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Request for Info: Static Thrust Measurement

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Victor Bravo

Well-Known Member
Supporting Member
Joined
Jul 30, 2014
Messages
13,443
Location
KWHP, Los Angeles CA, USA
Many folks on HBA have read about the trials and tribulations of my Kolb Firestar / HKS engine upgrade project. Today I had the new fuel system, oil system, and associated tomfoolery back together enough to make the first test run of the engine after the recent set of modifications.

As some of you may remember, my Kolb was accelerating on the ground and making what I thought were short takeoffs, but soon after takeoff something big was happening that limited the "cruise speed" to 45-50 MPH, which is 15 MPH slower than it "should" be going with this engine.

Many different opinions were solicited and considered as to the root cause of this. The prop pitch, the airflow into the prop, the oil cooler shoveling air up over the wing center section acting like a spoiler, the carburetors facing rearward instead of forward, etc. etc.

I decided to first fix the one thing that was almost guaranteed to be causing at least some of the problem, if not most of it... I moved the oil cooler and oil tank under the wing, which allowed me to create a "solid" unbroken wing center section cover. No upwards movement of air through the center section to spoil the airflow over the wing or into the propeller. So I did that first, assuming that this effort would notbe wasted.

Today was first engine run day (after the mods), and we were finally able to do a static thrust measurement. At 5850 RPM on the ground, the giant spring scale registered 250 pounds of thrust. The engine is nominally 58-60HP at its redline of 6200 RPM, which means I was making 94% of max RPM. This was with a 3 blade wide chord propeller, 65 inch diameter, with 11 degrees of pitch measured at the tip.

So the purpose of this post is to solicit data/opinion/experience from people who have experience with the Rotax 503, 532, and 582 engines and similar:

How does 250 pounds of thrust compare to what YOU got with your 503/532/582?

Does 250 pounds of thrust seem like a little, a lot, or average to oyu for what is "nominally" a 60HP class engine... somewhere between the 503 and 582?

How many pounds of thrust do YOU think is appropriate or acceptable for an ultralight and LSA style aircraft being set up for short takeoff performance?
 
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