Request for Info: Static Thrust Measurement

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Victor Bravo

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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?
 

lr27

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What's the prop rpm? The air really doesn't know what kind of engine you have. Stan Hall had an article about whether redrives are worth it in the August 1973 Sport Aviation. It's all computed, rather than tested, but he has a chart showing a 64.X 45 giving just over 250 lbs at 2,500 rpm, driven by 60 hp - a couple of percent for the redrive. i calculate that you have about 40 inches of pitch. So I'd say you're not TOO far off. Doing this on a phone, so I may not have caught every example of auto-misspell.
 

lr27

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It makes a difference just what prop you're using, so the previous is just a ballpark figure for what your engine is putting out. There was a thread on here someplace about substituting a rectangular "club" prop to act as a crude dyno.
 

Turd Ferguson

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Upper midwest in a house
Based on what people are measuring on youtube videos, that 250 number sounds good.

I also agree with what MRS is saying, if the RPM increases and the engine comes off the power band, the decrease in power is like putting on the brakes.
 

Wanttaja

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I'd love to see examples of static thrust measurements, including the engine and propeller types.

We've got a guy in the Fly Baby community trying a VW engine with redrive. The symptoms he's reporting sounds like he's not getting enough thrust. We've recommended a static test, but need examples of static tests of "standard" engines and propeller to compare it to.

Ron Wanttaja
 

henryk

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Location
krakow,poland
-now we start measuremants with conterrotatig propellers=2x 1.7 m ,3-blade...

-engine G13 (circa 70 HP at 5000 RPM)=

=one propeller +2:1 gear =180 kG thrust (390 lbs)

=two propellers +3:1+1 gear (differetial)=220 kG (480 lbs)

(the smoke allmost strite,good focused,silent stream but powerfull=no possibility to stay 5m after propellers !)
 

lr27

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3,822
Ron:

The prop that gives you the most static thrust may not be the one that gives you the most thrust at 40 or 60 mph, though I wouldn't bet against it unless it was a really big one with relatively flat pitch.

According to Great Planes:
http://www.greatplainsas.com/screddr.html

http://www.zenith.aero/video/701-static-thrust-test Yes, you can see the spring scale later in the video.

---------------
VB:

I don't know the company, but I wouldn't be completely amazed if Arplast had a chart showing thrust at different rpm's, power, and pitch. Or I could be COMPLETELY wrong, since I haven't dug up such a chart in the past.
 

Wanttaja

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Sep 15, 2013
Messages
1,479
Location
Seattle, WA
Keep 'em coming...
Engine
PSRU​
Propeller​
RPM​
Nominal HP​
Static Thrust (lbs)​
Source​
HKS
3.47:1​
3-blade, 65"​
5850​
60​
250​
HBA Posting​
Suzuki G13
2:1​
3-blade, 66"​
5000​
70​
390​
HBA Posting​
Great Planes VW 2180 cc
1.6:1​
72x40​
100​
350​
HBA Posting​
Great Planes VW 2180 cc
2.0:1​
84x56​
100​
450​
Great Plains Web Site​



Ron Wanttaja
 

lr27

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Nov 3, 2007
Messages
3,822
If it was my airplane, I might try to recreated the prop, more or less, in Javaprop and see what it said. A bit fiddly, but unless you can find some results with similar horsepower and a very similar prop, it might be a little more accurate.

http://www.mh-aerotools.de/airfoils/javaprop.htm
 
Last edited:

Wanttaja

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Sep 15, 2013
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Location
Seattle, WA
Ron:

The prop that gives you the most static thrust may not be the one that gives you the most thrust at 40 or 60 mph, though I wouldn't bet against it unless it was a really big one with relatively flat pitch.
Understood, and this might be what's affecting that VW-powered Fly Baby... the owner reports it gets off the ground, but doesn't accelerate.

But having SOME data is better than no data at all...

The problem is going to trying to ensure consistency...the RPM at the actually measurement, vs. someone supplying the red-line RPM of the engine. And like the Great Plains examples...they're listed as 100 HP, but only 60 HP continuous.

