An engine running bench

[Jo]

When I visited Old Warden earlier this year I saw a number of different engines being run by their various owners using their engine running benches. Ok so most of these were aero engines, I am not sure if the Ladybird  is an aero engine but there were other engine types being run on the benches but it was an aero engine meet 

So as I venture towards (successfully ) running my first infernal combustion engine I have lots of questions about constructing a suitable bench/mounting arrangement/ fuelling etc arrangement. I think I have got a solution for a single cylinder engine ignition system with my ignition box that I hope to receive on my getting older younger day in a week or so

So has anyone seen any good engine running benches? Any thoughts on what properties should they have? And most importantly what should I be designing into one of my own?

Jo
 -    -     -
P.S. Did I mention I would like a set of Ladybird castings 

[Roger B]

It needs to be strong enough to take the vibration from the engine. A horizontal engine will tend to have more horizontal forces, a vertical engine more vertical forces (unless the balancing is completely wrong  . Multi cylinder engines generally produce less vibration.  I have seen a few people using Workmates or their equivalents, but they don't seem to good with vibration. The aero engine people also have to consider how they resist the thrust.

Will it be just for workshop use of will you need to transport it? How many different types of engine will need to be fitted to it (or how many are your casting sets are you going to finish  )

Engines with a straight suction carb will need the fuel tank below the carb. If it has a float chamber the tank will need to be above the carb. Plastic tanks allow you to see the fuel level. You can spend a long time trying to start an engine attached to an empty metal fuel with a black pipe 

[Jasonb]

I suppose you need to decide if you will have one bench for all engines or one for bearer mounted like most small single cyl aeros, one for bulkhead mounted  and another for the hit & miss, horizontal and verticals.

I find the later can usually be held on a workmate and as most have integral tanks the fuel takes care of itself.

Bearer mounted would need some adjustment so you can fit both large and small. Most won't have an integral tank so you want to be able to hold a small klunk tank at the right height, some form of friction or spring close link to the throttle keeps your pinkies out of the way.

The same stand could be used for bulkhead mounts if you have a vertical board that can be drilled for the mountings.

All of these may require you to get your hands on some wood

But the main requirement for an engine running stand is an engine that ..............

J

[Jo]

To answer Roger first: I hope that I am young enough to finish all of my engines, so the challenging ones might be the Falcon and the two Anzani's and the  Aeronica but I seem to have acquired a few more standard aero engines to build I have been told they are a learning exercise  For now it is for me at home but I know I seem to have acquired a following at Old Warden who are demanding that I go back again and show them the performance of my engine(s) and it is so embarrassing that none of them work  . (I will not go back until I have at least one working engine   )

Jason I was rather thinking about making a mounting arrangement I noted that Eric's engine mount happily took Ramon's engines for running without modification  .

Fuel tank mounting is tomorrow's problem: Do all engine suck? so should the tank go below the engine? Do I need to vary the height for more or less suction?   

What is bearer mounted? What is a klunk tank  ?

Wood  All my attempts to find myself a man so that he can do all those "necessary" things for me to do with the brown stuff have 

Jo

[Bearcar1]

Jo, in regards to your last remark………. I volunteer!    Of course that would be in exchange for usage of that well equipped shop of yours    *ahem*


BC1
Jim

[philjoe5]

Fuel tank mounting is tomorrow's problem: Do all engine suck? so should the tank go below the engine? Do I need to vary the height for more or less suction?

My references say a model engine carb should be located so that the output of it should be just below the intake port of the engine.  This prevents fuel from dribbling into the engine and flooding it.  If the engine is hit-n-miss, a check valve is needed to prevent fuel from draining from the line back into the tank during the "miss" cycles.

My vapor carb,though, has been positioned well below the intake port, by an inch or more, but functions nicely. 

