TFF
Well-Known Member
That 54” prop is a lot smaller at the same pitch. If you had been given a 54x 50, you would normally see worse climb but better speed. Without the pitch, you went backwards. All props are a balance.
thrust expected from an 1834cc VW?
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rv7charlie
Well-Known Member
'better speed '
That's a possibility, but in the speed range being discussed (sub-100 mph), I wouldn't risk coffee money on that bet. It certainly doesn't work out that way with the 2 seat RVs, at twice the speed.
That's a possibility, but in the speed range being discussed (sub-100 mph), I wouldn't risk coffee money on that bet. It certainly doesn't work out that way with the 2 seat RVs, at twice the speed.
flitzerpilot
Well-Known Member
I vividly recall one of the test pilots on the Flitzer flight test programme diving near vertically from a few thousand feet with the original fine pitch propeller. With partially retarded throttle the blades went supersonic at an IAS of 126 mph. At a range of about one mile the noise was stupendous! He pulled out at about 200', and then went up and did it again. He evidently enjoyed it!
The current propeller limits the tip speed, although I've never dived at full throttle, only applying full power in a pitching manoeuvre as the nose broke the horizon. VNE is set at 120 mph.
The current propeller limits the tip speed, although I've never dived at full throttle, only applying full power in a pitching manoeuvre as the nose broke the horizon. VNE is set at 120 mph.
flitzerpilot
Well-Known Member
Not really! It was pretty terrifying and I had visions of something coming apart, not to mention flutter onset, although there was no hint of control surface buzz. I had to admire his courage and dedicatiion, but he did enjoy flying it. Around the same time an 18 year-old PPL who'd only flown Cubs and Aeroncas, flew the Z-1. On his first flight he performed a series of elegant slow rolls. Returning to the field he flew another overhead at 400' with just enough positive to keep the engine running sweetly. A natural!
He was still grinning 30 minutes later!
He was still grinning 30 minutes later!
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I also flew the plane with a 54"x46" Tennessee prop. It wouldn't turn up and performance was worse than the Sensenich props. It was about 10 mph slower and climb was a good 200 fpm lower.
Back to the Sensenich props. The 54x44 is a skinny little toothpick. The 60x44 has a lot more blade area. It could easily be half again as much area as the 54" has.
So TFF, suppose you increase blade area on the 54x44? Would it really need more pitch?
I don't think I got good fuel consumption numbers for the 54" prop.
Back to the Sensenich props. The 54x44 is a skinny little toothpick. The 60x44 has a lot more blade area. It could easily be half again as much area as the 54" has.
So TFF, suppose you increase blade area on the 54x44? Would it really need more pitch?
I don't think I got good fuel consumption numbers for the 54" prop.
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Doran Jaffas
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Years ago my Sonerai 2 had the VW 2180 cc. 54x44 Sterba propeller. Top speed was 150ish. Climb..times was 1400 fpm if I remember correctly. The high speed numbers were really ambitious. Maybe their climb was minimal. When talking to other Sonerai 2 pilot's...I was told their were inline with mine. Still, not bad but no where near the 200 mph that was supposedly possible.
TFF
Well-Known Member
Marc W, it’s all where the black art comes in. A wider blade or different airfoil could have taken away rpm overspeed, but better performance is a whole different question.
Each airplane has an ideal prop. Load on an engine does not equate to equal performance to the airframe. Load on an engine is a standard of the engine performance. Aerodynamics of the prop is separate. Putting a 54” prop where a 60” is standard is a really a big swing. What you would want is a 61 or a 59 with a pitch change that compliments the diameter change. Maybe even a 58. Too far away from what is close is really a miss.
It is all quantifiable in a computer program. The only one that was believable at our level is gone. The rest then is trial and error. That choice is do it yourself or buy a prop with a good reputation. That reputation was built on their trial and error.
It is what makes props so frustrating, you need about 6 different ones to find the keeper. Pretty rough on the pocketbook.
