Shrike 40 with thinner airfoil
12-16-2012, 07:41 AM
#101
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RE: Shrike 40 with thinner airfoil
ORIGINAL: Speedy-Gonzales
(1) You got some pics of these hinges? I'm interested in anything new or at least new to me!
(2) Have you done anything with the Shrike plans I sent you??
(3) Did you tell ''Santa'' I want a SD kit for Christmas???
(1) You got some pics of these hinges? I'm interested in anything new or at least new to me!
(2) Have you done anything with the Shrike plans I sent you??
(3) Did you tell ''Santa'' I want a SD kit for Christmas???
On 1/2A models I have successfully made continuous hinges on 3/32" sheet stock with a Dremel router table and the paper-thin circular saw cutter that comes with some sets (that should be outlawed but it works great for this) supported with 1/32 ply. I cut a slot in each side then slid in a strip of Coverite fabric covering, then CA. Works like a champ, but a bit fiddly at first.
(2) Yes, I have made some headway on a CAD design of a revised version, but there is quite a bit of work to do yet.
(3) Santa's cool with that, but it won't make it for Christmas. I am taking two weeks off over the holidays, I hope to make some headway on a kit run with the time off. Progress has been dismal so far, I've been working M-F 10-12 hours/day for ages and sideline tasks keep getting bumped.
12-16-2012, 07:54 AM
#102
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RE: Shrike 40 with thinner airfoil
ORIGINAL: Speedy-Gonzales
CBP,
Drop me some names for where I might find CF props in this range from custom manufacturers? I'm always concerned about throwing a blade above 22K with standard GFN APC's. I'm still running on a few 12 packs of RevUp wood pylon props and massaging them with a Prather pitch gauge.
CBP,
Drop me some names for where I might find CF props in this range from custom manufacturers? I'm always concerned about throwing a blade above 22K with standard GFN APC's. I'm still running on a few 12 packs of RevUp wood pylon props and massaging them with a Prather pitch gauge.
The other source is ZZ Props, you can find them through C/L speed forums (try ZZCLspeed at Ay Oh Ell dot com). His selection is much smaller, but the props come with far less finishing work needed. He has a few props in the right general range depending on the engine:
8x8 (couple of versions)
7 x 7-3/4
7x8
8x8-1/4
7-3/4x8
8-3/8 x 8-1/2
This is where I got all my D speed props.
12-18-2012, 04:36 PM
#103
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RE: Shrike 40 with thinner airfoil
Finally some time to play with the engine , I switched the prop to 9x10 APC , fuel Power Master 15% nitro and I added castor oil Klotz to bring it at 20% oil , and tuned pipe 10 cc , tach read was just 17,500 RPM.
I think is time to start with the dremel job on the sleeve to raise the exhaust timing. I did a wheel degree and measured the stock timing wich is 150°. I'm plannig also make the exahust timing wider as it looks a bit narrow compared with the crankcase.
I'll probably start raising 5° each time and have a tach reading between each mod. to see if there is any RPM gain.
GOD bless me !!
I think is time to start with the dremel job on the sleeve to raise the exhaust timing. I did a wheel degree and measured the stock timing wich is 150°. I'm plannig also make the exahust timing wider as it looks a bit narrow compared with the crankcase.
I'll probably start raising 5° each time and have a tach reading between each mod. to see if there is any RPM gain.
GOD bless me !!
12-18-2012, 04:51 PM
#104
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RE: Shrike 40 with thinner airfoil
17,500 sounds to me like a 10cc pattern engine on a 9x10 prop.
What is the pipe length, plug center to fat part of the pipe? The picture could be deceiving but that header/pipe system looks really short, I wonder if you are right off resonance. Bear in mind, for tuning a piped system like this, best to trim a good 10% off the diameter of the flight prop and then trim pipe length to max ground rpm on that setup. If the engine/pipe system is hyperactive enough, 15% is more like it. I'd go 10% with this engine unless you go ape with the timing.
What is the pipe length, plug center to fat part of the pipe? The picture could be deceiving but that header/pipe system looks really short, I wonder if you are right off resonance. Bear in mind, for tuning a piped system like this, best to trim a good 10% off the diameter of the flight prop and then trim pipe length to max ground rpm on that setup. If the engine/pipe system is hyperactive enough, 15% is more like it. I'd go 10% with this engine unless you go ape with the timing.
