The place for technical discussions about GA and flying.
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By foxmoth
FLYER Club Member  FLYER Club Member
#1707135
Does anyone know what the "MANU" selection on this actually does, I have been reading the manual and the explanation is very unclear! N.B. if you are looking at fitting one of these - DON'T!
By riverrock
FLYER Club Member  FLYER Club Member
#1707219
Presumably its the opposite of "AUTO"? Lets you control the propeller pitch manually?
https://www.mt-propeller.com/pdf/manuals/e-118.pdf
The control unit P-120-U and P-120-A (S/no. WA01-XXX and
beyond) offer the possibility to switch to the mode "MANU" and to
change the propeller pitch manually with the toggle or selector
switch. However, manual mode should only be used for testing or
in the case of a failure in the constant speed (AUTO) mode
By Big Dex
#1707253
Whilst I don’t have an MT, I do have an electric VP prop. I always switch from CS to manual once established in the cruise, otherwise with every 25rpm fluctuation in rpm, the pitch changes to correct it. I figure that this is going to cause much faster wear in the mechanism at that pitch range.

May I ask what your objection is to the MT prop?
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By Charliesixtysix
#1707308
A CS prop should compensate for power change to keep a constant governed RPM, that is its job.

If this prop is on the aircraft that I think it is, the concern may be to do with the very slow pitch change not keeping up during aeros perhaps?
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By foxmoth
FLYER Club Member  FLYER Club Member
#1707456
May I ask what your objection is to the MT prop?


As Charlie66 say, too slow a pitch change for aeros and even in a go around it is too easy to overspeed,whilst it might be good during cruise it is actually worse than a fixed pitch prop during these phases of flight!
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By Charliesixtysix
#1707467
You are right, it is not a good prop for aeros at all ( or at any other time involving anything but the slowest of power change settings).

I was asked to help with the LAA aeros approval and flight test on that aircraft by the previous owner and raised cornerns re slow response time in the inital paperwork process.

I only flew the aircraft the once but seem to recall that you can deselect the CS function (cannot remember exactly how without seeing the controller unit though) and run it as fixed pitch - I recall trying it at 25/25 set in level flight and then turned off the auto CS function after verifying that the slow response was indeed an issue during aerobatics , which I felt was better than in CS mode, but required a very busy left hand....

My main concern, apart from overspeeding the prop in CS mode, was that it can end up very coarse in certain circumstances and could get someone who was not aware of the issue into trouble if they asked for high power with the prop bogging the engine. e.g. entering a loop at low level and a tad short of speed perhaps...(and that is leaving aside the implications for potential engine damage in that situation..).


Overall, I was not impressed with that engine/ prop combination on an RV8 and understand MT's recommendation for it not being suitable for aeros.

All of this is in my report to Francis.
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By carlmeek
FLYER Club Member  FLYER Club Member
#1707470
That all makes sense, I wouldn’t install an electric prop on a lycoming. However for Aeros could the pitch not be set to a known middle position simply to emulate a fixed pitch prop?

I’ve flown a couple of hundred hours behind two different electric prop controllers and I’m about to replace a woodcomp electric rocker switch with a CS controller on another aircraft.

I think the electric CS controllers are a good thing, easing workload over a manual variable electric prop. Often they are just a single button press to change from a pre programmed take off and cruise RPM setting.

The pitch speed is something that has to be carefully managed and pilots need to be aware that you cannot just jam the throttle to the firewall as it may over speed the engine. However a smooth progressive power application on goaround doesn’t need to take more than about 2 seconds to apply full throttle. Stalls would be another example, you cannot do a standard full throttle recovery or it may overspeed.

Why does this happen? Because the prop blades will by physically set to full fine at the maximum static RPM without overspeeding the engine. As the take off roll progresses the controller will coarsen the prop to maintain that RPM and achieve 100% power for the whole take off. However in flight, Add airspeed on top of that fully fine setting and it would go through the engine redline. So the problem starts to manifest when you reduce throttle to zero. The prop controller keeps fining the prop trying to achieve the preset RPM but never achieves it because you are at idle.... so you end up full fine at 60kts on approach. Jam throttle to the firewall and full fine plus airspeed = overspeed.

Hydraulic obviously doesn’t have this issue and I prefer hydraulic, however for lightweight Rotax aircraft electric is fine as long as the pilot takes care.
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By foxmoth
FLYER Club Member  FLYER Club Member
#1707506
however for lightweight Rotax aircraft electric is fine as long as the pilot takes care.


I can see the advantage on a low powered aircraft where it will improve both the take off and cruise performance but on something like the RV8 you would need to be operating off a very short strip to need the improved take off performance so the only real advantage is a better cruise - and what you pay extra on maintenance would probably allow you to run a fixed pitch at a higher RPM to get the same cruise!
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By Charliesixtysix
#1707517
Agreed, but our hydraulic 3 blade MT prop on the RV7 gives excellent discing effect when landing too - great when operating into, as well as out of short strips, especially hot and high like we were the other week. (See thread over on the General Aviation forum where the OP is trying to defeat physics by looking at undercarriage leg length on an aircraft with a very coarse FP prop and wanting short field performance - just not going to happen is it...).

A good CS prop is a huge bonus for aerobatics too. Set the desired power and revs and forget - the governor looks after the RPM and leaves you free to fly the aeroplane.

However, as Foxmoth says, the total cost of ownership vs performance has to be considered and our dreaded six year overhaul approaches rapidly now...Hopefully we can take advantage of the LAA Low-Hours Inspection Protocol but watch this space, I might be living on sliced porridge for a year or two if a big overhaul bill lands on the desk.... :pale:
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By foxmoth
FLYER Club Member  FLYER Club Member
#1707522
Certainly no arguments for me for a normal CS prop though our RV7 works fine with a fixed pitch - for aeros I get to 150kts and set 2500rpm, I can then do pretty much what I want without having to touch the throttle and I will gain height in manouvres.
What they need on the electric prop is an aerobatic and approach setting that either locks the pitch or restricts it to a range that it would cope with - in fact it should be possible to programme the controller with personalised settings, you could then have different settings for different group members or situations, maybe one for aeros and another for normal landings where you don’t need short field performance but want to be able to put power on quickly for a go around!