Brian Turner custom stunt (F2B) engine


Brian Turner, well known for the winning F2C teamrace engines that he made and competed with over the last 10 years, has recently returned to flying F2B stunt. Brian last competed in F2B back in the 70's when he was a member of the British team at the Eurochamps. Brian designed his own stunt model using the Yatsenko wing section and basic areas and moments. This model named skytoane (an anagram of Yatsenko) has proved to be a capable performer and has been powered by a Stalker 61 LT LS stunt engine up to May 2008.

Brian's Stalker engines have been the subject of an extensively development program with changes to the inlet timing (changed from 56.5°/40° as delivered to 40°/45°), to the combustion chamber, the piston baffle, the crankcase volume and the addition of a plug shield. All of these changes have made these Stalkers quite competitive.
At the start of 2008 Brian decided that the Stalkers had been developed as far as possible without replacing the crankcase and other major components so he decided to make his own Longstroke 61 stunt engine based on the things that he had learnt during the development of the Stalkers. One of the main changes that has been made possible is the reduction in the height of the engine of about 3mm. This is made possible by the addoption of a backplate design that is held on with screws thus allowing a shorter conrod and the piston decending into a pocket in the backplate. This makes a considerable improvement to the crankcase compression and thus the pumping of the engine.
During the building of the first engine I loaned Brian a digital camera and he has taken pictures of all of the major machining operations.
The engine had its first outing on Sunday May 13th 2008. Brian reports that it ran well immediately with only a small tweak of the needle to get it circulating at a steady 5.5 secs/lap. Flying in a 14mph wind there was very little windup.

The drawings.

I have worked from Brians original drawings to create an accurate 3D model using SolidWorks. From this model I am producing component drawings in PDF format. Currently I have completed the drawings produced and they are available below. Most of the main drawings are checked and should be complete. If anyone is planning to start making an engine from these drawings I would strongly suggest that you email me so that I can keep you posted with any changes, updates or improvements.
You will see that there is one major difference between the original prototype and the drawings available here and that is the venturie is now on the engine centreline not offset as it is in Brians prototype. The experience of using the original engine in competition for the second half of 2008 has indicated that the slightly improved engine balance is not discernable in the running and is an unnecessary complication in the machining.
I have also included a normal prop driver for any one who prefers to use a commercial spinner

There is also an easy to use 3D model of the assembled engine that can be spun, sectioned and exploded to further explain the design. For more information on how to access the reading program to use this model please go to the CAD TOOLS PAGE

Click on a drawing link to open or save.


Brians Original Drawings




crankcase 2
tooling. Top centre of the picture is the mounting mandrel for the piston. The diameter on the right is a precision fit in the skirt of the piston and the front face butts against the gudgion boss. The drawbar (top left passes through the mounting and is located in the piston with a gudgion pin and the screw tightened gently (hand tight - only sufficient to stop the piston from moving whilst lapping or turning). The lap is shown at the bottom and is made from aluminimum and is a sliding fit on the piston before it was split. The clamp screw gives control of the size during the lapping.


