field calc'd horsepower for Hua Sheng/Grubee

[Vishnu Tensleep]

My Hua Sheng is now nicely broken in and I'm using a Grubee with about 200 miles on it, with gear oil in the box (which works very nicely I think). I'm running a 50-tooth sproket on the back which gives me a top speed on the flats of about 32 if I'm crouching. My bike can be seen on the picture forum.

I wanted to see what the real-world horsepower is, so I did some speed tests, one on a hill and one on the flats, and used a bike power calculator on the web at http://www.mne.psu.edu/lamancusa/ProdDiss/Bicycle/bikecalc1.htm. This site factors in wind resistance, tire type, etc.

To cut to the chase (details below), my Hua Sheng is putting out an estimated 1.25 to 1.3 HP between cruising RPM and wound out.

I'm interested in seeing what other folks have found in field tests. My bike works great on the flats and mild slopes, but at anything over 6% slope (common in Seattle) I have to pedal hard, and pretty much avoid anything over 9% for any stretch, which reduces the utility for commuting and errands. My choices seem to be a multiple-gear drive train, which seems expensive and adds more weight and moving parts, or maybe using a different engine - maybe a Honda is I want to stay with a 4-stroke and at or under 50 cc?

Has anyone else done such tests to quantify the many qualitative claims on this web site that the Honda is indeed significantly more powerful than the Hua Sheng?



Here's the details for all you gearheads.

I weigh about 210 lb with all of my riding gear on, my bike fully fueled weighs about 50 lb.

Test 1 - engine wound out on the flats, no wind, 32 mph

Assuming no mechanical losses

total power output needed = 0.97 HP
wind resistance = 0.75 HP
tire resistance = 0.22 HP

now, obviously there is lots of power loss in the transmission, and the calculator shows 'typical' bike losses at 3% to 5%. If I put in 25% for my bike I get

total power output needed = 1.3 HP

Obviously there is some uncertainly in my assumptions but this is in the ballpark of the manufacturer's claim of 1.5 HP (or maybe it's 1.4, or 1.1, depending on what piece of oil-stained paper you're reading)...


Test 2 - up 5% slope at 21 mph with est 15 mph tail wind, engine not winding out but not sounding or feeling too loaded either

Again assuming 25% losses in the bike, and putting a wind coefficient of 0.0012 instead of 0.0027 to allow for the tail wind, the web calculator gave:

total power output needed = 1.25 HP, with
HP for elevation gain = 0.72 HP.

Again in the ball park if my assumptions aren't too far off.

 

[xPosTech]

If you are going to put this much effort into testing you need more reliable input data. It is hard to estimate wind speed but very simple to put together a wind speed indicator. Good data is needed because the drag will vary as the square of velocity. The power needed to overcome drag will vary as the cube of velocity.

You will need a small dc motor, a small ammeter or voltmeter and either a horizontal prop or a vertical cone type drive. Keep every thing small. Just run the wires from the motor to the meter. You can mount it temporarily on the handlebars for your tests. Calibrate by holding it out the window (on a calm no wind day) of a car and recording the milliamperage or voltage at each speed, say 5, 10, 15, etc.

The cone type (like an anemometer) is easy to fabricate using the plastic eggs given out on Easter.

As far as frontal area, support your bike in riding position (a trainer is perfect) and take a picture from directly in front with a light background. A white wall would be good but make sure you aren't casting shadows that would interfere with the contrast conversion.

Wear your normal riding gear. Your helmet (you do wear one don't you?), jacket, etc.

A vertical and horizontal yardstick in the picture will help. Convert to high contrast black and white and use a photo editor like Photoshop or Gimp to calculate the frontal area.

At least I think you can do this. I'll look into it.

These two data should improve the accuracy of your calculations.

These are just suggestions. Since you're going to the trouble, might as well have good data.

Good luck. I'll be following your progress.

