What Should I Build?

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cluttonfred

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I am going to go out on a limb and suggest a plane that meets your criteria including mild aerobatic capability except only the wings are all aluminum, the fuselage and tail are fabric-covered 4130 tubing: John Monnett's Sonerai II in the low-wing, stretch model with your choice of conventional or tricycle gear. It's still a great design in terms of bang for the buck, still supported by Steve Bennet at Great Plains and you could probably even contact Monnett himself if you had a question. And you could meet your performance goals with an economical 2180cc VW engine from Great Plains or AeroVee.

19-5409_Monnett_Sonerai_IILS_(8543451673).jpg 8241621171_e6d409e2b6_z.jpg

S P E C I F I C A T I O N S

SPAN 18' 8"
LENGTH 20' 4"
HEIGHT 5' 5"
ENGINE 2180CC ONLY
FUEL CAPACITY - STD. 10 GALLONS
FUEL CAPACITY - OPT. 6 GALLONS
EMPTY WEIGHT (No Starter) 540 LBS.
USEFUL LOAD 610 LBS.
GROSS WEIGHT 1150 LBS.
WING AREA 84 SQ. FT.
WING LOADING AT GROSS 13.6 LB SQ FT
SEATS 2 TANDEM

P E R F O R M A N C E

DESIGN LIMIT AT FULL GROSS +/- 4 G's
AEROBATIC LIMIT SOLO W/755 LBS. +/- 6 G's
TAKE OFF DISTANCE 900 FT.
STALL SPEED 50 MPH
LANDING SPEED 60 MPH
MANEUVERING SPEED 115 MPH
CRUISING SPEED AT 75% 140 MPH
VNE 200 MPH
RANGE W/45 MINUTE RESERVE 245 SM
RATE OF CLIMB AT GROSS 700 FPM
 

Direct C51

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Do you think the Sonex is fast enough for your liking? They seem slow to me.

There are some pretty draggy designs which are faster, just by using a larger hp engine (without getting into engine choice). If you are going with a conversion, can you not bump up the power slightly without adding too much extra cost?

Similarly, composite materials, even fibreglass, are much more streamlined and faster as a result. Do you just love working with metal, or are you just a little cost-constrained?
The Sonex with 120HP cruises about 170KTAS at 75%, 150KTAS if you run 60% or so. That is the fastest all aluminum 2 seater on 120HP that I know of. Getting more power out of a conversion is not easy, cheap, or good for the engine. Aluminum and rivets fit my skills a lot better than composites. I also do not have a climate controlled workspace.

I have somewhat similar requirments as you and am leaning towards an rv-7. The sonex seemed appealing at first but it's just too small. I figure with a basic panel and interior, used engine, and fixed pitch prop the cost difference between the two isn't huge. My fear with the sonex was growing out of it, possibly before even finishing it. The rv offers a lot more capability and room to upgrade as needs might change or the bank account starts getting too full.
Every way I build an RV-7 on paper ends up costing about double, burns nearly double the gas, and overhauls are 5x more expensive. My intentions are not to build an airplane that uses a certified airplane engine. In my opinion and for my situation, they just cost too much. Sure you can buy a mid time engine for $15k, but your engine reserve is going to be $20 an hour. Compare this to maybe $3 an hour for a conversion. The spirit of experimental aviation is having each amateur homebuilder fly what they feel suits their needs. Frankly I am concerned that so many people on a homeuilt forum would try so hard to talk an experimental aircraft builder out of using an experimental conversion, and suggest certified engines.

The Sonerai is an airplane I have certainly considered. I am not opposed to tandem seating, but my wife might think differently. The major problem with it however, is that it is designed for a small engine. 65 to 80HP. a 120HP engine is a little big, and heavy. There isn't much room to get it close enough to the firewall. I only know of 1 or 2 Sonerais that have used Corvair engines. It's more than just a new motor mount and cowl. I bet they cruise pretty fast though. Maybe if I can find a deal on a kit I might look in to this further.
 

Aesquire

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Frankly I am concerned that so many people on a homeuilt forum would try so hard to talk an experimental aircraft builder out of using an experimental conversion, and suggest certified engines.
I'm new here and certainly don't speak for anyone else, while lurking I observed that car conversions are not mocked

Also, while some pretty wild fantasy planes have been discussed, real world realities are usually pointed out.