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Pictures 1 & 2 crank case parts at start of picture taking - some work done
crankcase 1 crankcase 2
Front housing threaded and having the back ballrace and plain section machined Machining fixture for the front housing.
crankcase 1 crankcase 2
Front housing on the fixture machining the front ballrace housing and the outside nose. Machining the front face and the female thread and c/bore the main bore was machine in the milling machine with a boring head.
crankcase 1 crankcase 2
The 2 parts of the case screwed together with Loctite high temperature retaining compound.
Note: The o/d of the front housing and the front face were skimmed when the ballrace housing was being machined so that these faces could be used as a location for the next operations.
Set up to machine the back bores for the crankshaft, the clearance for the conrod, the oring c/bore on the back and face off for the backplate.
crankcase 1 crankcase 2
The crankcase is set up in the dividing head on the milling machine to do the backplate mounting holes as these will be needed to mount the crankcase for further machining. Again set up in the dividing head ready to rough out the crankcase and front housing the case is mounted on a false backplate and the front is supported by a accurate pin located on the front ballrace housing and the plain 12mm bore this pin will be used to dial off to do some tricky machining. later.
crankcase 1 crankcase 2
Roughing out the crankcase - the mounting lugs are taking shape and a lot of material has been removed from the case. Mounting lugs finished and the crankcase shape machined. The backplate screw lugs are machine with hand ground form tools. The mounting holes in the lugs are positioned with great accuracy as they become the main location for the machining of the inside of the upper crankcase.
crankcase 1 crankcase 2
The front housing webs are machined to thickness but left full width to use as datums later. Next the spraybar hole is drilled then the venturie top surface is machined with the dividing head tilted to 30° the venturi hole is machined relative to the spraybar hole by putting a pin through it and wobbling off it. Finishing the webs and removing anything that doesn't look like a stunt engine.
crankcase 1 crankcase 2
The milling machine - no digital readout need apply - the dividing head is a proper solid tool. More venturie internal and external machining.
crankcase 1 crankcase 2
Now Brian is ready to machine the cylinder internal and external diameters. This is the fixture Brian has made to mount the crankcase both on a rotary table and in the chuck of the lathe. The fixture has a spigot locating in the centre hole of the rotary table. This rotary table is a very old but well made unit that has seen a lot of use and was showing the scars. Brian has skimmed the surface of the table and also remachined the centre hole to get the accuracy he demands. The engine is just standing in the fixture showing showing where it will fit when it is returned to the Miller after the machining of the internal bores that is the next operation.
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The same fixture is fitted to the lathe so that the round parts of the cylinder can be machined. As shown here the internal bores are finished and the transfer port outside shape has been turned (the front part of the crankcase behind the venturi). The exhaust port has been machined on the outside with the dividing head horizontal. Now the head has been tilted up to finish off the internal exhaust port machining (the upper face).
crankcase 1 crankcase 2
The case is now on the fixture mounted on the circular table and the fins are being machined. The tool is specially made for this engine to get the correct radius. Note it worked best when climb milling and all the slots were cut to depth in a single cut. This gave the best finish and the least chatter. Another trick Brian has used is to fit the dummy backplate fixture to the case to give even more stiffness to the case whilst machining.
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Machining the transfer port. This is the tool that Brian used - a single point tool with the largest shank that will allow the radius required for the internal port.
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The outside of the case below the exhaust port is now machined. The conrod clearance groove has been machined by rotating the case and using another Brian's custom tools.
crankcase 1 crankcase 2
crankcase 1 crankcase 2
The case is now finished and any of the little hand fettled areas where machining is impossible have been dremel'd.
crankcase 2 crankcase 2
Inside of finished piston Top of finished piston
A decision must be made at this stage on the piston fit in the liner. in this instance I wanted the finished piston to interfere (start to bind in the liner) at 2.5mm (0.1") from top dead centre. The liner has been measured and the taper is known so the actual diameter of the piston can be calculated. On this engine the piston is 5mm (0.197") from the top of the liner at top dead centre, so the fit required is 7.5mm (0.295") from TDC.
The piston is turned to 0.012mm (0.0005") oversize. Then the 0.75° taper is machined around the top of the piston including the baffle. The taper is machined so that after final lapping the width of the taper will be 2mm (0.080")approx. The cleaned liner is put over the piston and slid down until the piston just binds. This depth is measured with a depth gauge and the result noted.
The piston is now lapped to the final diameter using the lapping tool shown on page 8 with 1000 grit carborundum mixed in engine oil. The lap is set to size by placing it over the piston and tightening the clamp screw until it is just free. A tiny amount of the grinding past is then dabbed onto the piston and the lap is put over the piston with the lathe stationary. The lathe is then started at about 50RPM and the lap is held and moved bacwards and forwards a few times (about 4 times) the lap is then removed, turned round and a 4 passes made. The lap is then removed and the piston cleaned with a solvent and dried carefully. The clean and dry liner is then put over the piston until it just binds and the depth from the top of the liner to the top of the piston is again measured with a depth gauge. This will give an indication of how much lapping is required to move the piston up the bore to the required position. The proceedure is repeated. The lap is reset each time by putting onto the piston and tightening the clamp screw till it just starts to drag. A tiny amount of new grinding compound is added each time.
This is repeated until the required fit is achieved.
Note: when removing the lap is should be done in a swift move whilst the lathe is running or it may bind.
This proceedure sounds laborious but is actually quite straight forward in practice. Fitting the piston to the new engine took only about 1 hour and the lapping took only 10mins.
The piston and liner must now be thouroughly cleaned. This is done using washing up liquid and an old toothbrush in hot water. All vestages of the lapping compound must be removed.
The piston fit achieved by this method will not need any significent running in. The first engine had only 15mins on the bench before flying in the aeroplane.


