Not enough prop?
07-10-2009 | 07:50 PM
#1
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From: Nutley,
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Not enough prop?
How do I now if I dont have enough prop? Just wondering. I have a saito 100 with 15x6 which I was tuning and was hitting just over the stated 9300 rpm top end(9360). I find it strange since Ive never seen any of my engines hit the top end of the spec'd rpm range.
07-10-2009 | 08:22 PM
#3
RE: Not enough prop?
Sounds about right, might get better if this is a fairly new engine. I have a 14x8 apc on one ofmine and it turns 9700 to 9800 rpms. And a 16x4W on the other, never checked it.
I try not to prop any of my Saitos thay allows them to turn over 10.000 rpms. So far no problems .
I try not to prop any of my Saitos thay allows them to turn over 10.000 rpms. So far no problems .
07-10-2009 | 09:21 PM
#4
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RE: Not enough prop?
ORIGINAL: ro347
How do I now if I dont have enough prop? Just wondering. I have a saito 100 with 15x6 which I was tuning and was hitting just over the stated 9300 rpm top end(9360). I find it strange since Ive never seen any of my engines hit the top end of the spec'd rpm range.
How do I now if I dont have enough prop? Just wondering. I have a saito 100 with 15x6 which I was tuning and was hitting just over the stated 9300 rpm top end(9360). I find it strange since Ive never seen any of my engines hit the top end of the spec'd rpm range.
Ken
07-10-2009 | 10:29 PM
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From: Loveland,
CO
RE: Not enough prop?
I started breaking in a new Saito 1.00 today with a 15x8. I know things are still running pretty rich, but the best I could hit was 8800 rpm. Plus I'm at 5200 ft. above sea level. 15x6 is in the range of props for this engine, so go with it if it flies the plane. You'll have better throttle control with the 15x6. More speed with a 15x8. The more you run the Saito, the better it will run. Don't forget to set the top end a little rich on your final setting. Max rpm then richen to drop about 200-300 rpm.
Mike
Mike
07-11-2009 | 07:25 AM
#6
My Feedback: (1)
RE: Not enough prop?
Ken's right. Those 16000 RPM claims are bunk. What the OP is seeing is more reaslisic for the full open RPM for that engine and I would NOT prop it to try to get more out of it.
With a two stroke, there are no pushrods and valves that need to be mechanically operated by a cam shaft. They will tend to get up higher in RPM, although my OS 1.20 AX tops off at about 9000 RPM and that's a two stroke engine.
You will have plenty of power with the props selected as posted above with those engines. If you need more power, I might suggest a larger engine.
CGr.
With a two stroke, there are no pushrods and valves that need to be mechanically operated by a cam shaft. They will tend to get up higher in RPM, although my OS 1.20 AX tops off at about 9000 RPM and that's a two stroke engine.
You will have plenty of power with the props selected as posted above with those engines. If you need more power, I might suggest a larger engine.
CGr.
07-11-2009 | 08:25 AM
#7
RE: Not enough prop?
I just broke in my Saito 100 and with a 15x6 my digital tach was starting to get to read 10k, so I backed it down to 9600. I can see that it is rich at that, so I bought a 15x8 to put on it after I run a few more tanks through it in the air. Right now, the Thunderbolt I put it in only has 1 flight on it, so since it seems to fly well, but fairly slowly, I will use the 15x6 for a few more flights. I will admit, the engine and prop combination seems to pull it off the ground quite quickly. To me, the engine runs very strongly.
07-11-2009 | 09:01 AM
#9
Senior Member
RE: Not enough prop?
A 15x6 with the Saito 100 is about right. You should be getting close to 9750 RPMs max on like 25% nitro. A 16x6 will be too much for sure and on a 15x8 you will drop your RPMs to about 8,500-8,750 max. Again, it also depends how much nitro you are using. I love them with 25% nitro. Sweet ...
Different planes, different styles and different preferences means different props ...
Different planes, different styles and different preferences means different props ...
07-11-2009 | 09:27 AM
#11
My Feedback: (1)
RE: Not enough prop?
ORIGINAL: rgm762
so which has more effect on rpm's, diameter or pitch? or both?
so which has more effect on rpm's, diameter or pitch? or both?
Consider this, for either a two stroke or a four stroke:
The prop is like the transmission in your car. If you want to climb a steep hill, you can change to a lower gear. Your car will go slower or your RPM will increase, but you will pull much better.
