Any thoughts on the Yamaha Apex conversion? Verner Radial?

[libertyman777]

I'm asking some open ended questions that may only produce more questions, but I really don't know.

For the Yamaha, it seems like the installed weight is 180 pounds, as best I can tell, with 150 horse power. This is a popular choice in some other STOL designs including the Highlander and the Zenith planes. Steve Henry has a nice firewall forward package including the wiring harness and prop for $23,000.

Another, more radical choice is the Verner Radial. Weight is around 200 lbs wet IIRC. Max power is 124 hp at 2300 rpm, 103 hp continuous at 2000 rpm and 287 ft lb or tongue at 2200 rpm. I"m sure the radial will hurt cruise but what do you think about take off and landing performance? http://scalebirds.com/scarlett-7-series

I'm looking to get a LSA in the air as light as possible with a minimum of instruments for STOL flying. I would also like to get the most bang for my buck in the engine area.

I'm having a hard time getting good numbers on other conversions and rebuilds. If I could do something else for say half the money of the options above, I'd be willing to trade some performance for cost.

How much does it cost to rebuild a suitable Corvair? I understand that some of these engines can make 130 hp, correct?

How about rebuilding an O-200 or the C-85 like Mr. Barrows did on his LSA?

Sorry for the rambling and thanks for the help.

Paul

[JimParker256]

There are a couple of fairly extensive discussion about "conversion engines" already in existence elsewhere in the forum, if you just do a search you should find them easily. So I'll leave all the "pros and cons" of using "auto conversion" engines to remain in that discussion...

But the idea of being able to purchase Steve Henry's "firewall forward" Apex package for $23,000? Um, color me skeptical, at best. I doubt he's ever even seen a Bearhawk LSA, much less invested the time and effort to develop a firewall forward package for the airplane. If you're thinking you could take the SuperStol package and use it on the LSA (even with "slight modifications"), I think that is overly optimistic. Most people who use "non-supported" engines encounter plenty of challenges adapting them to a new airframe. You may have the requisite engineering and design skills, but I sure don't...

The Verner radial seems like a cool idea, but it doesn't really help your "low cost" objective: $23,800 base price - at the port of entry... Again, the entire "firewall forward" design process would be involved, and I think it would wind up costing a LOT of money to solve all the issues that would arise. (But if you decide to go this route, post LOTS of pictures along the way! We'd all love to follow along!)

There's at least one forum member here building an LSA that will have Corvair power. He's got a lot of experience with the engine, and is quite enthusiastic about it. I think that a slower-turning engine with a longer prop would be more the ticket for true STOL flying, but then the Corvair might just make up for that by producing more power. Once he's flying, we'll know a lot more.

But it seems to me, that if you're really looking to get an LSA in the air as light as possible with a minimum of instruments for STOL flying, AND want the best bang for your buck, look to Bob's personal LSA for the "how to" guide. To my knowledge, no one has built one any lighter that Bob's, and I doubt you can purchase any newly overhauled engine for less than Bob will charge you for one of his "special" C-85s that crank out about 100 HP. Go back and read Wayne Massey's LSA flight test report where he flew Mark G's LSA, and recorded the rate of climb starting at sea level and going way up to 14,000 ft... I was amazed by how well the "stock" LSA performed. Wayne also placed in the top-3 at one of the Texas STOL events in the LSA category, competing against some pretty tough competition, and without a whole lot of time in the airplane to practice ahead of time. (He's a heck of a pilot!)