12-18-2012, 05:17 PM
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RE: Shrike 40 with thinner airfoil
MJD , please dont pay atention on the picture above as reference on the set I described on my last post , that picture is with the 7.5 cc pipe , it was taken about 2 months ago.
The real measure ( pictures below ) is 11-1/5" from plug center to fat part of the pipe (just behind the fitting) and from plug center to the end of the pipe is 17-3/4".
I'll test with 10% nitro and see what it drops.
The real measure ( pictures below ) is 11-1/5" from plug center to fat part of the pipe (just behind the fitting) and from plug center to the end of the pipe is 17-3/4".
I'll test with 10% nitro and see what it drops.
12-18-2012, 05:26 PM
#106
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RE: Shrike 40 with thinner airfoil
Have you flown the plane yet? I would give it a throw ( as is ) to see how it performs, get a good feel for it, and see how it comes up on the pipe. 17.5K is low but at least you will have had the plane in the air and get some feel for it before going ballistic with it.
To me it would seem that the airframe presents more limitations than the engine.
I'm sure you will get some "pucker factor" the way it is now!
Speedy Gonzales
To me it would seem that the airframe presents more limitations than the engine.
I'm sure you will get some "pucker factor" the way it is now!
Speedy Gonzales
12-18-2012, 05:39 PM
#107
RE: Shrike 40 with thinner airfoil
SB..your plane looks SUPER[:-]!!
Remember that the engine will lose torque when the exhaust pressure leaves the cylinder early...but you gain high rpm ability.
So......your engine will become very critical about the amount of diameter it will turn. You have an airframe that should be clean enough and small enough to make a 8+ inch diameter prop work if the rpm is there. The real work isn't just doing the engine mods. The real work is finding the correct prop that compliments the engine mods. With a high timed speed engine [180 degrees or higher] you want to start your search UNDER PROPPED so that the engine runs cool and stays happy. Gradually you try bigger combinations of pitch, diameter, blade area and blade thickness until the engine starts showing signs that it can't handle it.
Remember that the engine will lose torque when the exhaust pressure leaves the cylinder early...but you gain high rpm ability.
So......your engine will become very critical about the amount of diameter it will turn. You have an airframe that should be clean enough and small enough to make a 8+ inch diameter prop work if the rpm is there. The real work isn't just doing the engine mods. The real work is finding the correct prop that compliments the engine mods. With a high timed speed engine [180 degrees or higher] you want to start your search UNDER PROPPED so that the engine runs cool and stays happy. Gradually you try bigger combinations of pitch, diameter, blade area and blade thickness until the engine starts showing signs that it can't handle it.
12-18-2012, 06:03 PM
#108
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RE: Shrike 40 with thinner airfoil
ORIGINAL: combatpigg
SB..your plane looks SUPER[:-]!!
Remember that the engine will lose torque when the exhaust pressure leaves the cylinder early...but you gain high rpm ability.
So......your engine will become very critical about the amount of diameter it will turn. You have an airframe that should be clean enough and small enough to make a 8+ inch diameter prop work if the rpm is there. The real work isn't just doing the engine mods. The real work is finding the correct prop that compliments the engine mods. With a high timed speed engine [180 degrees or higher] you want to start your search UNDER PROPPED so that the engine runs cool and stays happy. Gradually you try bigger combinations of pitch, diameter, blade area and blade thickness until the engine starts showing signs that it can't handle it.
SB..your plane looks SUPER[:-]!!
Remember that the engine will lose torque when the exhaust pressure leaves the cylinder early...but you gain high rpm ability.
So......your engine will become very critical about the amount of diameter it will turn. You have an airframe that should be clean enough and small enough to make a 8+ inch diameter prop work if the rpm is there. The real work isn't just doing the engine mods. The real work is finding the correct prop that compliments the engine mods. With a high timed speed engine [180 degrees or higher] you want to start your search UNDER PROPPED so that the engine runs cool and stays happy. Gradually you try bigger combinations of pitch, diameter, blade area and blade thickness until the engine starts showing signs that it can't handle it.
12-18-2012, 06:13 PM
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RE: Shrike 40 with thinner airfoil
ORIGINAL: Speedy-Gonzales
Have you flown the plane yet? I would give it a throw ( as is ) to see how it performs, get a good feel for it, and see how it comes up on the pipe. 17.5K is low but at least you will have had the plane in the air and get some feel for it before going ballistic with it.
