# What would these choices result in?

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#### blane.c

##### Well-Known Member
HBA Supporter
Needs around 180hp plus 3% for each thousand feet he will normally cruise at. So say 10,000ft normal cruise altitude 180hp + 30% = 234hp which is like a Continental O-470. Or 15,000ft then he needs 260hp or a Continental O-520 or a Lycoming O-540. Or a smaller engine turbocharged to compensate for the 3% loss of power with each thousand feet of altitude but will still cruise at altitude with 75% of rated power or less. Or 2 or more smaller engines that will give equal power to above.

#### mcrae0104

##### Well-Known Member
HBA Supporter
Log Member
I'm guessing around 125hp @ 3000rpm.
No need to guess. Sport Performance Aviation has dyno tested several of the various displacement combinations available.

2775cc 100hp 3300 RPM
3000cc 115hp 3300 RPM
3300cc 119hp 2800 RPM
3300cc 125hp 3300 RPM

SPA also provides a U.S.-manufactured 4340 billet crankshaft (normal or stroker--the 3300cc displacement above is stroked). Note also that 3300cc = 200in3, so what we're talking about is very directly comparable to an O-200 in terms of output.

Also, this engine is likely not a good candidate for a 4-place Sling. You will probably find the airframe needs a very specific weight and power output and virtually anything you substitute for the Rotax will be heavier (Corvair, Lycoming, whatever).

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#### TFF

##### Well-Known Member
If I was going to all this trouble, I would be putting the motor in a Fitch Sprint and go vintage racing. .

Get the Wynne manual and an engine and see what you can do. I would build one with stock parts , put a prop on it and make it run. dive in with the big guns if you liked it. I think it would be fun. I would put one in a parasol in a second.

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#### Toobuilder

##### Well-Known Member
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...unless you find another inexpensive Lycoming.

This calculation also makes the huge leap that you will actually fly enough to require overhaul. That's a rare feat these days

#### blane.c

##### Well-Known Member
HBA Supporter
115hp and four people, it has to be tiny somewhere. Tiny range, or tiny utility, or tiny seating/cockpit. Or it has tiny wings and needs lots of runway, there is no free lunch.

I don't believe a 914 weighs 150lbs installed anymore than I believe any of the other engine weights are installed weights, listed weight of engines is so ambiguous, some include this in the weight and others include that in the weight it is a lot of smoke and mirrors. It is predicated by the multitude of differences in individual installations. It is difficult to sort out the truth until you are way financially committed without investing a lot of effort in education and/or making trustworthy knowledgeable friends.

It is the total weight, and the frontal area of the installation one to another that matters. Oh yes and the hp and specific fuel consumption (sfc) best for my purpose's stated in lbs per hp hour but becoming more common in grams per kw hour.

Cheaper has different meanings to different people. Some would consider it cheap if they have to take out the front seat and sit in the back so they can stretch out there legs. I am not saying that would literally happen but you get the idea.

So some people are suggesting a Lycoming or Continental but I think the undertone between the lines is that they are not certified engines(to save money). You can obtain an engine without logbooks (which make it worth anything) for less money, my concern would be that I do not want stolen property, it can be missing it's logbooks for any number of reasons but that is the first concern I would want answered.

The D-motor interests me they have a 120hp or there abouts, I do not know how many engines they have sold or there record in service. But low moving parts count, liquid cooling and fuel injection with low sfc.

A Cessna 172 is a good airplane to compare to. 4 seats, 150hp more or less depending on year and modifications, 120mph, and as far as I am aware still the most produced light plane. It provided affordable entry to flying for many decades. Or a Piper Cherokee 140 or a 160 very durable little 4 seater with similar performance to the Cessna.

You would be hard placed to do better than a well cared for Cessna 182 or a Cherokee Charger 235 they have good utility.

I'm a multi fan, even a twin with poor single engine performance has better performance than a single with engine power loss. It's your family.

#### TFF

##### Well-Known Member
The TSI does have a decent load for its empty weight. I do bet it is a fragile airplane compared to something like a RV. Remember useful load means everything you stick in the plane. People, baggage and fuel all together. And it has to be in CG. You can’t put 300 lbs in baggage compartment just because no passengers are coming with you.

Actual firewall forward for the Rotax is about 200 lbs when you add radiator, coolant, engine oil and hoses they conveniently forget. Getting the CG right is important but there is as much advertising in airplane parts as there is in cars. Everyone tells the truths that make them look good and ignores the ones that don’t. Weight adds up quick.

Overhauls have to be qualified too. Lycoming can go 2000+ hours. There are plenty 40 year old planes out there now coming up on first OH, so unless you are flying 10 hours a week, 2000 hrs is a long time. One hour a week makes you a hero in this day and age. Corvair conversion is somewhere between 500-1000 hours. Still a long time but not same league. I know flight schools can get 3000-4000 hours out of an engine that flies every day. My opinion is a Lycoming will outlast you flying it. Unless the engine is flow on an airliner, TBO is a recommendation, and once on a homebuilt, it’s up to the owner. Essentially fix what is broken, keep going with what is not.

