Forrest Edwards radial 5

[josodl1953]

Yes, Peter, that's my idea, bearing in mind that I have the tooling for the cylinder/head assambly already.
But these are just ideas, I am still miles away from actually building them.

Jos

 

[josodl1953]

About the fuel, it is left -over racing fuel from my model boat racing career, containing 15 % oil ( castor/synthetic 50-50) and 10% nitro. I have no lubrication pump, the cam housing contains its own oil supply, the separated crankcase receives oil from blow-by of the pistons like all commercial four-stroke model engines. Time will tell if this will provide sufficient lubrication.

Proof of the pudding...

Jos

 

[Michael Rosenbauer]

Jos you are a son of a gun.
Chapeau you are a real home engine machinist!
Sehr gut!

 

[josodl1953]

Danke schön!
I will be at an exhibition in December where I will be demonstrating the engine, After that, I will take it apart to check for wear to see if it is fit to be used on an R/C plane.

Jos

 

[Michael Rosenbauer]

Sounds like plan.
Do you have the plane already?
Michael

 

[josodl1953]

No the plane has yet to be built. I already have downloaded plans of a Boeing Stearman ( also known as Kaydet) But I'm still thinking of the right size, bearing in mind that the engine is rather heavy ( almost 2 kgs) so tha plane should be not too small but not too big either because I could not measure the power of the engine. A wingspan of 1m 80 should be a feasible option and it should look a bit like this

But,like I said before, the engine must first prove its airworthyness before I start the construction.

Jos

 

[jquevedo]

Check Ziroli Plans for Big scale plane plans and some building materials, I bought the Stearman PT17 plans and they are great, I'm in the process of building the 87 inch wing span version, have a 9 cylinder radial I Bult from Hodgson plans.

 

[Jrcfiero]

How about using compressed gas?

 

[petertha]

Some pics of Mr. Edwards handiwork, the Polikarpov with a 5-cyl variant installed. It appears Forest was equally good at building scale model air frames as he was an engine designer & machinist.
https://www.flickr.com/photos/15794235@N06/sets/72157603556449257/

On a side note, does anyone have any information on his 2-cylinder supercharged engine? Was it ever written up or featured anywhere?

 

[awake]

Wow, what a smooth running engine. Fantastic work!

 

[josodl1953]

jquevedo; The Ziroli plans look good but slightly too big for my engine. Ziroli recommends from 75 to 250 cc, mine is only 30 cc.
jrcfiero: Do you mean compressed gas engines? In the early days of powered model planes there were very small motors running on compressed CO2 from cartridges.
Peter: A few of these pictures I already found on the web but these are even more revealing. The Polikarpov's fuselage was made of metal by the looks of it , with beautiful riveted panels. Forest Edwards must have been a craftsman with outstanding qualities. I wonder if he had fitted his engine with spark ignition. On the side view one can see the HT leads coming from some kind of distributor housing on the back of the engine. There are some more differences between the original engine and the design according to Robert Siglers drawings. The cooling fins of the cylinder heads of the original are slightly curved whereas the Sigler heads are flat. Also, the cam followers of the original are offset, on the Sigler drawings they are in line.

Maybe Robert has information on the supercharged twin, his email adress is on the front page of the set of drawings.

 

[petertha]

Yes in another (RC) forum post I read, it discussed modifications Forest made to the Polikarpov engine which deviated from the builder plans. But I have also read other postings which seem more speculative & light on details. Some have used the words 'ignition system' without really defining (or maybe understanding) what that meant. The braided cables could have been for scale show purposes & conventional glow plugs used in an on-board glow mode which is common on multi-cylinder RC engines. Or he could have converted to distributor/spark knowing his abilities & the wire shielding would have been required for RF interference. There is a distributer-ish looking can in the rear, but again was it functional or more for show? The plugs look about glow plug size but I've seen ingenious model engineers make spark plugs of that size. I'd love to know some of the details if anyone has good info. Yes, maybe Robert would be a good lead.

 

[Noel Gordon]

Nice chat theme guys...Almost finished my Edwards 5 and I plan to install into a 100" Strikemaster using Nick













Hi guys, a nice chat thread.. I have almost finished my Edwards 5 and I intend to install in a 100" Strikemaster using Ziroli plans which I now have.. I intend to run my radial using pump gas as Ive modded the heads to take mini spark plugs.... Slow to finish my radial because of selling our house and buying another (and I really hate the process)
















777777777777

 

[Shopgeezer]

We have sold houses and bought new ones all our married life. Career changes, new postings, and family situations meant constant changes. I would just get my shop set up to my satisfaction and get into some projects and Bingo, off we would go again. Lathes and mills don’t like moving. I like it even less. Moving house is awful, moving a shop is much worse. I still have projects in boxes from years ago. My current shop is my retirement dream and I’m staying put this time.

 

[josodl1953]

Now that the end of the 2019 is approaching, it is time to evaluate the build of my 80% Edwards radial 5.
First of all, the positive aspect is that I got it running. A less positive point is that I could not let it run at full power because when I did it died slowly. I could keep it running sometimes when I took back the throttle quickly. There was a substantial blow-by which was evident by the amount of oil and fumes coming out of the crankcase breather. After a few runs, this oil had a brownish colour , possibly caused by corrosion of the cast-iron cylinder. Apart from this, compression was fairly good
( cold) and ( electric) starting was no problem ,running half throttle was fine, including very short full-throttle bursts, and attracted a lot of attention at a show last week.

