Need some sage advice from those who know such things. My little Luscombe is not climbing that well, though it cruises at about 110 mph, which is OK for 85 horses. (of course my 5000 ft. msl is a factor)
I always hear about climb props vs. cruise. In Alaska, the Super Cubs had Borer props. Climbed great.
Now, here is the part I am puzzled about. Looking at a performance chart for the 182A I fly, every drop in RPM also drops the airspeed. If you want to go fast, you spin the prop fast. Simple. So, in a fixed pitch plane, how is it you can have your prop changed.... do they flatten it out for climb? If so, it is spinning faster in cruise and should go faster... right? I have always heard you choose one or the other.
When I think about what I see happen in the CS prop on my 182.. I don't see how that observation translates to my fixed pitch install. Anybody got a simple explanation? Thanks and have a great Sunday.

Its a trade off. The climb prop is longer and flatter giving you more thrust, but less speed. On my pacer I went from something like a 74X56 to an 82X41 so for each rotation of the prop I theoretically lost 15" of forward travel. The cruise prop would only give me around 2200 RPM on take off, but at cruise at 2350 I was truing out around 115. With the borer prop, I could turn 2500 on take off and at 2450 cruise I was getting around 92-95. The difference in climb was well worth the traded speed. On full lotus floats, 3 guys and full fuel I could pull up vertical and then do a tail slide backing down at 400 FPM. Climb solo was in the 1800 FPM range and loaded I still got over a 1000 FPM. Take off went from around 800' to less than 250'.

I remember the flight school I went to years ago had a few C-172...some were great for climb and some others for cruise...so for my long commercial x-try I always took the one who cruised the fastest and to play in the mountains I took the one who climbed best...the only difference between the two props was the built in angle... so when you change your prop, you need to make the decision whether you want a climbing prop or cruise prop... Buddy has a luscombe here, it performs quite well, I can ask about his set up if you wish. Cheers, BCT

In the two C150's I have had, the 2" difference between a climb prop and the standard setting gave me about 5-7 mph. The choices I have are 48"=climb, 50"=standard and 52" for a cruise prop. They are all the same length the pitch is how many inches forward it will go in one revolution.

You should check and see what your static runup RPM should be. Pitch the prop so it will let you take it to the upper limit. If you can get the RPM's close to redline in climb, your engine is producing maximum power and you'll be getting your best climb performance. More power equals more thrust.

I can't remember what each pitch will change the RPM but it is here on the site somewhere or someone else can post it. Altitude will also effect that too so what works here at 4500' might over rev an engine at sea level because it would be able to produce more power there.

Before you start twisting the prop, I'd make sure the engine is in good shape and running right. You don't want to set up the prop and find out you can make more power or you have a weak cylinder.

BCT, If you don't mind.... check with your Luscombe owner friend and see what his prop is.
Obviously I can't change the length of the prop. I get about 2250 rpm on takeoff. Not even close to redline.
I can hit redline in cruise though... so that warning not set it up for overspeed is a good one.

Better check the Type Certificate for your plane and engine and prop..there may be only certain props that will work on your engine. If you have the correct prop they can be retwisted by a certified prop shop. Find a prop shop in your area or check with your IA to find out the particulars. The last time I had the prop on the C-170 overhauled the guy asked me if I wanted the prop the same ( climb) or if I wanted it rebuilt as a cruise. We rebuilt an A-75 on a Cub and come to find out there is only one prop for that engine in that airplane with that motor. I bought a used prop from someone to save $$$, but when it came the IA and myself checked it..it was 1/2 inch too short even though it had the right prop number on it. The last time it was rebuilt, it was shortened just a little too much. Had to have a new one built from the factory because there were none in stock.
The rebuilt prop could have been used on other setups but not on our combination of motor and plane.
HC

HC, appreciate the good advice. Could make an expensive mistake by not doing homework.
Never done that before.....

flightlogic wrote:BCT, If you don't mind.... check with your Luscombe owner friend and see what his prop is.
Obviously I can't change the length of the prop. I get about 2250 rpm on takeoff. Not even close to redline.
I can hit redline in cruise though... so that warning not set it up for overspeed is a good one.

I've sent the 2 guys who have on an e-mail with your info and asked them about their set up, prop/engine. Will report back to you soon, BCT

HC's advice is good and another thing you might want to consider is that unless you know your prop is OK, I would keep it out of a Prop Shop. I sent my prop off a 172B in to get it repitched to a climb prop. They didn't red tag it but refused to work on it since I didn't have a prop log and there was microscopic corrosion on it by the bolt holes. Every one told me to just throw it back on but I went with a new prop instead. Funny how they can stamp letters and numbers in a prop, but if there is corrosion that you can just barely see, it is no good.

Here is my experience with a 170b. It might help. I have a 145 hp engine and I had a 76 inch prop with a 53 inch pitch. 7653. It cruised at 108kts. It was slow to climb and had longer takeoff runs. The other thing we noticed was with the old prop we seemed to fall off the cruise speed easily. Any turbulence or unintentional altitude deviation would slow us down. It would take forever to get back to 108kts.
We then bought a 7851 prop. It seemed to be the sweet spot for the airplane. Cruised at 103 kts but stayed there, never slowed. It climbed quicker and takeoff perfermance was better.
And it overall didn't slow us down. On the average 2 hour flight we spent less time at 80kts in climb and more time at 103 kts in cruise so the overall flight time was less.

my 2 cents.