The biggest thing is make sure you are talking apples to apples with whatever you are working on. Lycoming pushes its engines to around one horsepower to two cubic inches naturally aspirated. Sometimes a little more. Spinning an engine faster may make more horsepower but it starts becoming less and less useable the smaller the prop gets. Great advertising.

#### Vigilant1

##### Well-Known Member
In response to both of you (somewhat in agreement, but still analyzing), the Sling 4 (the predecessor to the Sling Tsi) hauls 4 + baggage with a Rotax 914 UL which is rated @ 115hp and weighs 150lbs. I was wondering how that was possible, being liquid cooled with all of the cooling hardware and turbo equipment, until I saw the displacement is only 1211cc. Incredible.
FlyCorvair claims the weight of the Corvair conversion is 205 lbs. If I have to sacrifice 55 lbs of luggage and move the wing forward (or engine back) a couple of inches, I think it is worth some engineering calculations to see if it is possible.

Also, again, anyone trying to argue that it would be "cheaper" to just buy a Lycoming or Continental, you may be right.... initially. But you have to add to your calculations the cost of overhauls. After that, you will see, even if I spend up to $15K on this engine (which I don't plan on spending half of that), I still win after my first overhaul. Maybe the Aeromomentum AM15 is worth considering? Approx$12K, as much HP as the Rotax 914, 185 lbs plus another approx 10 for the radiator, everything brand new and the engine is built.

#### geosnooker2000

##### Well-Known Member
Meh... I'm souring on the whole water-cooled/PSRU idea. Just two more things that can fail.

#### wsimpso1

##### Super Moderator
Staff member
Log Member
Maybe the Aeromomentum AM15 is worth considering? Approx \$12K, as much HP as the Rotax 914, 185 lbs plus another approx 10 for the radiator, everything brand new and the engine is built.
I have chatted with Mark a bunch and he impresses me. Ask him about firing order isolation of gyroscopic moments and he can talk about it and tell how he has designed for them. His engines have a bunch of time in airboats and powered parachutes and his airplane installs are going up. They do the whole deal with cooling, induction, exhaust and engine mounts for specific airplanes.

Billski

#### Vigilant1

##### Well-Known Member
I have chatted with Mark a bunch and he impresses me. Ask him about firing order isolation of gyroscopic moments and he can talk about it and tell how he has designed for them. His engines have a bunch of time in airboats and powered parachutes and his airplane installs are going up. They do the whole deal with cooling, induction, exhaust and engine mounts for specific airplanes.

Billski
Yes, that's the impression I have of Mark Kettering, too. He's approached the process in a professional, systematic way and has backed it up with lotd of airboat time before selling hardware for flight.
My only concern is about the FI/ignition reliance on Microsquirt software and hardware. I need to learn more, I am not throwing any stones here--maybe it is a fine choice. But it is so critical to flight and the failure modes are not obvious to folks who aren't fully schooled in the way that particular hardware/software works.
A product partnership between SDS and Aeromomentum would be interesting.

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#### rv6ejguy

##### Well-Known Member
The Rotax 914 has an all up weight of 164 lbs. including rad, exhaust system, engine mount, overload clutch and external alternator. Add 8 more pounds for coolant so say 172 lbs. No Corvair, Conti or Lycoming comes close to that which is why they are not viable alternatives to the Rotax, plus they are not turboed so will have worse altitude climb and cruise performance.

#### Winginitt

##### Well-Known Member
Unless I missed it somewhere in the thread, I think the first thing to determine is how much weight is the maximum that the nose can support. Also I would check if the recommended engine has any leeway in it's location that might allow a heavier or larger engine to be moved slightly aft with just a different mount. From that point I would then see what engines might work well. Most 4 place certified airplanes use an engine with more than 120 hp and heavier than a Corvair. The Corvair strokers weigh slightly more than the Rotax but supply more power. I think someone mentioned 100 HP for the Rotax. Lately TFG has been talking about his LS3 powered T51.
The design was originally for a 100 HP engine. It has morphed over the years to hold Honda V6 and Chevy V8 engines. TFG 's latest version has many mods to enable the latest high HP version to fly even faster. Several years ago I talked with a couple of brothers who built a Pazmany Storch and put a much larger engine on it. Said they had room to move the firewall back. Think they put an O-470 in it, but don't remember for sure.

The point here is that you might want to check not only what is recommended, but what things might actually be workable and possible weight wise. After you have weighed all options on engine placement and weight, then look again on what engines are viable. If you research various designs you will find that in many cases a planes
Gross Weight changes when a larger engine is used without requiring any other changes.Whether the design you are interested in fits that scenario or not is worth investigating before making your engine choice.