# Turbocharged engine options for a 2 seater - what would you consider?

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#### Puggo1

##### Active Member
Hi,
I'm looking at Honda 1.4-1.5 Civic engines. Weight is in your range and power is from 90 to 200hp.
happy flying.
Puggo

#### aeromomentum

##### Well-Known Member
While older Honda engines (for example D series) were very light, the newer Honda engines (for example L series) tend to be relatively heavy for their size. Some of the iron block Toyota motors (for example SZ series) of the same size are actually lighter weight than newer Honda's.

The Suzuki G series engines are very similar to the Honda D series engines and some parts are actually interchangeable. We have run Honda D series pistons in a Suzuki G series engine and many others have used Honda racing cranks and rods since racing parts for the Honda are more common.

In general, long stroke engines tend to weigh more for a given displacement. Engines with a bore about the same as the stroke tend to be lighter. Of course there are many exceptions.

#### dieseldanblue34

##### Member
I'm looking at turbo engine options for a 2 seat plane, something along the lines of a Whitman W8.

The big points I would like to consider are:

Under 220lbs installed
Minimum 90hp @ 9000ft DA
Ability to run on pump gas I can buy anywhere (including E10)
Forced induction for consistent takeoff performance

#### tcrbaker

##### Member
I'm looking at turbo engine options for a 2 seat plane, something along the lines of a Whitman W8.

The big points I would like to consider are:

Under 220lbs installed
Minimum 90hp @ 9000ft DA
Ability to run on pump gas I can buy anywhere (including E10)
Forced induction for consistent takeoff performance

#### wsimpso1

##### Super Moderator
Staff member
I'm looking at turbo engine options for a 2 seat plane, something along the lines of a Whitman W8...
Forced induction for consistent takeoff performance
I too have to question the need for turbo for takeoff performance. Turbos in that power range would have to be developed and made reliable yourself. There are a number of NA engines in your weight range that will still have close 90 hp at altitude.

Now if you want to turbo normalize for altitude performance, knock yourself out. Turbo sizing, oil lines, intercooler sizing, mounting, etc, they can all be done. Ross at SDS writes about it on here as rv6ejguy.

Billski

#### Vigilant1

##### Well-Known Member
Supporting Member
On a normally aspirated engine with a fixed pitch prop, as we climb and the engine loses power due to the less dense air, the prop also encounters this thinner air and it remains a good "match" resistance for the engine. It will still pull all the way to engine redline. With a turbo, the engine can continue to put out more HP at higher altitude, but the prop may not be able to use that power unless the pitch can be varied. This is one reason aircraft with turbo engines usually have variable pitch props.
Assuming your engine budget is reflective of your general budget, a variable pitch prop probably isn't in the cards.
Now, if your desire for a turbo is just due to your field elevation and you don't expect to fly much lower, the a turbo and fixed pitch would work okay. But I suspect a normally aspirated engine that meets your 90hp at altitude requirement will be easier to implement and less costly.

#### aeromomentum

##### Well-Known Member
The 3 cylinder 1.2 L Mitsubishi 3A92 is a long stroke engine and even though it is just 3 cylinders and aluminum block it is heavy for it's displacement and power. It actually weighs more that the larger, smoother and more powerful 4 cylinder Suzuki 1.3 L engines.

A 3 cylinder can be and normally are 100% balanced in primary and secondary modes. The strokes are each 120 degrees apart. This is better balance than an inline 4. There is a slight rocking mode and this does become a greater issue with longer stroke engines like the 3A92 but is not normally an issue with a better bore to stroke and rod ratios engines like the 1 L Mitsubishi 3A90. Balance shafts can greatly help but of course add weight. Racers normally replace the balance shaft with a straight no added weight shaft but this is still more weight than not having one. But the larger issue with 3 cylinder engines converted to aircraft use is the torsional vibration. The less power strokes you have the larger they need to be for a given power output. More cylinders, higher RPM and more power strokes make for a torsionally smoother engine.

##### Active Member
Thanks for all of the great information, I am learning a lot.

As for the prop question: right now I am planning for a ground adjustable.

My number one focus of the the turbo would be takeoff performance at high DA airports, but I would like to be able to climb up to 15K and cruise for longer trips.

I am researching other prop options, but what options are available will likely be determined by engine choice.