Finally, I vaguely recall reading that Bob was at some stage of looking into a Rotax 912 ULS mount for the LSA. If Bob has actually developed a mount (with attendant CG considerations from the lighter engine) for the Rotax, that is the engine I would seriously consider using in the LSA. The combination of light weight, low fuel consumption, and well-proven reliability record of the Rotax makes it a viable candidate to me. A brand-new Rotax 912 ULS is a bit spendy (close to $19K – and up to $23K for the fuel-injected 912iS), but they are now reasonably available in the used market. Today, Barnstormers has at least 3 listed. One that is "runout" for about $5K, another that is 3/4 TBO for around $8K), and an almost-new one (<200 hrs) for $12K. A "Rotax-approved" maintenance shop overhaul runs about $4-7K. So your total engine investment would be considerably less than a new one, even if you "splurged" for Hal Stockman's "Big Bore" kit that increases HP (up to 115) by way of higher compression pistons Edge also makes a nice "Big Bore" kit that is similarly priced. Both big bore kits would require either Premium Mogas or 100LL because of the higher compression ratios.

Last point I'll make today: Building the most capable STOL airplane in the world is pointless unless you have the flying skills to make use of it, and unless you're willing to sacrifice everything else for the sake of STOL. Steve Henry's plane cruises at about 75-85 mph, and can carry Steve's tiny little body and maybe a toothbrush on a cross-country flight. The "bone stock" LSA is easily 30+ mph faster in cruise, far more comfortable over even short distances, and can get into 90% of the places Steve's can go. (And at the upper difficulty range of the places he could go that the LSA might be able to handle, I personally would be crazy to attempt them...)

As always, you're the builder, and you get to make your own choices (and live with the result). Good luck!

[whee]

I think Jim covered things very well. One minor thing he missed is Hal does offer a low compression zipper kit so you can run low grade mogas.

If I were building an LSA I’d build a stroker C85 (c85 case and O200 crank) with forged pistons and ran at O200 rpms. You’d be in the 115-120hp neighborhood. It would be cheap, fairly light and as reliable as an engine gets.

[libertyman777]

There are a couple of fairly extensive discussion about "conversion engines" already in existence elsewhere in the forum, if you just do a search you should find them easily. So I'll leave all the "pros and cons" of using "auto conversion" engines to remain in that discussion...

But the idea of being able to purchase Steve Henry's "firewall forward" Apex package for $23,000? Um, color me skeptical, at best. I doubt he's ever even seen a Bearhawk LSA, much less invested the time and effort to develop a firewall forward package for the airplane. If you're thinking you could take the SuperStol package and use it on the LSA (even with "slight modifications"), I think that is overly optimistic. Most people who use "non-supported" engines encounter plenty of challenges adapting them to a new airframe. You may have the requisite engineering and design skills, but I sure don't...

The Verner radial seems like a cool idea, but it doesn't really help your "low cost" objective: $23,800 base price - at the port of entry... Again, the entire "firewall forward" design process would be involved, and I think it would wind up costing a LOT of money to solve all the issues that would arise. (But if you decide to go this route, post LOTS of pictures along the way! We'd all love to follow along!)

There's at least one forum member here building an LSA that will have Corvair power. He's got a lot of experience with the engine, and is quite enthusiastic about it. I think that a slower-turning engine with a longer prop would be more the ticket for true STOL flying, but then the Corvair might just make up for that by producing more power. Once he's flying, we'll know a lot more.

But it seems to me, that if you're really looking to get an LSA in the air as light as possible with a minimum of instruments for STOL flying, AND want the best bang for your buck, look to Bob's personal LSA for the "how to" guide. To my knowledge, no one has built one any lighter that Bob's, and I doubt you can purchase any newly overhauled engine for less than Bob will charge you for one of his "special" C-85s that crank out about 100 HP. Go back and read Wayne Massey's LSA flight test report where he flew Mark G's LSA, and recorded the rate of climb starting at sea level and going way up to 14,000 ft... I was amazed by how well the "stock" LSA performed. Wayne also placed in the top-3 at one of the Texas STOL events in the LSA category, competing against some pretty tough competition, and without a whole lot of time in the airplane to practice ahead of time. (He's a heck of a pilot!)