Ron Wanttaja
 

pictsidhe

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Jul 15, 2014
Messages
7,500
Location
North Carolina
I'll give javaprop a prod when I get a few minutes on the PC. Static thrust is a good measurement of static thrust, but a poor indication of in-flight thrust. Too fine and you'll over rev in the air. Props also have a habit of running part or all of thw blades stalled statically. In which case, thrust will initially increase as you gain speed. 250lb doesnt sound too wrong to me.
When you were troubleshooting the low performance, my calculator thought you may have had the pitch too fine. Since you have an adjustable prop, go fly it, then try tweaking the pitch.

Arplast is no more, a liability case killed them.
 

TFF

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Apr 28, 2010
Messages
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Location
Memphis, TN
Static rpm is a great health check when you have the setup right. Static thrust is not a tell all
Because it depends on which side of the power curve you are on to really know if you will accelerate into range or be already on the over run. I would test hop the plane and vary the pitch. I would test +2 and -2 pitch and see how it goes. Let flying teach you what the plane wants. From other posts it sounds like there is plenty of runway to take off and land without going around the pattern, so you can abort if it's straining to fly. One direction should prove better. if not you probably need more hp.
 

poormansairforce

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Mar 28, 2017
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Location
Just an Ohioan
I have never understood the need for 3 bladed props on these light weight airframes. IMHO, your out of advance on that prop/ redrive setup. A couple more degrees of pitch will help but it really needs a 2 blade prop turning more rpms. This will get you plenty of static thrust as well as more speed. I had a Kaw 340 w/2.58 redrive turning a 60x30" wood prop on my Minimax and had 200# thrust and cruised 50mph no problem. With 60 hp, well, wow!

Go to http://www.tn-prop.com/PropRecommend.html and see what they are recommending for the Rotax engines you mentioned.
 

Victor Bravo

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KWHP, Los Angeles CA, USA
I have never understood the need for 3 bladed props on these light weight airframes.

but it really needs a 2 blade prop turning more rpms.
The distance between the propeller shaft center and the fuselage tailboom is 33 1/4 inches. So the 65 inch diameter propeller I am limited to cannot be any bigger without smacking the tail off the airplane.

I will not raise the propeller higher because it will cause pitch problems with the aircraft, trying to nose it over with power application.

I cannot use a 4 blade propeller because it will prevent the wing folding and storage of this aircraft. So the option of keeping it assembled and not folding it (allowing a 4 blade prop) has also been taken off the table. No additional hangar rent for me at present.

This engine has a 3.47 to 1 gear ratio, which means a slower turning propeller. I cannot and will not change the gearbox ratio due to the fact that the cost of the change-over is simply not in the cards for me right now.

With this absolute limit on propeller diameter, combined with a very high gear ratio / low prop RPM, the one and only parameter I can change is the area and pitch of the blades. So I found a propeller with extra wide chord blades, more blade area, and that's all I have to work with. All of the other "easy" answers are things I cannot afford to do.
 

poormansairforce

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Messages
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The distance between the propeller shaft center and the fuselage tailboom is 33 1/4 inches. So the 65 inch diameter propeller I am limited to cannot be any bigger without smacking the tail off the airplane.

I will not raise the propeller higher because it will cause pitch problems with the aircraft, trying to nose it over with power application.

I cannot use a 4 blade propeller because it will prevent the wing folding and storage of this aircraft. So the option of keeping it assembled and not folding it (allowing a 4 blade prop) has also been taken off the table. No additional hangar rent for me at present.

This engine has a 3.47 to 1 gear ratio, which means a slower turning propeller. I cannot and will not change the gearbox ratio due to the fact that the cost of the change-over is simply not in the cards for me right now.

With this absolute limit on propeller diameter, combined with a very high gear ratio / low prop RPM, the one and only parameter I can change is the area and pitch of the blades. So I found a propeller with extra wide chord blades, more blade area, and that's all I have to work with. All of the other "easy" answers are things I cannot afford to do.
Sorry, I do understand about money constraints as I have them as well. I never mentioned a bigger diameter prop or more blades as that is not what you need. You need less blades with more rpm or less diameter with more pitch. Contact the prop maker and see if it's feasible to cut the blades down?
 

Armilite

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Sep 5, 2011
Messages
3,281
Location
AMES, IA 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?
=============================================================================

I don't know if this Helps You or not! Redline, on a 2 Stroke is what ever you want 5500 to 7500 for Stock Engines. UL Engines Industry Standard is 6500rpm. That Redline is Dictated by your Engines Carb Size and Exhaust Type. Do you have an Actual Dyno Print/Chart of your Engine?

