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  1. #1
    speedskixp's Avatar
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    max prop tweaking?

    How far can you tweak the trailing edge of a 4 blade prop before it is not efficient anymore. I ask because we have 2 boats running the ET 68-140 chargers, one with stock ecu and 1 with rr ecu. We both started with 15/20 r's. I have added 4mm to the trailing edge of mine and added an 81mm ring and still cant get my r's below 8150+. My boat is flying. I ran a 78.9 with 1 bar less than a full tank in 78degree weather @ 8150+ but it wont take much of a drop in temp to put me hard on the limiter.
    We are having the same problem with the rr ecu boat also. It is still pegging the limiter @8600 with 4.5 mm added to the trailing edge.

    I just dont know if adding anymore pitch will help the speed or just pull down the rpm's.
    How far can you pitch the trailing edge before you have to change the entire pitch.
    Does anyone make a 14/24 or any thing like that in a 4 blade?
    I hear the 15.5/22.5 3blades are hard to turn but I wonder if with the cooler temps if it would be possible with the chargers.
    Any input would be appreciated.


  2. #2
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    Jim,

    I'd send it back to Solas/Skat and have a 1 full degree added to your prop.. Adding mm to the trailing edge works but you'll be much happier with a re-pitched prop.

    Alex
    Quote Originally Posted by speedskixp View Post
    How far can you tweak the trailing edge of a 4 blade prop before it is not efficient anymore. I ask because we have 2 boats running the ET 68-140 chargers, one with stock ecu and 1 with rr ecu. We both started with 15/20 r's. I have added 4mm to the trailing edge of mine and added an 81mm ring and still cant get my r's below 8150+. My boat is flying. I ran a 78.9 with 1 bar less than a full tank in 78degree weather @ 8150+ but it wont take much of a drop in temp to put me hard on the limiter.
    We are having the same problem with the rr ecu boat also. It is still pegging the limiter @8600 with 4.5 mm added to the trailing edge.

    I just dont know if adding anymore pitch will help the speed or just pull down the rpm's.
    How far can you pitch the trailing edge before you have to change the entire pitch.
    Does anyone make a 14/24 or any thing like that in a 4 blade?
    I hear the 15.5/22.5 3blades are hard to turn but I wonder if with the cooler temps if it would be possible with the chargers.
    Any input would be appreciated.

  3. #3
    speedskixp's Avatar
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    Quote Originally Posted by Alex13 View Post
    Jim,

    I'd send it back to Solas/Skat and have a 1 full degree added to your prop.. Adding mm to the trailing edge works but you'll be much happier with a re-pitched prop.

    Alex
    Thats pretty much what I was thinking but I'm not sure if that will be enough. I guess all I can do is try and try again.

  4. #4
    S2R's Avatar
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    Quote Originally Posted by speedskixp View Post
    How far can you tweak the trailing edge of a 4 blade prop before it is not efficient anymore. I ask because we have 2 boats running the ET 68-140 chargers, one with stock ecu and 1 with rr ecu. We both started with 15/20 r's. I have added 4mm to the trailing edge of mine and added an 81mm ring and still cant get my r's below 8150+. My boat is flying. I ran a 78.9 with 1 bar less than a full tank in 78degree weather @ 8150+ but it wont take much of a drop in temp to put me hard on the limiter.
    We are having the same problem with the rr ecu boat also. It is still pegging the limiter @8600 with 4.5 mm added to the trailing edge.

    I just dont know if adding anymore pitch will help the speed or just pull down the rpm's.
    How far can you pitch the trailing edge before you have to change the entire pitch.
    Does anyone make a 14/24 or any thing like that in a 4 blade?
    I hear the 15.5/22.5 3blades are hard to turn but I wonder if with the cooler temps if it would be possible with the chargers.
    Any input would be appreciated.
    R&D has a 14/24 on their sight under X boat products.

  5. #5

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    Adding mm to the trailing edge does change the angle, depending on how you do it. I have a 15/20 that was re-pitched by IMPROS to 15/24. I measured it my self to verify and it was accurate. The trailing edge is very close to 4 mm lower than stock, too. That prop went 81 mph at 8100 rpm using an 81 mm ring (is 81 the new 23?). The only real difference is that a true "re-pitch" will start bending further forward on the blade than a "trailing edge tweak".

