thrust expected from an 1834cc VW?

[TFF]

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.

 

[rv7charlie]

'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.

 

[flitzerpilot]

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.

 

[plncraze]

Did you enjoy it? LOL

 

[flitzerpilot]

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!

 

[Marc W]

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.

 

[Doran Jaffas]

Thatcher CX4, 2180 cc and a Sensenich 60"x44". I climb at 80mph and see 2900 rpm there. My home airport is at 5,200' and I often climb to 11,500' or so to clear the local mountains. I don't have a VSI but I typically climb from takeoff at 5,200' to 10,200' in 7-1/2 minutes which averages out to 666 fpm. Wot in level flight at 8000' or so trues out to 137 mph or so at 3200 rpm.

The interesting thing is that last year I borrowed a Sensenich 54"x44" that came off a Sonex. Speeds and climb rates were virtually identical. The difference is that the 54"x44" took 400 rpm more to reach the same numbers.

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]

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.

 

[Marc W]

We agree then! There is a lot more to it than pitch and diameter. I don't care for the term "black art". I prefer to think of it as a very complicated engineering problem.

 

[TFF]

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.

 

[EzyBuildWing]

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.

 

[simflyer]

What about 63" - 65" prop? Does anybody have power/torque curves of VW 1700ccm and 1835ccm ?
Does anybody have drawings of newer airfoils and shapes for wooden props ?

 

[Vigilant1]

What about 63" - 65" prop? Does anybody have power/torque curves of VW 1700ccm and 1835ccm ?
Does anybody have drawings of newer airfoils and shapes for wooden props ?

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.

 

[BBerson]

The Grob prop is 63.5". People tell me it is not noisy.

 

[Pops]

1835 cc VW swing a 60" pitch prop at 3200 rpm. Prop noise. I know you have seen this many times.
Up hill 900' runway with trees.

 

[simflyer]

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.

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.