Finally, I vaguely recall reading that Bob was at some stage of looking into a Rotax 912 ULS mount for the LSA. If Bob has actually developed a mount (with attendant CG considerations from the lighter engine) for the Rotax, that is the engine I would seriously consider using in the LSA. The combination of light weight, low fuel consumption, and well-proven reliability record of the Rotax makes it a viable candidate to me. A brand-new Rotax 912 ULS is a bit spendy (close to $19K – and up to $23K for the fuel-injected 912iS), but they are now reasonably available in the used market. Today, Barnstormers has at least 3 listed. One that is "runout" for about $5K, another that is 3/4 TBO for around $8K), and an almost-new one (<200 hrs) for $12K. A "Rotax-approved" maintenance shop overhaul runs about $4-7K. So your total engine investment would be considerably less than a new one, even if you "splurged" for Hal Stockman's "Big Bore" kit that increases HP (up to 115) by way of higher compression pistons Edge also makes a nice "Big Bore" kit that is similarly priced. Both big bore kits would require either Premium Mogas or 100LL because of the higher compression ratios.

Last point I'll make today: Building the most capable STOL airplane in the world is pointless unless you have the flying skills to make use of it, and unless you're willing to sacrifice everything else for the sake of STOL. Steve Henry's plane cruises at about 75-85 mph, and can carry Steve's tiny little body and maybe a toothbrush on a cross-country flight. The "bone stock" LSA is easily 30+ mph faster in cruise, far more comfortable over even short distances, and can get into 90% of the places Steve's can go. (And at the upper difficulty range of the places he could go that the LSA might be able to handle, I personally would be crazy to attempt them...)

As always, you're the builder, and you get to make your own choices (and live with the result). Good luck!

I think Jim covered things very well. One minor thing he missed is Hal does offer a low compression zipper kit so you can run low grade mogas.

If I were building an LSA I’d build a stroker C85 (c85 case and O200 crank) with forged pistons and ran at O200 rpms. You’d be in the 115-120hp neighborhood. It would be cheap, fairly light and as reliable as an engine gets.

Thanks so much for the input. I did look for a thread but only found the discussion on the Corvair conversion. I will search "engine conversions".

I really didn't consider many of the things you spoke of and of course I have no idea how well the LSA actually flies. I guess that tried, true and proven should not be overlooked for sure.

JimParker256

whee

When I watched Mr. Barrow's video on the LSA page, he spoke of the plane being capable of 1500 lbs gross so that it would be experimental. On the other end of the envelope, what do you think that the tricked out C85 would offer in cruise? Would a ground adjustable prop be in order?

I realize that I'm contradicting myself but your advice rang true about Steve Harvey's plane and looking at this project practically from all sides. Even if I could get into only 75% of the places that Mr. Harvey can, I would be pleased. As you said, it's as much about flying as it is about the plane. So what do you think the cruise numbers would be with a 115-120 hp C85 would look like? Could a larger engine be fitted if not building LSA? Or would most of this extra power better translate into climb? (I apologize for all the boot questions and I appreciate everyone's patience).

[JimParker256]

Airspeed increases with the square root of power increase. Going from an O-200 (100 HP) to "some theoretical" 120 HP engine would yield a 20% increase in power. That would (in theory) give you a 10% increase in airspeed (1.1 being the approximate square root of 1.2). So if you can cruise at 120 mph with the O-200, you MIGHT be able to cruise at 131 mph with the theoretical 120 HP engine.

But (using Wayne's test flight data, which was done with a "Bob-massaged O-200" that makes roughly 105 HP) the extra 15 HP from the "theoretical 120 HP engine" would add somewhere between 150-250 fpm to the climb performance in that table, assuming the prop can absorb and apply that power properly. So, if you apply some "smoothing" to the data to eliminate some obvious atmospheric fluctuations in the table data), you'd probably see approximately 1400 fpm near sea level, dropping to around 1000 fpm at 7500 ft, and to about 650 fpm at 14000 ft.

The math behind all this is fairly simple, but not particularly interesting to most folks... PM me if you want the details.