My C150/150TD was originally fitted with a 74-54 Sensenich when the engine conversion was done up in Alaska. When I bought it, rebuilt after a wreck, it had a 74-52. Too flat, redlined immediately when firewalled in level flight. Tried have it repitched, but some paperwork issues on that prop prevented it. I tried a friend's 74-58 (which is the prop listed for this application) but it was too much-- poor takeoff & climb but OK after it had a chance to wind out, wouldn't quite hit redline though. After much thought, I bought a brand new 74-56 from Art Matson with his tip mod, which is supposed to let it turn up like it's 2" flatter. Nope, turns up about like a 56 should-- takes off & climbs pretty good and will hit redline or a bit over in level flight. I would like a bit better takeoff so this winter I'm planning on repitching it down to 54. I understand that 3 inches of pitch change equals about 100 rpm, so this oughta give me about 70 rpm more at takeoff-- should give me the increased performance I want but still let me cruise along at 120-125, just at a bit higher rpm. I'm hoping that whoever did the engine conversion knew what he was doing & that this 54" pitch is the "sweet spot" for this airplane.

What one prop shop will reject as not airworthy for a hint of microscopic corrosion-another shop will pass.

Story:
It has been probably15+ years ago when an AD came out that my partnership C182 prop had to be inspected and serviced. We sent it off to a prop shop in the greater Seattle area where it was promptley ruled as not serviceable due to corrosion. We ask them to return it to us, which they did. Neither my A&I, nor a friend A&I, could understand it, so I decided to take it personally to the Troutdale prop shop so they could show me where the problem was since I was headed to Portland anyway and would drive right by there. They agreed ahead by phone to do the favor of showing me the problem with the prop. After examining the prop halves he (shop owner) got a funny look on his face and wanted to know who had rejected it. I told him. He indicated a good friend of his owned and operated that shop. My heart sank. Then he said he would pass it on ONE condition-that I say absolutely nothing to anybody about it and especially to the other prop shop. Make absolutely NO waves-even small ones. He said the only thing he could understand would be that the owner was gone and one of his men rejected it....or his friend was in a really pissy mood that day. I happily/hastily agreed to the condition and left it with him for further testing/examining. That prop has been frequently flying just fine ever since. My then partner and I now each own 182s and he has that plane locally and we stay in regular contact.

So keep it quiet, guys!
We were both poor-and he did us a big favor!
lc

I forgot to say as Littlecub pointed out..maybe wouldn't hurt to check the prop yourself BEFORE you take it to the prop shop (as was pointed out to me), the prop has to have enough MEAT on it before it can be overhauled. If the prop shop measures it prior to overhauling it, and there is not enough material there to bring it to specs, all you have left is a red tagged paperweight.
HC

?

First, look at the propeller specs on the Luscombe Type Certificate, here: http://rgl.faa.gov/Regulatory_and_Guida ... enDocument

Be sure to check the propeller limits and models for YOUR model of airplane.

It doesn't appear to me that the TCDS limits prop pitch on these airplanes, but rather it limits static rpm. Which effectively limits pitch....

For best performance, I like to see a propeller turn up really close to the engine's red line (max rpm) in level flight, full throttle, at a reasonable altitude, say 2,000 feet msl.

With a fixed pitch prop, that pretty much dictates static rpm.

And, you can't compare fixed pitch to constant speed props, frankly.

MTV

MTV, sounds like the first place I got off track was trying to compare a fixed pitch and constant speed prop and the resulting airspeeds at different RPM's.
I looked up the static rpm values in the type certificate (thanks for the link) and I am not allowed much more spin than I am getting. This winter, I will try some lower altitude flights (normally the big city gives me nose bleeds... so I won't go there) and see what climb performance I get. Maybe I was just too optimistic for a little 85 horse engine over a mile high.

buzzlatka wrote:Here is my experience with a 170b. It might help. I have a 145 hp engine and I had a 76 inch prop with a 53 inch pitch. 7653. It cruised at 108kts. It was slow to climb and had longer takeoff runs. The other thing we noticed was with the old prop we seemed to fall off the cruise speed easily. Any turbulence or unintentional altitude deviation would slow us down. It would take forever to get back to 108kts.
We then bought a 7851 prop. It seemed to be the sweet spot for the airplane.

I was looking for this info. I have the O-300 and 7653 on the current POS I'm flying. My experience exactly with this prop... It doesn't climb well, doesn't cruise well, doesn't do much of anything well. I was gonna send it out to the prop shop next month with the annual, but now I think I'm gonna shitcan the thing and put something else on there.

Gump

Gump,

Yeah, shitcan that prop and the engine and put a real motor on that thing.....

Sorry, couldn't resist. The "seaplane" props seem to be the ticket for the 170 with the O-300.

MTV

How about a turbo O-300?...wirth nitros?

Gump,
I have a buddy with the stock 145 and prop in a 170A and another with a 57 C172. They both flattened their props to (I think) a 51 pitch.
It made a big difference in climb....I know when you level off you better have your hand on the go juice or they will over rev. I'm sure it cost them some cruise, but....
I could get more details if you want.