C172 Climb/Cruise Props

luvflyin

luvflyin

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Luvflyin
There are climb props and cruise props for C172's. There are 180hp conversions for C172's. The word is that the 180 gives you great climb but doesn't do much for cruise speed. So the voices in my head say put a cruise prop on the 180, climb at least as good as it did with 150 and fly fast. is it this simple? What is the best cruise improvement that you can get out of a 180 conversion and maintain at least the climb performance of the 150. The particular plane in question is a C172G.
 
With regard to rate of climb, there is no substitute for power.

With regard to cruise speed, power still counts but the 172 is a draggy airframe. Drag increases with the square of speed. That's why the 180 conversion doesn't help speed all that much. To reduce drag, you need to visit the folks who sell performance improving modifications to your airframe: vortex generators, wheel pant fairings, and many others.

I am not able to recommend which of these mods is most effective. Stay tuned!

-Skip
 
A rule of thumb that I've heard but know of no basis for is that for each ten HP increase, you can increase the prop pitch by two inches and keep the same RPM such as at wide open throttle straight and level. It worked for me on my Cherokee 140. I like WOT S&L to give me redline RPM. I repitched 4 inches and got the RPM that I expected.

Any excess HP not required to maintain climb speed goes into rate of climb. A horsepower is 550 ft*lbs/sec or 33,000 ft*lb/minute. Divide 33,000 by the max take off weight of your plane and you get the max theoretical rate of climb provided by each excess HP (100% efficiency of converting HP into thrust). With a 2200 MTW plane, a 30 HP increase yields 450 fpm max theoretical increase in climb rate. You may see close to a 40 to 50% increase in climb rate.

Going from 150 to 180 HP is a 20% increase. Start from your normal cruise speed or your max speed and see how much speed increase it takes to increase drag by 20% when it increases as a function of the square of speed. I expect that your speed increase is less than 10%.
 
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I have a 172N with 180 hp O-360-A4M and a cruise prop (Sensenich 76EM8S14-060), under the Air Plains STC. The Air Plains manual says static runup should be 2250-2350 rpm (mine is a shade under 2300). The other day a fellow over on the Cessna 172 Club board said he has the same engine under the Penn Yan STC, and gets 2400 rpm static, so I assume that's more a climb prop (I don't know what Penn Yan's manual says about static rpm). He says his airplane is slower than he thinks it ought to be.

Just as a data point, I have Power Flow exhaust, gap seals and full factory wheel and brake fairings, and cruise between 125 and 130 KTAS at 2600 rpm at 10,000', at light weights. Climb is considerably better than it was with the original 160 hp engine.
 
Pilawt said:
I have a 172N with 180 hp O-360-A4M and a cruise prop (Sensenich 76EM8S14-060), under the Air Plains STC. The Air Plains manual says static runup should be 2250-2350 rpm (mine is a shade under 2300). The other day a fellow over on the Cessna 172 Club board said he has the same engine under the Penn Yan STC, and gets 2400 rpm static, so I assume that's more a climb prop (I don't know what Penn Yan's manual says about static rpm). He says his airplane is slower than he thinks it ought to be.

Just as a data point, I have Power Flow exhaust, gap seals and full factory wheel and brake fairings, and cruise between 125 and 130 KTAS at 2600 rpm at 10,000', at light weights. Climb is considerably better than it was with the original 160 hp engine.
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What do you mean by "static run up?" Sounds like the RPM you get at full throttle sitting on the ground. Is that correct?
 
When they give you the numbers you're supposed to get on a static run up, is it adjusted for conditions? Seems like one in Denver on a hot day might give different RPM's than one at sea level on a cool day. Or is the effect on engine output balanced by the effect of air resistance on the prop?
 
