cs management

[s_tones]

So as not to hijack the other thread....

Anybody care to summarize the operational management of the cs prop in the different phases of flight for a simple minded fp guy?

I'm particularly interested in how you stay out of trouble in terms of over speeding the prop and what is the most efficient way to run the cs prop in flight.

Steve

[Andy Hill]

Steve...

Here follows a few thoughts / suggestions They are not comprehensive, some will probably disagree with some/all of them... They are based on a UK education, so even more room for disagreement

1. Training Nothing will substitute for some proper "training" by an Instructor. In the UK now you need a "differences training course" signed off by a qualified instructor for a VP/CS Prop. It might only be an hour or 2, but worthwhile...
2. Setup You need to ensure both the "static RPM" of the engine / prop combination are set [see Prop Manual] to a little below 2700 RPM (typically), but also the governor. In practice you might find the governor is factory set OK, but the prop will need doing. When you "smartly" set full power for takeoff, the governor will not act quickly enough to prevent exceeding 2700 RPM for a period... So you set the "fine pitch stop" to, say, 2650 RPM to limit the initial RPM to that... and then the governor maintains it...
3. Overspeeding You will only tend to overspeed for Fine Pitch stop not set (see above), governor not set (see above), or lack of oil pressure (non-aerobatic prop) e.g. under negative 'g'. Suggest set 2400RPM for aerobatics, and smartly retard throttle if you hear engine speeding up... lack of oil for any period of time is hardly doing the engine any good either! Apart from these, the prop/engine is basically impossible to overspeed, one of it's advantages for aerobatics etc. (i.e. "carefree handling").
4. Handling At "Max RPM" / "Fine Pitch" = Blue Lever fully forward, you enable the engine to produce full power (e.g. 180HP), albeit at a cost in noise / lack of fuel efficiency etc. Since you usually want full power for takeoff and landing (in case of a Go Around), then you will check/select the Blue Lever all the way forward in your pre-takeoff and downwind checks. In the cruise, when you might not want full power, and do want fuel efficiency, you will select a lower RPM e.g. 2400 RPM/2200 RPM.
5. Over-boosting Selecting too much manifold pressure / too little RPM can "over boost" the engine, with potential damage (apparently!). Various rules of thumb are out there, but 1st 2 digits of RPM + 4.5 for Max MP is one... e.g. 2200RPM, don't use a lot more than 26" MP - if you want to go faster, use more RPM as well... As a consequence, when changing power settings, if increasing set RPM first, then MP, and reducing power, reduce MP first, then RPM...
6. Pre-Take off With, say, 1800 RPM set, cycle the prop lever 3 times (1st flight of day, maybe only once later flights) to reduce RPM by (some say only 50RPM on 1st cycle) 200-300RPM. Checks the system, and (allegedly) circulates the warm engine oil into the prop.

As I say, I am sure your question and my reply will offer lots of room for debate

Andy & Ellie Hill
RV-8 G-HILZ

[N131RV]

Originally Posted by s_tones

So as not to hijack the other thread....

Anybody care to summarize the operational management of the cs prop in the different phases of flight for a simple minded fp guy?

I'm particularly interested in how you stay out of trouble in terms of over speeding the prop and what is the most efficient way to run the cs prop in flight.

Steve

It depends on the airplane and engine of course:

For me, it's very similar to the way I fly a 210 with C/S Prop.

For takeoff, full fine (max rpm). I usually leave it there until I've got the gear and flaps up, then reduce power FIRST (always with C/S) then reduce RPM to cruise (2350 or so).

Cruise, at 75% power or less, "oversquare" gets maximum efficiency (but not always). Square means MP in inches and rpm/100 and MP match, like 25"/2500.
So oversquare means rpm/100 is less than MP in inches IE: 23"/2200 rpm ( a common cruise number).

I typically cruise at 5000' MSL and above: WOT, lean of peak at between 2250 and 2350 rpm with whatever MP I can get.

Landing, that C/S is a nice fat brake. Enter the pattern, drop power to around 15" or so (varies from plane to plane) and push the prop full in (fine pitch).

Over speeding is not normally a problem as the prop will adjust to stay at the current RPM setting. You can over speed your prop if you lose oil pressure.

Just how I do it, YMMV.

JP

[KirkGrovesRV8]

Originally Posted by s_tones

So as not to hijack the other thread....

Anybody care to summarize the operational management of the cs prop in the different phases of flight for a simple minded fp guy?

I'm particularly interested in how you stay out of trouble in terms of over speeding the prop and what is the most efficient way to run the cs prop in flight.

Steve

Hi Steve,
You don't get more simple minded than me
I take off max rpm and reduce rpm to below 2600 at around 500ft (hartzell blended airfoil prop) usally 2550 or so. I leave the throttle wide open as I climb, as I reach my altitude I level off reduce MP to around 21" and then reduce rpm to 2350rpm. And then basically leave it alone until you are abeam the numbers on downwind and slowed down. Then as a final check boost pump on and prop and mixture full forward, then land

[Webb]

When you want to increase power - Prop first then throttle
When you want to decrease power - Throttle first and then prop

If you can remember this, the rest comes easy.