As far as a bench goes, I suppose that depends upon you entirely.  Most folks like to hide the electrics out of sight.  When I take an engine to shows, most often someone will ask me about how the darn thing runs.  So I like to keep everything out in the open to make it easier to explain.  I just clamp the engine base to whatever bench is handy and let 'er go.

 

That's just me.

Good luck with your IC engine project.  They are lots of fun

Cheers,
Phil

[PStechPaul]

Hmmm.  Being more of an electronics engineering and electric motor aficionado, I would want a test bench to have instruments to measure RPM, torque, fuel flow, air flow, and other properties, as well as possibly graphic computer displays showing crankshaft position and ignition timing and voltage.  It would incorporate a built-in generator and programmable load to take the data needed for a full RPM/power/torque specification. 

As for the mechanical construction, I think something like a milling machine table would be useful, with T-slots and other means for conveniently mounting the motor and ancillary equipment, and perhaps it can be in turn mounted on a rotary table, probably motorized, that might assist with working on the engine and also provide a cool-looking moving display at shows. 

Add any number of blinking lights, bells, whistles, horns, and amplified sounds of the operating engine (like a high-tech mechanic's stethoscope), which will add visual and audible appeal to the presentation. 

And don't forget to add a multiposition adjustable arm with a camera mount so you can take videos of the machine in operation. 

[Jo]

Jo, in regards to your last remark………. I volunteer!    Of course that would be in exchange for usage of that well equipped shop of yours    *ahem*

BC1
Jim

Jim  , My plan is that any fella will not be moving in my workshop especially if he likes working in the brown stuff, I have plans to have one built for him and stocking it with quality machine tools (to encourage him to use his own workshop  ).

Currently it looks like I will be moving in .

Jo

[Jasonb]

Jo your typical single cylinder aero engine with the two mounting lugs that stick out the side is designed to screw down onto two hardwood engine bearers that project out beyong the bulkhead, that is why I refered to them as bearer mounting.

A clunk tank is a term used for most of the plastic tanks made for model aircraft, to keep a constant supply of fuel while the aircraft may be performing various manovers the pickup insid ethe tank is weighted and on a bit of flexi tube. This weighted part tends to go "Klunk" as you move the tank about and it hits the sides.

Yes all such but some like hit and miss don't suck constantly and all won't suck so well while trying to start - OK when running. If there is no provision you may need to add a non-return valve, some engines like the centaur and those with the Lunkenheimer carbs have an inbuilt valve so its not needed. You may find on some of the aero engines that they perform best when you help them suck by presurizing the fuel tank, this is done by taking a tube from the silencer to teh tank. You also nee dto make sure the tank is not too high as you don't want to flood the engine or have fuel dripping all over your feet. So some adjustment of height would be handy.

Wood, you only have to ask, may be a long delivery though

You are also going to need a source of power for the glow plug engines at some time, I just use the small self contained one that slips onto the plug and has an integral rechargable battery.

J

PS don't forget you will want a chicken stick as well

[Ramon Wilson]

Hi Jo - I can see you're looking well ahead 

For what it's worth you don't need anything very substantial bench wise  for running 'aero engines' but it is best if they are held in a  decent mount such as Eric's.
This one will take from the smallest engine to most 60's and possibly above and the stand itself is made from 3/4" square box section. It stands about 15 " high and if use on the ground is held captive by wire stakes pushed through holes into the ground or just clamped to a table - I usually use a fold up plastic camping table - quite rigid enough for these engines though at the top end of the scale ( a powerful 60)  it might be a bit light The actual mount is adjustable , the left hand side is fixed with the base the right hand side fully movable


This is fitted with a 'Klunk' tank which is nothing more than the feed inlet tube in the neck of the tank having a silicone tube extension to the bottom of the tank which in turn is fitted with a small brass tubular weight - the 'klunk'. When fitted in an aircraft or boat the weight will follow the fuel as it is moved about by action. The other two tubes are the fill and vent.