To me it would seem that the airframe presents more limitations than the engine.
I'm sure you will get some ''pucker factor'' the way it is now!
Speedy Gonzales
Have you flown the plane yet? I would give it a throw ( as is ) to see how it performs, get a good feel for it, and see how it comes up on the pipe. 17.5K is low but at least you will have had the plane in the air and get some feel for it before going ballistic with it.
To me it would seem that the airframe presents more limitations than the engine.
I'm sure you will get some ''pucker factor'' the way it is now!
Speedy Gonzales
I know this is not a f3D or so , but something tells me that this aiframe could brake the 300km/h mark at some point. Probably a bit optimistic but feels good when dream.
We'll see.
12-18-2012, 06:33 PM
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RE: Shrike 40 with thinner airfoil
ORIGINAL: combatpigg
SB..your plane looks SUPER[:-]!!
Remember that the engine will lose torque when the exhaust pressure leaves the cylinder early...but you gain high rpm ability.
So......your engine will become very critical about the amount of diameter it will turn. You have an airframe that should be clean enough and small enough to make a 8+ inch diameter prop work if the rpm is there. The real work isn't just doing the engine mods. The real work is finding the correct prop that compliments the engine mods. With a high timed speed engine [180 degrees or higher] you want to start your search UNDER PROPPED so that the engine runs cool and stays happy. Gradually you try bigger combinations of pitch, diameter, blade area and blade thickness until the engine starts showing signs that it can't handle it.
SB..your plane looks SUPER[:-]!!
Remember that the engine will lose torque when the exhaust pressure leaves the cylinder early...but you gain high rpm ability.
So......your engine will become very critical about the amount of diameter it will turn. You have an airframe that should be clean enough and small enough to make a 8+ inch diameter prop work if the rpm is there. The real work isn't just doing the engine mods. The real work is finding the correct prop that compliments the engine mods. With a high timed speed engine [180 degrees or higher] you want to start your search UNDER PROPPED so that the engine runs cool and stays happy. Gradually you try bigger combinations of pitch, diameter, blade area and blade thickness until the engine starts showing signs that it can't handle it.
I hope you mean about it wont be able to run bigger props like 11x7 APC , or do you mean the 9x10 APC could be too much load to this displacement after raising the timing???
I don't pretend to use something under 9" in diameter for this airframe. Im not sure if a 8" long prop would be enough to overcome the drag of this model.
I'll be careful after doing the first 5° timing job , if no gain there , I probably wont make any more raising timing.
12-18-2012, 06:35 PM
#111
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RE: Shrike 40 with thinner airfoil
ORIGINAL: SpeedBoy
MJD , please dont pay atention on the picture above as reference on the set I described on my last post , that picture is with the 7.5 cc pipe , it was taken about 2 months ago.
The real measure ( pictures below ) is 11-1/5'' from plug center to fat part of the pipe (just behind the fitting) and from plug center to the end of the pipe is 17-3/4''.
I'll test with 10% nitro and see what it drops.
MJD , please dont pay atention on the picture above as reference on the set I described on my last post , that picture is with the 7.5 cc pipe , it was taken about 2 months ago.
The real measure ( pictures below ) is 11-1/5'' from plug center to fat part of the pipe (just behind the fitting) and from plug center to the end of the pipe is 17-3/4''.
I'll test with 10% nitro and see what it drops.
I would think 300kmh is within reach if you get the engine singing.
12-18-2012, 07:20 PM
#112
RE: Shrike 40 with thinner airfoil
ORIGINAL: SpeedBoy
Thanks for the compliment Chuck !!!
I hope you mean about it wont be able to run bigger props like 11x7 APC , or do you mean the 9x10 APC could be too much load to this displacement after raising the timing???
I don't pretend to use something under 9'' in diameter for this airframe. Im not sure if a 8'' long prop would be enough to overcome the drag of this model.
I'll be careful after doing the first 5° timing job , if no gain there , I probably wont make any more raising timing.
ORIGINAL: combatpigg
SB..your plane looks SUPER[:-]!!
Remember that the engine will lose torque when the exhaust pressure leaves the cylinder early...but you gain high rpm ability.
