I fly an 80hp Rans S-7. I'm going to upgrade my pistons which will goose my hp to about 95. My 2-blade Warp prop is a bit beat-up and needs an overhaul. I'm wondering, however, if I wouldn't be smart to just change to a new 3-blade prop. I know most of you guys fly larger and more powerful aircraft, but if any of you flying lower-powered and lighter aircraft and would offer your views or experiences concerning prop issues, I'd be very grateful.

Thanks to all of you as well. I have learned a ton simply reading and searching the posts.

Chip

I believe that generaly you go faster with a two blade than three blade. Smoother and quieter with a three blade.

Tim

qmdv wrote:I believe that generaly you go faster with a two blade than three blade. Smoother and quieter with a three blade.

Tim

Tim - It' s my understanding that the "go faster" part of the equation has more to do with how the prop is pitched than the number of blades it has ... the fastest production piston aircraft (military) had four bladed props, and some of the fastest turbo props have even more blades; in a couple of cases they used dual counter-rotating props to get the most speed out of the engine and airframe.

The more blades the smoother the aircraft, certainly. And a three-bladed prop can be a little smaller diameter than an equivalently-pitched two-blade, which can help with prop clearance on backcountry airstrips - it's more of an issue with tri-gear than taildraggers.

nmflyguy wrote:

qmdv wrote: Tim - It' s my understanding that the "go faster" part of the equation has more to do with how the prop is pitched than the number of blades it has ... the fastest production piston aircraft (military) had four bladed props, and some of the fastest turbo props have even more blades; in a couple of cases they used dual counter-rotating props to get the most speed out of the engine and airframe.

No problem with what you said except that as the HP goes up, the more prop you need. You have four blade props cus if you had two blades you would have them so long that the tip speeds wuold be too fast. Add 10 % hp to my 182 and the stock prop would be OK. Ad 50% then you have a different situation.

tim

nmflyguy wrote:Tim - It' s my understanding that the "go faster" part of the equation has more to do with how the prop is pitched than the number of blades it has ... the fastest production piston aircraft (military) had four bladed props, and some of the fastest turbo props have even more blades; in a couple of cases they used dual counter-rotating props to get the most speed out of the engine and airframe.

Three blades have more drag than two. Generally, three blade will cost you a few knots of speed in exchange for better climb, smoother operation and improved ground clearance.

They are designing some neat three-bladers nowadays that have almost erased the increase in drag. As Tim said, the higher horsepower turbines need the extra blades to harness the engine else the two blades would need to be 12 feet long

You probably won't notice alot of speed difference in your S7.
A slicker plane design the speed difference will be more pronounced.

as 62Leemer says; You will gain some prop clearance because of the smaller diameter.
Also you may have a little shorter take off roll

A few guys around here are using the Ivo adjustable propeller. You can get an electric governor for them.

I've always thought that one of those electrically controlled Ivo props would be a pretty slick deal-- dial her flat for takeoff, then coarse for cruise. Even a ground adjustable would be cool-- set at coarse pitch for the cross-country flight to Idaho (or wherever), then flatten her out at the last stop before you hit the back country.
But the Ivo prop blades themselves seem kinda cheesy and flimsy. Does the airfoil they utilize perform well? I see Sensenich has a ground adjustable prop now, I think maybe some light sport Cubs are using them?

I have tried a few diferent props on my Avid and always come back to the IVO IFA. I have been running a 72" 3 blade for awhile on the Kitfox and Avid. One day for shits n grins I decided to go from 3 blade to 2 blade just to see what it would do. With the IFA I can dial in the pitch to exactly where the engine likes it for max performance in all flight phases. It takes about 15 minutes to go from 3 blade to 2 blade by putting in spacer blocks. The test flight was on floats, and RPM for RPM ( I used the same max RPM at WOT) Took me alot longer to get off the water, and climb SUCKED. At the end of a 6000' long lake where I would normaly be at about 700' I was skimming the tree tops looking for the smallest diameter tree I could find to drag the floats through. One turn around the lake and I changed my prop back to 3 blade and my drawers, and not in that exact order. I have not tried it on wheels or skis, but I know that lot of guys are running a 2 blade on the same type plane and love it. Maybe I will try it when I get back home this time and see how it compares on skis.

The consensus on the IVO with the KF crowd is that the 80 hp 912 likes the ultralight prop, but higher HP engines may benifit from the IVO medium. I am working on adapting a 2 stroke I have to take the rotax gear box, and that should give me a minimum of 130 HP on take off ( I could easily go 140 but I was planning on running it at the same limited RPM that the 582 uses) and I will be running the Medium blades on that engine.

nmflyguy wrote:

qmdv wrote:I believe that generaly you go faster with a two blade than three blade. Smoother and quieter with a three blade.

Tim

The more blades the smoother the aircraft, certainly. And a three-bladed prop can be a little smaller diameter than an equivalently-pitched two-blade, which can help with prop clearance on backcountry airstrips - it's more of an issue with tri-gear than taildraggers.

The smooth part is especially true if you are running a two stroke engine where the two cylinders on power stroke tend to cause harmonic and shock at exactly the same spot on ignition at the same point in the rotation each time the piston fires with a two blade prop. The three blades caused that to be spread out. I ran a 68" Ivo ground ajustable on the 582 and a 68" DUC on the Simonini, both were on the 701 which is a nosedragger. With the big nose wheel I had 9" of ground clearance to the prop.