Ted

 

[xPosTech]

Calculating Frontal Area

I've thought a little more about calculating your frontal area. Place the yardsticks on the plane that dissects the center of your area. I.E. the plane equidistant from your wheels. I don't think it's that critical but if you're into it this much might as well do all you can to get good data.

After the pic is opened in your editor crop the picture to an easy dimension to work with. I. E. using your yardsticks, make the image six feet by six feet. Carefully airbrush out any extraneous "stuff" (the trainer, any shadows on the wall, etc.

When you start converting to black and white you might have to go with a gray scale intermediate step(s). Keep

Once you convert to black and white, compare the two images. You might have to play around with touching up to get a true idea of the area we're going to calculate.

Hmmm . . . I just played around with Gimp for a while. It's the first time I've tried to do anything like this. Years ago at the Post I used Photoshop to test color on CRTs in Tech Services but I'm totally lost now. Unless you know current Photoshop or Gimp image editors I suggest finding someone who does know and send the pic to them to posterize (reduce to two color) and get a percentage of black as relating to the whole pic.

Since we know the pic is six feet by six feet it's 5184 (36 X 144) square inches. If the black in the much edited pic is 21.2% then your frontal area would be 1099.008 square inches.

This may be too time consuming for your measurements but I just thought I'd throw it out there. I know Photoshop will give a percentage of color when you select that color. Color percentages equated to ink settings on the presses. Gimp should do the same but I have yet to find it.

Speaking of time consuming I've got to drop an engine in a frame.

Again, good luck.

Ted

 

[Vishnu Tensleep]

Ted -

While your approach would undoubtedly impove the accuracy of my calc's, I'm not so much interested in knowing the real numbers but only in a comparison of the two engines with roughly equivalent drive trains. There are lots of folks on this site who claim that the HS 142 engine has less power than the Honda GHX50, and the mfgrs claim that too. My question is "has anyone had the two motors on the same or similar bikes, ridden the same route, and actually looked at numbers - even comparative top speeds?"

But I do appreciate the thoughts. You and my friend Ross, who is even more of a gearhead than I am, would get along famously.

 

[Irish John]

Ted -

While your approach would undoubtedly impove the accuracy of my calc's, I'm not so much interested in knowing the real numbers but only in a comparison of the two engines with roughly equivalent drive trains. There are lots of folks on this site who claim that the HS 142 engine has less power than the Honda GHX50, and the mfgrs claim that too. My question is "has anyone had the two motors on the same or similar bikes, ridden the same route, and actually looked at numbers - even comparative top speeds?"

But I do appreciate the thoughts. You and my friend Ross, who is even more of a gearhead than I am, would get along famously.

I've had several Hondas and Hs on the same bike on the same roads and I can tell you for certain that the Honda will pull harder than the HS. It also has a higher cruising speed. On a steel framed Schwinn D7 cruiser - a heavy bike - the HS can't handle the weight with a 48T sprocket but the Honda can and drives almost like a car. On a Schwinn Alloy 7 cruiser - a light bike the HS is pretty good on a 48T sprocket but the Honda will fly and hits speeds of 10 km\hr faster flat out. The 48T is the best sprocket for a Honda and the HS probably needs a 50T (which I can't get but which Don Grube tells me will come standard on future kits) but not a 56T because that is too slow and causes too much vibration and has more clearance problems.
A 44T is a waste of time on either bike but there is a guy in Florida who thinks otherwise but I can only assume that all of Florida is downhill and that you never have to stop and start again at traffic lights. Because I've ridden a 44T on the flat and a strong headwind will kill it.
The Honda valves don't rattle like the HS which becomes really loud after a few thousand kms. The Honda valves rattle but nowhere near as badly. The rattle doesn't seem to affect the motors incidentally.
The oil changes on a Honda have noticeably more metal dust in the oil and I can only presume that this is because they are engineered to a finer precision.
I suspected this for a while but now I know it after building several bikes with each type of engine. The HS is a great motor but the Honda is considerably greater.
Also wet gearboxes don't work as well as lithium grease and there is a long thread here that confirms this fact.