So......your engine will become very critical about the amount of diameter it will turn. You have an airframe that should be clean enough and small enough to make a 8+ inch diameter prop work if the rpm is there. The real work isn't just doing the engine mods. The real work is finding the correct prop that compliments the engine mods. With a high timed speed engine [180 degrees or higher] you want to start your search UNDER PROPPED so that the engine runs cool and stays happy. Gradually you try bigger combinations of pitch, diameter, blade area and blade thickness until the engine starts showing signs that it can't handle it.
SB..your plane looks SUPER[:-]!!
Remember that the engine will lose torque when the exhaust pressure leaves the cylinder early...but you gain high rpm ability.
So......your engine will become very critical about the amount of diameter it will turn. You have an airframe that should be clean enough and small enough to make a 8+ inch diameter prop work if the rpm is there. The real work isn't just doing the engine mods. The real work is finding the correct prop that compliments the engine mods. With a high timed speed engine [180 degrees or higher] you want to start your search UNDER PROPPED so that the engine runs cool and stays happy. Gradually you try bigger combinations of pitch, diameter, blade area and blade thickness until the engine starts showing signs that it can't handle it.
I hope you mean about it wont be able to run bigger props like 11x7 APC , or do you mean the 9x10 APC could be too much load to this displacement after raising the timing???
I don't pretend to use something under 9'' in diameter for this airframe. Im not sure if a 8'' long prop would be enough to overcome the drag of this model.
I'll be careful after doing the first 5° timing job , if no gain there , I probably wont make any more raising timing.
My comments are to be taken as general advice. When you want more speed from a 2 stroke engine, you must do mods that raise RPM.
With mechanical engineering, every time you try to improve one aspect.....you make another aspect worse.
If you are serious about speed, it has been proven that 180 degrees of exhaust duration is the STARTING POINT for a properly designed full wave pipe to be able to do it's magic. The trick is to find the best combination of propellor characteristics to fully take advantage of the narrow power band that a high timed 2 stroke engine has. If you expect the perfect propellor is just a phone call away....it might be, or it might take a lot of trial and error to find the prop that marries your engine to that airplane just like a wedding ring.
12-18-2012, 07:44 PM
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RE: Shrike 40 with thinner airfoil
A good data point is the fact that a popular prop used by RC speed fliers in Europe on 10cc engines timed for the low 20's is a CF 9-10. The pattern is from a 10x10 APC trimmed and reshaped so it has better hub strength than a direct copy of the 9x10. The guys who go smaller and higher pitch as in 8x12 or so are flying very low drag pure speed designs. I'd say 9x10 is real close to to the right choice for that airframe on a hot 10cc. If you were leaving the timing as is and running in the higher teens I'd say run a 10-8.
For safety's sake note that if you get that engine really spinning, that APC 9x10 could be a safety issue. Right now you're fine.
For safety's sake note that if you get that engine really spinning, that APC 9x10 could be a safety issue. Right now you're fine.
12-18-2012, 08:47 PM
#114
RE: Shrike 40 with thinner airfoil
What guys don't appreciate is that unless the compression and nitro % is just perfect, you can't just whip out your ultimate killer prop without taking a big chance on cooking your engine.
A piped engine with high timing [+180 degrees] is a supercharged engine and it will behave like a weight lifter trying to impress his new girl friend if you go for too much load too soon.
It is capable of developing more power. stress and heat than the parts can tolerate..but only for a run or 2.
Piped engines below 180 degrees timing don't hit resonance as brutally..so they don't have the same handling precautions. They have more margin for error
Both Henry Nelson and Dave Shadel will tell you that setting up a "full race" engine is not much different than tuning a model diesel engine. You have to find the balance between load, compression and nitro by working from the safe side towards the most powerful...or else keep these guys on speed dial and give them your credit card number.
Dave was able to finally hammer this point home with me during a call for another P/L/rod set and head button.
Finally, any "full race" speed engine that has a nice idle and good transition to full throttle doesn't have a big enough carburetor.
A piped engine with high timing [+180 degrees] is a supercharged engine and it will behave like a weight lifter trying to impress his new girl friend if you go for too much load too soon.
It is capable of developing more power. stress and heat than the parts can tolerate..but only for a run or 2.
Piped engines below 180 degrees timing don't hit resonance as brutally..so they don't have the same handling precautions. They have more margin for error
Both Henry Nelson and Dave Shadel will tell you that setting up a "full race" engine is not much different than tuning a model diesel engine. You have to find the balance between load, compression and nitro by working from the safe side towards the most powerful...or else keep these guys on speed dial and give them your credit card number.