crankcase 1 crankcase 1

Making the Crankshaft

crankcase 1 crankcase 2
The crankshaft is made from a piece of EN24 A hardening carbon steel. as shown here the billet has been roughed out to plus 1mm all over to allow for any movement in the steel. (EN24 is a high quality, high tensile, alloy steel . Usually supplied readily machineable in ‘T’ condition, it combines high tensile strength, shock resistance, good ductility and resistance to wear). The roughed out shaft now has a centre in the end and is turned to plus 0.3mm ready for hardening.
crankcase 1 crankcase 2
This is the machining of the 2 fixtures needed for machining the crank pin. There are two fixtures as the shaft mounting holes are different sizes. One is used for the machining when the shaft is plus 0.3mm and one for when the shaft is at the final size. The two are made from a single piece of aluminium and parted off when finished thus ensuring that the offsets are identical.
crankcase 1 crankcase 2
Using the roughing fixture for machining the pin. Machining the crankshaft web. The crankshaft is fitted to the dividing head for this job and the horizontal flats are machined accurately to use as datums for setting up the shaft for the next operations.
crankcase 1 crankcase 2
Machining the inlet port in the crankshaft. The bore has been drilled previously. The machining is done with the milling machine head set over at 30° so that the crankshaft is parallel to the bed enabling the crankshaft to be supported with a centre (not shown). This is Brian's home made muffle furnace that he uses for all his heat treatment. it should be capable of working up to 1000°C. The shaft was heated to 840°C then quenched in oil. Tempered to 180°C and quenched in oil.
crankcase 1 crankcase 2
The shaft is set up in the lathe for the final grinding to final size. The power is a Dremel driving a custom made toolpost grinder.
crankcase 1
This is the centre pin in the chuck used for mounting the shaft turned to allow the driving dog to clamp on it and the crankpin.

I got some times from Brian for the case machine. Excluding the tooling he spent about 35 hours for the machining. The tooling for the Case took a further 12 hours. The design and detailing (all by hand with a pencil) took about a week - For Brian this is about 20 hours at the drawing board plus a lot of thinking time. The project so far has taken 5 weeks elapsed time and Brian aims to spend about 20 hours per week actually making the bits.

crankcase 1 crankcase 2
Final grinding of the crank pin in the lathe
BTW I checked with brian and he doesn't have any drawings for the toolpost grinder. He made it from simple hand sketches and some "design on the fly".
Crankshaft finished - the ballrace fit was finally lapped to get the interference fit.
crankcase 1 crankcase 2
Light aluminimum insert is fitted to the front of the axial hole in the crankshaft to fill the end of the hole and to flare the end of the inlet. Here you can see it fitted into the shaft. locktite is used to fix it in place.
crankcase 1 crankcase 2>/a>
Conrod blanks milled to 1mm over size all round. Brian made 2 so as to have a spare. Conrod blanks drilled and fitted with the phospher bronze bushes.[br] The holes are drilled Ø7.5, the bushes are pressed in and the blank is then returned to the mill to ream the bearing inner diameters and the blank is then milled down to final thickness.
crankcase 1 crankcase 2
Here is the fixture for machining the conrod to shape. Machining the sides and the top and bottom.
crankcase 1 crankcase 2
Basic rods with all the simple milling completed - just the round ends to machine. Fitted in the chuck of the dividing head for shapeing the ends.
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Radius cutter - home made of course for finishing the ends. Finished rods
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Finished piston. This was made before the current engine build was started and was intended as a replacement for the standard Stalker item. Brian has moved the baffle away from the cylinder wall to improve combustion. The long stroke Stalker has the baffle very close to the side probably as a consequence of using the same piston as was originally designed for the short stroke version that had a larger diameter bore.