Side note my project has a 72x50. A friend had the same type plane with a 70x60. Same general engine. Mine will turn at max RPM and I know his was a lot lower. He had a better design prop. I think my plane will be faster, but I bet his would have been better on a trip. He had plenty of performance. You don’t really know what you got unless you have one to test.
Each airplane has an ideal prop. Load on an engine does not equate to equal performance to the airframe. Load on an engine is a standard of the engine performance. Aerodynamics of the prop is separate. Putting a 54” prop where a 60” is standard is a really a big swing. What you would want is a 61 or a 59 with a pitch change that compliments the diameter change. Maybe even a 58. Too far away from what is close is really a miss.
It is all quantifiable in a computer program. The only one that was believable at our level is gone. The rest then is trial and error. That choice is do it yourself or buy a prop with a good reputation. That reputation was built on their trial and error.
It is what makes props so frustrating, you need about 6 different ones to find the keeper. Pretty rough on the pocketbook.
Side note my project has a 72x50. A friend had the same type plane with a 70x60. Same general engine. Mine will turn at max RPM and I know his was a lot lower. He had a better design prop. I think my plane will be faster, but I bet his would have been better on a trip. He had plenty of performance. You don’t really know what you got unless you have one to test.
TFF
Well-Known Member
Unluckily at our level only artists practice prop building. Some are Rembrandts and some are paint by numbers.
Jan Carlsson was as close as we, as home builders, got to design software, and since he is passed on, It’s gone.
I think Hercules props in the UK used his software some but head to head with some of the Rembrandts it was off by that much. Very good starting point. He had a better program for his own use, again all gone.
Jan Carlsson was as close as we, as home builders, got to design software, and since he is passed on, It’s gone.
I think Hercules props in the UK used his software some but head to head with some of the Rembrandts it was off by that much. Very good starting point. He had a better program for his own use, again all gone.
EzyBuildWing
Well-Known Member
1835cc VW 3600rpm Troyer prop 50" x 28" 280 lbs Static Thrust (measured)
1835cc VW fitted with Race Cam at 3600rpm Troyer prop 50" x 26" 310 lbs ST (measured).
1756cc VW fitted with Race Cam at 3650rpm Troyer 50" x 28" 330 lbs Static Thrust (measured)
Lyc 125 hp 2600rpm Sensenich 66" x 38" 550lbs ST.
2100cc VW 3500rpm with Race Cam Troyer 54" x 26" 360 lbs ST.
1700cc VW 3250rpm Shaus prop 51" x 27" 270 lbs ST.
1594cc VW 2900rpm Aerial prop 51" x 27" 232 lbs ST.
Franklin 125 hp 2500 rpm Troyer 66" x 42" 550 lbs ST.
All these ST's physically measured at GyroCopter fly-in, Rockford 1977. PRA Magazine October 1977 carried the Chuck Beaty story, plus calculations for HP's and thrusts.
So, for an 1835cc VW with 9:1 CR, stub-exhausts, ample carburation, and a cam-shaft chosen for max torque at 4000rpm, 85.3 hp can be reasonably expected. Calculated ST for a 54" diameter prop will be about 300 lbs,......which is pretty close to what the 50" diameter prop at Rockford was actually producing.
As a rule of thumb, Static Thrust for a GyroCopter needs to be about half the MTOW...... so a Gyro with an 1835cc VW producing 300 lbs ST can have a MTOW not exceeding 600 lbs. The 125 hp engines above gave massive thrusts, and power 2-seaters.
For Gyros, a disc-loading of less than 1.8 lbs per square foot is essential, and a power-loading of less than 8 lbs per hp is also essential.
So an 1835cc VW with a cam ground for optimum torque at about 3600rpm should produce about 72hp easily. Such an engine should be fitted with sodium-filled valves and a large oil-cooler so oil-temperature runs at 200-240 degrees and NEVER goes above 250 degrees.
