does anyone have any experience with the mod that installs a dedicated prop control. always used it before cirrus.
But isn’t that why you bought a Cirrus . . . so you didn’t have to mess with the prop anymore?
not really. actually bought because of increased room and comfort. been driving mooneys. have to say comfort makes up for the extra speed you get with mooney. thinking i may try the mod.
Expensive & Voids Warrantee
If you really like the speed and comfort, try the parachute. It’s real cool as well . . . and the gear . . . I’ve never once had the gear fail to lock into place in my Cirrus. As for the prop . . . heck, I can’t figure out why I ever even wanted a prop that I could adjust. Oh wait . . . girls . . . that’s right . . . girls are really impressed with a bunch of knobs, levers and handles. And if you’re into that sort of thing, this is what you want. This alone will get you into the mile high club.
Whatever happened to that fake landing gear switch that was offered a while back? That should be part of the package. Rj would call it the RealMen upgrade.
Was the landing gear lever ever approved? I did see the documentation online as a supplement to the manual but have no idea which company provides it. I have considered getting my commercial license using this gadget.
I encourage you to give yourself more time before modifying your airplane.
Question: what benefit do you see, operationally, in adding a separate prop control?
Having come from a 182 with a prop control, I had the same initial reaction. After 1000 hours in a Cirrus, I can’t imagine any benefit as there is no MP/RPM combination I would want to use that I cannot get with the single power lever. I really appreciate the simpler operation of the single power lever.
And keep in mind this modification will actually make it harder to sell someday.
Norman - as a long time die hard Mooniac, I felt the same as you in the beginning. I’m over it now and concur with Tim’s experience. Once family and friends experience the pleasure of two doors and the cabin room, there is no turning back. I said for about 3 years into Cirrus flying that I would go back to a Mooney after my last child went to college. Well the time is here and I’m sticking with the Cirrus.
Apologies for having a little fun at your expense. Serious question: What benefit would you hope to get from a separate prop control?
I haven’t got it yet, but about to, with the following pros :
improve cruise speed or better fuel efficiency. They claim it pays for itself through a 1 gph saving. in my country, 1gph = 13,50$)
lower RPM = lower noise= more comfort for passengers
harder resell? there is always the possibility to return to the original Cirrus setup for the cost of 6 hours of labor, so it’s actually a plus as you offer an option to your buyer.
Please do not hesitate to argue me away from that move
Well, since you asked:
I don’t buy that claim, at the same power setting (if that is even achievable).
Does the STC come with new power setting tables for the aircraft? Or otherwise, how do you know which RPM/MP/FF combos are ok for the engine?
RealMan? Well, first, wouldn’t you need a gear lever for that? Second, I prefer the SmartMan feeling.
Color me skeptical.
Here’s a test I did in my 2003 NA SR22:
Decreasing the rpm for any given fuel flow had little effect and no gain in efficiency below 2650 rpm. Extrapolating, its hard for me to see how and where a 1 gph saving would come from, at least without an accompanying loss of airspeed.
Remember, down to abut 2,500 rpm we can already retain pretty close to WOT and still set rpm.
But I keep an open mind on this, and would readily admit to being wrong once the data was in.
My understanding is there is a relation between %power and TAS, the combination you use to get the that can be done with more or less fuel.
lower RPM would imply lower fuel burn for the same speed, the same way you get better mpg for the same speed when you gear up on your car. the reason for that is the reduction of friction in the engine with lower rpm.
the limit down being reached when the increased drag on the prop erases the lower friction in the engine.
I mean . . . what do I know . . . I’m no engineer, but there IS a relationship between% power and TAS. The more power the faster you go. BUT, the combination you use . . . . ? % power decreases with less fuel flow.
Less flow = less % power = slower.
Thanks, Dennis for not whipping me with a picture from your book of spells, but :
once you’ve set your % power with MP and FF, you decrease rpm, have less friction, therefore more efficiency therefore more power delivered to your prop
at that point, you may than either decrease FF or enjoy 2-3 more kts
note that at 3500$+ labor, we are within RJ’s equation of 2000$ per 1KT.
Could you explain a bit more. I’m not quite up on my “prop” theory. % of “power”, as such is the result of fuel flow with a given engine. Is that correct?
Therefore, I don’t set my % power with MP & FF. I set my % power with just FF for a given RPM; the rest (MP) results.
As to “friction” and “efficiency”, I thought friction was a good thing, but varies with air density (altitude and temp) After all, friction on the prop is what grabs the air, that creates thrust. And as for “efficiency” each prop has a sweet spot. For me, 2600 rpm seem to yield the best bang for the buck. Of course, this might differ for other blades, and certainly for the SR20 and the occasional 2 blade props which are more efficient by design.
My test did not show that - lower rpm did not increase speed or efficiency at any given fuel flow. I have no reason to think that pulling the rpm back even further would help, since the TAS was trending downward with each reduction in rpm below 2,650, on the same fuel flow.
While there’s less friction at lower rpm, many other factors come into play, propeller design and efficiency high on the list.
Using the car analogy, yes, overdrive may result in better gas mileage, but even that depends on many factors. If an engine is designed to run most efficiently at a particular rpm, running it in too high a gear may hurt, rather than help fuel economy.
I’d suggest going up in your plane and trying a test similar to mine. You might be surprised at the results.
I’m not an engineer and I’m in a little over my head. I know we have some engineers (or wannabe engineers) here and maybe they can speak up on this.
At the point where you decrease your RPM, you will also decrease % power and FF and MP.
While you are correct that lower RPM normally yields better efficiency, the effect is small. Depending on many factors, it could be VERY small. Ed’s tests point in that direction for the SR22. You are hoping for a 7-percent increase in efficiency, assuming 15 gph fuel flow. That would be enormous - I doubt the total effect of all internal engine friction on speed amounts to that, let alone the effect of reducing RPM by 10 percent or so. And that’s the reason why I say: Show me the numbers!
I am pretty sure the fine print says “up to 1 gph saving”. Well, yeah. Up to 100 gph, too.
2664.Cirrus CQU.pdf (1.8 MB)
Here you go, Tom, if i didn’t screw up, you have their doc. if i did, i will e-mail it direct to you and you can post it if you like.