Static Thrust Number?

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tomz28

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Mar 14, 2021
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Hello gents!
I am interested in what others are reporting for static trust numbers. my baseline last weekend was 216lbs. this was my 1835cc at 2800rpm with a 60x28 prop. my crab settings still need to be dialed in and my timing was a few degrees low. i am going to build a oil box around my intake like pops did. before i try again. cylinder number 3 is the hottest by far.

thanks

 

Pops

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My 1835 cc VW engine with a Culver 60"x26" prop at static turns 2950 rpm. On climb out at WOT the rpm is 3200. Never checked the static thrust.

If #3 is running hotter than the others, try making more volume on the eyebrows over the cylinders and heads. I would try adding about 1.5" to the height of your eyebrows. See if that makes a difference. Mine runs within 25 degrees on all 4 cylinders.
Sure is a pretty airplane.
What is the empty weight ?
 
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tomz28

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My 1835 cc VW engine with a Culver 60"x26" prop at static turns 2950 rpm. On climb out at WOT the rpm is 3200. Never checked the static thrust.

If #3 is running hotter than the others, try making more volume on the eyebrows over the cylinders and heads. I would try adding about 1.5" to the height of your eyebrows. See if that makes a difference. Mine runs within 25 degrees on all 4 cylinders.
Sure is a pretty airplane.
What is the empty weight ?
pops just over 400 lbs i think. i need to put it back on my scales and see
 

Pops

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Check and make sure all the air passages down between the fins in the head are clean of any flashing and restricting the airflow.
 

tomz28

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Check and make sure all the air passages down between the fins in the head are clean of any flashing and restricting the airflow.
it is very clean. The amount of condensation on the intake was unreal!!!! i think a hot box on the intake is a must! before i get to crazy.
 

Pops

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Just comparing it with my SSSC with the same size engine. My EW was 450 lbs, then I went from small 5" wheels and tires to large 6" wheels and tires. Built a new wing stressed for the extra weight of 8 gal of fuel to 16.6 gal. Added electric elevator trim and a 5 lb , 12 volt battery for the trim servo and the handheld radio. Weight went to 485 lbs EW.
 

tomz28

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Just comparing it with my SSSC with the same size engine. My EW was 450 lbs, then I went from small 5" wheels and tires to large 6" wheels and tires. Built a new wing stressed for the extra weight of 8 gal of fuel to 16.6 gal. Added electric elevator trim and a 5 lb , 12 volt battery for the trim servo and the handheld radio. Weight went to 485 lbs EW.
So im doing good is what you are saying lol
 

Dan Thomas

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Static thrust numbers don't mean that much. You can get good static thrust out of a small engine with a low-pitched prop, but as soon as you start moving the thrust will drop off and you might not even get to flying speed, and the engine will shoot past redline.
 

Pops

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Local friend of mine built this Skyraider . Both the SSSC and Skyraider has 120 sq' of wing area, same EW. The SSSC has a 1835 cc, 60 HP VW engine and the Skyraider has the 60 HP, HKS engine. Both has the same ROC and Cruise speed. I weigh about 30 pounds more than the owner.
 

trimtab

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Static thrust numbers don't mean that much. You can get good static thrust out of a small engine with a low-pitched prop, but as soon as you start moving the thrust will drop off and you might not even get to flying speed, and the engine will shoot past redline.
....and the static thrust is also dependent on the prop diameter. A prop that is double the diameter is capable of producing roughly 60% more static thrust, and will run into the same wall described at speed unless variable pitch.

It's roundly how the engine used in the C-130 is able to be used to lift the entire V-22 on a single engine. Very different static thrusts and conditions, different props and prop diameters.
 

challenger_II

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Always bear in mind that "static thrust" is a tool, not the whole tool chest. When determining what a given power package will do for a given airframe, One must combine the static thrust, as measured, with the theoretical speed of the prop. There are more variables, but these two will give a quick and dirty answer to whether the power package may fly the plane.

An example comes from my days experimenting with the AO-84 genny engine:
One of our test subjects was a Fisher FP-101. With the engine, and the required tail ballast, the plane weighed 360# empty. She carried 30# of gas. Pilot weight was 180#. Static rpm 3150, unloaded rpm varied with propeller.
The team each individually worked out what prop we should use (apples to apples, each prop was a Tennessee wood prop, cut to request).
One team member recommended a 60x22 prop. This prop developed the most thrust of any we tested, and would haul the plane off the runway in a short distance, and climb close to the rate a two-stroke would. However, when you leveled off, it was like hitting a brick wall. The plane would barely make 40mph (measured by GPS, boxing the compass), which is about 67% of theoretical pitch.
Next, we used a 54x26 prop, at the same static rpm as the 60x22. This gave about 2/3rd the static thrust as the 60x22. However, while the climb was reduced by a third, when you leveled the plane, the top speed shot to 75mph (again, verified by gps, boxing the compass), which works out to a staggering 98% of theoretical pitch.
For reference, the tests were conducted on the same day, within two hours of each.
 
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tomz28

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Static thrust numbers don't mean that much. You can get good static thrust out of a small engine with a low-pitched prop, but as soon as you start moving the thrust will drop off and you might not even get to flying speed, and the engine will shoot past redline.

this thing was a rocket
Local friend of mine built this Skyraider . Both the SSSC and Skyraider has 120 sq' of wing area, same EW. The SSSC has a 1835 cc, 60 HP VW engine and the Skyraider has the 60 HP, HKS engine. Both has the same ROC and Cruise speed. I weigh about 30 pounds more than the owner.
i see Tennessee props says to run a 52x28 prop
 
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