Hi all,
What kind of thrust would you expect to get from an 1834cc VW?
What kind of thrust would you expect to get from an 1834cc VW?
thrust expected from an 1834cc VW?
- Thread starter Twodeaddogs
- Start date
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Thrust is determined by pitch, number of blades, and diameter of the prop, not by the horsepower. HP only determins top speed and rate of climb. For instance a fully loaded J-3 Cub has 40 Watts per pound, a Mooney has 80 Watts per pound and a Spitfire has 130 Watts per pound (Sorry about the units but power is power). Start with how fast you want to go. From there you can figure out what power loading you need and from that you can figure out how heavy an airplane can be driven by a VW with an appropriately pitched prop.
So if I put a Spitfire prop on a VW, I get the same thrust? Cool! Same pitch, number of blades, and diameter of the prop, right?
I think you're bending the laws of physics with that statement.
At what airspeed and maximum prop diameter? The airspeed matters a lot.
Maybe I should have also said "RPM" in that sentence but I did mention that you need an appropriate prop for the engine a bit later.
typical 57 to 60 inch prop for 3400 rpm?
Start with 250 pounds of thrust as a wild-ass-guess estimate, that seems reasonable to me for something like a Sonex or Thatcher. That is a rough guess but nobody else has made one 
From there, you can do all sorts of calculations and get a better "real" number.
From there, you can do all sorts of calculations and get a better "real" number.
Assumptions: SL, std day. 60 HP, 3400 RPM. Two-bladed wood prop with a pitch optimized for the given airspeed (so, the same prop won't produce all the numbers shown below). Prop diameter chosen to keep tip speeds below 880 FPM and reasonable camber ratios.
Airspeed.....Pitch....Diam............Est. Thrust
50 MPH........22.2".....59".................249 lbs
60 MPH .......24.4".....58"................231 lbs
70 MPH .......26.7".....57"................213 lbs
80 MPH........29.1".....56"................198 lbs
90 MPH........31.7".....55"................184 lbs
100 MPH.....34.6".....55"................172 lbs
110 MPH.....37.5".....54".................160 lbs
120 MPH.....40.5".....53".................150 lbs
130 MPH....43.7"......53".................141 lbs
Airspeed.....Pitch....Diam............Est. Thrust
50 MPH........22.2".....59".................249 lbs
60 MPH .......24.4".....58"................231 lbs
70 MPH .......26.7".....57"................213 lbs
80 MPH........29.1".....56"................198 lbs
90 MPH........31.7".....55"................184 lbs
100 MPH.....34.6".....55"................172 lbs
110 MPH.....37.5".....54".................160 lbs
120 MPH.....40.5".....53".................150 lbs
130 MPH....43.7"......53".................141 lbs
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Didn't we just do this recently? ... Static thrust
Engine on the SSSC. 1835 cc, 60 HP, 3200 rpm at WOT @ 94 mph. Prop Culver 60" x 26" . Cruise at 2650/2700 rpm at 80 mph @ 3 GPH. ROC= 1200+ FPM.
I know that prop and engine combo has proven to be great for your SSSC. I'm guessing that the prop blades have quite a bit of camber to their airfoil if it gets you to 94 MPH with a 26" pitch. Sounds like it climbs great.
I don't know about the pitch except its stamped 26" Could be different, I don't know. That climb of 1200/1250 fpm is at about 780 lbs.
BrianW
Well-Known Member
If your aircraft has an expected climb/cruise speed of 20 mph, then secure it to a ground anchor with a load meter, apply full throttle and read the force indicated. What could be simpler?
Brian W
rv7charlie
Well-Known Member
Running into the trees at the end of the runway while still in ground effect?
the VP-2 that I flew had a 57 x 32 prop on an 1834cc engine and gave 70 mph in the cruise, so it falls somewhere between 184 and 213 lbs.
The thrust in cruise is same as the drag. So just shut off the engine and measure the airspeed and sink rate to calculate drag.
If you want exact then remove the prop and tow it aloft. But who needs exact?
pictsidhe
Well-Known Member
CAFE set up switches to measure end float on the crank. They could tweak the throttle for zero thrust.
flitzerpilot
Well-Known Member
With the original 'Clark Y' section propeller 60" x 32" on the Flitzer Z-1 prototype equipped with an 1834cc VW, it delivered some 150 lbs of thrust (from memory) with an Avoscale on a cable attached to the tailskid, using a Jaguar saloon as an anchor.
I took the propeller home and modified the section to approximate the USA 5 as a theoretical low drag section, rebalanced the propeller and the following weekend tested it again. This time it indicated 212 lbs of thrust and dragged the Jaguar across the grass, gradually accelerating throughout. I shut down to avoid colliding with a hangar, otherwise who knows how fast it would have gone (estimated 4 mph).
Current prop was pitched at 34" at the root and 32" at mid-diameter which holds the full throttle RPM to 3000 with no loss of maximum level speed (92 mph) or climb rate >700 fpm at typical load. I think the bullet cowl contributes to available thrust from closer to the hub. This theory is based on the experience of the Austro-Hungarian Luftstreitkraeft in WW1 when they removed the bowl spinners from their OAW Albatros 253-series fighters, cowling tightly around their Austrian-Daimler crankcases, to gain over 10 mph as a result.
This propeller was inadvertently cropped by about 2" following an incident with a deer which charged me on take-off. After trimming and rebalancing this has not appreciably affected performance, although I do intend to fit an optimal Hercules propeller in due course. The Flitzer Z-21 demonstrator for Hercules propellers allows full throttle operation during a continuous (+g) aerobatic sequence to be performed without overspeed, maintaining 3000 RPM throughout.
I took the propeller home and modified the section to approximate the USA 5 as a theoretical low drag section, rebalanced the propeller and the following weekend tested it again. This time it indicated 212 lbs of thrust and dragged the Jaguar across the grass, gradually accelerating throughout. I shut down to avoid colliding with a hangar, otherwise who knows how fast it would have gone (estimated 4 mph).
Current prop was pitched at 34" at the root and 32" at mid-diameter which holds the full throttle RPM to 3000 with no loss of maximum level speed (92 mph) or climb rate >700 fpm at typical load. I think the bullet cowl contributes to available thrust from closer to the hub. This theory is based on the experience of the Austro-Hungarian Luftstreitkraeft in WW1 when they removed the bowl spinners from their OAW Albatros 253-series fighters, cowling tightly around their Austrian-Daimler crankcases, to gain over 10 mph as a result.
This propeller was inadvertently cropped by about 2" following an incident with a deer which charged me on take-off. After trimming and rebalancing this has not appreciably affected performance, although I do intend to fit an optimal Hercules propeller in due course. The Flitzer Z-21 demonstrator for Hercules propellers allows full throttle operation during a continuous (+g) aerobatic sequence to be performed without overspeed, maintaining 3000 RPM throughout.
