Running two engines connected via chain in one dir :-)

[materialboy]

Hey Friends,

I am trying to design Hovercraft and the lift system in hovercraft uses two Honda Gx- 120 engine. These engines are arranged adjacent to each other to give overall 2000 rpm through V-chain connected with shaft of engine.

These engines need to be started together and I need both the engine to rotate in one dir (either clock wise or anti clokwise). Is there someway I can resolve the problem of running two engine in one dir ???


Honda Gx- 120 Specification

Starting System - Recoil or electric start
Stopping System - ignition primary circuit ground
Max Horsepower - (4.0hp / 4,000rpm )
Max Torque - 2500 rpm

[Tim B]

I'm not sure I see the problem with running both in the same direction. Running both at the same RPM is a bit different.

If I were you I'd try to find a single engine that will do the job you want it to. It will be much simpler.

Tim B.

[materialboy]

Thanks TimB

Yeah you are right - it is running two engines at same RPM. I could not change the design because it is already in the manufacturing stage.

But I will really appreciate if you/ someone can give me some advice on how can I mantain running two engine at same RPM.

[longliner45]

2 trottles 2rpm gauges?

[PAR]

There are mechanical methods (governors) and electronic methods. If you link them with a chain, you'll break a lot of chains and probably output shafts too, until you devise a method to isolate the engines during startup, synchronize and run up to target RPM.

If your engines are spinning props (for lift or thrust) then don't slave them with a chain. Just use a simple governor to synchronize them at the target RPM, spinning a single prop each. Linking engines like this can get frustrating pretty quickly. Think simple, less is usually better and more reliable.

You can use an electric or vacuum operated throttle positioner to get the engines to a specific loaded RPM, but you will need some sort of electronic control (or mechanical) to keep the engines at a constant synchronized state. If the engines are slaved with a hard link (like a chain) if one picks up some load, it will pull both engines down in RPM. This will require a pretty fancy arrangement to keep them running at target RPM.

You may be interested in trying a fluid coupling or clutches where one engine can slip a little until the other one catches back up to target RPM as loads change. This is where things will get complicated and likely expensive. I'm assuming you're using one prop, a common shaft with two engines driving it.

For what it's worth, the design phase is generally reasonably completed, or has at least has addressed (or attempted so) the major engineering issues, before moving on to manufacturing. This basic concept usually keeps the eraser at the opposite end of the pencil, if you understand my meaning.

[Frosty]

There is a magicall little thing called a sprag clutch. This is used in torque converors for the stators.

This is quite robust and looks like a large ball bearing. It will ony transmit drive when the input speed is more than the output.

Therefore 1 engine could do all the work with one engine off. Start 2 engines and they will both pull providing input speed exeeds output.

Chaining two engines together as small as this would not cause too much problems. You would not need 2 tachs as the two engines are chained together--start one you start both, just get a decent firing order, ie not 2 compressions at the same time.

Uk has a silly thing called tractor pulling these home built tractors will have as many as 8x V8 engines 6 inch tooth belted to a common shaft to acheive thousands of horse power for a short duration,long enough to drag massive wieghts 100yards.

Some times they use Allison singles or RR Merlins singles.

The point is they belt multiple engines together-- simple matter to remove or add one more.

[materialboy]

Originally Posted by PAR

If your engines are spinning props (for lift or thrust) then don't slave them with a chain. Just use a simple governor to synchronize them at the target RPM, spinning a single prop each. Linking engines like this can get frustrating pretty quickly. Think simple, less is usually better and more reliable.

You can use an electric or vacuum operated throttle positioner to get the engines to a specific loaded RPM, but you will need some sort of electronic control (or mechanical) to keep the engines at a constant synchronized state. If the engines are slaved with a hard link (like a chain) if one picks up some load, it will pull both engines down in RPM. This will require a pretty fancy arrangement to keep them running at target RPM.

Thanks for your advice PAR, Yes I am using one prop, a common shaft with two engines driving it. I have to use it to get the overall RPM of 3000 revs/min.
I will reaserch on Fluid coupling

Just use a simple governor to synchronize them at the target RPM, spinning a single prop each ??? - What is simple governor and how can i use them to synchronize at the target RPM by spinning a single prop each. I did try to google it but unable to come up with good results. Is it possible to send some link or pic- which might give me clear pic.