Experimental Aircraft is a brilliant websitsite for Gyros....check out the JT-5 and the ATE-3 ......both were VW powered.
The ATE-3 was simplest gyro-airframe ever......just a few pieces of welded 4130 round tube.
1835cc VW fitted with Race Cam at 3600rpm Troyer prop 50" x 26" 310 lbs ST (measured).
1756cc VW fitted with Race Cam at 3650rpm Troyer 50" x 28" 330 lbs Static Thrust (measured)
Lyc 125 hp 2600rpm Sensenich 66" x 38" 550lbs ST.
2100cc VW 3500rpm with Race Cam Troyer 54" x 26" 360 lbs ST.
1700cc VW 3250rpm Shaus prop 51" x 27" 270 lbs ST.
1594cc VW 2900rpm Aerial prop 51" x 27" 232 lbs ST.
Franklin 125 hp 2500 rpm Troyer 66" x 42" 550 lbs ST.
All these ST's physically measured at GyroCopter fly-in, Rockford 1977. PRA Magazine October 1977 carried the Chuck Beaty story, plus calculations for HP's and thrusts.
So, for an 1835cc VW with 9:1 CR, stub-exhausts, ample carburation, and a cam-shaft chosen for max torque at 4000rpm, 85.3 hp can be reasonably expected. Calculated ST for a 54" diameter prop will be about 300 lbs,......which is pretty close to what the 50" diameter prop at Rockford was actually producing.
As a rule of thumb, Static Thrust for a GyroCopter needs to be about half the MTOW...... so a Gyro with an 1835cc VW producing 300 lbs ST can have a MTOW not exceeding 600 lbs. The 125 hp engines above gave massive thrusts, and power 2-seaters.
For Gyros, a disc-loading of less than 1.8 lbs per square foot is essential, and a power-loading of less than 8 lbs per hp is also essential.
So an 1835cc VW with a cam ground for optimum torque at about 3600rpm should produce about 72hp easily. Such an engine should be fitted with sodium-filled valves and a large oil-cooler so oil-temperature runs at 200-240 degrees and NEVER goes above 250 degrees.
Experimental Aircraft is a brilliant websitsite for Gyros....check out the JT-5 and the ATE-3 ......both were VW powered.
The ATE-3 was simplest gyro-airframe ever......just a few pieces of welded 4130 round tube.
Assuming we're talking about direct drive . . .
The tip speed of a 65" prop will be 888 FPM (at 70 MPH) at just 3100 RPM (thus leaving a lot of HP on the table--these engines are fine at 3600 RPM). 888 FPM is faster than a wood prop should be going. Also, with these small HPs and a long prop, the prop blades necessarily have very small chords (the engine doesn't have enough torque to turn anything beefier). Too-fast tips and too-wispy thin blades are a recipe for a thrown bade and all the drama that follows.
Example: >If< you can make 50 HP with an 1835cc engine at 3100 RPM and wanted a 65" Dia prop optimized for 100MPH, the prospective blade width at 75% radius would be less than 2" and the blade thickness would be about 1/4". I wouldn't recommend anyone fly behind a wood prop like that under those conditions.
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The Grob prop is 63.5". People tell me it is not noisy.
I think You're not right - most VW engs producers are pushing RPM at 3400-3600, but SAUER S1800 gives 68hp at 3200 and 65hp at 3000RPM - 253m/s , so pretty lower under 0.8M (272.24m/s). Then 63" prop could work with 62hp at 2800 (236m/s). S2100: 85hp / 3000rpm, 80hp / 2700rpm. Also prop blade mustn't be so narrow, as could see.
