Engine selection

[Palimino]

A useful selection technique was developed when I had reason to select a modern car engine for an experimental aircraft. This technique can be applied to other selections. The usual aircraft engines, Lycomings and Continentals, are horizontally opposed, push-rod operated dinosaurs (design hasn’t changed since the 1940’s) and are ridiculously expensive for what you get. They are horizontally opposed so that the pilot can see over them (especially in a tail dragger). This engine geometry constraint forced me to look only at V8’s. The ‘V’ configuration allows the pilot to see between the cylinder banks (especially in a tail-dragger) and makes the engine shorter (as well as more powerful). So, the ability to see over the engine, 200HP+, as light as possible and developing maximum power at low RPM, was my selection criteria.

The plan (I was working from an American plan) incorporated an underpowered, heavy, gestonky American (car) engine. If you are not good at math (like me) but want to analyse many engines, this is what I did. From the appropriate textbook I coded my requirements (carefully – once) into a spreadsheet program (RPM, max power, gear ratios etc). I ran several examples through to ensure it was correct. On the back page of Car Magazine they used to have the engine data for popular models. I plugged these values into my spreadsheet program and got answers immediately. Viola!

Trivia - I selected the all-alloy, V8 Rover engine after this exercise.

 

[zamicro]

Just be careful with your new center of gravity. Are you building a kit? Which kit?

I am to scared to use a standard engine. Will look at least for dual ignition.

 

[Stokstert]

What about a Subaru or Porsche engine, although the second choice would most probably also be quite expensive? Porsche could possibly run without blower if the air is channeled correctly.

 

[Palimino]

Just be careful with your new center of gravity.

Yes, that would change radically. The plan was to hang it off the floor (and calculate it of course).

Are you building a kit? Which kit?

No. I was building under LS/1 rules (SA) and EAA rules. From plans (plenty of them). No ultralight/microlight weight limits.

I am to scared to use a standard engine. Will look at least for dual ignition.

Think about it. How many times does a normal car have an ignition problem? Even without the regular, paranoid pre-flight inspection? I considered dual ignition. Electronic and mechanical in case the electronic one got taken-out with an EMP (lightening or something). The problem was they would get out of synchronisation. Too much trouble. A well-earthed faraday cage on the standard electronic ignition.

 

[Palimino]

What about a Subaru or Porsche engine, although the second choice would most probably also be quite expensive? Porsche could possibly run without blower if the air is channeled correctly.

Subaru and Porsche engines are both expensive (I was on a budget and looking for the most bang for my buck). I wasn’t too concerned about the cooling (although I never went into it). Cylinders sticking-out into the airstream with a dirty great propeller blowing a gale onto them.

 

[Paul_S]

I've read about a few home builders using Mazda 13B rotary engines.
Downside is that they need a decent oil cooler and radiator but otherwise they compare quite favourably to an IO-360. Similar power output and fuel consumption but much cheaper to run and maintain and virtually no vibration.
Can use standard motor vehicle fuel instead of 100LL and if you want more power you can bridge port the engine.

 

[Pyro]

Whereabouts do you intend on flying this? And how high?

 

[Thugscub]

What about a motorcycle air-cooled motor. Lot of power + low weight. Most of them are bullet proof as well.

 

[Pyro]

What about a motorcycle air-cooled motor. Lot of power + low weight. Most of them are bullet proof as well.

Not a lot of torque though. I don't know exactly what Rover motor he's looking at, but they should have quite a bit of power. If he's looking at higher altitudes, he might consider a turbo model though.

 

[ponder]

What about a motorcycle air-cooled motor. Lot of power + low weight. Most of them are bullet proof as well.

Know little about aircraft but don't they strive for low rpm (2000-3000) motors generating more power at lower rpm?

Else you would end up with a high rpm prop which would need a gear reduction box which adds more weight.

 

[Palimino]

I've read about a few home builders using Mazda 13B rotary engines.
Downside is that they need a decent oil cooler and radiator but otherwise they compare quite favourably to an IO-360. Similar power output and fuel consumption but much cheaper to run and maintain and virtually no vibration.
Can use standard motor vehicle fuel instead of 100LL and if you want more power you can bridge port the engine.

The Mazda rotary is a good engine, but the RPM and fuel consumption are too high. All car engines use standard motor fuel (this is no advantage for the Mazda engine). To reduce the RPM to a usable figure would require a complex, high-speed gearbox. More to go wrong (and the gearbox is critical).

Pyro

Whereabouts do you intend on flying this? And how high?

These are related questions. There are essentially two types of aircraft. A low altitude, unpressurised, normally aspirated (non-turbo’ed – mixture control only) (10 000 ft. ceiling), land anywhere bakkie of the skies. A high altitude, pressureised, fast, turbo’ed plane (with a fragile undercarriage) that lands only at regular airports. I went for a 4-seater bakkie of the skies.

Thugscrub

What about a motorcycle air-cooled motor. Lot of power + low weight. Most of them are bullet proof as well.

Nope. Not enough power. They were considered for drone aircraft, however. Even there, they couldn’t handle the payload of an efficient drone.

ponder

Know little about aircraft but don't they strive for low rpm (2000-3000) motors generating more power at lower rpm?