My personal observation from messing round with go-cart engines back when the Earth was still cooling, NO experience with auto engine conversions ( but I've had a Corvair ! ) and just recently rereading Kitplanes mags going back to when they started, is............

Unless you are a gear head an auto engine will cost more. If you think you can hop it up, it will cost an order of magnitude more. 10x a Lycoming.

If you're pioneering a conversion, I bet I never see it fly. This is based on decades of promises and fails. ( it's also a cheater bet. Like always betting a random horse will lose )

End rant.

I think you have a proper set of priorities. You want fast, but are not hung up on a arbitrary speed. That's good, and unusual for first time builders, it seems.
You Also understand that getting more power is not cheap, or easy. That's wise.

A well done VW or Corvair conversion seems to be the most successful with Subaru 3rd. ( That would make an interesting survey )

So if you decide to freeze the engine Early in the choice process, I think that's a good choice. Avoids the money creep in several ways.

And.....I too am happier driving a rivet than doing a layup.

So my best suggestion is sit in one before you decide.

If you fit in a Sonex Go for it. I'm waiting to see how the Xenos works once a few have been made. But I have to sit in one first because I am not a petite flower.
 

Georden

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Calgary, AB Canada
Sonex claims 170mph true at 8000'. I've read they match the factory claims with a cruise prop.

Seems your mind is pretty set against the rv. Just wanted to point out that you don't have to run a lycoming in a rv any more than than you have to run the $20000 jabiru to have 120hp sonex.
 

skier

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Seems your mind is pretty set against the rv. Just wanted to point out that you don't have to run a lycoming in a rv any more than than you have to run the $20000 jabiru to have 120hp sonex.
Seems like a lot of people here really love the RV line. I'm with Direct C51 here and just don't like that they take such large engines. Larger engines tend to be thirstier and hence more expensive to operate. Sure people will say that you can always throttle back, but a 200hp engine producing 75hp is probably going to consume more fuel than a 100hp engine producing 75hp. It also adds additional weight that must be countered by using more power. That bigger engine yielding higher top speeds will also require a beefier structure to support it and to support the air loads at the higher speeds.

It's like being stuck in a "do loop" for aircraft design. more power --> heavier engine and structure --> requires more power --> requires a heavier engine and heavier structure.....

Taken to the extreme, a lot of people around here seem to be suggesting that a PT-6 run at lower power settings would be just as cheap to operate as an A-65.
 

Direct C51

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Yes 170 MPH TAS. Sorry, I'm so used to using KTAS, the aircraft I fly to pay the bills reads airspeed in KTAS.

I am in no way pioneering this engine. Plenty of 120 HP Corvairs have been built to WW specs. It won't cost 10x more than a Lycoming. A test run complete 120HP Corvair is less than $12k, I can build it for much less than $10k.

Geordan- I agree you don't have to put a $20k Jab in a Sonex to have 120hp. A 120HP Corvair is half price. What engine can you put in an RV for half price?
 

Georden

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Not sure the prices on the Subaru or rotary options, I'd imagine all in with psru they aren't substantially cheaper than the lycoming, but overhaul would be much less.

It it takes a certain amount of power to carry a specific load with a given performance. The sonex achieves near rv
performance by sacrificing load carrying ability. I'm not trying to argue for or against the rv for your needs, just saying in my case the sonex was really tempting, but just couldn't really do what i wanted to do. I'd rather spend 60k on a basic rv that can do what I want to do than 45k on a sonex that can't. I'd really prefer to have a wittman tailwind, but didn't suggest it as it's not rated for aerobatics, and in my case I think I'd be a lot more likely to finish the build starting with a kit rather than a pile of raw materials and I don't feel comfortable buying someone half finished project which the only way to get a tailwind "kit"
 

Battson

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The Sonex with 120HP cruises about 170KTAS at 75%, 150KTAS if you run 60% or so. That is the fastest all aluminum 2 seater on 120HP that I know of. Getting more power out of a conversion is not easy, cheap, or good for the engine. Aluminum and rivets fit my skills a lot better than composites. I also do not have a climate controlled workspace.
170KTAS? Hahahaha... right, must be an Oops. The day one of those overtakes me (more than double the hp) I will eat my propeller covers. I have flown beside one, they aren't "super fast". I would say "nippy" and fun.