The height of the tank wants to be positioned so that roughly the centre line of the fuel is on the centre line of the needle valve. Suction is not usually a problem but if too high then flooding is a distinct possibility especially on initial starting/ finding settings etc.
As you can see this one is fixed which has never been an issue of the many years of use but  it would be easy enough to make something adjustable for height should you desire.

Bench wise - for your larger engines something far more substantial will obviously be necessary but bear in mind you need to be able to move it as you don't really want to run anything indoors even with good ventilation. Even these little 'tiddlers' as you call them will soon have the room filled with exhaust fumes 

Looking forward to seeing that first build - are you going to have one running for next years 'Guildford' 

Regards - Ramon

[Ramon Wilson]

Further to that Jo I should add that the pick up tube inside the tank needs to be compatible with the fuel. As you have already found silicone tubing reacts to some fuels and especially so with model aircraft diesel fuel, I used to have two tanks for this stand but now only use the one the tubing inside is the black stuff which seems to handle both, You may note the vent tube is silicone which isn't a problem here but the fuel tube proper needs to be compatible with diesel. Now, if you are especially nice to Uncle Eric he may just part with some of his precious Red Line tube 

[Jasonb]

Jo Put "testing model engine" into google and look at the images, there are quite a few things there that may give you some ideas.

If you don't want to make legs then a piece of 2x2 screwed to the bottom of a stand like Ramons could be clamped in your small workmate or a bench vice

Do they not make Red Line anymore Ramon, I use that on my first RC heli and that was when I was 15.

J

[Ramon Wilson]

Ah I wish Jason - Eric had some at Guildford but it's been many a day since I saw that for sale 
PAW engines (that I know of) are about the only provider of diesel compatible tubing these days though I may be wrong there. It's the translucent yellow stuff and comes in two diameters I think.

Ramon

[footloose]

PAW engines (that I know of) are about the only provider of diesel compatible tubing these days though I may be wrong there. It's the translucent yellow stuff and comes in two diameters I think.

Ramon

This chap sells diesel tubing. http://www.densmodelsupplies.co.uk

Bert

[Jasonb]

The Tygon tube is said to be OK for Derv and thats quite easily obtainable even if you have to resort to getting it from far off places to save a couple of moths

http://www.justengines.co.uk/acatalog/Just_Engines_Online_Fuelling_Gear_72.html

[Ramon Wilson]

Well whadya know - I've been using 'Tygon' tube for some time now  Same stuff as PAW sells - I just had no idea that that's what it is called.

Thanks Bert ( that site is a bit of a nostalgia trip  ) and you too Jason for the links.

I remembered this source too - long time since I used it but the tube was clear when I bought it last - look under Sundry Equipment
http://www.freeflightsupplies.co.uk/

Sailing's off today - far too windy - so I've made a tap and now making the gas canister valve

Ramon

[Ian S C]

For my hot air motors I have two tables. They are made with the legs from old folding ironing boards, the top replaced with ply wood about 10 mm thick.  The top is about the same area as the one shown by Ramon, this might be ok for a small IC engine.  Ian S C

[Allen Smithee]

For ordinary model aero engines your bog-standard engine test stand looks something like the picture below - one side fixed and the other adjustable to cope with different sizes and the sort of thing you could knock up in a mill from whatever gash metal you had lying around in an hour without breaking into a sweat. This is usually screwed to a bit of blockboard which is then gripped in a workmate for use. The blockboard is typically about 12" long by 4"- 6" wide and would usually have four cuphooks screwed into it so that the fuel tank can be put on top of a bit of sponge and held down with elastic bands (this allows the height to be adjusted and reduces frothing of fuel in the tank from the vibration). My motors were mostly piped (ie they used tuned-pipe superchargers) and so th.ere would be a pipe mount as well, but you may not need this. If there is a throttle control the cunning plan is to operate it with a bit of wire (usually 2mm soft iron bike spoke) that is threaded though the elastic bands on the fuel tank for a bit of friction (I always prefer a little bit of friction).

