# Weighing an Engine

Discussion in 'Workshop Tips and Secrets / Tools' started by Lucrum, May 7, 2010.

1. May 7, 2010

### Lucrum

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Couldn't find what I was looking for in a search.

Are there any simple/inexpensive methods for weighing an engine.

I'm anticipating 425 - 450 LBS. My first thought was to buy a spring scale and weigh while the engine is hanging from the hoist. But I hate to spend $250 -$500 for a scale capable of handling that weight that I'll likely only use once.

2. May 7, 2010

### Joe Fisher

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Suspend the engine from a beam between two benches. The beam is on top of a scale on one end.If the engine is in the middle of the beam the scale will read 1/2 of the actual weight+ the weight of half the beam. You could use say 1/3rd and 2/3rds to read 1/3rd of the total weight + half the weight of the beam.

3. May 7, 2010

### Dana

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Or use a smaller spring scale and rig up some pulleys for a block and tackle to divide the weight.

-Dana

The Definition of an Upgrade: Take old bugs out, put new ones in.

4. May 7, 2010

### dhammer

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I once put one in the back of a truck and drove to the scales at a grain elevator. Weighed the combo then returned to weigh again without the engine. Topped off the fuel before each trip. Subtracted the difference and had my weight.

5. May 7, 2010

### Dan Thomas

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Couple of bathroom scales with a plank across them. The scales can be checked for accuracy on scales of known accuracy (like the balance-beam scales at the doctor's office or at the place where you get your BBQ's propane tank filled) by putting the bathroom scale on the good scale and standing on that; the bathroom scale should read your weight and the good scale should read the same weight plus the weight of the bathroom scale.

Dan

6. May 7, 2010

### lr27

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If you've got an accurate way to measure water, you can use that as a counterweight. Or, you can weigh yourself on a known good scale and use yourself as a counterweight. But do it quickly before you sweat too much, drink too much, change clothes, etc.

So the idea would be to suspend a beam by a rope close to one end, with another rope on it to fasten to the engine, and some counterweights so it balances level with the rope on it. Then tie it to the engine and try your big counterweight at various distances. (If you had the beam at 6 feet or so off the ground, you could just hang on and pick up your feet.) When the engine just BARELY lifts, you've got the right distance. Then just take the ratio of the distances.

Another trick, though it's a bit silly, works if you have a small swimming pool or tank, an accurate way to measure water volume, and a little boat or some floating thing that will hold the engine. Fill level with a hole, then plug the hole and put a container under it. Put the engine in the boat, and the boat in the pool. (hmm,... maybe weight the "boat" first) Pull the plug and fill a measured container. Replug, dump the first load, and refill. Count the number of containers and you've got it. I know it sounds silly, but if you happen to have that stuff on hand, and you don't have a beam, it's an easy way to do it. And I think a fairly small kiddie pool would do. Maybe a small one and one a little larger. The smaller one is your "boat", perhaps with a bit of plywood in the bottom. Don't let it touch the bottom.

7. May 7, 2010

### jumpinjan

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Ah, how about just borrowing or renting a scale...? That would be a LOT easier than finding a swimming pool?

8. May 7, 2010

### lr27

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You're no fun at all!

9. May 9, 2010

### deskpilot

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:roll:

As an aside, when talking engine weight, should that include all ancillary equipment and prop assy?

10. May 9, 2010

### DarylP

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I would be curious to know how many people have actually weighed their engine. Take a 912 ULS, that has a radiator which is not included in the specs as far as listed weights are concerned. How would you really know what the weight would be until you installed it and then weighed it. If anyone has done that, it would be great info for those of us that have yet to purchase an engine. I always wonder just how close those weights from the manufacturers are, and if the FAA requires the specified weights to be validated. Its not like you can weigh one before you buy it.

11. Jun 26, 2010

### waterinthefuel

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Maybe I'm being ignorant on this, but why not get the plane on some actual airplane scales, weight the plane before and after the installation, and then derive the engine weight from that? Why won't that work? It's a heck of a lot more accurate than using water as a counterweight.

12. Jun 26, 2010

### Lucrum

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Good idea, I don't know why I didn't think of it.
That would work, but I don't have an airframe yet.

13. Jun 27, 2010

### waterinthefuel

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Well, then why does the weight of the engine matter? I mean unless you have a few engines to choose from, isn't it pretty much "ya get what ya get?" I mean if you buy an engine, you can't change its operating weight and it doesn't matter until the plane is built?

I guess some of this doesn't make much sense to me but I sure know it's not the first time! lol

14. Jun 28, 2010

### Lucrum

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Center of gravity, moving a 400 lb + engine even just a couple of inches has a noticeable affect on C.G.

15. Jun 28, 2010

### TFF

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If it is based on a certified engine, the Type Certificate Data Sheet shows the weight and CG of the engine. If you are using an auto or like, when you weigh it also find the CG so CG calculations can be accurate.

16. Jun 29, 2010

### dreamflyer

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I see where your coming from but i'd hate to see him reply or start a thread on how to remove a boat and a aircraft engine from a swimming pool.lol

17. Jun 29, 2010

### waterinthefuel

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Oh I understand that and you are absolutely right, but I mean if you know an engine is about 400lbs, does it really matter that much if its 395 or 405? I would say no. if you did the calculations it might move the CG a 1/16" which is negligible.

I guess if you had absolutely no clue what it weighed then weighing it would be ok but I mean with todays internet access you should be able to google any engine on the planet and get its specs, including weight. This would definitely get you into the ballpark of where you need to be.

18. Jun 29, 2010

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I think that's the problem. Most engine specs (like motorcycle specs actually) are empty. No oil, no pumps, no radiator fluid, no electrics, starter, exhaust, heat exchanger cowling, prop, engine mount and so on.

By the time you're done, the total weight, forward of the fuselage is in the cases I've considered (almost) doubled, compared to the manufacturers statement. Thus you need an accurate measurement, since the errors introduced in your engine weight estimate are considerable.

19. Jun 30, 2010

### dreamflyer

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I think they call it "DRY" weight? On motorcycles atleast.

20. Jun 30, 2010

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