[rodsmith]

I've put a lot of thought into how I would build an LSA, even though I have a lot of obstacles in doing that, like completing my 4-place. I would build it as light and simple as possible, no starter, or alternator, but maybe a ground rechargable lithium battery to power a few electric instruments. While there are lots of tempting alternative engines, I think the above advise about having Bob build you a C85 stroker or O-200 is hard to beat. The ULPower engines look good and Larry Silverone is making a FWF package for them. Downside is they make their power at 3300 rpm, and are totally electrically dependent.

[svyolo]

I had a new Jetski I used for offshore fishing in Guam about 5 years ago. I looked at the motor in that thing and thought it would make a great aircraft engine. I don't know about an Apex in a LSA, but I think if Jim Bede was alive he would have finally found his perfect BD-5 engine, 45 years too late.

[zkelley2]

If you're looking at the rotax and live in the west, the 914 makes more power than a o320 due to altitude. If I were building an lsa in the west it would be turbod. It makes more power than the apex naturally aspirated to.

The modern rotax engines make turbos a non issue. Slightly more expensive at purchase but no more expensive to run. Plus 50+% more power than a NA engine anywhere west of Denver.

The difference in takeoff performance is stark. A TIO360 makes more power than an IO720 in Denver in the summer.

[libertyman777]

I've put a lot of thought into how I would build an LSA, even though I have a lot of obstacles in doing that, like completing my 4-place. I would build it as light and simple as possible, no starter, or alternator, but maybe a ground rechargable lithium battery to power a few electric instruments. While there are lots of tempting alternative engines, I think the above advise about having Bob build you a C85 stroker or O-200 is hard to beat. The ULPower engines look good and Larry Silverone is making a FWF package for them. Downside is they make their power at 3300 rpm, and are totally electrically dependent.

rodsmith
I wonder how efficient and light weight a small solar panel array would be to keep something like what you're talking about charged up and ready to go. Maybe a fixture to hold a panel or two up in on the dashboard in front of the pilot. Seems like it would be very easy to do and just keep a couple of small battery packs charged.

[Clint B]

A few years back Hal Stockman flew into my place for a custom exhaust for his S7 with his big bore. at the time, I had an experimental cub with a C90 and c-85 pistons+ Catto 76-38. This cub weighted about 750 empty.
Of course we had to have a fly off to strut our stuff. The c-90 easily out accelerated and outclimbed his big bore rotax, but he cruised faster.
ymmv, Hal’s big bores are the real deal, and I’m certainly not knocking them, but a mildly hot rodded continental will make more power than a rotax.

[rodsmith]

If you're looking at the rotax and live in the west, the 914 makes more power than a o320 due to altitude. If I were building an lsa in the west it would be turbod. It makes more power than the apex naturally aspirated to.

The modern rotax engines make turbos a non issue. Slightly more expensive at purchase but no more expensive to run. Plus 50+% more power than a NA engine anywhere west of Denver.

The difference in takeoff performance is stark. A TIO360 makes more power than an IO720 in Denver in the summer.

A pilot in our airpark has a 914 in the kitfox he built. It is the quietest plane here. Very nice engine, too bad they are so expensive. I saw a Rans S-7 that had a turbo converted 912. The owner got the converted engine government surplus off a drone and was very happy with it. Said the supply had dried up.

[Cguy]

I think Jim covered things very well. One minor thing he missed is Hal does offer a low compression zipper kit so you can run low grade mogas.

If I were building an LSA I’d build a stroker C85 (c85 case and O200 crank) with forged pistons and ran at O200 rpms. You’d be in the 115-120hp neighborhood. It would be cheap, fairly light and as reliable as an engine gets.

Thanks, Whee for bringing that up. My low comp Hal Stockman Big Bore runs exclusively on low octane/regular, even E10 regular, just fine at our field elevations, (4500'+) and down to 2500' where I rarely get. The best bang for the buck engine and Rotax wise, is to call Hal, and "get a deal".