luvflyin said:
There are climb props and cruise props for C172's. There are 180hp conversions for C172's. The word is that the 180 gives you great climb but doesn't do much for cruise speed. So the voices in my head say put a cruise prop on the 180, climb at least as good as it did with 150 and fly fast. is it this simple? What is the best cruise improvement that you can get out of a 180 conversion and maintain at least the climb performance of the 150. The particular plane in question is a C172G.
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I used to be a Cessna engineer and have flown most single engine Cessna models. Also an A & P. My preference with fixed pitch is a climb prop, I will take safety over another 3 to 5mph any day. Unless you are only flying with one additional passenger near sea level it is usually better to have short field and climb performance, and it is easier on the engine as it does not work it as hard and CHT's are less of a problem during climb in hot weather. On a 300 mile leg or trip the difference in time between 120 vs 125 mph is 0.1 hour total (6 minutes) offset by the difference in time to climb to cruise altitude. A 4,000 foot climb at 500 fpm vs 800 fpm is 5 minutes vs 8 minutes. So you gain 3 minutes, my recommendation is enjoy the extra 3 minutes of a nice trip. If the extra performance is that important go to a constant speed prop conversion then you will have the best of both worlds. Good flying!
 
Where does the "word" come from. Here is my "word" based on flying close to 100 hours in the Penn Yan demonstrator as well as test flying 20 or so of the aircraft converted at Penn Yan while I was managing partner there. The standard prop on both the Penn Yan and Air Plaines 180 conversions is the 60" pitch. They climb much better and typically cruise close to if not 10 KTS faster. A properly rigged M,N, or P model will true 130 KTS WOT at 7-8,000'. The disparity in static RPM between the 2 airplanes mentioned here could be different pitch in the props but is more likely a tach out of calibration. More than half of the several hundred tach I have checked were not reading correctly. Charlie Melot
 
charlie said:
Where does the "word" come from. Here is my "word" based on flying close to 100 hours in the Penn Yan demonstrator as well as test flying 20 or so of the aircraft converted at Penn Yan while I was managing partner there. The standard prop on both the Penn Yan and Air Plaines 180 conversions is the 60" pitch. They climb much better and typically cruise close to if not 10 KTS faster. A properly rigged M,N, or P model will true 130 KTS WOT at 7-8,000'. The disparity in static RPM between the 2 airplanes mentioned here could be different pitch in the props but is more likely a tach out of calibration. More than half of the several hundred tach I have checked were not reading correctly. Charlie Melot
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Hi Charlie, if the owner needs an overhaul your 180 hp conversion Will be worthwhile. The 60"pitch does not sound too aggressive, I do not remember what is standard on the "M's"? What climb rate were you seeing at full gross around 5,000 feet?
 
Power to overcome drag is related to the cube of velocity, the force of drag with the square of velocity. Climb is roughly related to (thrust-drag)/weight. So more power may create a significant difference in thrust-drag at climb speeds, without as much of an effect on cruise speed for a dirty airframe.

Id go for a midrange prop in a 172, or a climb prop if you are usually at gross.
 
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Or, if your are going to go with a 180hp conversion, get a CS prop.
 
Briar Rabbit said:
Hi Charlie, if the owner needs an overhaul your 180 hp conversion Will be worthwhile. The 60"pitch does not sound too aggressive, I do not remember what is standard on the "M's"? What climb rate were you seeing at full gross around 5,000 feet?
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I left Penn Yan 25 years ago so I don't recall what the climb was like at 5,000 at gross. IIRC the M uses a 57" pitch prop but it's a whole different McCauley prop. A constant speed prop gives a slight improvement in takeoff and climb with no improvement in cruise. Also the CSP does not facilitate increasing the MGW to 2550#.
 
luvflyin said:
There are climb props and cruise props for C172's. There are 180hp conversions for C172's. The word is that the 180 gives you great climb but doesn't do much for cruise speed. So the voices in my head say put a cruise prop on the 180, climb at least as good as it did with 150 and fly fast. is it this simple? What is the best cruise improvement that you can get out of a 180 conversion and maintain at least the climb performance of the 150. The particular plane in question is a C172G.
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Hi. I'm on the other side of the equation. Most of my flying is within an hour of Talkeetna, AK and I'm all about getting the best take-off performance with my little C172G with Cont O-300. Were doing an overhaul with porting, polishing, flow-matching and balancing for some additional performance and, I would like advice/recommendations on the best performing climb prop. Not concerned about top speed... Thanks!
 