Now, shift up to a higher gear. Your car will go faster, but your engine RPM will decrease, or you will go faster with the same RPM as you had in a lower gear, but you will have less "power" to the wheels (the engine is generating just as much "power" but the demand because of the gearing, will cause the car to accellerate at a slower rate.
Same with props. Increase the pitch and you will go faster. Decrease the pitch, you will go slower for the same RPM, but the engine could over-rev too.
This is probably beyond the scope of this topic, but maybe it will help.. and maybe you know this already, but here goes:
Pitch is how much or how far the prop will move forward for each rpm. A 10 picth, for instance will move forward 10 inches for every rotation. Multiply that times the engine RPM (Revolotions per MINUTE), say 10,000 RPM and you have 70,000 revs per minute or 70,000/60 for 1166.666 inches per second or 97.xx feet per second. 60 miles per hour is 88 feet per second, so your prop, at full RPM and in the air AND under ideal conditions, will travel somewhere over 60 miles per hour.
Lower the pitch, and that speed will decrease.
That's speed. Equate that to power as you would a car transmission and you can see how this relationship works. Note, this is under ideal conditions.. no drag, perfect conditions, which do not exist.
Hope this helps.
CGr.
07-11-2009 | 09:32 AM
#12
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RE: Not enough prop?
ORIGINAL: GaryHarris
Man, I just back in from breaking in my Saito 100 too! Think I may be under propped with a 14x6 on a 4* 60?
10% nitro.
Man, I just back in from breaking in my Saito 100 too! Think I may be under propped with a 14x6 on a 4* 60?
10% nitro.
07-11-2009 | 09:40 AM
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From: Houston, TX
RE: Not enough prop?
ORIGINAL: tIANci
14x6 will take you over 10,000 RPM for sure ... go with a 14x8 for some speed or 15x6 for nice huge loops.
ORIGINAL: GaryHarris
Man, I just back in from breaking in my Saito 100 too! Think I may be under propped with a 14x6 on a 4* 60?
10% nitro.
Man, I just back in from breaking in my Saito 100 too! Think I may be under propped with a 14x6 on a 4* 60?
10% nitro.
07-11-2009 | 10:34 AM
#14
My Feedback: (1)
RE: Not enough prop?
As a suggestion, larger light weight wheels maybe? We fly off of grass and it seems that every plane I buy, build (assemble for arf's 
) always has those 2 1/2 inch wheels and they just don't cut it. That extra half inch radius with the 3 1/2 inchers raise me just enough. And, those lightweight Dubro's are just that, lightweight, but they do the job.
CGr.
) always has those 2 1/2 inch wheels and they just don't cut it. That extra half inch radius with the 3 1/2 inchers raise me just enough. And, those lightweight Dubro's are just that, lightweight, but they do the job.CGr.
07-11-2009 | 11:41 AM
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From: Garland, TX
RE: Not enough prop?
ORIGINAL: tIANci
Eeerrr ... is the 4* not a tail dragger? I am sure the prop will clear.
Eeerrr ... is the 4* not a tail dragger? I am sure the prop will clear.
07-11-2009 | 11:49 AM
#17
My Feedback: (1)
RE: Not enough prop?
Yeah, but at least, if you do a classic tail dragger takeoff, forcing the tail down pulling full elevator, until it gains speed, then settling in with less elevator after the first 10 feet or so, it would most likely have enough speed to get off the ground.. eventually.. It takes timeing, but I think it works ok.
CGr.
It takes timeing, but I think it works ok.CGr.
07-11-2009 | 12:55 PM
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From: Houston, TX
RE: Not enough prop?
ORIGINAL: CGRetired
As a suggestion, larger light weight wheels maybe? We fly off of grass and it seems that every plane I buy, build (assemble for arf's ) always has those 2 1/2 inch wheels and they just don't cut it. That extra half inch radius with the 3 1/2 inchers raise me just enough. And, those lightweight Dubro's are just that, lightweight, but they do the job.
CGr.
As a suggestion, larger light weight wheels maybe? We fly off of grass and it seems that every plane I buy, build (assemble for arf's
) always has those 2 1/2 inch wheels and they just don't cut it. That extra half inch radius with the 3 1/2 inchers raise me just enough. And, those lightweight Dubro's are just that, lightweight, but they do the job.CGr.