After reaching the 2000 hour TBO and then some on my first 912S, (totally trouble free) I made a deal with Hal.....and bought a brand new 80 hp Rotax direct from the North American distributor. After a days rest back home, I loaded my old engine plus the new into my Prius and drove to Elko, dropped them off and headed home. 2 days later I repeated the trip and picked up my new engine with the basic goodies from the old one on it, zero timed in effect. I'm now 450 hours into that engine and all is good!

One thing that concerns me in putting the 912S into the LSA, is over the nose viz. An even longer cowl to make things balance out would be required, well and good, but the viz on short final suffers. It all depends on the type of flying you do, off airport good viz is of paramount importance. No question the LSA would be a real performer with my current power plant in it, but man that nose would be long!

[Cguy]

If you're looking at the rotax and live in the west, the 914 makes more power than a o320 due to altitude. If I were building an lsa in the west it would be turbod. It makes more power than the apex naturally aspirated to.

The modern rotax engines make turbos a non issue. Slightly more expensive at purchase but no more expensive to run. Plus 50+% more power than a NA engine anywhere west of Denver.

The difference in takeoff performance is stark. A TIO360 makes more power than an IO720 in Denver in the summer.

My 400' strip hillside strip is at 5640', with 8 and 9K ridges all around, and I don't have a 914. They weigh more, have more heat to get rid of, and just have more "stuff" to go wrong. They also burn a bit more fuel in cruise. I know several 912S pilots that also fly my area, with no turbo's, quit handily. When I've flown with turboed 912's, they didn't beat me off the ground, and the climb difference was minor, the only difference being they could maintain that climb up into the teen's! Mine drops off to only 300' FPM at 13,500' last time I checked, good enough for me.

[zkelley2]

A big part of that with the rotax is probably that nearly everyone is running fixed pitch props. Another significant handicap. But a 914UL vs a 912USL at 5640DA is 115HP vs 80HP, roughly 30% more power out of the 914 than that standard 15% at SL. The only way the 914 would not handily outperform a 912 at altitude is if the other airplane had enough extra weight in it to make up for the 35 extra horsepower. Which is possible.

I'm not saying you need a turbo, it's just that turbocharged airplanes have wildly better performance at altitude, and as you go up it gets a lot different. You can see this in any turbo charged certified airplane's takeoff numbers vs the NA version. For example with a Field elevation of 8k, 20C and gross weight, a 206 needs 2000ft for the takeoff roll. A T206 needs 1625. The 206 will have a max performance climb rate of 390fpm while the T206 has 745.

[Cguy]

A stock 912S Rotax is supposedly 100 horsepower. And the planes I've seen with a turbo are the type that want and have every bell and whistle they can get, so for sure almost all are heavier overall in addition to the turbo install weight. In other words, the pilots who aspire to keeping things light as possible usually don't go 914. Most 914 installs have a bigger radiator, some have two oil coolers, etc., the extra weight adds up. Watch Trent Palmer's takeoffs with his 915 powered Kitfox, (probably the world's heaviest Kitfox....) with a controllable pitch prop (NOT an LSA with that FWIW), as compared to Hal Stockman's light S-7S, and his landings, though for sure Trent's will climb a bit better at high altitude and cruise faster, it for sure does not make for better STOL ops. Where the 914 makes sense to me would be a fast cruiser type plane, at altitude, getting there and staying there. For knocking around grass strips and off airport, keeping things lights works fine for, even at my field elevations.

Mark Pringle, a fellow Rans guy, is into the 914's, and he talks about cruising at 17K with fantastic true airspeeds! Of course he has an oxygen system, as he flies long trips up high often. His plane probably weighs 100 pounds more then mine, but it really performs up high.

[zkelley2]

I`m the reason that Homebuiltairplanes.com has a Yamaha section...I`m very hot on this engine.,..