    That said, I still ran out of prop, so I went to the 15.5/22.5 and later a 15.5/23 from Skat. I found that these props ran the same speeds at the same boost levels as the Solas, but less rpm. Remember, with the turbo you don't have to hit 8100 rpm to get max boost. I ran ~81 mph with both the Solas and the much steeper Skat at the same boost level, but the Skat was turning 400 rpm less.

    Inefficiency starts falling off as soon as you start bending a prop. The more you bend, the worse the efficiency will be due to the disparity between the root and tip angles. I actually bent a stock RXP prop to 16/25 or so and went 76+ mph at 8100 rpm on the stock nozzle, but it took 13+ psi boost to get there meaning the efficiency of the prop/pump was poo.

    I think the stock X prop is 14/24. I tried one once and if I remember right, it performs really close to a 15/20. The trailing edge has a significant "hook" to it, which is where the 24 comes from. The majority of the prop is not 24 pitch.

  6. #6
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    Quote Originally Posted by speedskixp View Post
    Thats pretty much what I was thinking but I'm not sure if that will be enough. I guess all I can do is try and try again.

    Tell them on the phone how many RPM's your turning now and how many RPM's you'd like to be turning after and they will do the rest.

  7. #7
    speedskixp's Avatar
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    Quote Originally Posted by engineermike View Post
    Adding mm to the trailing edge does change the angle, depending on how you do it. I have a 15/20 that was re-pitched by IMPROS to 15/24. I measured it my self to verify and it was accurate. The trailing edge is very close to 4 mm lower than stock, too. That prop went 81 mph at 8100 rpm using an 81 mm ring (is 81 the new 23?). The only real difference is that a true "re-pitch" will start bending further forward on the blade than a "trailing edge tweak".

    That said, I still ran out of prop, so I went to the 15.5/22.5 and later a 15.5/23 from Skat. I found that these props ran the same speeds at the same boost levels as the Solas, but less rpm. Remember, with the turbo you don't have to hit 8100 rpm to get max boost. I ran ~81 mph with both the Solas and the much steeper Skat at the same boost level, but the Skat was turning 400 rpm less.

    Inefficiency starts falling off as soon as you start bending a prop. The more you bend, the worse the efficiency will be due to the disparity between the root and tip angles. I actually bent a stock RXP prop to 16/25 or so and went 76+ mph at 8100 rpm on the stock nozzle, but it took 13+ psi boost to get there meaning the efficiency of the prop/pump was poo.

    I think the stock X prop is 14/24. I tried one once and if I remember right, it performs really close to a 15/20. The trailing edge has a significant "hook" to it, which is where the 24 comes from. The majority of the prop is not 24 pitch.
    Thanks for the info Mike. I knew you had played alot with this. Infact I was going to send you a PM on this if you did not respond to this thread.
    The problem I am having is a good one but every time I get it dialed in close it gets cooler the next week. What prop do you think I should start with? Should I try a 15.5/22.5 3blade or is there a four blade with a root angle that may work?

  8. #8
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    Quote Originally Posted by Alex13 View Post
    Tell them on the phone how many RPM's your turning now and how many RPM's you'd like to be turning after and they will do the rest.
    I know what you are saying but I'm not sure the root angle on the 15/20 will work and still be efficient. I would love to be able to buy a prop that is close out of the box for the cold weather.

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    Quote Originally Posted by speedskixp View Post
    I know what you are saying but I'm not sure the root angle on the 15/20 will work and still be efficient. I would love to be able to buy a prop that is close out of the box for the cold weather.
    I think I'm gonna buty a speed freak modded 15/22 and give it a shot for top speed runs

  10. #10
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    Quote Originally Posted by Alex13 View Post
    I think I'm gonna buty a speed freak modded 15/22 and give it a shot for top speed runs
    I would be curious to try this also but it seams like he is depitching it on the leading edge. I think it comes out to be a 13/23. Atleast the one he pitched for Steve that is. The 15/22 still has the 15/20 root angle though.

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