Nice job on the comparison. It means a lot more when you can fix some of the variable like you did: same plane, same day, just two vs three blades.

I've thought about adding the IFA to my IVO prop. How much difference in pitch gets you from max takeoff setting to most economical cruise?

tom

I took the plunge and ordered a 3-blade Kiev. The upgraded pistons appear to have increased single person, full-fuel climb by about 300-400fpm using my beat-up Warp. I should have the Kiev in January and I'll let you know how I like it. It was overwhelmingly praised by all those with whom I spoke and I'm looking forward to it. The only thing I'm still uncertain about is where I'm going to get a new spinner without blowing my brains out cost-wise.

Savannah-Tom wrote:Nice job on the comparison. It means a lot more when you can fix some of the variable like you did: same plane, same day, just two vs three blades.

I've thought about adding the IFA to my IVO prop. How much difference in pitch gets you from max takeoff setting to most economical cruise?

tom

I have never put a pitch gauge on it to be able to accurately answer the question, however, on floats I did do a test once. I set the prop to 66-6800 as soon as I come in with the power. This gives me max to pull it on top of the water, once I start gaining speed I bump the pitch a couple times to keep it around 6500 for the rest of the take off run and climb out. Once I have reached the altitude I want, I keep bumping in the pitch till I am able to go level, WOT about 6400 to 6500, then pull the power back to 5800 and dial in the EGT and fuel burn with the needles. I know based on the fuel flow meter, EGT and several plug readings that at 5800 and 1150 EGT at sea level to 1000' I will be running at 5.1 to 5.2 GPH depending on AOT. The higher I go the less the fuel burn as I lean it out.

With a 2 stroke, if you keep the power in and begin a decent your EGTs will go through the roof and you will burn the engine down if you let the prop drive the engine. For decent and landing I twist in one turn to richen the mid range mixture, bump the prop pitch back to take off setting and pull the power as needed to keep the EGTs in check. One day I decided to leave the prop pitch set at cruise and land, come to a stop (on floats) then take off to see what the T.O. RPM would be. I was only able to get 4600 or 4680 RPM and was not able to even get on step with the prop set for cruise. I used up about 4000' of lake trying every trick in the book to get it on step and just could not do it with the prop set for cruise.

Savannah-Tom wrote:.....I've thought about adding the IFA to my IVO prop. How much difference in pitch gets you from max takeoff setting to most economical cruise? tom

I would think a controllable prop'd be a no-brainer. How much does the in-flight-adjustable set-up cost, and how much does it weigh? I would love to have some sort of controllable prop on my C150/150-- in some ways a simple adjustable type ight be preferable to a constant speed. The weight & cost (and approval issues) are what stops me.

For the medium IVO, the cost is about $1200 and 12# additional weight.

tom

Savannah-Tom wrote:For the medium IVO, the cost is about $1200 and 12# additional weight.

tom

Wher are you getting the Medium IFA for 1200??? Let me know and I will order one today. That is what I paid for the Ultralight IFA. The Medium is closer to 2600 and 19 pounds.

akavidflyer wrote:

Savannah-Tom wrote:For the medium IVO, the cost is about $1200 and 12# additional weight.

tom

Wher are you getting the Medium IFA for 1200??? Let me know and I will order one today. That is what I paid for the Ultralight IFA. The Medium is closer to 2600 and 19 pounds.

Sorry I wasn't clearer. That is the incremental cost and weight in adding the inflight adjustable stuff to an existing IVO prop. For an additional $300 you can get a constant speed controller as well. I'm with a previous poster that I'd rather be the "controller" and skip the constant speed part.

tom

What a bargain compared to certificated airplanes! I understand that MT has a controllable (not c/s) prop, which could be retrofit onto my airplane. But I think the price tag after the dust settles is probably close to $10K for all the stuff. If I could legally hang a 19# controllable prop on mine for $2600, I'd be on it like a bum on a baloney sandwich.

A buddy up here put the MT prop on his cub. After flying it on floats, wheels ans skis, he went back to the Hartzel cause the MT just did not pull worth a darn. The Beta was cool on floats, but she just would not pull as hard as the big metal blades for what ever reason.

akavidflyer wrote:A buddy up here put the MT prop on his cub. After flying it on floats, wheels ans skis, he went back to the Hartzel cause the MT just did not pull worth a darn. The Beta was cool on floats, but she just would not pull as hard as the big metal blades for what ever reason.

Which MT are you referring to?? Numerous Husky drivers (Lyc O-360) have switched to the two blade constant speed MT (either 205 or 210 cm). In all flight regimes it slightly bests the Hartzell 80". It is over 25 lb less weight, spools up faster, acts as a better brake for a steeper descent profile. More better in every way - - well, except cost. But even that's better long term, as Hartzell has a nasty habit of condeming their hubs now and then. Plus you can field repair little dings with epoxy - no filing notches of metal to get rid of stress risers as with an aluminum blade.

IVO...ya...I know to much about that prop,wont use one.
Warp Drive or PowerFin Are good props dont know about the Kiev.
Still again Ivo manufacturing QA not so good, I wouldnt touch one with a 10 ft pole.