Quarter Scale Merlin V-12

[mayhugh1]

Roger,
I'd be happy to take a look at what you have. I sent you a personal email.
Terry

 

[AAFitArm]

Looks awesome! You could always do an approximate copy of the airframe mount! It'd just have to be cantilevered out the front.

 

[ddmckee54]

So tell me Terry, when you're working on the engine do you pause periodically to pat it on the head covers and say "Let's get ready to RUMBLE"?

Just askin',
Don

 

[kvom]

I can imagine Terry sitting there thinking, "I better slow down on getting this thing finished, 'cause what the heck am I going to build next"?

 

[wirralcnc]

Sleeve valve engine ????

View attachment 1494360719859.jpg

 

[bananarchy]

Incredible work. I agree on the sleeve valve - the wow factor on this is hard to beat, and about the only way to go from here would be a Bristol Centaurus or a Napier Sabre.

 

[mayhugh1]

Before moving the engine from the rotisserie assembly stand to its new static display stand, I tried, while I still had easy access, to address some oil leaks that I'm already seeing. Although the leaks themselves probably won't be of interest to anyone, one of the techniques that I used to fix them may be.

My original plan to rely on the large numbers of screws holding the supercharger cover, wheel case cover, and prop drive cover halves together for metal-to-metal oil sealing turned out to be pretty naive. Oil from some of my earlier tests has been collecting on the interior floors of these sections and has been seeping through the junctions between their halves. At this point the seepages are minor and mostly just annoying, but they will likely grow worse after the engine is running and being temperature cycled. If I had it all to do over, I'd use Permatex Aircraft Sealer between the halves of all three sections and not be concerned, as I originally was, with the issues it might create for a future disassembly. As far as I'm concerned, disassembly right now isn't an option, and so I decided to try something much easier.

There is a product sold by Eastwood called Diamond Clear Coat

http://www.eastwood.com/eastwood-diamond-clear-dtm-and-painted-surfaces-aerosol.html

that's designed to clear coat bare metal. I've used it on polished aluminum and steel motorcycle parts for years, and they continue to look bright and shiny. The coating remains flexible and doesn't yellow or peel even in our hot Texas sun. One of my more demanding applications for this product has been on a piece of kinetic yard art that included a lot of polished copper. After over five years in the weather, that copper looks the same as it did the day it was coated. The satin version of this product is essentially invisible on castings.

I loosened about a dozen screws on the lower portions of each of the three seeping sections and wicked in several doses of acetone from a tiny eye dropper to remove the oil from the mating surfaces. Then, using a fine plastic pipette, I carefully directed a bit of sealer into the seam between the halves where it wicked in between the surfaces. This product has the viscosity of water and is quickly drawn into the tiniest cracks. Since I usually purchase the coating in aerosol cans, I had to collect some in a paper cup in order to apply it with a pipette. It's also available in quart cans, but with a higher viscosity. I retightened the screws while the coating was curing, and after several days there doesn't appear to be any sign of seepage.

There was a somewhat bigger leak at the oil pump located on the bottom of the lower crankcase. This leak is the result of a marginal boss on the lower crankcase onto which the oil pump was mounted. The boss seems to have too little area and too few screws to provide a reliable metal-to-metal seal between the lower crankcase and the oil pump. It may have been designed for an earlier version of the oil pump. A gasket isn't appropriate here since the crankcase is being used as the pump cover, and the use of even a thin sealer would affect the pump's clearances. This time I didn't loosen any screws. After thoroughly cleaning out the oil, I wicked sealer in between the portion of the pump body that was overhanging the mounting boss and the crankcase surface around the perimeter of the boss. The narrow space around the boss easily retained a healthy bead of sealer while it cured. Again, this appears to have fixed the problem.

A final leak of even more significance was again underneath the engine but at the adapter for the coolant pump. The originally specified pump shaft bearing inside this adapter was an open type which allowed oil to easily pass through it and flood the area above the pump seal. I replaced the open bearing with a more difficult to find sealed equivalent. More importantly, though, I also replaced the .004" thick gasket that I had been using between the crankcase and the flange of the adapter with Hylomar sealant.

Hylomar was also added between the rear mounting surface of the oil pump pressure regulator housing and the side of the crankcase. I had previously overlooked potential leaks here due to some unused mounting screw holes behind the regulator when it was installed a couple months ago.

After all my efforts to get the stand's four mounting pads coplanar to machinist-level tolerances, I realized after setting the engine down on the stand that I had never actually machined the bottom surfaces of the Quarter Scale's motor mounts. What my aging mind had confused was the facing of the top surfaces of those mounts which had been necessary for the fixturing required to line bore the crankcase. The top surfaces and not the bottom surfaces were machined because the crankcase was inverted for the boring operation. To absorb the 'rough' cast bottom surfaces I inserted .030" thick pads made from automotive gasket material between the stand's mounting pads and the engine's motor mounts.

