Fora 15D Pioneer Engines

[flyingkiw1]

Just out of interest Fora have introduced a new (mK III ?) version of the Pioneer/Jr engine, looks more like a Para now, single exhaust, same price, picture below:

Fora 15D.JPG (24.08 KiB) Viewed 204 times

[locktite401]

The quoted rpm with the CF 7.25 x 5.5" prop of 16500 is probably very good if the motor still has that 3 mm venturi hole. It's likely Schnuerle ported though by the look of the crankcase, which may play havoc with it's acceptability in Classic TR. Looks promising for DGY.

Now who's going to buy one to try it out?

Ray

[flyingkiw1]

After talking to Aleksey at Technohobby I have purchased one. They are 3 port according to Aleksey, not sure if that means Schnuerle and boost or Schnuerle and exhaust it got lost in the translation.

I'll know soon, its on the way . 16,500RPM is good for a 7.25 x 5.5. Looks like quite a thick bladed prop too.

Lance

[AusBrent]

Certainly tempting.

Any word on the conrod construction?

Brent

[flyingkiw1]

Hi Brent

So far my con-rod question has been ignored by both Fora and Aleksey....

[ARGHETT]

Maybe there designed to bend if people belt the propellor and try to get racing performance out of them ,
rather than break more expensive components .

[flyingkiw1]

Automatically self adjusting componentry. New-age crumple zones. Never thought of that.

[flyingkiw1]

Hi Guys

Just got two of these engines to test to Classic FAI.

Nicely made, 2 cost USD$190 plus postage from Ukraine, so not a bad deal at all.

FORA 2.5D vitals

Bore 0.550" Stroke 0.631"

Exhaust opens 142 deg
Boost and transfer open 118 Deg
rotor opens 153 BTDC closes 30Deg atdc
Head shape much better and head has been machine to give almost flat squish as it comes


RPM 17200-17500 on an APC 7x6 sports prop with only 1/2 turn on compression to get tune.

It comes with a better made 5 hole peripheral venturi made of hard plastic, hole 3.8mm about right for us.

Using Timmy Tigre fuel, 2.75 IPN and at 15C it started and ran first flick after minimal port priming and 4 drops in the venturi, 2.0 turns open on the needle.

When bolted into Andrew's Classic FAI did 23.25sec/10 laps for 32 laps using a stock APC 7x7 prop, still being run in so rich with a more than modest amount of popping and banging. Still to optimise the prop and the fuel yet, but when the tank runs out we can hear that its going to go better with a leaner tune.

It's the latest Junior, the Mk IIl version, single exhaust, el cheepo sports diesel ACC, inside it the same running gear as the original jr, crankcase has been redesigned and strengthened as has the stronger con-rod, same crankshaft (as I have said different timing) and bearings, head been redesigned to actually allow the engine to work. Comes with a glow conversion kit and spare head shim. Porting is opposed reverse loop and boost.

Probably slightly heavier than the original Jr but not significantly, Andrew found it has a slightly smaller diameter head, slightly shorter and case it a bit larger (rounder) so he had to take to the pan with a file and file a little off the edge for a fit. The new engine has a band running around the middle or the crankcase that the original did not have, maybe to make it stronger, but I have never heard of anyone breaking a case in the original. The venturi is just slightly lower in an inverted set up, but basically you can drop it in to the existing Fora ( or S/T G20D) model with slight modifications.

The time/10 and RPM on a 7x7 is not much better than the reworked original FORA that Andrew took out of the model, but it probably is very close in performance to that reworked engine. Bear in mind that Andrews Mk I FORA has a Nelson 15D con-rod now and a remade remachined head which looks remarkably like the new FORA engine's head.

Its not a Nelson 25D or a Para, its never going to do 19,000 RPM, (the crank will never take it) but if goes remarkably well out of the box, costs about 100$ and with it we can go Classic FAI racing, without owning a lathe and mill.

We can buy them from FORA at a bulk discount too, and for those that own FORA Mk 1's a replacement Mk III con rod is available to replace the Banana/Cheese one supplied with the original design Mk I and (II). Andrey and Alexy at FORA said that they listened to the feedback from the disgruntled FORA Jr engine owners and this engine should and does operate out of the box and we can confirm that now.

I cannot understand how the other Mk I and II engine with it major design faults (non-functional head, bendy rods and crazy inlet timing) was every allowed to escape from the factory, let alone the 100's that were sold and are still for sale....

Lance

[doc]

Head shape much better and head has been machine to give almost flat squish as it comes

In an earlier post on the previous page, Harry Potter expresses his belief that in a diesel, the compressed fuel/air mixture ignites "in several places at once", if not all together... in which case the need for squish bands and attempts to create turbulence are probably not necessary. Do you agree with this theory?

[flyingkiw1]

Dr Bair, Late of the University of Belfast School of Engineering, has noted that early high performance diesel 2 stroke engines (leading also to the development in the 1920-40's of JU 2 stroke diesel aero engines) all used squish in the head design with smallish combustion chambers to get the desired compression ratios. These were fixed compression ratio engines, and they all led the way early in improving combustion using a combination of squish and Dr. Schnearle fine transfer ports. I bet they never gave it a name at the time as the design is basically a result of the engineering limitation of the engine design at the time and the need for high compression ratios.

One of the most important things that Blair pointed out was that in high speed diesels combustion is still in progress as the piston starts to travel downwards so anything that improves mixing of the combusted mixture at TDC should be employed to improve power. When one looks at modern F2C engines they pretty well follow this design in the head area. If combustion was completed at TDC then squish would be pointless, as it turns out it is instrumental in giving the burning process a good hurry along and making it safer and more efficient. The faster the engine revs, the more pronounced this lag is as the combustion flame speed is relatively constant (unless we add "stuff" to speed it up or slow it down).

The other factor that is often ignored is that close clearance at TDC puts the piston and head close together affording very rapid heat transfer from this very thin layer of hot gas into the head and piston metal, thereby inhibiting uncontrolled (notice I did not say pre-ingition) ignition from hot gas in the head, and improving and smoothing-out the running characteristics of the high speed diesel engine.

Anyone chip in here with your ideas of ideal combustion chambers for diesel (see http://web.me.com/flyingkiw1/Model_Airc ... signs.html ) for some thoughts, mostly from Dr. Blair...