Originally Posted by Lithosis
The horsepower is rated differently on the turbo “220 hp @ 2700 rpm up to 15000 ft“ from their website. The 390 thunderbolt is over $60k today, while the 520T is still in the 48k range. I forget my source but fuel burn should be very comparable to 390. Don’t remember if that was a testimonial or using their numbers. What’s a constant speed prop cost? I thought they were in the 12k+ range anyway. It will be a more difficult install, unless it’s supported by vans which is certainly my hope. The added weight of the turbo really helps bring in the CG. I think most of the points you make are just a little dated and you don’t give it any credit for the improved performance up high. These are the opinions I want to hear though so thank you. Another big piece of info we’re missing is what the Vne will be on this airframe. Then we’ll know if we can take advantage of that turbo up high to help a slower plane kill it cross country. There’s certainly a lot to consider.
That is good to know. I would reserve judgement on any engine until it has flow for 100's of hours or better 1000's of hours. I also would not buy an engine until I talked to person that flies it with real flight test data collected. Better still fly the plane with that engine. I don't mean someone who bought it and has it in a crate on their hanger floor or hanging on their project yet to fly.
You are right the Vne might be an issue, but in a utilitarian plane like the RV15 the turbo would be for high hot altitude operations in mountain airstrips. Most turbos on small piston aircraft have typically been for normalizing, to maintain SL power to higher altitudes, as well as pressurize the cabin. In the case of the UL520T they must have the boost turned up as it is only 320 cu-in. and advertised as you say 220HP at 2700 RPM. The little engines like Rotax get power by running at 5500 RPM and using PSRU. So we shall see. I know there are some flying I think but don't hear much?
As far as prices you I heard $12,000 a while back so I said $15,000 to account for inflation and shipping. If the prop is $12,000 great. Exotic composite props, electrical I am sure are expensive. MT props are even more. However when they don't widely publish prices you have to guess. You have to factor in shipping and handling from Australia.
I totally appreciate flying with Turbos high up. Flew a Ted Smith Aerostar later became Piper Aerostar twin with turbocharged Lyc 540's. It was certified to FL250. Yes it is great to fly high, sucking O2 all day not so much. RV15 or any plane that operates in and out of high altitude mountain strips at max weight would benefit from Turbo. However you can put a Turbo on Lycoming's or Continental's and they did on certified planes. Ray Jay use to sell kits to add them to Certified planes. I flew turbo charged planes but never owned one nor would I ever. Besides the Aerostar I flew for a Company, the flight school I taught at had a few Turbo planes, one being a Cessna P210... The plane was in the shop every 50 hours, intercoolers, turbo it was complicated. Love the performance but would hate to pay for the maintenance.
UL520T is about 320 cubic inches. I assume it is not aerobatic and there is still no hydraulic prop control. If they can squeeze 220HP out of 320 at 2700, that would be great if reliable, light and not too much money. However watching the latest greatest THING in EAA world my advice is wait until you see them fly, they have 100's if not 1000's of hours with proven real world performance. Ideally the plane you are building is made for the engine so you don't have to invent the installation. At this time we don't have that. In 10 years who knows if they will be in business or dominating the market. The later I personally doubt.
I know of one RV with UL520 and it cruises slower and has similar fuel burn as a Lycoming powered RV. I don't have detailed info. There is no free lunch. People equate Lyc with not modern, but they are powerful for weight. Yes there are lighter engines but the Lyc is built stout. Lyc can achieve very high fuel efficiency in cruise properly leaned. Before 2020 they were a bargain. I still think today even though the prices are shocking they are a good value. We had it really good when you could buy a new O360 for $19,000, then it was $25,000. Now they are $39,000 or more. However that is cheaper than a UL520T I believe. Again prices are not widely advertised.
Van's recommendation is Lycoming. The design, the testing, and kit will be tailored to the Lycoming. I am 100% opinionated, stick to the plans. That is not to say people have not tried alternative engines before and will keep on trying them in the future. Go do it. Let us know how it went. My opinion is alternative engines can be OK, but never better and more often not so great. Alternatives always take more time and fiddling to get built and flying.
The failures I mentioned are dated but not that long ago. As I said they improved the design. Many boutique engine companies like Jabiru are on Gen4. I understand Gen4 is pretty good. It is one of only 3 engines approved for S-LSA's along with Rotax and Continental O-200. The UL is not listed as an approved S-LSA engine at this time. Not S-LSA's are not type cert by FAA. The oversight is by an industry standard and groups like ASTM International, and others.
Lycoming is known, has service and parts widely in USA and world wide. As far as wiz bang "Modern" EFI and EI, you can have that with a Lyc. or go with a Carb or Mechanical FI and Mags for 100% electrical independence. The value of the Lycoming was clear until inflation. However the Lycoming I think is still a better value and way less risk.
A Lyc powered RV will have higher resale than a UL powered one. By the time you buy, ship the UL, make all the custom changes and engine mount to fit it to your RV, the price is likely the same or more, especially in build time and working out kinks. Put a Lyc in go fly.
Red Bull Air race, Reno Sport Class, every plane has Lycoming or Continental (except the Thunder Mustang with Falcon V12). If you want to ring out a Continental or Lycoming with Turbos or HC pistons or NOX for racing that can be done. I just don't see an advantage of going UL. the Lyc 320-340-360-370-390 are hard to beat. I like the lower compression 8.5:1 or less Lycs. I don't need the extra HP. I would rather have fuel flexibility.