New Rotax 915is trubo fuel injected 135 hp

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roger lee
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New Rotax 915is trubo fuel injected 135 hp

Postby roger lee » Tue Jul 21, 2015 3:07 pm

New Rotax 915is trubo fuel injected 135 hp

With an intercooler it will make it a little harder to fit under a cowl and it is a heavier engine. At 185 lbs. this will be more in line with the weight of Cont. and Lycoming.
Will be more likely to see certified aircraft use.

http://www.rotax-owner.com/en/rotax-blog/item/43-915is
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Re: New Rotax 915is trubo fuel injected 135 hp

Postby c162pilot » Wed Jul 22, 2015 6:42 am

Roger, interesting, this engine will be over 100 lbs lighter than the Continental CD-135 and have a 500 hour longer TBO. I expect it will be cheaper also. Do you think over time that this engine could give the CD-135 some serious competition?

http://continentaldiesel.com/typo3/index.php?id=65&L=1

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Re: New Rotax 915is trubo fuel injected 135 hp

Postby drseti » Wed Jul 22, 2015 7:21 am

When I did my most recent Rotax Heavy Maint renewal with Eric Tucker in January, we discussed both the 914 and the 912iS. I asked him if Rotax was planning to combine the two into an injected, turbocharged engine, and he deftly declined to discuss or answer the question. So, I suspected such an engine was in the works. Glad to see I guessed correctly! :D
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designrs
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Re: New Rotax 915is trubo fuel injected 135 hp

Postby designrs » Thu Jul 23, 2015 3:19 pm

This is exciting if it greatly ups performance for LSA. So if you had 35% more horsepower, could you expect to see 35% better climb rate & cruise?
- Richard

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Re: New Rotax 915is trubo fuel injected 135 hp

Postby FastEddieB » Thu Jul 23, 2015 3:55 pm

designrs wrote:This is exciting if it greatly ups performance for LSA. So if you had 35% more horsepower, could you expect to see 35% better climb rate & cruise?


Yes it's exciting.

But, no, the performance gains would be less.

Climb rate would benefit more than cruise, since it's excess hp that lets you climb.

But in cruise, parasitic drag increases as the square of the increase in velocity. To go twice as fast requires four times the power. One of our engineer/math types can do the math and tell us how much speed could be gained from an extra 35% power. I think the math is easy, but is not my forté.

To complicate matters, you would have 35% more power at SL - but that power gain would tend to increase as a normally aspirated plane loses substantial power as it climbs, while a turbo can hold SL power to a higher altitude - 15,000' in the case of the 915is if ROTAX can be believed. At 15,000', a normally aspirated engine will only be able to develop about 60% of its rated power.

As an aside, I recall the joy when Cirrus first announced its turbonormalized SR22. And, in fact it's a marvelous machine. But over time, owners discovered that turbocharging carries very real additional maintenance costs. No free lunch and all that.
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Re: New Rotax 915is trubo fuel injected 135 hp

Postby drseti » Thu Jul 23, 2015 5:21 pm

Eddie, a 35% power gain would increase speed 16%.
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Re: New Rotax 915is trubo fuel injected 135 hp

Postby SportPilot » Thu Jul 23, 2015 5:27 pm

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Last edited by SportPilot on Fri Jul 24, 2015 2:04 pm, edited 1 time in total.

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Re: New Rotax 915is trubo fuel injected 135 hp

Postby FastEddieB » Thu Jul 23, 2015 5:42 pm

Thanks, professors!
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designrs
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Re: New Rotax 915is trubo fuel injected 135 hp

Postby designrs » Thu Jul 23, 2015 7:25 pm

Sea-level power at altitude and 16% faster cruise.
Sounds pretty good then!
Might just be what LSA needs for a little extra capability.
I'm especially craving better climb rates in the hot Summer.

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dstclair
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Re: New Rotax 915is trubo fuel injected 135 hp

Postby dstclair » Thu Jul 23, 2015 7:55 pm

Ah, but several LSAs could not legally increase their cruise by 16% at sea level since that would exceed the US LSA regulations (120KCAS). The extra 40lbs would also be problematic for many of the current designs. I could see ICON migrating to the new engine since they have excess MTOW they could use and cruise well below the regulatory limit.
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Re: New Rotax 915is trubo fuel injected 135 hp

Postby 3Dreaming » Thu Jul 23, 2015 10:19 pm

In my experience a 16% increase in speed is a little optimistic.

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Re: New Rotax 915is trubo fuel injected 135 hp

Postby drseti » Thu Jul 23, 2015 10:39 pm

I agree, Tom, the square root equation overlooks the inevitable increase in parasitic drag. But, at LSA speeds, that should be fairly minor.
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Re: New Rotax 915is trubo fuel injected 135 hp

Postby FastEddieB » Fri Jul 24, 2015 6:33 am

drseti wrote:I agree, Tom, the square root equation overlooks the inevitable increase in parasitic drag. But, at LSA speeds, that should be fairly minor.


Wait.

I love thought the main (whole?) reason for the square root equation was the increase in parasitic drag.
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designrs
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Re: New Rotax 915is trubo fuel injected 135 hp

Postby designrs » Fri Jul 24, 2015 8:01 am

dstclair wrote:Ah, but several LSAs could not legally increase their cruise by 16% at sea level since that would exceed the US LSA regulations (120KCAS). The extra 40lbs would also be problematic for many of the current designs. I could see ICON migrating to the new engine since they have excess MTOW they could use and cruise well below the regulatory limit.


Just placard it or pitch the prop for 120 knots at sea level at gross. If the turbo provides that sea level performance at altitude I'd be thrilled!

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Re: New Rotax 915is trubo fuel injected 135 hp

Postby drseti » Fri Jul 24, 2015 8:02 am

Eddie, I believe the square root equation comes from the relationship between energy and velocity (KE= 1/2 m v^2) . This equation comes into play because power is directly proportional to energy. The effects of parasitic drag are another loss on top of that basic relationship.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
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