Forrest Edwards radial 5

[DiegoVV]

With the valve train complete, I went on with the cylinder liners and barrels. I cut the cooling fins with the barrel fitted on a mandrel, usingView attachment 106365 a parting tool.

Turning the liners was pretty straightforward, so no pictures. I used a light shrink fit of about 0,02 mm so after fitting them in the barrels I had to rework some of the bores to avoid the piston from seizing up at TDC.

View attachment 106366

Looks rather nice....

Merry Christmas everyone!


Jos

Congratulation Jos for this beautiful exercise of mechanical art.
Your posts showing us how an entire engine is built using only a lathe are the demonstration that determination and know how are by far more important than owning a ton of equipment. I am really enjoying this thread.

I hope to start soon an Edwards radial build but converted into metric. Wish me luck, I´ll need it. hehe

 

[josodl1953]

Hi Diego, I used an Excel sheet for the metric conversion, one sheet for each part... comes in very handy!

Jos

 

[jacobball2000]

If you use the same set up as Mister Edwards original design from the 1980,s. I would have to still use the distributor system for the glow plugs to save on battery life.

 

[petertha]

If you use the same set up as Mister Edwards original design from the 1980,s. I would have to still use the distributor system for the glow plugs to save on battery life.

Can you please elaborate on this. Are there plans or schematic that Edwards developed? I've seen someone scratch built systems but I no longer have the web link. There are also commercial units as well but I'm not entirely clear what they do. I always thought it was more about pulsing to preserve glow plug element while keeping them lit vs. battery capacity in 'always on' mode. Battery capacity is actually pretty cheap these days. If this discussion goes on a detour, I am happy to re-post elsewhere. I'm sure its been discussed before.

http://www.sonictronics.com/xcart/product.php?productid=16210&cat=308&page=1
http://www.sonictronics.com/xcart/home.php?cat=308

 

[jacobball2000]

I came up with this idea when I seen the first 5 cylinder radial engine that was using glow plugs. I would have just ran a normal distributor system and just run a hot wire from the glow plug battery system to the distributor. I haven,t seen any thing on the web just something I was thinking of. I would say look up the old full size 5 cylinder engine and copy them.

 

[petertha]

So you mean something like a mechanical distributor but its basically closing the circuit and lighting up a glow plug? What I am confused by is you made reference to Edwards original design & I have not seen a system like that. This brings up an interesting point. When would you actually tim ethe plug to come on? Its not a spark. On a conventional glow engine, you hook up the driver plug, get the engine running & that's it, It runs on its own. The fuel, compression, glow wire, timing... all kind of take care of perpetuating the glow for the next combustion cycle. Some folks use on board glow to simply the hookup, for example multiple cylinders especially if they are under teh cowl etc. And some guys will add on board glow kind of as a precautionary measure like when they are idling. Although I can confidently say I have never found the need for that in 2S or 4S, upright or inverted engine.

Here is how this fellow did his 7 cylinder.
http://philsradial.blogspot.com/#!/2013/02/glowplug-driver.html

 

[jacobball2000]

My bad. When I first seen His design I thought it was using spark plugs. Only to find out they were glow plugs. I was thinking at the time to run the glow plugs as if it was under a distributor saving on the battery and glow plug life. I been trying to find the old sigh where it showed the hole distributor system including the gear train set up. What I remember the gears were 8, 12, 24 and one other one but can,t remember what it was. If I can find it I will post it on here. Look up Morton 5 cylinder radial.

 

[jacobball2000]

After Re-looking at The Morton M5 Radial engine I believe that,s the road I might go down. http://modelenginenews.org/~modeng74/m5/m5.html This is the orignal engine I found and the eb sigh.

 

[tornitore45]

Hi folks, I am a late comer to this thread but I am in the process to try to download the plans, unsuccessfully so far.
I see a concern about powering the glow plug. From my day flying control line I can tell the plugs are powered only during start up. After the engine is running full throttle, the combustion and a catalytic reaction between platinum and alcohol keep them hot. There may be a concern at low RPM. In such case rather than a pulser to supply a reduced current a simple relay can insert switching converter or a resistor is lower efficiency is not objectionable. The main advantage is to wire all plugs with a ring, eliminate the 5 individual wires from each plug and have only one wire to process.