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PMD
Well-Known Member
When I first got involved with airboats we were a VW restoration business, and I was the engine guy. These were very light commercial boats used for harvesting wild rice, and the universal engine was a 1600 cc single port pretty much dead stock for cam, compression, heads, etc. I built exhaust and direct drives (thrust bearings and torsional dampers mounted flywheel end), so estimate we could deliver about 50 HP at 3400 RPM. We spent a couple of years designing and building literally hundreds of 60" props, and the best we could do was something close to 200 lbs. thrust after a LOT of development. So, the 250 lb. guestimates for an 1835 dual port with a cam sounds pretty good to me. As volume increased we went to Rotax 503 as volume meant I no longer had time to build engines and components, but most of all they were half the weight of the VW and 50% more thrust (300+ static with 72" dia) and cost a heck of a lot less (that was 30 years ago).
Anyhow, after doing to much prop building, I can agree there is a LOT of sophisticated engineering that can be applied, but harsh reality is you need to be able to build something reliably, consistently and affordably so the "black art" part comes up in a big way. That being said: I doubt greatly that I could duplicate today what I became somewhat skilled at 3 decades ago as familiarity and skillsets needed a LOT of volume/experience to develop. BTW: after getting our 72" design features just right, I had them built by someone with a copying mill and a lot more time than I had. A version of them using some of our unique design features is still in production to this very day. I guess what I am saying is that the laws of physics are pretty much the same today as they were a century back, and a prop that was right a very long time ago can be just as right today. I strongly suspect that people at Seinsenich and more than a few skilled practitioners out there do the same things the same way and get the same results pretty consistantly. Of course, speaking of wood here.
Anyhow, after doing to much prop building, I can agree there is a LOT of sophisticated engineering that can be applied, but harsh reality is you need to be able to build something reliably, consistently and affordably so the "black art" part comes up in a big way. That being said: I doubt greatly that I could duplicate today what I became somewhat skilled at 3 decades ago as familiarity and skillsets needed a LOT of volume/experience to develop. BTW: after getting our 72" design features just right, I had them built by someone with a copying mill and a lot more time than I had. A version of them using some of our unique design features is still in production to this very day. I guess what I am saying is that the laws of physics are pretty much the same today as they were a century back, and a prop that was right a very long time ago can be just as right today. I strongly suspect that people at Seinsenich and more than a few skilled practitioners out there do the same things the same way and get the same results pretty consistantly. Of course, speaking of wood here.
jeffwalin, The Jack Norris's book is a difficult book to read, I don't know if there still available, but probably should be. It's a fundamental step beyond traditional methods that Jan Carlsson used in his original Prop Program, however Jan said he used an approach similar to that Jack Norris book in his later (but lost) program. There is also Paul Lipps's Elliptical Lift Approach which has also been proven. As both Jack Norris and Jan Carlsson mentioned Paul Lipps in their discussions with me, I suspect that there is an overlap of ideas which I am currently trying to establish.
Who knows what the difference will be in the outcome - time will tell.
George
Who knows what the difference will be in the outcome - time will tell.
George
davidjgall
Well-Known Member
No offense intended to anyone, but,
"OMG we lost Carlson."
"OMG we lost Lipps."
"OMG Norris' book is inscrutable."
"OMG Theodorsen is opaque."
"OMG we need to go back to the dark ages and conjuring shadowy spirits to get good thrust."
Really, people, it's not that dire. NACA TN 212 by Weick as republished and expanded in Sport Aviation magazine in 1960 is ALL YOU REALLY NEED.
Stop the hand-wringing and go buy some clear 4S4 birch and FPL16A or T-88 epoxy and some giant C-clamps from Homebuilders Freight....
"OMG we lost Carlson."
"OMG we lost Lipps."
"OMG Norris' book is inscrutable."
"OMG Theodorsen is opaque."
"OMG we need to go back to the dark ages and conjuring shadowy spirits to get good thrust."
Really, people, it's not that dire. NACA TN 212 by Weick as republished and expanded in Sport Aviation magazine in 1960 is ALL YOU REALLY NEED.
Stop the hand-wringing and go buy some clear 4S4 birch and FPL16A or T-88 epoxy and some giant C-clamps from Homebuilders Freight....