I just checked the clearance on my LT-40 with a Magnum .52 FS, 12x5 prop and a landing gear lift kit and I have a 1 3/8" of GC which has been working great. 3 weeks and I havent changed a prop yet over the standard LG. I also added Du-bro low bounce wheels. I know they are heavy, but they definitly help.
From what I have read here thanks to you RCU guys is, the 4* 60 builds tail heavy. I have heard/read of guys having to add 10 oz. to the nose of the plane. In my demented thought process, I'm thinking of rather than adding lead, adding a much stronger, less flexy composite LG and Low Bounce wheels to the front end. Maybe raise the front end another half inch.
Of course that brings up two other issues. With raising the front end, that lowers the rear end and that transistion from tail dragging to level, will be more extreem. I don't know if thats a real problem or not, but I have also read that when using the Sullivan tail wheel, the rear sits a little high anyway and guys bend the wire to lower it. May be a wash.
The second issue will be added weight and a less "forgiving" landing gear. Hard landings with stiff LG will transfer more of the load to the air frame since the stiffer LG isn't absorbing as much shock as the original design was ment to. (As if that was the intention of the designer and not the bean counter who selected lower cost hardware.) (And not that Ill be having any hard landings with my 3 months of experiance. lol) Ill have to beef up the LG mounting area and most likely that will add more weight and transfer the load up and down the fuse which may need more attention.
Am I crazy? Any thoughts?
Thanks.
07-11-2009 | 02:21 PM
#20
RE: Not enough prop?
You also have the option to go with a 3 bladed prop, and up the pitch to a 14x8 .. you'll love that 4 star, with that engine it is a monster combination for fun. I have the 91 on a Venture 60 and get very nearly unlimited vertical, it flies great.
http://rcuvideos.com/video/Gone-in-15-seconds
http://rcuvideos.com/video/Gone-in-15-seconds
07-11-2009 | 09:25 PM
#23
Senior Member
RE: Not enough prop?
ORIGINAL: GaryHarris
The 4* 60 calls for 3 1/4'' wheels and I bought Dave Brown's Lite Flite wheels. My plane is about 99% ready for covering so for grins I installed the supplied landing gear, those 3 1/4'' wheels and checked the props ground clearance with level fuse. I have about 2 1/4'' of ground clearance with the 14'' prop. So with a 15'' prop I should have a 1 3/4'' before ''KnicksVille''.
I just checked the clearance on my LT-40 with a Magnum .52 FS, 12x5 prop and a landing gear lift kit and I have a 1 3/8'' of GC which has been working great. 3 weeks and I havent changed a prop yet over the standard LG. I also added Du-bro low bounce wheels. I know they are heavy, but they definitly help.
From what I have read here thanks to you RCU guys is, the 4* 60 builds tail heavy. I have heard/read of guys having to add 10 oz. to the nose of the plane. In my demented thought process, I'm thinking of rather than adding lead, adding a much stronger, less flexy composite LG and Low Bounce wheels to the front end. Maybe raise the front end another half inch.
Of course that brings up two other issues. With raising the front end, that lowers the rear end and that transistion from tail dragging to level, will be more extreem. I don't know if thats a real problem or not, but I have also read that when using the Sullivan tail wheel, the rear sits a little high anyway and guys bend the wire to lower it. May be a wash.
The second issue will be added weight and a less ''forgiving'' landing gear. Hard landings with stiff LG will transfer more of the load to the air frame since the stiffer LG isn't absorbing as much shock as the original design was ment to. (As if that was the intention of the designer and not the bean counter who selected lower cost hardware.) (And not that Ill be having any hard landings with my 3 months of experiance. lol) Ill have to beef up the LG mounting area and most likely that will add more weight and transfer the load up and down the fuse which may need more attention.
Am I crazy? Any thoughts?
Thanks.
ORIGINAL: CGRetired
As a suggestion, larger light weight wheels maybe? We fly off of grass and it seems that every plane I buy, build (assemble for arf's ) always has those 2 1/2 inch wheels and they just don't cut it. That extra half inch radius with the 3 1/2 inchers raise me just enough. And, those lightweight Dubro's are just that, lightweight, but they do the job.
CGr.
As a suggestion, larger light weight wheels maybe? We fly off of grass and it seems that every plane I buy, build (assemble for arf's
) always has those 2 1/2 inch wheels and they just don't cut it. That extra half inch radius with the 3 1/2 inchers raise me just enough. And, those lightweight Dubro's are just that, lightweight, but they do the job.CGr.
