Spitfire Replica. Any Lower Cost Power Unit Alternatives?

Looks very real apart from that long tail wheel spring doesn’t it? I’m not jealous honest guv.

I have my sources… 😉

Seriously, though, I run a discussion group over on Yahoo specifically set up for Spitfire replicas – quite a few folk on there doing either Mk.26s, MJ.10s, Isaacs Spits or full-scale MJ.100s, or even the odd own-design job.

Dave Austin is/was a member (I believe he still is), though sadly he put his Spit up for sale not so long ago.

I seriously don’t think there’s much that hasn’t been discussed on that group already! So long as the ‘king spammers haven’t scared everyone away. :rolleyes:

Another shot of Dave Austin’s Spit:

How did the crazy Scotsman(dazdaman) get the picture of those two spits? yes have spoke to Dave Austin a few times.

Yes Dazdaman it is Ross Fergusons Spit, as I recall he made his own prop blades, used to go see him at home in Scarborough and check out his Spit progress in his garage! Another chap here has one of those Aussie kits, so we sometimes see them both in the air! cheers Darrell

That’d be Dave Austin, I think.

Somewhere in the archives, there’s a pic of both of them in the air. Wait one sec and I shall fetch it….

Here it is. Pic via Dave Austin:

Yes Dazdaman it is Ross Fergusons Spit, as I recall he made his own prop blades, used to go see him at home in Scarborough and check out his Spit progress in his garage! Another chap here has one of those Aussie kits, so we sometimes see them both in the air! cheers Darrell

The Australian Supermarine company Mk26A and Mk26B use a Jabiru 8 cylinder, which is no longer produced and a GM V6 unit. The latter is aiui now the preferred unit.

http://www.supermarineaircraft.com/

If you are going for a flier, why not consider this kit option? The build time will be quicker.

MK 1. I like your soapbox. Your soapbox is helpful.

Hi;

OK, good points and bad points. The 100K estimate for this project is a bit of a spleen crusher. I hate reality, but at least my dear sweet wife won’t likely read through this forum. You are no doubt closer to the grand estimate than I would be, me trying to put a positive spin on cost control. 100K, huh? In the immortal words of E.T., Ouch.

But then there is some good news. Your homemade PSRU intrigues me, but as you’ve alluded to, this is a pretty significant piece of hardware. And using a Chevy LS2 means more power, more reason to get it right, more likely self destruction if I get it wrong. My biggest concern in making a PSRU is the vibration issue. I believe I can manage most other challenges, from casting or machining from billet, choosing flight-worthy spur gears, bearing choices, oil circulation, and possibly even accessory services drives that exit the PSRU at various locations. But the vibrations in their many forms, well, that’s like black magic to me.

I guess what you’re relying on, in your particular case, is the appearance of smooth operation in the first 62 hours of service. Question; are all damaging vibrations detectable through the seat of your pants, or are there types of vibrations that are damaging yet un-feelable? I went through the EPI website, and have gotten some pretty awesome replies from Jack Kane, who based on his replies, I’d have to label “Mr. PSRU.” I believe there are enough separate forms of vibration to scare away the average higher-math-challenged rookie like myself. But again, if the vibration issues were solvable, I would be willing to at least do some preliminary designs and hardware sourcing. Metal working on a mill has its challenges, but that’s the stuff I enjoy.

Now there’s the prop. Again, a homebuilt affair for you. Please, tell me more. Three blade, 6 plies of birch, kevlar coated. Do you mean a layer of kevlar is epoxied to the surface of each blade? And the bosses, I see these as cylinders that the prop ends get stuffed into and epoxied. I think the props made in BC by GSC Systems have a bolt through the wood to act as a fail-safe to keep the blade in the hub if the glue fails. Do you have that arrangement? Just curious. I assume the sandwich block hub is much like GSC’s but again, correct me if needed. I’m not sure if you ground adjust all the blades at the same time (they all move as one unit) or if you adjust each blade spearately. If so, you have to use some sort of angle gauge, no?

Do you happen to have any pics of the prop close up, or the PSRU?

Like any over-zealous homebuilder, I have given thought to making the prop. I cannot believe it’s impossible, even at the higher power levels. That just sort of ups the ante. With cnc machinery, at least the likelihood of getting 4 or 5 blades all the same shape is pretty good.

Thanks again and hop onto your soapbox any time.

Tom.

How many rpms does the prop actually need to turn at? What I mean is – is there a way to do away with the reduction unit?

Spitfire Replica. Any Lower Cost Power Unit Alternatives?