 

[jacobball2000]

When I first seen this Web sigh. I thought of Edward,s engine and him using glow plugs. But half to keep power to the glow plugs to keep them hot. But if you use the timing and distributor system from the Morton engine. You can power the glow plugs when needed. Saving on battery life and glow plug life. You won,t need the point system. Making the distributor a mechanical switch.

 

[josodl1953]

I found this pictures of Forrest's own engine on his Polikarpov biplane. Ik looks very much like he was using spark plugs, on the side view you can see a cylindrical part on the rear of the engine, this might be the distributor but it would require a major design change because normally the inlet manifold is fitted there.

 

[jacobball2000]

I see where the intake manifold is. I bet it is fuel injection the engine looks new. But I am wondering if he is using a crank position censer?

 

[petertha]

I remember reading he made several design changes over time. This link shows one of the later iterations. Not sure if thats the same one in the Polikarpov, does kind of look like. It wiring harness kind of gives a hint of some kind of pickup (as opposed to geared distributer). But the plans that are in public domain are for sure methanol glow, no distribution. Very ingenious man.

https://www.craftsmanshipmuseum.com/KnappCol.htm


02—Edwards 5-Cylinder Radial, designed and built by Forest Edwards, early 1980's, L=12", W=12", H=13"

Forest Edwards builds and flies scale model airplanes and engineers miniature engines. He has won numerous awards for his scale airplanes, engines and flying skills. In the early 1980s, Edwards designed and developed this 5-cylinder radial engine to power his 1/4-scale Fleet model airplane, based on the 1930 Fleet Biplane. He received many requests to manufacture the engine, so between 1982 and 1994, Edwards produced 30 engines. Many were installed into model airplanes and some are still being flown today.

The 5-cylinder radial burns regular gasoline, incorporates a dry sump lubrication system and produces more than six horsepower. In his last few engines, Edwards added a centrifugal advance in the distributor and a crankshaft-driven supercharger for maximum performance. Edwards’ engines are completely machined from 7075 aircraft-grade aluminum and are perhaps the most reliable model radial engines built to date.

To see a video of how a radial engine works CLICK HERE. The link is to a YouTube.com video generated in a 3D drawing program called Autodesk Inventor. The cutaway view shows the pistons in action on a 7-cylinder radial engine so you can see how all the internal movements are related.

 

[jacobball2000]

If so ingenious. Why only one flight with the glow plug set up then have to do a battery recharge? The point was made.

 

[petertha]

I'm not really clear what you are talking about jacobball2000. After designing his own 5 cylinder glow ignition engine it appears he made an additional version adapting spark ignition & gasoline fuel. Not exactly a trivial task IMO, never mind incorporating ignition plus supercharger. If you don't think that requires some skill, then you must be working on some really amazing projects I look forward to seeing.

Glow plugs do not need to be maintained 'hot' after initial starting. That is not how they work. Once lit, they perpetually glow. At least if they were set up like a conventional methanol engine. There are some exceptions, read my post #46. Some folks have added an airborne battery to come on at idle for insurance purposes. Others add a battery purely to simplify hooking up a harness to multi-cylinder engines every time to start, especially under a cowl or other constraints. Even under starting 2A/plug is a good rule of thumb. So for a few minutes of on time during starting & landing it doesn't take much of a battery to provide that capacity. I've seen many dating back to NIMH days. Now you can get 5X that capacity in a lithium cell for the same weight. But its a moot point, 99.9% of RC aircraft, car, helicopter.... do not have augmented on board glow power.

 

[tornitore45]

On Sheet 19, Cylinder Liner" the plans call for: "At assembly check compression ratio and adjust to 8.5 :1 by trimming top of liner as needed."

That raises questions
Why does the compression ratio need to be adjusted?
The volumetric CR is set by design, and is set by dimensions
The effective CR is a dynamic thing depending on valve timing and leak, speed and the dead volume of the measuring gauge; on small engines is nearly impossible to measure.
Exact compression ratio is what make a Glow engine fire at the right time, so what is the deal with this adjustment instruction?