But it's not an RV6A, which I have also flown.
That was properly fast, with only 160hp, so same ballpark. We were doing 160-170KIAS at 500ft.
Plus they can carry something. The Sonex is really quite small, you couldn't take much with you. Definitely an airplane you could out-grown in a months not years, if you fly 200hrs a year.

I am not saying don't consider Sonex - hell, I would love one, they are cool. Just remember - you get what you pay for in aviation. Speed costs, payload costs, performance costs. There are no short-cuts or wonders of design, without associated cost - and the cost is always directly proportional to the performance.

I thought I would fly 50hrs a year, it will probably be closer to 300 in reality. I would hate to have invested emotionally and physically in a plane which I grew out of too soon.


You can fly light in a slightly bigger aircraft.
You cannot fly heavy in a smaller aircraft.
 
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cluttonfred

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The William Wynne Corvair conversions in the 100-120 hp range are well-proven and solid. I wonder if the best way forward given your goals would be to find a part-built RV kit with good workmanship and power it with a Corvair?
 

Battson

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If you're pioneering a conversion, I bet I never see it fly. This is based on decades of promises and fails. ( it's also a cheater bet. Like always betting a random horse will lose )
I have seen this too.
One fellow I met, trialled one particular 8 cylinder auto engine with his own conversion, then swapped for another 8 cylinder engine after the first one failed, I think overheated?? I can't recall. Last I heard, his engine cuts out about 6 seconds after take-off due to some problem with the computer, then clicks back in a few seconds later.
He is a braver man than I.
He has also dead-stick landed more engine failures than anyone else I have met...

The worlds needs inventors.
 

Direct C51

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Battson - What do you mean by outgrow? I've been flying recreationally for 10 years and professionally for 8. I think I know what my needs are. I'm not sure how a few months of flying a Sonex is all of a sudden going to change that. This is really the silliest suggestion I've heard.

Geordan - $45k for a Corvair Sonex is really high, and $60k for an RV-7 is somewhat low. Sure you can skew the numbers and make it sound better. A Sonex is more like $35k.

I think putting a Corvair in to an RV goes against my entire mission. I am not looking for the roomiest airplane that flies on 120HP with the best payload. My mission is simply the fastest 2 seater on 120HP. I don't think an RV is going to perform well, or be very fast on 120HP.

This whole exercise is basically asking which 2 seat aluminum airplane has the least drag, which means fastest speed, which really means most efficient. Of course weight comes in to play, more weight means bigger wings, more parasite drag, more induced drag...
 
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cluttonfred

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My mission is simply the fastest 2 seater on 120HP.
Personally, I am not a RV fan, too expensive for me and they don't really tickle my imagination. But given your mission parameters including desired materials, engine and budget, I still think a second-hand RV kit is the way to go, though I'd probably revise my recommendation to an RV-4. There are other options out there that would also work if you are willing to scratch-build -- T18, Midget Mustang, etc.
 

Direct C51

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How does an RV-4 meet my mission? Seriously? Read what you quoted of me. An RV-4 is designed for 150HP - 180HP. It says right on their website. I just said my mission is the fastest 2 seater on 120HP and you think an RV-4 is faster than a Sonex on 120HP?
 

rv6ejguy

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A Sonex would seem to be the way to go if you fit and have enough baggage space.

BTW there are at about 30 times more Subarus flying than Corvairs- very successful if done right.

How fast can a 120hp Sonex be?

imagetas.jpg

201 KTAS with a turbocharged 912...

My friend flew a Q2 with DD turbo Subaru for over 800 hours, 190 KTAS at 12,500 feet on 5.5 GPH.
 

Direct C51

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I find it ironic that the RV owner is one of the only ones not trying to sell me on an RV. I really like RVs and had intended to build one until reality hit and I realized that I just cannot resonably afford to build or fly one.

The Subaru is a good auto conversion, but a little more complicated than I would like. Having a PSRU and cooling system adds too much complexity to a simple airplane like the Sonex in my opinion. The Corair is pretty similar to an air cooled flat airplane motor. That picture you posted is awesome, but I think had you shown the right side, the VSI might be a bit telling. Not to mention it is 33 MPH over design Vne. Impressive nevertheless.
 

rv6ejguy

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I find it ironic that the RV owner is one of the only ones not trying to sell me on an RV. I really like RVs and had intended to build one until reality hit and I realized that I just cannot resonably afford to build or fly one.

