Hirth 2702

[ironnerd]

I bought a CGS Hawk a while back. It was a darn good deal, but upon inspection, I realized it could not be completed or flown. I kept hearing a song from that Disney movie... "Do ya wanna drill a snowman?"

Anyway, it came with instruments and a freshly overhauled and pickled Hirth 2702. I would classify this as a "nice" engine, and I plan to use it as "Engine Zero" on my LEU.

Hirth claims 40 hp @ 5,500 rpm, and a 1,000 tbo if run at (or below) 75% power (30 hp @ 4,000 rpm - 2.3 gph claimed). As with all engine performance claims I am somewhat skeptical.

I put it on a shipping scale, and got a weight of 103.5# with
> Carb and air filter
> Dual ignition system
> Pull Start
> Muffler (10#)
> G-50 Gearbox (19#)
> Electric starter (4.5#)

I'll drop the Electric Start (down to 98.5#), and the G-50 gearbox (down to 79.5#), and use the 5# Hirth Belt reduction drive (back up to 84.5#). Round that to 85# and that is on par with a 1/3 VW, 1/3 Corvair, Industrial V-twin(?) once things like oil and oil coolers are taken into account.

So I am thinking that the Hirth 2702 could make an acceptable Engine Zero to get the LEU flying while I tinker with a nice Industrial V-twin.

[Chuck in Indiana]

I'm a believer in "run what you brung" and you have it. Of course, it will be a little heavy..but doable I think.

[ironnerd]

I received the following information from RecPower.com:

Even though the 2702 was discontinued it is still fully supported. The F-23 engine uses the same pistons, cylinders, heads, and crank parts so all those are still in production. They also use the same belt drive and ignition system. So as long as they keep making the F-23 there will always be parts for the 2702.

[ironnerd]

I'm a believer in "run what you brung" and you have it. Of course, it will be a little heavy..but doable I think.

Do you happen to know the weight of an installed of a 1/2 VW or the 23hp BS? I have asked around on other forums, but it seems like a state secret.

[IflyHG]

If you think you might use the BS23V engine then it is worth buying the plans from Leonard's website, there is a lot of good information in them.  According to the plans it comes in at 81#, inclusive of the re-drive, warp drive carbon fiber prop, exhaust pipes (but not muffler(s)), if you substitute the ARC aluminum flywheel for the stock cast iron one (and you lose charging as a result).  Check the math on the plans, I think there is some oz to lbs conversion issues.  In any case, if you work at it you can get down to BetterHalfVW weights and that includes the weight of the prop.  If you went with a wood prop it could be lighter.  When the BS23V was my plan of record I was planning on contacting ARC to ask if they could make a version of their flywheel without the cooling fins (they rob power that could go to the prop) but with the charging magnets back in.  I was also investigating an EFI conversion but all of the aftermarket solutions require lots of development still.

I have since changed my plan of record to the Aero1000.  They claim 83# for the complete FWF package sans prop.  There are 2 versions, a 250cc 35HP unit (red head) and a 275cc 39.4HP unit (blue head), the only difference being the bigger one is bored and stroked, all else is the same.  For your money you get a really complete unit with, the re-drive, EFI (with altitude compensation), electronic ignition, a charging system, electric start, the exhaust system with a real muffler, full pressure lubrication, and water cooling.  My plan is to design station 1 so that the Aero1000 isolators bolt directly to station 1 just like the 1/2VW.  In my opinion, this approach requires the least amount of additional fabrication as compared to 1/2VW, Verner, and BS23V, and the only solution that comes with EFI out of the box.  I still have many questions to ask BlackHawkUSA (the US distributor) but assuming there are no show stoppers this is the path I'm taking.

[ironnerd]

So the BSV23 is 81# +oil (about 3#) and mufflers, if I don't need a charging system, and less 8# for the prop. So figure a wet engine weight of 76# w/out mufflers or alternator. That's actually not bad. (BTW, I weighed a 68", 2-blade IVO-prop and it came out to 4# - much lighter than the Warp Drive Mr. Miholland used in his video).

The Aero1000 interesting an engine, but web site states an ENGINE ONLY DRY weight of 83#. They are not including the PSRU (probably 5ish lbs) in that, and an 83# DRY ain't 83# FWF. You still have to take into account coolant and oil at least. They may not even include the radiator, coolant lines, or oil cooler and plumbing in that dry weight either - engine manufacturers are a sneaky bunch when it comes to engine weight and output. And, I think the $18k to $21k price tag puts it out of my reach.

On the other hand (and moving back towards the thread topic) my 2702 is free, and looks like it'll weigh 85# (plus prop) ready to fly (muffler, redrive, ignition, and intake).

[IflyHG]

The pricing you saw was for a full paramotor package, the price for the 35hp engine is $7800, more in line with the Verner.  If you go to the Helvenco site they advertise the weight as 80.25lbs for the complete kit inclusive of oil and water.  They specifically say so.  I agree, historically engine manufacturers have advertised weights for just the bare motor dry with no "accessories" (carbs, exhaust, starter, alternator/magneto, battery, cooling system, re-drive etc. I have also seen video showing a fully assembled engine on a scale coming in at just over 80lbs so I think this is a real weight.

As you say, you already have the Hirth so might as well use it, at least to start.  You mentioned investigating other options so I mentioned the Aero1000.

What I like about it over any of the other options is for your money you get the most complete package with the least amount of fabrication and, no other solution comes with EFI from the factory (the BS23V EFI doesn't count because it electronically limits RPM to 3600 so you can't make enough power).  If you want to tinker with your power plant this is not the solution for you.

[ironnerd]

There are a couple of photos in the gallery of a two-cycle installation. It looks similar to what I have in mind. I planned on an inverted installation, but I'm not going with a multi-belt PSRU. I'll go with a Hirth Cog-belt unit.
I do like that his throttle cable does not require a hole in the firewall.