Dave was able to finally hammer this point home with me during a call for another P/L/rod set and head button.
Finally, any "full race" speed engine that has a nice idle and good transition to full throttle doesn't have a big enough carburetor.
12-19-2012, 11:12 AM
#116
RE: Shrike 40 with thinner airfoil
Sounds like a tough way to make a living....
I'd volunteer to play that game if they would just pay my expenses....no salary. Of course I consider an ice chest full of beer "an expense".
I'll bet there are a lot of other flyers who would do the same.
I'd volunteer to play that game if they would just pay my expenses....no salary. Of course I consider an ice chest full of beer "an expense".
I'll bet there are a lot of other flyers who would do the same.
12-19-2012, 04:20 PM
#117
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RE: Shrike 40 with thinner airfoil
What do you know, a Shrike Forum. Guess I missed it. I build Shrikes all the time. Scratch of course. I have a number of them. A Shrike 40 with an OS 61 SF. A couple of 10s. One with OS 32. Another modified with a Rossi 40 F.I.R.E with pipe. Just needed to widen the fuse. Another in the works with a Thunder Tiger modified buggy engine. I also built the 1/2A with an OS 15 CV engine. You should try the 1/2A with the CV 15. Quite the handful to fly. Such a great flying model. I have modified the frame a number of ways but the original design still flys the best....
12-19-2012, 05:20 PM
#118
RE: Shrike 40 with thinner airfoil
ORIGINAL: europatc74
What do you know, a Shrike Forum. Guess I missed it. I build Shrikes all the time. Scratch of course. I have a number of them. A Shrike 40 with an OS 61 SF. A couple of 10s. One with OS 32. Another modified with a Rossi 40 F.I.R.E with pipe. Just needed to widen the fuse. Another in the works with a Thunder Tiger modified buggy engine. I also built the 1/2A with an OS 15 CV engine. You should try the 1/2A with the CV 15. Quite the handful to fly. Such a great flying model. I have modified the frame a number of ways but the original design still flys the best....
What do you know, a Shrike Forum. Guess I missed it. I build Shrikes all the time. Scratch of course. I have a number of them. A Shrike 40 with an OS 61 SF. A couple of 10s. One with OS 32. Another modified with a Rossi 40 F.I.R.E with pipe. Just needed to widen the fuse. Another in the works with a Thunder Tiger modified buggy engine. I also built the 1/2A with an OS 15 CV engine. You should try the 1/2A with the CV 15. Quite the handful to fly. Such a great flying model. I have modified the frame a number of ways but the original design still flys the best....
Was there a 1/2A kit or is that your own version..?
12-19-2012, 06:29 PM
#119
RE: Shrike 40 with thinner airfoil
I'm wondering if your Picco is intended for pattern use the same as my Rossi was. My Rossi did not work at all with the short pipe/high RPM approach even though I raised the exhaust port .030. What ended up working the best was a total pipe length of 25" and a large prop. In this case an 11X11. I did try a pipe length of 18" with an APC 9X10 and the airplane was a dog. Changed to a longer header for a total length 21" and got best results with a 10X10. Finally had a section welded to the pipe that increased the inlet ID to 7/8" and made up a 7/8"x 12" header for a total length of 25" and installed a Picco 12mm carb. First tried an 11X10 and it was a huge difference in speed. Tried an 11X11 and was even faster, 11X12 and the speed dropped. Now the 60 is going into a classic pattern airplane and a Rossi 90 is on the way. I'm going to start off with the 25" pipe and 11X12 and see what she does. Lots of engine for a 6 lb 450 sq in airplane lol
I just pulled the Rossi 61 and pipe out of my race plane to get it ready for the arrival of the 90. You can see that the header/pipe is quite long in comparison. You have to love that carb. I'm assuming that the Picco the OP has is fitted with an 8mm carb indicating that it was intended for pattern. It may just be that it develops it's peak power at a lower RPM like the Rossi does.
I just pulled the Rossi 61 and pipe out of my race plane to get it ready for the arrival of the 90. You can see that the header/pipe is quite long in comparison. You have to love that carb. I'm assuming that the Picco the OP has is fitted with an 8mm carb indicating that it was intended for pattern. It may just be that it develops it's peak power at a lower RPM like the Rossi does.
12-19-2012, 08:47 PM
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RE: Shrike 40 with thinner airfoil
Combatpigg
Yes there was a 1/2A kit. I still have a 40, 10 and 1/2A kits which I use as templets. Kits occasionally pop up on E Bay. Pricey, considering the original kit prices.