Tank heights aren't that critical on the test stand - most engines will happily suck fuel through a vertical inch or two even without silencer/pipe or crankcase pressure. In an airframe it's a different matter, but the issue is the *variation* in fuel head affecting the mixture rather than the ability to pull the fuel to to carb. On the test stand a lower tank is prefered to a higher one as too much head results in stuff spurting all over the place.

AS

[Jo]

  Pete, You forgot your attachment.

Jo

[Allen Smithee]

Oh gosh - all that focus on the problems of having too much head and the attachment went clean out of my mind....

AS

[Ramon Wilson]

In an airframe it's a different matter, but the issue is the *variation* in fuel head affecting the mixture rather than the ability to pull the fuel to to carb.

Are you not familiar with the 'uniflow' tank set up Allen? Gives a very consistent run without pressure too.

Ramon

[Allen Smithee]

In an airframe it's a different matter, but the issue is the *variation* in fuel head affecting the mixture rather than the ability to pull the fuel to to carb.

Are you not familiar with the 'uniflow' tank set up Allen? Gives a very consistent run without pressure too.

Yes, it minimises the variation in head as the fuel level drops in the tank but it won't correct for the variation between upright and inverted from a tank that's (say) 1" below spraybar height. Most of my stuff ran on either pipe pressure (around 3psi) or untimed crankcase pressure (up to around 11psi, but varies with mixture setting). Most modellers don't actually realise that the reason for running pressuresed fuel systems isn't to push the fuel into the engine - it's to provide a high pressure "bias" so that the variations due to changes in head when manoeuvering are a small proportion of the overall pressure at the spraybar, thus minimising mixture changes. That's why you never see a CL stunt engine running anything but suction feed - these variations in pressure are actually *used* to kick it from a rich 4-stroke in level flight to a lean 2-stroke though manoeuvers.

AS
 

[Allen Smithee]

I should have added - there are refinements on the basic test stand design (around a gazilion and twenty three at last count), but one of the more important ones is to add a squared-off lip at the front of the two engine seating surfaces so that the engine isn't restrained purely by the friction of the two clamps.

AS

[Jasonb]

Yes, you don't want this happening

<a href="https://www.youtube.com/watch?v=1Pk9y5t1N9Q" target="_blank">http://www.youtube.com/watch?v=1Pk9y5t1N9Q</a>

[Ramon Wilson]

Yes, it minimises the variation in head as the fuel level drops in the tank but it won't correct for the variation between upright and inverted from a tank that's (say) 1" below spraybar height. Most of my stuff ran on either pipe pressure (around 3psi) or untimed crankcase pressure (up to around 11psi, but varies with mixture setting). Most modellers don't actually realise that the reason for running pressuresed fuel systems isn't to push the fuel into the engine - it's to provide a high pressure "bias" so that the variations due to changes in head when manoeuvering are a small proportion of the overall pressure at the spraybar, thus minimising mixture changes. That's why you never see a CL stunt engine running anything but suction feed - these variations in pressure are actually *used* to kick it from a rich 4-stroke in level flight to a lean 2-stroke though manoeuvers.
 

I'm not sure I would quite see it that way Allen - no self respecting stunt flier would ever put a tank on anything but the centre line  of tank to centre line of spray-bar give or take a millimeter or two of shimming to get an even run from upright to inverted level flight.

As for the variations in fuel head/pressure as the means to kick the run from a four stroke to two stroke I think you may find this is very much down to the timing of the engine. Dedicated C/L aerobatic engines excepted very few engines will run in this fashion 'out of the box' The Fox35 and OS Max 35S being the predominant ones but many others require the timing, along with other tweaks such as head shimming and venturi size, to be modified to create this in flight characteristic. Most R/C motors simply converted by using a standard venturi will not run in this fashion until the blowdown period is altered.  Well, it was in my day which ended in 2006 - perhaps things have changed since 

The uniflow set up has been used for many years in stunt circles, sometimes on pressure - though personally I have never had any consistent results going down that path - but mainly without. As the vent pipe uncovers toward the end of the run that's just when the extra power as the engine increases in revs is helpful to get round that last manoeuver - the four loops in the clover leaf. There are a lot of factors that go into getting a good four two four run besides the tank though.