Image the prop is the standard transmission in a car. You do not want to step on the accelerator at slow speed in high gear (coarse pitch). You want to have it in a lower gear (fine pitch) when you want to increase the power. Shift to the lower gear (prop to fine pitch) and then add power. When you want to slow down or reduce power, you take your foot off the gas and let the engine slow down, not shift it into a lower gear (fine pitch) that increases the rpm. Simple right?

Here's a great example....On take off, the prop is all the way forward and full power is applied. When at a safe altitude, the power and rpm needs to be lowered. Let's assume you want to finish climb out at 25 squared. The old pro pulls the throttle back to 24 inches of MP and then backs the prop back to 2500 rpm. Amazingly, the MP increases 1 inch and the engine is now set at 25 squared. If you pulled the prop back first, you would have lots of power on an slower running engine which is harmful.

Hope this makes sense now.

[Bryan Wood]

(Agree with everything previously posted.) However, when you are setting up to land you will now be flying a fixed pitch prop for all practical purposes. After stuffing the prop control forward for landing and with the power back your prop will be in fine pitch and you will then need to transition from the manifold pressure guage to the tach. This is likely the only time during flight where your tach will act like you are used to seeing it in a fixed pitch plane by changing in relation to throttle movements. The manifold pressure guage will either not be reading at all, or only showing minimal pressure.

[erich weaver]

Originally Posted by Webb

When you want to increase power - Prop first then throttle
When you want to decrease power - Throttle first and then prop

If you can remember this, the rest comes easy.

Image the prop is the standard transmission in a car. You do not want to step on the accelerator at slow speed in high gear (coarse pitch). You want to have it in a lower gear (fine pitch) when you want to increase the power. Shift to the lower gear (prop to fine pitch) and then add power. When you want to slow down or reduce power, you take your foot off the gas and let the engine slow down, not shift it into a lower gear (fine pitch) that increases the rpm. Simple right?

This is the standard operating procedure that is written in all the instructional books, and I have no problem with it. However, under normal operating conditions and using normally aspirated engines like ours, you would be hard pressed to come anywhere near engine damage by simply adjusting the RPM and MP in the "wrong" order.

Furthermore, RPM is typically only adjusted two or three times once the flight has started: maybe a slight decrease in RPM after take-off to lessen noise, again at cruise altitude to "go into high gear" and save fuel, and once when preparing to land (back to high RPM). That last change isnt really a change at all, since at that point, the low MP setting prevents any increase in RPM from occurring - you are simply preparing for a possible go-around. These three standard RPM changes are not necessarily accomanied by an associated adjustment in MP. Many folks reduce MP upon reaching cruise altitude for fuel savings, but you dont have to, and there are definte advantages to operating oversquare (MP > RPM/100), if you are low enough to be able to achieve that condition. Better yet, push that throttle all the way in and go lean of peak to get your fuel savings - whole 'nother topic there.

Anyway, my point is we really dont need to get too hung up on whether to push the throttle or the prop knob first - it simply isnt going to matter under normal circumstances. That said, if you happen to be throttled way back, cruising at 2000 feet at 2200 RPM and you decide you have to catch your buddy that just went screaming by, yes, you are well advised to increase RPM first, then MP, so that you avoid encountering a condition where MP is very high, and RPM is very low.

erich

[hecilopter]

Take off - prop forward, full throttle
500 ft - prop back to 2500, climb to cruise altitude
at Altitude - prop back to 2300 for cruise & lean

--Notice I never touch the throttle from full for takeoff, in climb & cruise

Decent to land - pull throttle back to 23" and pull back gradually to maintain 23", richen as required
Pattern - reduce throttle to 100 mph
Downwind - Now push prop all the way forward & fly with throttle

--Notice I never touch the prop in decent

None of the above conditions even come close to hurting the engine.
Makes it dirt simple.

[L.Adamson]

Originally Posted by hecilopter

Pattern - reduce throttle to 100 mph
Downwind - Now push prop all the way forward & fly with throttle

--Notice I never touch the prop in decent

None of the above conditions even come close to hurting the engine.
Makes it dirt simple.

Yep....................if you're somewhere over that 100 mph & shove the blue knob in; you'll feel it in the stomach & you'll most likely remember not to do it again!

Other than that, I'm typical full throttle too. But at my altitudes it's usually 22" mp at best.

L.Adamson --- RV6A

[frankh]

Care to elaborate on where the "reduce throttle before RPM" rule comes from?

I'm hving a hard time beliveing reducung RPM with full throttle is harmful but I'd like to know what evidence is out there on engine damage one way or the other.

Frank