Yes there was a 1/2A kit. I still have a 40, 10 and 1/2A kits which I use as templets. Kits occasionally pop up on E Bay. Pricey, considering the original kit prices.
12-20-2012, 08:48 PM
#122
RE: Shrike 40 with thinner airfoil
Speedboy, what an awesome job you did on your Shrike. I love it!
Good luck on your flight.
I built one a few years ago. It had a piped OS 40 FSR abc engine. It was fast enough for me. My only mod was to add a dual rudder set up. That was great for snap rolls and spins.
Unfortunately, I sold it but I made rib & former templates so I may have to build another one. My thought was to make it with a twin boom tail to resemble a BVM Bobcat. I have a YS 45FR looking for something to do.
Good luck on your flight.
I built one a few years ago. It had a piped OS 40 FSR abc engine. It was fast enough for me. My only mod was to add a dual rudder set up. That was great for snap rolls and spins.
Unfortunately, I sold it but I made rib & former templates so I may have to build another one. My thought was to make it with a twin boom tail to resemble a BVM Bobcat. I have a YS 45FR looking for something to do.
12-20-2012, 11:38 PM
#123
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RE: Shrike 40 with thinner airfoil
ORIGINAL: combatpigg
I have never played with any engines larger than .50 sized for speed so I can't tell you about which sized prop will work best for you. All I can say is that 9x10 sounds large to me, but it might be just fine.
My comments are to be taken as general advice. When you want more speed from a 2 stroke engine, you must do mods that raise RPM.
With mechanical engineering, every time you try to improve one aspect.....you make another aspect worse.
If you are serious about speed, it has been proven that 180 degrees of exhaust duration is the STARTING POINT for a properly designed full wave pipe to be able to do it's magic. The trick is to find the best combination of propellor characteristics to fully take advantage of the narrow power band that a high timed 2 stroke engine has. If you expect the perfect propellor is just a phone call away....it might be, or it might take a lot of trial and error to find the prop that marries your engine to that airplane just like a wedding ring.
you want to start your search UNDER PROPPED so that the engine runs cool and stays happy. Gradually you try bigger combinations of pitch, diameter, blade area and blade thickness until the engine starts showing signs that it can't handle it.
A piped engine with high timing [+180 degrees] is a supercharged engine and it will behave like a weight lifter trying to impress his new girl friend if you go for too much load too soon.
It is capable of developing more power. stress and heat than the parts can tolerate..but only for a run or 2.
Piped engines below 180 degrees timing don't hit resonance as brutally..so they don't have the same handling precautions. They have more margin for error
ORIGINAL: SpeedBoy
Thanks for the compliment Chuck !!!
I hope you mean about it wont be able to run bigger props like 11x7 APC , or do you mean the 9x10 APC could be too much load to this displacement after raising the timing???
I don't pretend to use something under 9'' in diameter for this airframe. Im not sure if a 8'' long prop would be enough to overcome the drag of this model.
I'll be careful after doing the first 5° timing job , if no gain there , I probably wont make any more raising timing.
ORIGINAL: combatpigg
SB..your plane looks SUPER[:-]!!
Remember that the engine will lose torque when the exhaust pressure leaves the cylinder early...but you gain high rpm ability.
So......your engine will become very critical about the amount of diameter it will turn. You have an airframe that should be clean enough and small enough to make a 8+ inch diameter prop work if the rpm is there. The real work isn't just doing the engine mods. The real work is finding the correct prop that compliments the engine mods. With a high timed speed engine [180 degrees or higher] you want to start your search UNDER PROPPED so that the engine runs cool and stays happy. Gradually you try bigger combinations of pitch, diameter, blade area and blade thickness until the engine starts showing signs that it can't handle it.
SB..your plane looks SUPER[:-]!!
Remember that the engine will lose torque when the exhaust pressure leaves the cylinder early...but you gain high rpm ability.
So......your engine will become very critical about the amount of diameter it will turn. You have an airframe that should be clean enough and small enough to make a 8+ inch diameter prop work if the rpm is there. The real work isn't just doing the engine mods. The real work is finding the correct prop that compliments the engine mods. With a high timed speed engine [180 degrees or higher] you want to start your search UNDER PROPPED so that the engine runs cool and stays happy. Gradually you try bigger combinations of pitch, diameter, blade area and blade thickness until the engine starts showing signs that it can't handle it.