Making cylinder head.

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These are the parts need to machine the head. On the left is the head blank now finish machined where it fits into the cylinder but the combustion chamber is not machined at this stage so as to give plenty of thread depth for the bolt. The middle component is a machining fixture with a bore the same as the cylinder and the bolt on the right is 1/4"X 32tpi to clamp the head to the fixture using the plug thread. Here is the blank and the machining fixture assembled ready for the lathe.
crankcase 1 crankcase 2
Faced to the final thickness, plug recess bored and the radius around the edge of the fins machined. Mounted in the dividing head using the same fixture for machining the fins. The cutter Brian is using is one he has made himself. A small piece of high speed steel is silver soldered to the end and ground. This sort of cutter takes a lot of care to use as the cutting forces are quite high.
crankcase 1 crankcase 2
Setting up the head to machine the clearance for the baffle and the hole for the plug shield. The head is held in the chuck of the dividing head in a split ring. The setting pins are in the head mtg holes and the direction of the fins is marked with a felt tip pen. Because Brian takes a lot of care in the size and position of the head mounting holes he can rely on them for setting later in the machining. Baffle recess is machined with a Ш75mm x 1mm slitting saw. The slot is first machined with the dividing head parallel and then the angle is machined with the head angled.
crankcase 1 crankcase 2
The plug shield hole machined - in from both sides as it is too long to do from one side and expect it to be straight. Also it is 1/16" offset from the centre so the machining is onto a slightly angled face. Plug baffle pin machined ready to part off. made in stainless steel it has been turned in the lathe and the centre portion that crosses the combustion chamber thinned down by machining the flats shown here.
crankcase 1 crankcase 2
Head and pin finished. and assembled. The pin is loctited in to make sure it doesn't rotate. It can't fall out (unlike the Retro version that is pressed into a hole) as it is fully located in its hole by the cylinder walls.
crankcase 1 crankcase 2
Jig to make the gudgeon pin circlips. Sorry the picture is not sharp I may try to get a better picture later - the jig is quite small!. It is a short turned diameter - trial and error to get the right diameter so that the clip is the right diameter when it is in the relaxed condition. The wire Brian uses is Ш0.4mm. The slot in the end is 0.3mm deep so that the wire can be clamped into it by the pad on the tailstock. The edge the wire bend round as it leaves the slot is radiused to ensure that there is not a stressed part of the clip that might break off as it would do a lot of damage if it did. The tailstock with a pad fitted on a rotating centre holds the Ш0.4mm wire into the 0.3mm deep groove while the chuck is rotated by hand nearly 2 revs to allow for the unwind. the second turn is on the chuck side of the first wind not over the top of the first wind as that causes a small kink in the clip.
crankcase 1 crankcase 2
Finished circlips. All the components ready to assemble You will see that the cylinder is not back from the Ukraine where is has been sent for the chrome plating.
crankcase 1 crankcase 2
Assembled engine. Fitted with the spinner. The spinner backplate is also the prop driver.


Brian makes his own spinners. No fancy machinery just a good old lathe. Here are the drawings and the photos of the spinner and prop driver for the new engine: First the drawings.

crankcase 1 crankcase 2
crankcase 1 crankcase 2
crankcase 1 crankcase 2
crankcase 1


Dispal 250 produced by Peak Werkstoff GmbH dispal250.pdf may also be available from:-
Powder Light Metals GmbH Am Wiesenbusch 2 Gladbeck, Nordrhein-Westfalen 45966 Germany. TEL: +49 2043944465 FAX: +49 2043944475

Cylinder. Brass CZ 121 - this is a common material and should be easily available.

Crankcase. Alcoa 4032
This as a 12% silicon al alloy also known as "Deltalloy 4032"

EN 24 also known as 817m40 or AISI: 4340
AISI: 4340 Chemical composition in weight %: 0.38% C, 0.69% Mn, 0.20% Si, 1.58% Ni, 0.95% Cr 0.26% Mo.


Обновлен 31 янв 2012. Создан 16 янв 2012

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