I just checked the clearance on my LT-40 with a Magnum .52 FS, 12x5 prop and a landing gear lift kit and I have a 1 3/8'' of GC which has been working great. 3 weeks and I havent changed a prop yet over the standard LG. I also added Du-bro low bounce wheels. I know they are heavy, but they definitly help.
From what I have read here thanks to you RCU guys is, the 4* 60 builds tail heavy. I have heard/read of guys having to add 10 oz. to the nose of the plane. In my demented thought process, I'm thinking of rather than adding lead, adding a much stronger, less flexy composite LG and Low Bounce wheels to the front end. Maybe raise the front end another half inch.
Of course that brings up two other issues. With raising the front end, that lowers the rear end and that transistion from tail dragging to level, will be more extreem. I don't know if thats a real problem or not, but I have also read that when using the Sullivan tail wheel, the rear sits a little high anyway and guys bend the wire to lower it. May be a wash.
The second issue will be added weight and a less ''forgiving'' landing gear. Hard landings with stiff LG will transfer more of the load to the air frame since the stiffer LG isn't absorbing as much shock as the original design was ment to. (As if that was the intention of the designer and not the bean counter who selected lower cost hardware.) (And not that Ill be having any hard landings with my 3 months of experiance. lol) Ill have to beef up the LG mounting area and most likely that will add more weight and transfer the load up and down the fuse which may need more attention.
Am I crazy? Any thoughts?
Thanks.
You are not crazy, not by a long shot. Your thinking on load transferring of landing stresses to the airframe are exactly on the mark. Stiffer LG definitely are not the best for our purposes. The gear I have designed and been building for my pattern planes are balsa cored and carbon laminated specifically to produce a more flexible, shock absorbing gear strut. The fuse mount can be minimized with such gear, reducing weight overall.
Commercially available composite gear are far stiffer than they need to be and will tend to do damage in a rough landing. Nevertheless, do not take dremel to a composite gear unless you really know what you are doing.
MattK
07-11-2009 | 09:27 PM
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From: Lawrence,
KS
RE: Not enough prop?
ORIGINAL: CGRetired
Pitch is how much or how far the prop will move forward for each rpm. A 10 picth, for instance will move forward 10 inches for every rotation. Multiply that times the engine RPM (Revolotions per MINUTE), say 10,000 RPM and you have 70,000 revs per minute or 70,000/60 for 1166.666 inches per second or 97.xx feet per second. 60 miles per hour is 88 feet per second, so your prop, at full RPM and in the air AND under ideal conditions, will travel somewhere over 60 miles per hour.
CGr.
Pitch is how much or how far the prop will move forward for each rpm. A 10 picth, for instance will move forward 10 inches for every rotation. Multiply that times the engine RPM (Revolotions per MINUTE), say 10,000 RPM and you have 70,000 revs per minute or 70,000/60 for 1166.666 inches per second or 97.xx feet per second. 60 miles per hour is 88 feet per second, so your prop, at full RPM and in the air AND under ideal conditions, will travel somewhere over 60 miles per hour.
CGr.
10 inches per rotation X 10,000 rotations per minute = 100,000 inches per minute.
100,000 inches per minute / 12 inches per foot = 8333.33 ft per minute
8333.33 ft per minute / 60 seconds per minute = 138.89 ft per second
8333.33 ft per minute X 60 minutes per hour = 50,000 ft per hour
50,000 ft per hour / 5280 ft per mile = 94.69 mph
where is my math wrong?
07-11-2009 | 10:55 PM
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From: Houston, TX
RE: Not enough prop?
ORIGINAL: MTK
Gary,
You are not crazy, not by a long shot. Your thinking on load transferring of landing stresses to the airframe are exactly on the mark. Stiffer LG definitely are not the best for our purposes. The gear I have designed and been building for my pattern planes are balsa cored and carbon laminated specifically to produce a more flexible, shock absorbing gear strut. The fuse mount can be minimized with such gear, reducing weight overall.
Commercially available composite gear are far stiffer than they need to be and will tend to do damage in a rough landing. Nevertheless, do not take dremel to a composite gear unless you really know what you are doing.