Though I have no personal experience of them in aerobatics, tuned pipes have been used too though not so much to extract power but to give that 'consistent' run so desired of stunt fliers - the difference is quite distinct, the higher rev on a fine pitch prop the speed almost constant no matter at what attitude the aircraft the pipe acting as a 'brake' to prevent an increase in revs as the model goes 'downhill'. I believe that these set ups do usually run on pressurised feed as opposed to plain suction.

All of this must be a bit academic for 'poor old Jo' - all she wanted to know is what kind of bench to get make - you're very quiet Jo have you come to a decision yet 

Re the sound advice to have lips at the front to prevent a wayward engine - all well and good until you have an engine that has to come forward to clear any protrusion at the back. 'Touch wood' I've never experienced it as yet and that old stand has seen a few runs in it's time but two pieces of 1/32 ply under the clamp bars on top of the lugs will hold most things - providing you tighten the bolts of course 

Regards - Ramon

[Allen Smithee]

Yes, you don't want this happening

Indeed - next time you're in the office remind me to show you the video of a J85 (engine from the Northrop F5) bench run that follos a pretty similar script...

AS

[Marinus]

I had to build one a few years ago for my ABC-12 glow engine , just made it from a few scraps and the throttle was kinda like a Boeing's.

[Jo]

A lot All of this is going over my head  .

What I am interested in is the dimensions of that engine clamping arrangement. Is it about 150 to 200 mm wide? What is the height of the clamping blocks?

Looking at my Kiwi, it needs 30mm clearance under the mounting lugs and is 75mm wide. So I would guess the block need to be 35mm tall.

Width wise the Stentor has 25mm wide mounting lugs the Kiwi nearer 50mm. So some sort of tool maker's clamping arrangement of say 40mm wide?

Jo

[Ramon Wilson]

As I said Jo quite academic to your original point  .

Without measuring it my engine mount is about 180mm long and 50 or so wide. The blocks are about 30 mm high. Ignore the slot you can see in the outer side - that was for an (unsuccessful, wear wise) adjustable clamp support to ensure the clamp itself was parallel depending on engine lug thickness. It now has a pan head screw fitted from the top which does the same but that really does need improving too to be honest. The right hand block slides through about 50mm to adjust for width. Like clamping on the mill table the clamps should be near parallel - it's when they are not that an engine could work its way loose

It was made around 1982  so has worn well. I've never had an engine pull itself out though as said that is not to say it couldn't. Throughout it's day its handled from .5cc to some quite powerful 60's but bear in mind this is a 'running stand' not an all out test bench

So to that end then I guess you just need to take the basic principal and make the dimensions to suit your ideas.

Will you have your Stentor for next years Guildford ? - will I have my Stentor for ... How longs a piece of fuel tube
Keep on with that Centaur - at least you've got a handle  just remember you'll have to develop a well practiced flick to start these little beggars

Ramon

[Allen Smithee]

What I am interested in is the dimensions of that engine clamping arrangement. Is it about 150 to 200 mm wide? What is the height of the clamping blocks?

What size engines are you likely to be building? If they're all in the range (say) 1.5-10cc then you will be able to cover the whole range with one stand like the one above. If you want to do "small stuff" under 1.5cc then you might benefit from making a smaller version and above 10cc it's usually better to make a dedicated mount from a but of 4mm dural plate screwed to a bit of wood.

If you're not likely to do very many of these standard beam/lug mounted engines then don't bother making anything and just borrow my test stand when you need it...