[marshmat]

One prop, two engines.
This has been a major headache for aircraft designers, pretty much since the dawn of powered flight. Two props one engine is a lot easier. It's very, very rare to see two reciprocating engines coupled like this. I've only ever seen it done successfully with turbines. (Most large helicopters, for example.) Even then it involves a pretty substantial and very complicated gearbox.
What exactly is the problem with getting a single engine that would do the job on its own? This would be lighter, cheaper and more efficient.

[PAR]

Automotive applications tinkered with multiple engine arrangements for a short period. They too had coordination difficulties and lots of quite spectacular explosions.

A simple governor for your application could be done several ways. One might be to retard spark timing, another a cutout switch set at a specific RPM. These mechanical systems can employ weights spinning on a gimble, mounted on a shaft. The basic problem would still exist, which is you'd have one engine trying to keep up with the other and without active controls (like electronic throttle position or spark advance) to make quick and accurate adjustments, things will go pop. Do yourself a favor and build a heavy gauge shield around the chain and sprocket assembly, so when it does take a dump, you'll keep your crown jewels intact.

Your solutions can be reasonably simple or complex. A twin engine, single shaft arrangement will require the most complex accommodation.

[Frosty]

Well I dont think you have a problem. Its not a good idea, but its not that hard to do.

A 'simple governor' on a petrol engine is not simple. Retarding ignition advance will make the engine run hot and reduce power significantly.

In a 4-5-6 or 8 cylinder engine some cylinders are more efficient than others, rings, valve etc making always one cylinder working the best--not much but there is some diifference.

Motor cycles run 150hp plus and in some specials twice that through a chain.

Chain your 2 engines, I would use belts personally-- and time them to TDC and BTDC. ( if they are two strokes) I dont think you have a problem especially as you are running them at 80% power constantly.
A pair of exhaust temperature guages would give you an indication of shared load.

When you up and running calibrate and balance air intakes. Just like a muti cylinder multple carburetor motorcycle does.

There are engines on the planet that have 2 crank shafts geared together internaly. That is no difference to what you are doing,--only you are chaining them externally!!!

[materialboy]

Thank you guys on your creative ideas and help.
Yes- I have taken necc health and safety measurement
Only the reason why I have to stick up with using two engines, is because budget wise we had the option to use the engines provided by uni and so to get overall lift from lift engine I had to use two engines,

I do not know why using BTDC did not strike me bfre-

BTDC/ATDC is all about the control of ignition process.

For example
At 900 rpm the crank rotates one degree in 0.18519 milliseconds.
The crank turns 360 degrees in one rpm. Therefore 360 degrees X 900 rpm = 324,000 degrees per minute = 5,400 degrees per second = 1/5400 of a second per degree = 0.00018519 seconds or 0.18519 milliseconds per degree.

By advancing the timing by 4 degrees i will start the ignition process 0.741 (0.18519 X 4) milliseconds sooner at 900-rpm (0.111 milliseconds at 6,000 rpm).
Ref - http://www.miata.net/garage/KnowYourCar/S10_Timing.html

--But how will it still solve the problem of running two engines at same RPM ?


Thank for ur time and effort

[Frosty]

They will be at the same RPM --youve chained them together.

[vmowrey]

What about hydraulic motors driven off a single pump engine? Just imagine plenty of power, high torque and independent control to put power where you need it.

[nero]

The engine need to be bedded to the same solid structure when chaining them together. Then as jack frost wrote they effectively become one engine with per cylinder carburaters.

Problem with hydraulic drives is keeping the fluid cool. Also there is a big loss in power to the prop. Hydrostatic drives on tractors reduce the power to the wheel by several horsepower. They also make a terrible noise.

[StianM]

Running two engines as one is not more truble than running a multicylinder engine with more than one carburator.

If you put load on a engine the rpm will drop and get stabile once the other engine start to take the load. There are 100's off ships using two diesels on one propeler shaft without anny problem.

I think the easiest way to make it work is to get a local guru to come and adjust your carbs so the engines will runn well linket together and get a stronger electric starter so you can turn them both at the same time so they will start together.