MattK
ORIGINAL: GaryHarris
The 4* 60 calls for 3 1/4'' wheels and I bought Dave Brown's Lite Flite wheels. My plane is about 99% ready for covering so for grins I installed the supplied landing gear, those 3 1/4'' wheels and checked the props ground clearance with level fuse. I have about 2 1/4'' of ground clearance with the 14'' prop. So with a 15'' prop I should have a 1 3/4'' before ''KnicksVille''.
I just checked the clearance on my LT-40 with a Magnum .52 FS, 12x5 prop and a landing gear lift kit and I have a 1 3/8'' of GC which has been working great. 3 weeks and I havent changed a prop yet over the standard LG. I also added Du-bro low bounce wheels. I know they are heavy, but they definitly help.
From what I have read here thanks to you RCU guys is, the 4* 60 builds tail heavy. I have heard/read of guys having to add 10 oz. to the nose of the plane. In my demented thought process, I'm thinking of rather than adding lead, adding a much stronger, less flexy composite LG and Low Bounce wheels to the front end. Maybe raise the front end another half inch.
Of course that brings up two other issues. With raising the front end, that lowers the rear end and that transistion from tail dragging to level, will be more extreem. I don't know if thats a real problem or not, but I have also read that when using the Sullivan tail wheel, the rear sits a little high anyway and guys bend the wire to lower it. May be a wash.
The second issue will be added weight and a less ''forgiving'' landing gear. Hard landings with stiff LG will transfer more of the load to the air frame since the stiffer LG isn't absorbing as much shock as the original design was ment to. (As if that was the intention of the designer and not the bean counter who selected lower cost hardware.) (And not that Ill be having any hard landings with my 3 months of experiance. lol) Ill have to beef up the LG mounting area and most likely that will add more weight and transfer the load up and down the fuse which may need more attention.
Am I crazy? Any thoughts?
Thanks.
ORIGINAL: CGRetired
As a suggestion, larger light weight wheels maybe? We fly off of grass and it seems that every plane I buy, build (assemble for arf's ) always has those 2 1/2 inch wheels and they just don't cut it. That extra half inch radius with the 3 1/2 inchers raise me just enough. And, those lightweight Dubro's are just that, lightweight, but they do the job.
CGr.
As a suggestion, larger light weight wheels maybe? We fly off of grass and it seems that every plane I buy, build (assemble for arf's
) always has those 2 1/2 inch wheels and they just don't cut it. That extra half inch radius with the 3 1/2 inchers raise me just enough. And, those lightweight Dubro's are just that, lightweight, but they do the job.CGr.
I just checked the clearance on my LT-40 with a Magnum .52 FS, 12x5 prop and a landing gear lift kit and I have a 1 3/8'' of GC which has been working great. 3 weeks and I havent changed a prop yet over the standard LG. I also added Du-bro low bounce wheels. I know they are heavy, but they definitly help.
From what I have read here thanks to you RCU guys is, the 4* 60 builds tail heavy. I have heard/read of guys having to add 10 oz. to the nose of the plane. In my demented thought process, I'm thinking of rather than adding lead, adding a much stronger, less flexy composite LG and Low Bounce wheels to the front end. Maybe raise the front end another half inch.
Of course that brings up two other issues. With raising the front end, that lowers the rear end and that transistion from tail dragging to level, will be more extreem. I don't know if thats a real problem or not, but I have also read that when using the Sullivan tail wheel, the rear sits a little high anyway and guys bend the wire to lower it. May be a wash.
The second issue will be added weight and a less ''forgiving'' landing gear. Hard landings with stiff LG will transfer more of the load to the air frame since the stiffer LG isn't absorbing as much shock as the original design was ment to. (As if that was the intention of the designer and not the bean counter who selected lower cost hardware.) (And not that Ill be having any hard landings with my 3 months of experiance. lol) Ill have to beef up the LG mounting area and most likely that will add more weight and transfer the load up and down the fuse which may need more attention.
Am I crazy? Any thoughts?
Thanks.
You are not crazy, not by a long shot. Your thinking on load transferring of landing stresses to the airframe are exactly on the mark. Stiffer LG definitely are not the best for our purposes. The gear I have designed and been building for my pattern planes are balsa cored and carbon laminated specifically to produce a more flexible, shock absorbing gear strut. The fuse mount can be minimized with such gear, reducing weight overall.
Commercially available composite gear are far stiffer than they need to be and will tend to do damage in a rough landing. Nevertheless, do not take dremel to a composite gear unless you really know what you are doing.
MattK