The Yamaha engine is rock solid....my issue is not with the engine...its with the PSRU(gear box/after market part added to the Yamaha engine)

like what happens if your engine quits....or you put your engine to idle

guess what.... your prop will windmill....the prop and engine are NOT CONNECTED....just like a PT6 turbine...the prop spins freely but.... you cant feather or stop the prop on the yamaha.....

because this conversion uses a sprag clutch in the PSRU....this means that your propeller will windmill if you go to idle or engine quits... ...most pilots dont even know why a windmilling prop is bad....,...unless you fly twins or turbines...you probably dont know why I have my panties in a bunch.

I wrote to Viking Engines to see if they would modify one of thier gearboxes(engine stops.... prop stops) to fit the Yamaha...they are too busy and have their hands full to take on another project, they are also not big fans of the very high RPMs the yamaha runs at to achieve its HP rating...

they are going into unknown territory here by putting this gearbox on faster planes.....for trikes, gyro and stol planes that have slow best glides ...maybe you can live with a windmilling prop...but if your best glide is 70-80 mph or more....if your engine dies...you might have a big solid disk on your nose...giving the same drag as a parachute...

nobody there has done side by side testing to see whats going on with this(and the only way to test this is 2 planes side by side of similar type one with windmilling prop...one with stopped prop)....maybe its 15% reduction.,..maybe 5%....maybe its more maybe less...maybe depends on plane and speed.....they dont know...and they are mad at me for asking or talking about it....

on the Yamaha Facebook group there is a sonerai(fast acrobatic plane) close to doing a maiden flight....nobody has tried to give this guy a heads up...that you might want to know if you go to idle or is the engine dies...your prop might slow you down.......

they all tell me to shut up and I don't know what I`m talking about....maybe they are right and a windmilling prop is Gods gift to aviation.,...


so go ahead and put a windmilling prop on your plane....and dont listen to nay sayers like me...

All you can do is advise and if people want to kill themselves it's really hard to stop them. The could put a feathering prop on it and take care of the windmilling issue just like on a turboprop.

I'm not very sold on the engine yet, but a LOT more so that the PSRU and prop on them. They're not doing any harmonic testing at all. And then they say they have lots of hours on them. No. Lots of hours is millions and they should expect a bunch of failures in that time. Every engine manufacturer has had those failures while doing the testing, so I'm not sure why they think they can slap something together with no testing and only paper engineering and say it'll be good. That's almost never happened in real life. Rotax had issues they fixed. Lycoming and Continental have harmonic issues with different props and they don't have a gearbox.

A guy in his garage is not doing better QC or testing than the multi million dollar testing budgets of the commercial manufacturers who all find problems.

Other people also have more risk tolerance than me. I get slightly uncomfortable flying over the land I fly over with only one 540. Places I were yesterday had absolutely no possible way to put an airplane down. Probably could have had a better outcome over the middle of the pacific.
In the land of an airport ever 10 miles and 1 mile by 1 mile road grids, sure. But when your life very truly depends on the engine continuing to run and then you actually put yourself in the air there, there's not a single warm and fuzzy when you get into that experimental of an engine.

[way_up_north]

All you can do is advise and if people want to kill themselves it's really hard to stop them. The could put a feathering prop on it and take care of the windmilling issue just like on a turboprop.

I'm not very sold on the engine yet, but a LOT more so that the PSRU and prop on them. They're not doing any harmonic testing at all. And then they say they have lots of hours on them. No. Lots of hours is millions and they should expect a bunch of failures in that time. Every engine manufacturer has had those failures while doing the testing, so I'm not sure why they think they can slap something together with no testing and only paper engineering and say it'll be good. That's almost never happened in real life. Rotax had issues they fixed. Lycoming and Continental have harmonic issues with different props and they don't have a gearbox.

A guy in his garage is not doing better QC or testing than the multi million dollar testing budgets of the commercial manufacturers who all find problems.

The sprag clutch is the secret sauce in all this...there is no harmonics....no torsional vibrations....the power pulses can only go one way...are not bounced to the prop and back.....but with this cure...comes the windmilling prop issue

[zkelley2]

Well then put a feathering prop on it. Solved.