The placement and orientation of the oil filter looked reasonable in my SolidWorks model, but after bolting it onto the actual stand it was obvious that the routing of the oil lines to it was going to be awkward and their lengths excessive. I machined a black Delrin adapter to alter its orientation to improve the appearance of the routed 5/32" copper feed lines.

I plumbed as many of the interconnecting coolant lines as I could using 1/4" i.d. clear Tygon tubing. The clear tubing is only temporary so I can more easily verify coolant flow while the engine is running. It will eventually be replaced with black hose.

The next step is to fabricate and install a coolant tank on the rear of the running stand. - Terry

 

[Blogwitch]

Terry,

Showing these pictures and text proves that none of us are infallible and that you are in fact human and not a reprogrammed robot.

Beautiful work, as usual.

John

 

[Ken I]

Terry,
I read a 1946 air minstry test report which gave the Spitfire a thrust of 2.77lbs per HP at takeoff power of 1375 HP = 3800 lbs thrust.

Some musings...

Now your motor is 1/4 scale - for each scale halving the capacity is 1/8 but the specific HP doubles so it's 1/4 - so a rough guess would put your engine at 86 HP - that's too much (200 HP per liter).

So if you were to assume a fairly sporty 100 HP per liter then your motor is going to be in the 40 HP realm and therefore capable of producing something like 110 lbs thrust.

How are you going to restrain the horses - I'd hate to see it fly away.

Just out of interest what are you expecting to get out of this engine ? (I know that's not the intent.)

I remain overawed by this project - fantastic work. More than that, thanks for the documentation effort to have all us lookenpeepers along for the ride.

Regards,
Ken

 

[kvom]

Last photo was a teaser. We want to see the whole engine on its stand. :thumbup:

WRT Ken's musings, the thrust will depend on the prop pitch and RPM, so takeoff power might not be what we'll see.

 

[Lakc]

Wonderful work.

 

[Stieglitz]

I'm with you ripcrow!

 

[mayhugh1]

Terry,
I read a 1946 air minstry test report which gave the Spitfire a thrust of 2.77lbs per HP at takeoff power of 1375 HP = 3800 lbs thrust.

Some musings...

Now your motor is 1/4 scale - for each scale halving the capacity is 1/8 but the specific HP doubles so it's 1/4 - so a rough guess would put your engine at 86 HP - that's too much (200 HP per liter).

So if you were to assume a fairly sporty 100 HP per liter then your motor is going to be in the 40 HP realm and therefore capable of producing something like 110 lbs thrust.

How are you going to restrain the horses - I'd hate to see it fly away.

Just out of interest what are you expecting to get out of this engine ? (I know that's not the intent.)

I remain overawed by this project - fantastic work. More than that, thanks for the documentation effort to have all us lookenpeepers along for the ride.

Regards,
Ken

Ken,
If you look back at the photo labled 'painting completed' on post 676, the stand is sitting on an outdoor bench where I usually run my engines. I usually clamp the big engines down to this bench when they're run. There are two feet sticking out the bottom rear of the Merlin's stand that I plan to clamp down with c-clamps to this bench. The pitch of the prop I plan to use is not very aggressive, and at a max rpm of 3600, or so, I don't expect the engine to be able to even pull its own weight and that of the stand which is currently about 50 lbs. - Terry

 

[ddmckee54]

Terry:

Slightly OT but definitely related. Back in post #680 it was suggested that you make a scale P-51 spinner. That got me wondering how they originally made the spinners back in the 40's. Were they spun out of sheet as the name implies? I doubt that they were carved out of billet, maybe welded up out of stamped sections? Do you know, or does anybody on the forum know? It would be very cool if a video existed showing how this was done. I imagine you've just about worn out your screen watching the videos of both Rolls and Packard assembling the Merlins.

Don

 

[kvom]

I found this contemporary article that discusses spinner design without describing the way they were made. However, a drawing on the second page shows that they had numerous parts.

https://www.flightglobal.com/pdfarchive/view/1940/1940 - 3291.html

 

[MrCat63]

I would suspect they were spun from aluminum and then mounts and supporting structure added. Much the same way they are still made. Here's a modern spinner being made.

[ame="https://www.youtube.com/watch?v=yrTDBW6q7Xg"]https://www.youtube.com/watch?v=yrTDBW6q7Xg[/ame]

 

[gld]

That was very interesting, Thanks for posting. That fellow was putting some heavy mussel into that tool.

 

[gunna]

Always a pleasure to watch a real craftsman at work, no matter what he is producing.
Of course, that applies to Terry as well!
Ian.

