am trying to do.

The figures in that table are still original POH figures but for the blue ones, which are guestimates as the POH does not provide for them. We now need to get a reliable correction factor for the speed loss. I have not even started to figure out the long range cruise tables per altitude as the figures we have so far are so sketchy.

If we have to count on 5-8 kts loss troughout, this would mean a considerable performance loss, ending up with a 125-135 kt airplane and a loss of range of up to 80 NM. That is not what Mooneys are about.

From what we have experienced now, the new installation has done the following:

We lost around 5 kts cruise speed througout the spectrum, that is with %power set by fuel flow vs altitude.

We gained about 10 kgs of weight at the front. Consequence is that the airplane is out of CG if flown with 2 up front (Training configuration) unless it has 30 kgs of ballast in the baggage hold.

The noise problem has not been addressed just yet, even though in Switzerland we got the same class back that we had. So at least that problem is gone.

Projections on performance data would suggest a net loss of about 5 kts throughout and consequently a loss of range of about 20-30 NM. Flown at the previous cruise speed, we are faced with a significantly increased fuel flow and a range loss of about 5-6%.

To say that I am disappointed in the whole thing is putting it mildly. We were trying to do a good thing and got the maximum penalty of achieving none of the goals while loosing significant performance. We will need to evaluate carefully what to do. Most probably we will try to sell the 3 blade prop and find a servicable 2 blade with a new type hub.