Else you would end up with a high rpm prop which would need a gear reduction box which adds more weight.

Yes they do [strive for low RPM]. The idea is to keep the tips of the aircraft propeller from exceeding the speed of sound – which requires a low RPM (length of propeller etc. all have an effect). Generally, an engine with a longer stroke is required. The only car engine which you can direct-drive the prop. is a VW – and that is too underpowered. It is used on some single seat homebuilts.

The gear reduction disadvantage is not weight (although it would be heavier). Up to about 500 hp you can use gear reduction belt drives. Silent, reliable, cheap and simple (no machining of gears required). After 500 hp a mechanical gearbox is advised and things get more complicated.

 

[ponder]

Off topic but I heard the blades on a turboshaft chopper rotate at a constant rpm irrespective of engine rpm/power. I can understand why you would want constant rpm but how do they achieve this?

 

[Palimino]

Off topic but I heard the blades on a turboshaft chopper rotate at a constant rpm irrespective of engine rpm/power. I can understand why you would want constant rpm but how do they achieve this?

I’m not sure of details, but engine rpm/power **are** critical. A turbine (or an engine with similar characteristics) is generally high revving. The rpm is reduced to a usable value, thereafter it is a constant speed entity. Lift/forward motion etc. is achieved by varying the pitch (the angle at which they meet the air) of the propeller blades. A helicopter works like this. The throttle lag-time (slowing and speeding-up the engine to regulate the prop. rpm) would be huge swinging a prop. as big as a helicopter’s.

 

[zamicro]

Did you look at any diesel engines? Nice torque@low revs...

 

[Pyro]

Palamino - on the whereabouts I meant - would it be on the Highveld? Around here you're already at 1700m, around 5000ft. That would already sap into your power at takeoff.

I don't have the numbers to know what you use for flight, so I don't know exactly how much is necessary.

Wouldn't mind a 4x4 flier myself though But even a microlight would be too much for my budget at this time

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A helicopter turbine doesn't run a truly constant RPM, but it does adjust the throttle as load varies in an attempt to keep the blades at a constant/optimal speed.

I wonder if there was much progress in using CVT style gearboxes to keep things at proper optimal engine speed and optimal blade speed.

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I'm not too sure about the modern diesels, but the older ones were way too heavy to justify their use in planes. I don't know how well diesels would handle the increasing altitudes either.

 

[Palimino]

Did you look at any diesel engines? Nice torque@low revs...

I didn’t (concept too new). Diesel engines are being considered for aero engines. The weight and power output were always the problem but the new diesels with the turbo technology (I’m not keen on turbos for aero engines) may provide a solution. An excellent idea!

**Technical rant deleted**. The only problem I have is with the whole reciprocating engine model. If diesel engines work-out, it weakens the case for a paradigm shift away from reciprocating engines (which I support). IMO the ****el engine (like the Mazda) or turbine technology is the way to go (for any engine – not only aero engines). Alas, their are too many special interest groups invested in the stone-age reciprocating engine. Don’t hold your breath.

 

[Sensorei]

X2 for Subaru engine. My cousin's gyrocopter uses one and he's swears by Subaru engines for reliability and bang vs buck.

 

[Paul_S]

A helicopter turbine doesn't run a truly constant RPM, but it does adjust the throttle as load varies in an attempt to keep the blades at a constant/optimal speed.
I wonder if there was much progress in using CVT style gearboxes to keep things at proper optimal engine speed and optimal blade speed.

Is there any reason why helicopters don't use a reverse flow, turboprop design?
i.e. Where the prop shaft is driven from an isolated free-wheeling internal turbine in the exhaust gas.
The prop shaft turbine can be kept at constant speed while the thrust from the turbine engine section can be adjusted automatically to compensate for loads on the prop shaft.

I'm not too sure about the modern diesels, but the older ones were way too heavy to justify their use in planes. I don't know how well diesels would handle the increasing altitudes either.

Diamond Aircraft Industries are using diesel engines (Thielert Centurion) in some of their aircraft and there are lots of people who have converted to aviation diesel engines.
Thielert AG manufacture a Centurion range of diesel engines for aviation use:
http://en.wikipedia.org/wiki/Thielert

 

[Palimino]

Palamino - on the whereabouts I meant - would it be on the Highveld? Around here you're already at 1700m, around 5000ft. That would already sap into your power at takeoff.

I flew microlights for many years (cheaper). I have only flown them [not regular planes] on the Highveld. The trick was to carry a handful of different carburetion jets and fit the appropriate one for the altitude. You could do this with microlights because the flights were largely area bound (same altitude). In a conventional plane the mixture control generally had the range to handle altitude changes. Anything more severe usually required oxygen, pressurisation and turbocharged engines (where jetting doesn’t matter).

 

[zamicro]

X2 for Subaru engine. My cousin's gyrocopter uses one and he's swears by Subaru engines for reliability and bang vs buck.

Hi. Which gyro is it? Did not know about any in SA using a subaru. I thought all gyros were using rotax 914s.