So , I decided it was time to take the engine apart to check for wear and the suspected corrosion problem.
On removal of the rear crankcase cover and a cylinder head the corrosion of the cylinder was confirmed. I think I should have been paying more attention on after-run cleaning . Nitro-containing fuels seem to be rather corrosive.

So far the things that were not so good. Positive was that there was very little wear on conrods . At the front side, there was the camdrive to be inspected. From the beginning, I was worried about wear on the camgears because they were not hardened. Also there was the question of wear on the camring and followers. They were hardened but, well, you never know..

Luckily, there was no excessive wear on any parts of the camdrive which was a relief because there are no obvious alternatives, especially for the idler gear.

I could do with a bit less sealant on re- assembly....

Piston looks a bit brownish but no excessive scoring marks.

Cylinder head has no obvious weaer, exhaust valve is a bit darker as can be expected.

So I'll have to think about a solution for the full-throttle problem. Maybe I will have to fit second piston rings to get rid of the excessive blow-by. Another reason might be a too lean mixture but I use a carb from a 5 cc Super Tigre so I think that is not the problem. Fuel mixture has 17 % oil, does seem to be OK.

Any ideas to solve this problem will be welcome....

Jos

 

[tornitore45]

Great report
My guess about dropping out at full throttle is that the carb is too small.
You are using a 5 CC engine carb for an 11 CC. There is always 1.25 cylinder in the intake phase equivalent to about a 13 CC single cylinder displacement.

I am almost finished making parts for mine, last minor fittings then I must make the display base. My engine does not fly but mount with all the accessories to start it and run it. I plan to run the glow plugs with AC out of a transformer with 5 separate winding. Guessing which plug is blown is not going to be fun so I have a circuit checking the individual currents.

 

[petertha]

About the fuel, it is left -over racing fuel from my model boat racing career, containing 15 % oil ( castor/synthetic 50-50) and 10% nitro. I have no lubrication pump, the cam housing contains its own oil supply, the separated crankcase receives oil from blow-by of the pistons like all commercial four-stroke model engines

That's great that you are provide us real life running conditions update. The cam gears look much cleaner, do you think because it was in a separate chamber isolated from the crank case? What kind of oil did you have in there?

The corrosion looks like its concentrated around the CI liners extending out of the crankcase, quite red around the ends that protrude into the crankcase. I've seen RC engine that look like this but usually confined to many, many years of dormant storage where spent fuel is sitting in a puddle. The liner ID's are typically hard chromed but the OD & other components still non-coated steel. Methanol is a bugger for attracting moisture out of the air but I would not have expected that after a short period. Even with generous after run oil between runs I think it would be hard to get a coating on all those surfaces. And then you would have to do good job of pre-draining before runs. The pistons & top end looks nice.

Hmmm... I have CI for my liners too, that step is coming around the corner. I am still oscillating back & forth between CI & 1144 stressproof. But so many homebuilt engines call for CI. Nobody really shows pictures like this. Do you happen to recall what alloy you used?

 

[bobden72]

After seeing you internals I think I will have to strip my Edwards 5 down and check it, its been six years since I saw the insides.

 

[propclock]

Thanks for the tear down, just a thought. almost as corrosive as nitro fuel
is silicone seal. the gas it emmits for curing can be very corrosive.
There are modern no acid silicone seals but the older ones can be nasty.
I at one time RTVd (silicone seal) a limit switch bracket to my mill.
The following day there was a 3 " rust area around it.
In a sealed environment( crankcase)
it could be as nasty as no after run oil. Beautiful engine.
Just my 1.414 cents worth.

 

[josodl1953]

Hi Mauro,
Typically, four strokes require much smaller carbs than their two-stroke counterparts.
I looked up the recommended carb size based on the internal dia of the Edwards manifold flange, being 0,437".
This is from the official Perry website:

Carbs this size (2100) are intended for .21 to .50 cu. in. ( 3,44 to 8,1 cc)two-strokes. Now I downsized my engine from the original 55 cc to 31 cc, so i don't think the size of the carb is the problem.
However, I did notice that some cylinder bolts came loose very easily so I must investigate the correct torque for this bolts (M2,5)

Peter,
I use outboard gearbox oil , it smells like the oil that is used in ( manual) car gearboxes and diffs and I think it is basically the same stuff.

I filled the camhousing slightly more than half with oil but I had to block the breather on top of the housing
beacuse the oil was blown out, by centrifugal force I guess.
The camring hub has two scoops to help the oil circulation from the outside of the camring to the inside ,
but of course I don't know if it really works.

For corrosion prevention, I think spraying with an anti-corrosion agent such as WD-40 in the in take while spinning the engine with the electric starter would help. There is a breather in the rear crankcase cover but if I fit another on the opposite side I can also flush the crankcase after running.

As far as the corrosion of CI is concerned: it should be best avoided but on the other hand, it is not the end of the world.
Although is does not look like this way, CI is fairly corrosion resistant. You must remember that a lot of products
containing water such as cisterns and drainpipes were made of CI before plastics came along, and they lasted for decades.
I used GGG 40 for the liners and GGG60 for the rings, these are European standards, the numbers referring to the tensile strength in kgf/mm2. Hardened and/or chromium plated cylinder liners work fine for commercial produced engines
but for hobby/home made engines, CI is, to my humble opinion, the best choice. It seems to me that non-hardened steel liners are OK for short runs but not if a certain amount of longevity is required.

Propclock, I did not use silicon based sealer but Hylomar, the blue non-hardening paste. Works fine , parts are easily separated, only cleaning up requires thinner or an alcohol-based detergent.

Jos