On a mildly related note: @Areomomentum, on the website for the Veloce 400, when paired with the 300hp AM engine it specs a fixed pitch prop and says "Ask Us Why", but quite annoyingly does not offer any more explanation. Do you know why they suggest a fixed pitch prop with AM20T and constant speed props with the other options?

#### rv6ejguy

##### Well-Known Member
Supporting Member
Having been involved with and flying turbocharged aircraft for around 40 years, there is no way a fixed pitch prop will provide a good compromise between takeoff, climb and cruise at high altitudes. A prop pitched for cruise at 15K will be mostly stalled during takeoff. Plenty of folks have tried it and found out it didn't work well.

You'll note that almost all factory turbocharged aircraft have CS props. The air density at 15,000 feet is close to half of that at SL. Therein lies the problem with the prop if SL power is maintained to that altitude.

IVO and Airmaster may be prop options for you for you.

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#### aeromomentum

##### Well-Known Member
Thanks for all of the great information, I am learning a lot.

As for the prop question: right now I am planning for a ground adjustable.

My number one focus of the the turbo would be takeoff performance at high DA airports, but I would like to be able to climb up to 15K and cruise for longer trips.

I am researching other prop options, but what options are available will likely be determined by engine choice.

On a mildly related note: @Areomomentum, on the website for the Veloce 400, when paired with the 300hp AM engine it specs a fixed pitch prop and says "Ask Us Why", but quite annoyingly does not offer any more explanation. Do you know why they suggest a fixed pitch prop with AM20T and constant speed props with the other options?
I am sorry for the page being annoying! I am involved with the plane, company and engines but not with the website.

The AM20T can put out over 360hp at MSL and can also put out over 300hp at MSL at just 4800 rpm. We limit the power to 300hp but it is flat from 4800 to 7000. Keep in mind that the "rated power" is at 5800 and the factory red line is 7000 rpm. So even if the fixed pitch or ground adjustable prop is pitched for cruise you will still be able to get full rated power at the start of your takeoff roll and during your climb.

Ross is right about a fixed pitch prop being stalled but this is only during part of the takeoff roll. This does greatly reduce prop efficiency and thrust but due to the high available power and short time this has little impact on takeoff performance. The props are also a little less efficient in climb but in this case the reduced efficiency is much smaller than when they are stalled.

So will it perform better with CS props? Absolutely. But is the difference worth the added cost and added weight? That is up to the builder/owner to decide. For me, it is not since the takeoff/climb performance is already very good even single engine. This is similar to the classic RV-6 choice between the IO-320 with CS or the IO-360 with fixed pitch. And due to the much wider power band of the geared and boosted AM20T the numbers push the choice more to the fixed pitch and higher power side.

Yes, the air is less dense at altitude. But the speed is higher so the mass flow through the prop disk is not reduced as much. For our example if the prop was pitched for 2050 RPM (5000 engine rpm) for MSL cruise, the prop would be at about 2400 RPM (5890 engine rpm) at 30KMSL cruise. This would not be acceptable for a direct drive engine especially a turbo direct drive engine! But for the geared and boosted AM20T it is not only acceptable it is actually needed since the AM20T needs to turn a little faster at altitude to make the rated power.

There is also other precedent for fixed pitch props on high speed aircraft. Look at the Schneider Trophy aircraft of the 1930's. They had very high pitch fixed pitch props and they had the added issue of needing to get on step and takeoff from the water. Some had speed records of over 400 mph with their fixed pitch props and high drag floats. Most later aircraft used geared and boosted engines.

#### rv6ejguy

##### Well-Known Member
Supporting Member
An interesting discussion.

The RR R engine developed 2000-2600 HP so given the weight of the S.6B airframe, the power loading is a little over 2 pounds/hp. The M.C. 72 had an even better power loading. These are in a different league from the aircraft we are discussing here which are at around 9 pounds/hp. In addition, these aircraft raced at sea level so the props could be optimized for max speed at one altitude and takeoff and climb were unimportant. Those last two things ARE important for most GA aircraft.

Not only does thrust drop off considerably with stalled blades but drag, hence input power required, massively increases. We've seen this first hand when running engines on the test stand with a variety of props and test clubs.

I'm curious to know if the Veloce 400 has flown at 18,000 feet yet with the AM20T and FP prop? What is the TO distance and ROC?