I see a lot of talk about running this engine on spark, I wonder if it was the result of difficulties with the Glow version. Any info on Glow running versions?

 

[mu38&Bg#]

It probably means the design did not compensate for the varying compression ratio due to the master/slave rod arrangement used in most radial engines. This results in differing compression ratios (as well as valve and ignition) in each cylinder.

 

[tornitore45]

Soon after my post I calculated the compression ratio based on the original plans I have. PDF file drawn by Robert Sigler.
The CR for the cylinder associated to the master crank results to be 12.8.
Trimming the liner is only going to increase the CR, will never reduce it to 8.5.
I am not very familiar with the motion geometry in a master crank with satellites con rods but gut tells me is further from harmonic motion and it may even result in a reduced stroke for all other cylinders but the master cylinder will still have a much higher CR than called for.
According to my calculations the space left between the combustion chamber and the piston at TDC is 0.082.
The shape of the piston head has no effect on the CR as long as it matches the combustion chamber.

 

[petertha]

The Edwards engine has a master rod geometry with link rod crankpin holes phased at equal 72 deg (360/5=72). So if the link rods + pistons + liner deck are identical, it will result in slightly different CR on various cylinders. This is generally not desirable from a tuning standpoint especially on glow. So you have some choices. Either you modify the angular geometry of the master rod crankpin holes to achieve equal CR (this has been discussed on the forum). Or you modify the top end (piston + liner) to achieve this. Edwards elected the latter. There are pros & cons to each method. Sometimes there are other issues like rod angle requiring cutting of the skirts so it’s not necessarily straightforward or confined to CR.

It is customary in glow engines to see some variation in CR, or maybe a better way to say it – at least not to paint yourself in a corner & have some ability to alter CR. The Edwards presumed pure methanol fuel & separate lubrication oil pump. Most glow engines are a premix of methanol, varying % of nitromethane & oil pre-mix (castor, synthetic or blend). Now throw in different kinds of glow plugs meaning different wire sizes which have different heat properties… Collectively it’s kind of a recipe of what works best for the application. Sometimes there are trade-offs especially when it comes to how well it starts or idles vs. running.

Converting a methanol/glow engine to gasoline is nothing new. Kits & commercial engines have been doing it for years.
https://www.ch-ignitions.com/?SID=09b364f7b7a3ed14fe933e2c11f1fdce
At minimum you may need to modify the CR to something more optimal to gasoline, so that has been discussed. The glow plug is replaced with a miniature spark plug. The timing & energy are typically magnetic pickup dedicated solid state black box modules respectively. Of course multi-cylinder spark conversions necessitates specific firing order so that is a different black box. There are kit & commercial versions, but not that many examples of those who have converted their own.

Classic distributors, points & coils are seen on shop made multi-cylinder engines which in itself is amazing at this reduced scale. But they are not exactly easy to make or compact or low weight such that they lend themselves to becoming power plants for airborne in RC models. I can’t say for certain if the Edwards was contemplated entirely for flight duty but there certainly examples of his design in working models & of course his inroads towards commercialization. Modern buy-off-shelf methanol radials like OS Engines look & operate on very similar principles. When you see ignition or gasoline versions, they are typically dedicated solid state ignition modules. If a home made engine will not see flight duty, I suppose that lends itself to more options to accommodate the ancillary ignition equipment, but I think is still remarkable achievement because many aspects do not 'scale' without other complications.

 

[tornitore45]

petertha,
I appreciate your comprehensive tutorial. This is my first glow engine an my first radial. Although I was flying single cylinder glow in the '60 and know the CR is critical in glow engines I never had to consider the factors since I bought a FOX 35 Stunt and flew, and flew and flew.
What worries me now is the high compression ratio of the master rod cylinder that calculates to 12.8. Minor variation due to the geometry won't come close to the 8.5 specified.
While increasing the CR is easy, reducing it is not. It may need to move the wrist pin (new piston) or cutting the cone on the top.
At this point I like to hear from anyone that has built and run a glow version of this engine.