New Subie Developments

rv6ejguy · #1 11-24-2008, 02:29 PM

Maxwell Propulsion is now offering their Subaru based FF packages and there is a good writeup in Contact! magazine. It also mentioned that they have started dyno testing a turbocharged version. http://www.maxwellpropulsion.com/

JHines · #2 11-24-2008, 02:55 PM

Ross,

You seem to have one of the most objective viewpoints on auto conversions. Have your formed an opinion about their offerings?

rv6ejguy · #3 11-24-2008, 05:21 PM

I just read the full article and there seems to be a few inconsistencies in the hardware, probably updates or revisions.

There is mention of the MPS designed PSRU but the website specifically mentions the Autoflight PSRU. Not sure which is current info. The Contact article was prepared soon after Osh so that is some time ago.

I like the fact that they are using new STI short blocks and going right through them. I found too that piston clearances in these engines vary widely. They can machine other parts to a .0002 tolerance but can't bore the cylinders even within .0015. MPS is blueprinting and balancing to much finer tolerances.

I hope they decide to use the highly regarded Autoflight PSRUs from NZ. It is far more proven then their own new design. If they plan to use their own, they need to do many hundreds of hours of actual flight testing.

I'm not keen on the returnless fuel system. I really worry about vapor lock problems. I know it solves many tank plumbing issues but it scares me a bit.

Not sure I believe that the engine produces 161 hp at 4800 rpm. I hope they are not using the old NSI dyno which had some accuracy problems in the past. Some people may remember the impossible SFC and torque figures quoted in the past.

The complicated cooling system layout is under review for redesign and that is probably a good thing as there is no way ground cooling would be adequate on hot days and drag would be high with the early layout.

Looks like they have some redundant systems on it which give many some peace of mind and they've addressed electrical warning and control well IMO.

They've ditched the terrible NSI prop design and gone with Whirlwind supplied blades and a new cuff design. Hopefully they flight test this extensively.

They've documented the weights by components and have apparently achieved a lighter package than a Lyco/ Hartzell. This is impressive if true. We'll have to wait for an actual RV to be weighed with one in place.

I'd be a bit concerned about exhaust valve life on the turbo version since they fit atmo SOHC heads. The exhaust valve material is better in the OEM turbo engines and they see hard use in the aviation environment. I also hope they understand turbo matching and how to build a reliable exhaust system. The turbo is a great idea to make good power at lower revs if done right.

Most important of all, they don't wish to repeat the mistakes of the past from NSI. They say they want to do it right, treat the customers honorably and won't be taking massive deposits to fund R&D or production. With that attitude, they should go far.

My advice is to test, test, test.

I wish them well. It looks like they have a good chance of success with the path they are on.

I dealt with some of their engineers a couple years ago and was favorably impressed with the people they had working on the project.

I eagerly await a flight test in an RV at Van's or a side by side with a Lyco powered model.

David-aviator · #4 11-24-2008, 06:59 PM

"Do the Comparisons" on the Maxwell site doesn't really do it.

They are comparing a 200HP Lycoming with their 165HP engine. A more telling comparison would be with an 0320 and a fixed pitch prop.

To each his own, I won't knock anyone for leaping into the auto engine conversion world but you better have deep pockets, an infinite amount of patience and like to fly test flights.