Even if we use your Engines Max 6200rpm/3.47(Redrive) = 1786.743515850144 Prop Rpm (1786.7)!

Prop Thrust Calc.
http://godolloairport.hu/calc/strc_eng/index.htm

At your (58-60hp) Props suggested for a a 503(50hp).
http://ultralightnews.com/engineinfo/propeller_chart1.htm

Rotax 503 Engine Dual Carb - 2. to 1 ratio
56 x 32, 58 x 30, 60 x 28

Rotax 503 Engine Dual Carb - 2.23 to 1 ratio
62 x 28

Rotax 503 Engine Dual Carb - 2.58 to 1 ratio
68 x 32
-------------------------------------------------------------
Props suggested for a a 532UL(64hp).

Rotax 532 Engine - 2. to 1 ratio.
52 x 40, 56 x 38, 58 x 36, 60 x 34, 62 x 36

Rotax 532 Engine - 2.23 to 1 ratio.
60 x 40, 62 x 38, 64 x 36

Rotax 532 Engine - 2.58 to 1 ratio.
68 x 44
------------------------------------------------------------
Props suggested for a a 582UL(65hp)

Rotax 582 Engine - 2. to 1 ratio.
66 x 30

Rotax 582 Engine - 2.23 to 1 ratio.
68 x 32

Rotax 582 Engine - 2.58 to 1 ratio.
68 x 46, 70 x 44
-----------------------------------------------------------
3.47 is quite a Reduction.

Your 65" x 11 (3) Blade at 6500rpm/3.47 = 1873.1 Prop Rpm = 235.09 pounds Static Thrust!

Your 65" x 11 (3) Blade at 6200rpm/3.47 = 1786.7 Prop Rpm = 213.90 pounds Static Thrust!

Your 65" x 11 (3) Blade at 5800rpm/3.47 = 1671.4 Prop Rpm = 187.18 pounds Static Thrust!

==============================================================
Your 64" x 11 (3) Blade at 6200rpm/3.47 = 1786.7 Prop Rpm = 213.9 pounds Static Thrust! (Math doesn't lie)
Changing the Pitch didn't change the Static Thrust! Only changing the Lenght did the Static Thrust change.
If Max Rpm is 6200rpm, I would think you would want to Pitch it for 6100rpm!

Your 64" x 11 (3) Blade at 6200rpm/3.47 = 1786.7 Prop Rpm = 201.04 pounds Static Thrust!
Your 65" x 11 (3) Blade at 6200rpm/3.47 = 1786.7 Prop Rpm = 213.90 pounds Static Thrust!
Your 66" x 11 (3) Blade at 6200rpm/3.47 = 1786.7 Prop Rpm = 227.37 pounds Static Thrust!
Your 67" x 11 (3) Blade at 6200rpm/3.47 = 1786.7 Prop Rpm = 241.47 pounds Static Thrust!
Your 68" x 11 (3) Blade at 6200rpm/3.47 = 1786.7 Prop Rpm = 256.21 pounds Static Thrust!
Your 69" x 11 (3) Blade at 6200rpm/3.47 = 1786.7 Prop Rpm = 271.62 pounds Static Thrust!
Your 70" x 11 (3) Blade at 6200rpm/3.47 = 1786.7 Prop Rpm = 287.71 pounds Static Thrust!
 

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poormansairforce

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Ok, now I understand why my 340 performed almost as well as your "60" hp HKS. It's not 60 hp.

680cc at 6200 rpm at 90% effecient= 45 hp! There is no way it's 60 hp. At 5850 it's about 42 hp. That prop will never work on it as the pitch will be limited. The video I watched claimed 2.5 gal/hr which is a BSFC of .24 at 60 hp. I would seriously doubt it's much more than a 40hp engine......

Edit: Unless they are claiming that as cruise BSFC which would still be stellar but the prop doesn't have the advance needed.
 
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Highplains

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Jun 2, 2014
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Location
Over the Rainbow in Kansas, USA
I don’t think static tests of a prop mean very much, as much of the prop is stalled. You measured 11 degrees at the tip, but using what reference? Th backside of the blade or the actual zero lift point of the airfoil, or the center line of the airfoil.

Of course, I disagree with adjustable props too, because a slight change in degrees throws off the pitch curve of the entire blade. Unfortunately the propeller is the most complex part of entire airplane.
 
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