The Subaru is a good auto conversion, but a little more complicated than I would like. Having a PSRU and cooling system adds too much complexity to a simple airplane like the Sonex in my opinion. The Corair is pretty similar to an air cooled flat airplane motor. That picture you posted is awesome, but I think had you shown the right side, the VSI might be a bit telling. Not to mention it is 33 MPH over design Vne. Impressive nevertheless.
I've looked at a Sonex myself and I read your post about costs.

The aircraft is level in that screenshot: From the owner: 147KTS - 3000ft with only 30". Normally I cruise at 32-35" 5000rpm @ 8000-10.000ft with gives me 170KTS TAS

I did warn him about the Vne...!

The same guy had a turbo VW in the Sonex before, cruise was over 150 knots at altitude.

He has also done EFI and EFI turbo Jabiru 2200s in Sonex airframes.

Turbos are magic if you want speed up high.
 

Victor Bravo

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IMHO you have two valid choices, the Tailwind and the Vari-EZ. Both represent compromises in order to get most of your desired results.

The professional pilot (airline) in the hangar next to me just bought a used Wittman Tailwind, which was very well built and properly set up. He just did several two-way runs with a good GPS to figure out how fast he is going and not going, because like all experienced pilots he does not trust the pitot-static system.

On a relatively stock 125 HP engine, he is just under 200 MPH at full throttle. At cruise power, he is at about 180. A very clean Tailwind, but no wheel pants yet. When he puts the wheel pants on, these speeds will likely go up by 4-7 mph. An O-200 powered Tailwind would still be a 170 MPH airplane if you keep it light and pay attention to aerodynamic cleanup.

There was a recent article within the last year in Sport Aviation about the Tailwind. For 50 years, it has been the hands-down winner by far in the "best bang for the buck" category.

I realize that this airplane represents a significant change (construction materials) from your original airplane choice parameters. However, I have to agree with several others here that in order to meet your most important requirements, you may have to allow your thinking to be flexible in one or two areas.

Scratchbuilding the Tailwind will require that you learn two different building skills (welding and wood). You will need to find a hangar to keep it in. It is not a hard acro airplane. In exchange for these three concessions you will get the following benefits:

- The speed you want, from the engine size you want.
- You will be at, or under, your target budget of $30K, a very rare feat in homebuilt aviation!
- Two seats, and a surprising amount of room compared to most other small homebuilts.
- A solid network of builders and mentors. Not as many as RV of course, but plenty.
- A little more pride and unique-ness when you roll up to the flight line at an airshow.

You can also save significant time and money by getting a half-finished Tailwind project of course.

A PROPERLY built and clean Vari-EZ will cruise at 180-190 MPH on 100 HP. With a 120HP Corvair (if it balances on the airplane) it should do another 10-12. You can scratchbuild a Vari-EZ, or buy a half-built one, for under $30K if you don't get carried away with avionics. Once again, you are going to compromise on the material, but you will achieve several benefits:

- If built per plans, your loops and rolls and half-Cubans are no problem.
- You will achieve very VERY high levels of cruise fuel efficiency and XC speed.
- Your non-pilot passengers will feel like you gave them a ride in an F-104.
- There is a group of educated owners, builders, and experts to mentor you.

Both of these airplanes will be very very hard to match or beat with sheet aluminum and realistically stay within your budget/engine size.
 

flyvulcan

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Perhaps the old Lancair 235 might work for you, if you can squeeze into it. It was designed around the O235 which is around the hp that your Corvair is. I don't know whether the Corvair would fit but you could look into it.

The Lancair 235 fits the bill with "higher" speeds, probably more so than the Sonex and possibly on a par with the RVs. I've seen different speeds quoted for the Lancair 235 so speaking with owners who won't exaggerate would be required.

There is a decent looking kit advertised for sale in Florida for $11900. You can see the ad at 1994 Lancair 235 Kit The Aircraft Pages.

Maybe this might appeal to you.

Good luck with your search and build.
 
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