MT-Prop restriction on RPM ??

[Pilottonny]

Hello,

I am at the stage that I need to order my prop to be able to carry on with the cowling. I was going to order the MT 2-blade hydraulic CS-prop (MTV-11-C/183-59), but found out today, that it has a restriction from 2050 RPM to 2300 RPM, above 22 MAP. The restriction means that the prop should not be operated within this RPM range continously. Running it within this range for a minute or so, is not a problem, just not run it continuous. BTW the MT-tech-rep explained to me that the blades will not fly-off on their own, but the problem is that if you do run the prop in this range, continuous, you will ruin the bearings and seals, in the long run.

I have not flown a CS-prop yet, but will you ever fly between 2050 and 2300 RPM, anyway?? What I mean is, is it a "restriction" at all, or is it just a minor issue.
I have a Dynon EMS-120 that allows to mark the restricted RPM-range yellow, on the RPM-guage. So it is not a question of forgetting about it and running the engine at the wrong RPM.

The alternative is the 3-bladed MTV-12-C/180-57, which is 8 lbs heavier and $1.460,- more expensive . Also it seams that a three blade prop causes more drag . On the other hand the 3-bladed should be more efficient in climb and is quieter and smoother than the 2-bladed .

Choices, choices !!

Anybody flying a CS-prop, please chime in and let us know: Do you ever fly in the 2050-2300 RPM range?

Regards, Tonny.

[Scott Hersha]

I have a Whirlwind with the same 2050 - 2300 restriction, and don't find it to be a problem at all. Just don't run it there since you control it. It doesn't seem like it would be worth an extra $1400. to give you that range.

Scott

[Andy Hill]

Hi Tonny...

We have a Hartzell BA (2 Blade) on an XP-IO-360 with no RPM restrictions. No Restrictions is obviously ideal, but at what "cost" in operating? Alternatives? Fuel? etc.

We do now run at 2200RPM as an efficient cruise, with 24" MP (i.e. "over square"). On our RV-8, this is giving at ~1500', 150+KIAS on 30L/Hr. As you increase altitude, I suspect that you want higher RPMs - and most of the USA based arcraft do not have the airspace restrictions we do in the SE of the UK around the London TMA. I believe in the NL you now have (large?) areas restricted to 1200'?

If we use 2300/23" we get about the same fuel flow as above, but 5-10K slower.

I have flown a couple of RV-8s with the 3 blade MT. I do not notice it is noticeably smoother or quieter... but it is a VERY effective airbrake in formation / joining the circuit

Given all you say, and you are set on MT over Hartzell, I doubt the restriction will be serious to you... And the Hartzell still has RPM restrictions with some models / engines...

Andy & Ellie Hill
RV-8 G-HILZ

[Steve Sampson]

Tonny - I am running that same prop on my O-320/P-mag RV4. I was irritated when I became aware of the restriction, mostly because it is the second time that MT have introduced a limitation after I have bought the prop.

Having said that, now that I have got used to the fact that the band is there, it really is not an issue. For cross country cruising I use 2049/22.5" and 22 to 23 lph. That gives me a very relaxed 160mph cruise. (Its easy to get below 2050 because the AFS turns the rpm number yellow in the avoid band)

For climbing I use rpm settings well above the restricted rpm band.

If I were buying now I would certainly buy the same prop. 3-blades are a pain in lots of ways. In the hangar you can never get away from them, there is more weight, more cost, more shipping cost, more to damage. Theoretically less efficiency.

For very high power engines you need more blades, but not for our little Lycos. When I ask why people bought 3 blades they say 'its so sexy' so I think they are perhaps trying to make up for a personal shortcoming.

Go for it!

[kiwipete]

Andy

I'm interested in the fact you now run 2200-24'.
I'll try this in my -7 as I have the exact same engine and prop and will be interested to see if I get a difference.

Peter

[kiwipete]

Andy

Yesterday I tried both 23' - 2300 and 24 - 2200. Both give 65% power and the same fuel flow and to be honest I couldn't see any difference in speed. Both giving 148 KIAS. at 1200 ft. It was a little bit bumpy yesterday I'll give it a go on a smoother day. However my engine prop comb. seemed to feel smoother at 2300.


Anyone else have any info on slower prop speeds giving better cruise performance. I remember when I used to fly Cessna 208 Caravan's we always left the prop at maxium rpm unless overflying the city on approach as the performance cruise was better.


Peter

[RVjim]

Lycoming says the peak torque occurs at 2200 RPM. The highest power pulses at this RPM is apparently why some propeller/engine combinations have the mid range RPM restriction.

I found it interesting to just change the RPM and not move the throttle.
The fuel flow follows the RPM. Increased RPM, increased fuel flow.
However, the airspeed has a mind of its own. :-)
And the characteristics vary with altitude.

I found a RV-6A with a 180 hp Lyc. 360 at full throttle (constant MP) and a Hartzell propeller at 12,500' density altitude had a maximum airspeed at 2400 RPM.
Increase the RPM, airspeed decreases.
Decrease the RPM, airspeed decreases.

The critical RPM at 7,500' density altitude was 2550.

I didn't try any partial throttle tests. Getting eight data points takes me about an hour for each altitude.

Jim Ayers

[Pilottonny]

I am getting closer to my decision!

Today I spoke to MT again and found out that the 2-blade Prop needs an overhaul after 6 years (or 1.000 hrs. whatever comes first, I gues the 6 years) and it costs: EUR 1.850,- + VAT = $ 2.885,- (at current rate) !!!
Another downside is: if MT ship the propeller directly to Belgium, they charge EUR 155,- = $ 203,- (more than double for the 3-bladed) although the shipment to Vans would be free of charge ??!! I guess I could pick it up by car, but it is still a 450 mile drive, each way, which is also not for free.

In the meantime I also checked the Whirlwind website and spoke to "Greg". The 200RV-prop, that they make specially for the RV's, is $ 175,- more expensive than the MT through Van's, but has no RPM restrictions. It has a TBO of only 5 years (or 650 hrs.), but the overhaul only costs $ 500,-

I have to give Greg an other call for some more info.

Any comparison info available?

Regards, Tonny.

[DanH]

<<What I mean is, is it a "restriction" at all, or is it just a minor issue.>>

After some number of vibratory cycles you'll reach an unacceptable fatigue level. Think of it this way: You start with a full bank of available cycles, and you can use them up at whatever rate you please.

For purposes of illustration assume the prop is good for 1,000,000 cycles at peak stress, and each cycle to corresponds to each cylinder firing event (which is not necessarily true). 2175 RPM would be 4350 cycles per minute. If you ran it one minute in the restricted range every flight, you would get 230 flights (1,000,000/4350) before prop components need replaced. If you only run 15 seconds in the restricted range each flight, you get 920 flights.

Run in the restricted range as little as possible.

[ao.frog]

Tonny: can you please tell me where you found out that your prop has RPM-restrictions?

I've a 2 bladed M/T prop: MTV-15-B/183-402 and I think I recall that there was no RPM-restrictions on this prop.

Does anyone else know?