Should also mention that the 180hp conversion also gives a huge increase in useful load. Our CAP 180hp P model has a useful load of 1,050lbs.
 
labbadabba said:
Should also mention that the 180hp conversion also gives a huge increase in useful load. Our CAP 180hp P model has a useful load of 1,050lbs.
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Not by itself. You also have to limit flap travel on those models with 40 deg flaps (i.e., almost all of them).
 
labbadabba said:
Should also mention that the 180hp conversion also gives a huge increase in useful load. Our CAP 180hp P model has a useful load of 1,050lbs.
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MAKG1 said:
Not by itself. You also have to limit flap travel on those models with 40 deg flaps (i.e., almost all of them).
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True. I have a 172N with the Air Plains 180 hp conversion. We bought both the engine STC and the flap limit/MGW increase STC. But we never installed the flap limiter. MGW is still the original 2300 lb and useful load is only 770 lb, but we still have 40 degrees of flap. I like short fields and have no friends, so for now it'll stay that way.

But that decision is moot as to the 172P (1981-86). Those came from the factory with 160 hp and only 30 degrees of flap travel (to get a 100 lb MGW boost over the 172N), so the engine swap automatically qualifies it for the 2550 lb MGW.
 
Tom Redman said:
Hi. I'm on the other side of the equation. Most of my flying is within an hour of Talkeetna, AK and I'm all about getting the best take-off performance with my little C172G with Cont O-300. Were doing an overhaul with porting, polishing, flow-matching and balancing for some additional performance and, I would like advice/recommendations on the best performing climb prop. Not concerned about top speed... Thanks!
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Tom, your question deserves it's own thread and photos of your ship as you progress thru the overhaul. Would really enjoy following along on your journey...pull up a chair & stay awhile.
 
iflyvfr said:
Tom, your question deserves it's own thread and photos of your ship as you progress thru the overhaul. Would really enjoy following along on your journey...pull up a chair & stay awhile.
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Thank You! Any advise on the best climb Prop to use?
 
charlie said:
I left Penn Yan 25 years ago so I don't recall what the climb was like at 5,000 at gross. IIRC the M uses a 57" pitch prop but it's a whole different McCauley prop. A constant speed prop gives a slight improvement in takeoff and climb with no improvement in cruise. Also the CSP does not facilitate increasing the MGW to 2550#.
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At 2400 RPM cruise and with a pitch increase of 3" (57" to 60") the theoretical increase in cruise speed is 6.8 mph with 100% efficiency. It will never be 100% efficient so my thought is 5 mph increase will still be likely going to the cruise prop. And on a 300 mile trip the difference still works out to a tenth of an hour total or less depending on the amount of climb to altitude. On a 150 mile trip the difference in additional speed will mostly be offset by the increased time to climb to cruising altitude. My advice is stick with the climb prop scenario, if during climb you are exceeding red line on your engine then add an inch or two of pitch. CSP though is a different scenario.

Tom, get your engine done and try your existing prop and see what your RPM's are in a steep climb and shallow climb. Do you know what the pitch is now?
 
There are some really cool mods out there but they can be pretty expensive for the limited increase in performance - unless you have to do something like an engine overhaul anyway. A late model 172 was pretty well refined as an economical airplane over many years by the factory.
 
Briar Rabbit said:
At 2400 RPM cruise and with a pitch increase of 3" (57" to 60") the theoretical increase in cruise speed is 6.8 mph with 100% efficiency. It will never be 100% efficient so my thought is 5 mph increase will still be likely going to the cruise prop. And on a 300 mile trip the difference still works out to a tenth of an hour total or less depending on the amount of climb to altitude. On a 150 mile trip the difference in additional speed will mostly be offset by the increased time to climb to cruising altitude. My advice is stick with the climb prop scenario, if during climb you are exceeding red line on your engine then add an inch or two of pitch. CSP though is a different scenario.

Tom, get your engine done and try your existing prop and see what your RPM's are in a steep climb and shallow climb. Do you know what the pitch is now?
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Hi. It's the stock Propeller so far as
I know. A low time airframe of 2300 hrs with one overhaul. It's a 1966 172G model. I'll take a look at the prop and get numbers. Thx!
 
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