 

[mayhugh1]

Because of overheating concerns with the engine, I wanted to provide it with a robust cooling system, but I didn't want a large assemblage that overshadowed the engine itself. In addition to the 18 cubic inch belly radiator, I added a reservoir to increase the volume of coolant in the system. Additional coolant can extend the running time of a model engine that's prone to overheating when heat extraction from the coolant isn't adequate.

I considered two possibilities. The first was to add a fan-cooled radiator mounted to the accessory rails at the rear of the running stand. As Ghosty pointed out earlier, there are double and triple tube radiators available that are similar to the ones used in the belly radiator. I purchased one of the triple tube models since it would have nearly doubled the amount of coolant in the system and also provided an efficient mechanism for removing heat from it. I tried to integrate the radiator into the accessory mounting scheme that I had planned for the stand; but the radiator's form factor kept getting in my way, and its input and output fittings were difficult to deal with.

In the end, I opted for a custom machined reservoir that fits in between the stand's accessory rails. I designed it around a sizable chunk of aluminum in my scrap collection that had enough volume in the right proportions to add another 45 cubic inches of coolant. I machined an array of cooling fins into its rear for a bit of heat removal, but considering typical model engine runtimes (and the fact that the fins are shielded from the prop wash) they're probably more cosmetic than functional.

Although my main objective for adding the reservoir was to increase the system's coolant capacity, its heat extraction might have been improved a bit by reducing the thickness of the fins and increasing their number. After deciding to cut the eight inch long array of 1" x 3" fins with an end mill, though, the machining time would have become an issue for anything much thinner than a couple tenths of an inch. A more efficient way to have cut them in my shop would have been to use a carbide tipped circular blade in my radial arm saw. But, my saw's rather worn table was going to require some significant refurbishing to get results I'd be happy with. This particular operation would have been an ideal candidate for the right angle milling attachment that I once considered purchasing for my Enco mill.

My Tormach with a 3x spindle speed multiplier spent nearly three hours cutting the .2" thick fins using a 3/16" cutter spinning at 13 krpm. The full-width 10% deep roughing passes in the valleys between the fins left significant chatter marks on them, and so I had to run an additional pair of time consuming finish passes on either side to clean them up.

A 1/2" 3 flute hogger was used to remove the 45 cubic inches of chips from the tank's interior. Hogging out the relatively large three inch deep cavity was a new experience for me, and it required another couple hours machining including the time needed to recover from a clogged-flute cutter. The Micro-drop coolant system that I use doesn't perform very well in such deep voluminous operations even with all its settings max'd out.

I didn't want to end up with any leaks especially since the reservoir will eventually sit directly above the engine's ignition modules. I drilled and tapped holes for some 45 2-56 screws that will be used to seal its gasket'd cover. The bottom of the tank was drilled and tapped for a 3/8" stainless steel hose fitting. A hose from this output fitting will feed the input of the coolant pump on the engine. Hoses from the belly radiator will return coolant from the engine to a pair of 1/4" hose fittings that will be machined into the top of the reservoir's cover.

The side of the reservoir was machined for a sight gage so the level of coolant in the tank can be monitored. After cutting the vertical viewing slot, a groove for an o-ring was machined around its perimeter. A trimmed glass microscope slide sits in a machined recess against the o-ring in order to seal the viewing slot. A bezel, screwed into the side of the reservoir, holds the glass window in place against the o-ring. The exterior of the tank was bead blasted and painted with matte black Gun Kote. In order to improve the visibility of the coolant level inside the dark tank after the lid is installed, a white backplate was mounted inside the tank just behind the viewing window to reflect exterior light back out through the coolant.

I designed an overly elaborate cover for the reservoir with the fittings for the return hoses integrated into its top along with a 3/4" threaded o-ring'd port for a filler cap. This cover became my part from hell after two workpieces with a total of nearly ten hours of machining time in them wound up on the scrap pile. The first was the result of a storm related power glitch during machining, but I have to take full credit for the second one.

To wrap up the cooling system I still need a filler cap and a means for draining coolant from the lowest point in the system which is where the two return hoses will exit the radiator. I was hoping to complete both of these before my hip replacement surgery which is scheduled at the end of the week. I spent much more time than expected on the lid, and so they'll have to be done later. It's been pretty painful for me to walk or even stand during the past several months, since a slight defect in my right hip has, over time, caused it to wear out prematurely. I'm not sure what my recovery is going to look like, but it will likely keep me out of my shop with all its tripping hazards for a few weeks. - Terry

 

[stragenmitsuko]

I designed it around a sizable chunk of aluminum in my scrap collection . - Terry

Quite a piece of scrap that is