I hope you mean about it wont be able to run bigger props like 11x7 APC , or do you mean the 9x10 APC could be too much load to this displacement after raising the timing???
I don't pretend to use something under 9'' in diameter for this airframe. Im not sure if a 8'' long prop would be enough to overcome the drag of this model.
I'll be careful after doing the first 5° timing job , if no gain there , I probably wont make any more raising timing.
My comments are to be taken as general advice. When you want more speed from a 2 stroke engine, you must do mods that raise RPM.
With mechanical engineering, every time you try to improve one aspect.....you make another aspect worse.
If you are serious about speed, it has been proven that 180 degrees of exhaust duration is the STARTING POINT for a properly designed full wave pipe to be able to do it's magic. The trick is to find the best combination of propellor characteristics to fully take advantage of the narrow power band that a high timed 2 stroke engine has. If you expect the perfect propellor is just a phone call away....it might be, or it might take a lot of trial and error to find the prop that marries your engine to that airplane just like a wedding ring.
you want to start your search UNDER PROPPED so that the engine runs cool and stays happy. Gradually you try bigger combinations of pitch, diameter, blade area and blade thickness until the engine starts showing signs that it can't handle it.
A piped engine with high timing [+180 degrees] is a supercharged engine and it will behave like a weight lifter trying to impress his new girl friend if you go for too much load too soon.
It is capable of developing more power. stress and heat than the parts can tolerate..but only for a run or 2.
Piped engines below 180 degrees timing don't hit resonance as brutally..so they don't have the same handling precautions. They have more margin for error
I dont want to overheat the engine and your advices has much sense to me. If the smaller prop is better , I'll start up the engine again with the new prop to have a reading and then I'll work on the sleeve to compare the RPM.
12-20-2012, 11:43 PM
#124
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RE: Shrike 40 with thinner airfoil
ORIGINAL: MJD
A good data point is the fact that a popular prop used by RC speed fliers in Europe on 10cc engines timed for the low 20's is a CF 9-10. The pattern is from a 10x10 APC trimmed and reshaped so it has better hub strength than a direct copy of the 9x10. The guys who go smaller and higher pitch as in 8x12 or so are flying very low drag pure speed designs. I'd say 9x10 is real close to to the right choice for that airframe on a hot 10cc. If you were leaving the timing as is and running in the higher teens I'd say run a 10-8.
For safety's sake note that if you get that engine really spinning, that APC 9x10 could be a safety issue. Right now you're fine.
A good data point is the fact that a popular prop used by RC speed fliers in Europe on 10cc engines timed for the low 20's is a CF 9-10. The pattern is from a 10x10 APC trimmed and reshaped so it has better hub strength than a direct copy of the 9x10. The guys who go smaller and higher pitch as in 8x12 or so are flying very low drag pure speed designs. I'd say 9x10 is real close to to the right choice for that airframe on a hot 10cc. If you were leaving the timing as is and running in the higher teens I'd say run a 10-8.
For safety's sake note that if you get that engine really spinning, that APC 9x10 could be a safety issue. Right now you're fine.
12-20-2012, 11:46 PM
#125
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RE: Shrike 40 with thinner airfoil
ORIGINAL: europatc74
What do you know, a Shrike Forum. Guess I missed it. I build Shrikes all the time. Scratch of course. I have a number of them. A Shrike 40 with an OS 61 SF. A couple of 10s. One with OS 32. Another modified with a Rossi 40 F.I.R.E with pipe. Just needed to widen the fuse. Another in the works with a Thunder Tiger modified buggy engine. I also built the 1/2A with an OS 15 CV engine. You should try the 1/2A with the CV 15. Quite the handful to fly. Such a great flying model. I have modified the frame a number of ways but the original design still flys the best....
What do you know, a Shrike Forum. Guess I missed it. I build Shrikes all the time. Scratch of course. I have a number of them. A Shrike 40 with an OS 61 SF. A couple of 10s. One with OS 32. Another modified with a Rossi 40 F.I.R.E with pipe. Just needed to widen the fuse. Another in the works with a Thunder Tiger modified buggy engine. I also built the 1/2A with an OS 15 CV engine. You should try the 1/2A with the CV 15. Quite the handful to fly. Such a great flying model. I have modified the frame a number of ways but the original design still flys the best....