I noticed that some planes, e.g. a PA28-181 Archer or a C172 can have an electrically adjustable prop from MT-Propeller installed.
What what I can’t find is how much gain is to be expected, both in knots (for cruise and top speeds) and in dollars (for the added maintenance), nor the possible decrease in e.g. fuel flow at a given speed, or length of takeoff roll. IOW, is such a prop a worthwhile endeavor for a roughly 180HP engine? FWIW the price seems to be around $12k.
The Arrow and Cutlass might provide some rough comparison, if you say the folding gear adds around 10-15 KTAS. This suggests the constant speed doesn’t add much at cruise, but may help in rate of climb, especially as the retractables have higher MAUM.
Presumably at theoretical max range cruise at full throttle height there is some efficiency gain, but a 180HP four pot rarely is operated in this regime.
In addition to the cost, you have the recurring variable prop overhaul schedules which probably cause more engineering complications than they prevent – unless you are on the N reg where this does not apply.
RobertL18C wrote:
This suggests the constant speed doesn’t add much at cruise, but may help in rate of climb, especially as the retractables have higher MAUM.Presumably at theoretical max range cruise at full throttle height there is some efficiency gain, but a 180HP four pot rarely is operated in this regime.
For me, this is actually the prevailing mode of operation, yet I’m having the same doubts. On the other hand, recent MT props may actually even save the owner some money in the long run when operating from rough strips, as the blades have erosion-resistant nickel-clad leading edge and are also individually repairable in the event of FOD.
tmo wrote:
I noticed that some planes, e.g. a PA28-181 Archer or a C172 can have an electrically adjustable prop from MT-Propeller installed.
I have an electrically actuated MT prop installed on a 150 HP Lycoming, on a certified airframe. It’s not on an Piper or Cessna so I can’t comment on specific improvements in aircraft performance for your types of interest. I can say more generally that you’re right, there is a nice improvement in climb rate. The ability to cruise over square is also useful if you do enough cross country to care about the small reduction in fuel flow (and noise) that results from lower engine rpm at the same percentage power. You do have to be aware that the speed at which pitch changes is much slower than a hydraulic prop, but for the intended purpose that’s OK.
The installation needs to be done very carefully because the pitch control hardware is not really what I consider aircraft quality, and is consequently not ‘dummy proof’: the motor power wiring is tie-wrapped to the exterior of the rotating prop hub and motor, and includes an unsecured loop where its terminated on the rotating engine flywheel. The brush block bracket is a flexible and imprecisely made steel bolt-on, making it difficult to properly align the brushes to the slip rings and set up proper brush block clearance. My original speed sensor was unreliable and was replaced with an upgraded MT-supplied sensor. The part wasn’t expensive ($100) but it took a while to determine that it was a superseded type and failing intermittently. Also, the electrical grounds need to be very secure. I had some intermittent grounds with my installation, which was poorly done by a previous owner. The symptom was the prop pitch control locking in place which is not always a good thing, particularly on take off as you may find yourself limited to partial throttle and partial power on the upwind, at red line engine rpm. Once all the bugs in my particular installation were worked out I’ve found the prop to be reliable, but certainly it requires careful inspection at each annual due to the fragile construction.
I had mine overhauled with relatively few hours and it was $3 or 4K IIRC. It didn’t really need it, very little work was done, but I was chasing control problems that ended up being the speed sensor and poor grounding. I believe MT would like you to overhaul it every 6 years. The blades on mine are wood, secured to the hub with lag screws and covered with a thin layer of fiberglass. The fiberglass can’t be very thick or it will come off, but its thick enough to provide weather protection. The leading edge protection on mine is mechanically formed stainless steel.
If you were prepared to deal with all that, I think the improvement in take off and climb performance could be quite useful on a Piper or Cessna that normally has a marginal climb rate, even at sea level density altitude. Just be very careful with details of installation and plan on careful periodic inspections.