Hello Tom:
A few more words from the replica builder/modifier soap box:

1. Budget at least $100K to get a properly scaled replica Spit flying, regardless of much of it you scratch build/machine. $$$ are directly offset by fabrication time.
2. A LOM will likely set you back @ $30+K, its designed for a 2-bladed prop (ie. only esthetically applicable to very early Mk.1’s), its air cooled and impossible to cowl esthetically accurate in the Spit nose profile (except the PR VIII model)). I would stay with a V8 auto engine as they lend themselves to a more realistic looking/sounding replica and the substantially lower acquisition cost will offset the higher-priced PSRU. Terry Wilshire can give you valuable guidance in this area of engineering.
3. My 70% replica runs a 100% homebuilt prop/PSRU combination, bolted to the back of the 215 Buick V8. It was built at very low cost by the original builder and his machinist partner. This combination runs extremely smooth and does not appear to suffer from destructive harmonics albeit it only has 62 hrs flying time on it. If you plan on using a high power/high rpm LS2, I would strongly recommend spending the bucks on a proven PSRU. This is the most critical lump of metal in the entire airplane.
4. My 3-bladed prop is hand carved 6-ply laminated birch. It is kevlar coated and precisely balanced with epoxied and turned aluminum no-crush bosses that fit into a machined aluminum sandwich-block hub (making it ground-adjustable). I may eventually break down and by an MT for the bird after I get her flying again (upon gathering enough flight performance data to accurately spec a new prop). Terry Wilshire and others have used certified or cut-down (eg. Twin Otter) propellors on their replicas in the 66-80% scale range. You need a bit of luck and a few connections in landing one of these propellor “opportunities”.
5. My PSRU is a cog-belt unit fabricated of welded aluminum plate. It employs both sealed and “interval greasable” bearings (via injection tubes/nipples). I suspect the lead ballast “donut” molded around the PSRU likely has a significant positive damping effect on any vibration that the prop/drive combination may try to generate.

Good luck and keep at it sir,
Mk.1
———–

My own opinion is: build as much of it as you can, and buy as much as you can afford. So yes, you may well end up buying a LOM engine for your replica if you can afford it. It may even work out to be the better option in the end. I know there’s a Jurca MJ.10 being built here in the UK that will use one, and also the Martyn Cole’s “Spitflyer” design will have one, too, I believe.

also my pal built a 2/3 Spit from scratch and used a Buick 6 cyl aluminum block and made his own props, there are lots of options unless you need exact specs, of course took me pal 20 years to build er, but it sure flies well and looks great, cheers Darrell

Ross Ferguson’s MkXIV? A beauty, that one. Would look fantastic in PRU blue, mind! 😉

C-GLVC pics

Hi Bolyman;

Thanks for the reply.

I have heard of the group in Australia, assuming that you mean the MK 26 Spit. I think the kit is enormously expensive, and I think you’d have to buy the PSRU and prop anyway. Again, assuming we’re talking about the same outfit. Is the engine a LOM? And they run a 2 bladed prop?

I ultimately was hoping to fit a 5 blade prop on my “Griffon” powered Spit. This is fantasy thinking, so I realize this may not be practical at all. But dropping down to a 2 blade prop seems, well, not the kind of look I was looking for.

Now I am interested in the idea of building a prop. Obviously this would take research. The approach I would take is find the best wood for the job, design a blade in CAD the best I can, and use some sort of homemade cnc machine or tracing mill to whittle out 5 blades, probably without front wear strips, since I’ve read how improperly bonded wear strips killed lots of people after flying off. Of course, the hub is another concern. I think most hubs are bonked pretty hard with the forge process to get the grain lines correct around the prop blade holes. I always wondered if machined billet of top grade aluminum would be as good.

So, you see it’s pretty easy to wander a bit, but in the end, how much do I make on my own, and how much do I buy? And I’d still need a PSRU with the Chevy V-8. I would be willing to machine out a PSRU casing, add bearings and shafts, and go flying, IF vibration were a concept that I really understood, but I don’t.

In terms of specs, I don’t have to be exactly to scale. As long as it looked good, held together and made thrust, I’m happy. But that is a tall order.

Thanks again, Tom.

Hello Tommy, yes what about the group in Aussie that sell the 3/4 kits, they use that Czech built straight 6 cyl engine with 2 bladed prop, prices are reasonable, also my pal built a 2/3 Spit from scratch and used a Buick 6 cyl aluminum block and made his own props, there are lots of options unless you need exact specs, of course took me pal 20 years to build er, but it sure flies well and looks great, cheers Darrell