AS

[Ian S C]

Just a little bit about the reason for my folding tables.  My means of transport is my bicycle, I have a trailer for it, and I can load two tables, two motors, fuel etc., and head off, these days about 10k is about my limit.    Ian S C

[Jo]

I have just been made aware that the great Edgar Westbury published a design for an universal engine test stand for miniature i.c. engines  .

So it looks like I have my starting point for mounting my engines. Just need to balance the missing dimensions with what can be found on the come in handy pile 

Jo

[Jo]

The running bench is nearly made  .

I just have to decide how far apart to mount the blocks  .  This is it with one of my diddly little CM14 crankcases mounted in it. Most of my engines are of a much more sensible size 

Jo

[Allen Smithee]

I assume you'll be bolting those blocks to the baseplate? If so then why not drill a selection of mounting holes in (say) 1" increments so that you can increase or decrease as required. You'd be better off adjusting the spacing of the mounting blocks so that the overhang of the clamp plates was kept to a minimum (as large overhangs will risk vibration issues).

Alternatively you could bolt one block permanently, and have the clamping bolt on the other run right through the vertical block into a T-nut slotted into the baseplate so that it can be adjusted to suit. The clamp plates could then be short and non-slotted, and all the adjustment to fit an engine would be done via the single clamp bolt.

How are you intending to mount this in (I presume) your workmate? I would hate to rely on just G-cramps holding the fixture to the jaws! A piece of 2" square steel could be bolted to the underside to be gripped in the workmate jaws, but it's a bit of a waste of steel. Perhaps you could make some shouldered bushes that can fit into the vertical holes in the workmate's jaws from underneath, with tapped holes in the bushes so that you can bolt into them from above?

AS

[Jo]

So obvious a series of mounting holes for the blocks  it would probably only need two sets of holes

Mounting plans are on a cheap workmate clone, on that piece of wood clamped using the existing jaws on the workmate.

Jo

[Allen Smithee]

So obvious a series of mounting holes for the blocks  it would probably only need two sets of holes

Or do the holes you need now and add others as you need them...

Mounting plans are on a cheap workmate clone, on that piece of wood clamped using the existing jaws on the workmate.

That would work fine, although you must admit shouldered bushes and bolts would be *so* much cooler! I would consider making provision on the woodwork for mounting fuel tanks (just a variable-height or shimable platform with some cup hooks for lacky-bands to hold the tank). And possibly a throttle bar with a friction linkage, although that can wait for your first throttled engine as the linkage positions vary.

Oh yes, and don't forget a mounting for a mobile phone and a first aid kit, so you can staunch the bleeding from the severed fingers and then call for an ambulence...

 

AS

[tangler]

My experience is that the workmate type clone won't hold a tenon firmly enough to stop it pivoting

 <a href="https://www.youtube.com/watch?v=pp-XtpECNpo" target="_blank">http://www.youtube.com/watch?v=pp-XtpECNpo</a>.

I recommend a G clamp as well

Rod

[Jasonb]

If Jo Keeps that bit of wood as long as it is in the photo things should be OK, you want it at least 2/3rds of the workmates length so the jaws can grip it easily without twisting.

J

[Jo]

The piece of wood is 200mm long but having seen that video 

  This is of course jumping to the assumption that one day one of these infernals will run

Jo

[Jo]

The base is all machined and the clamps in place. There are two sets of holes for mounting the brackets which add an additional 40mm to the width if required. Both the Stentor and the CM fit in on the central pair of mountings.

It is clamped in place with two M6 threaded clamps using 19mm aluminium square extrusions, with some threaded knobs recycled from an old lawnmower for clamping it to the bench. It is no problem mounting it on this workmate that I have already had to replace the top so that has 22mm ply as a top but the original is rather thinner 

So one engine running bench mount 

Jo

[tangler]

That'll do it.  I'll borrow that idea if I may.

Cheers,

Rod

[Jo]

By all means Rod 

Jo