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  #1  
Old 06-25-2017, 10:51 AM
weissfamily97 weissfamily97 is offline
 
Join Date: Jun 2017
Location: Decatur, IL
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Default Continental CD155 for RV-9A?

Can someone help me make sense of some of the data I'm seeing?

Cessna offers the 172 with a 180hp IO-360, as well as now with the CD155.
The CD155 is of course rated at 155hp.
From their book numbers, the traditional C172 has a max cruise of 124kts, and burns roughly 10gph of 100LL.
The Turbo Jet-A C172 cruises at 134kts (on less horsepower) and sips roughly 7gph of Jet-A.

That's significantly better performance (8% increase in cruise speed), for significantly less cost per hour (7 gph x difference in 100LL/Jet-A).

So, taking a leap of faith, in a -9A would it be safe to assume that using the CD155 instead of an O-320 would yield similar cruise speed enhancement? Fuel burn would be similar (only a little better), but you could take advantage of using Jet-A/diesel.

Has anyone done this yet for a -9/9A?
It seems like it might be a good fit (aside from price)...weight is similar.
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  #2  
Old 06-25-2017, 11:29 AM
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airguy airguy is offline
 
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Default

Turbodiesels are inherently more fuel efficient than our standard old-school Lycoming engine (with the exception of the newer FADEC injected ones) so the improvement in efficiency is not surprising. The improvement in speed is going to be another issue entirely, as that is going to be strictly a function of horsepower into the prop, prop efficiency, and aircraft drag. Cessna may have made quite a few other changes to the Jet-A model besides the engine.

As for doing it in a 9A, I would have one in mine today except for the ludicrous price of the CD155. I can buy an awful lot of 91E10 autofuel for my IO360 for the cost differential.
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  #3  
Old 06-25-2017, 11:37 AM
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DanH DanH is offline
 
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Default

Quote:
Originally Posted by weissfamily97 View Post
Can someone help me make sense of some of the data I'm seeing?
In a word....altitude.

Quote:
Originally Posted by airguy View Post
I would have one in mine today except for the ludicrous price of the CD155.
Can't just buy one right now anyway. Continental controls the program or you don't play.
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  #4  
Old 06-25-2017, 01:07 PM
RV7ForMe RV7ForMe is offline
 
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Default

funny you bring it up. I started looking at this question. Different config before I actually started building and even asked Vans and Austro engines about it...

The AE300 diesel at 170HP that is used in the diamonds is crazy reliable so far and has a far better track record than the Continental... but either way. The price of one of these engines is north of 65K and that is again a whole lot o Fuel. Not to mention Vans has a great design and if you go with alternative engines you are likely to extend build time by a few years....

Sad really I thought the RVs could be truly great platform.
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  #5  
Old 06-25-2017, 01:50 PM
weissfamily97 weissfamily97 is offline
 
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Default Diesel Experimental

[quote= The price of one of these engines is north of 65K and that is again a whole lot o Fuel. Not to mention Vans has a great design and if you go with alternative engines you are likely to extend build time by a few years....

Sad really I thought the RVs could be truly great platform.[/QUOTE]


For the IO-series, the experimentals are considerably less expensive than the certified versions. With that in mind, I did email Continental to see if there was any chance of adding experimental versions of their diesel engines. I haven't heard back yet.
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  #6  
Old 06-25-2017, 02:17 PM
BillL BillL is offline
 
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Location: Central IL
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Default Kinda two words, altitude & turbocharger

Since diesels will use higher compression ratio and the intake system is not throttled, they are limited on cylinder pressure. Turbocharging will allow the engine to be flat rated for some altitude yielding better power than the normally aspirated Otto cycle engine.

The diesels are have a box limit for cylinder pressure, exhaust temperature, and turbo speed. PCP on the ground, and either Ex-temp or turbo speed at altitude depending on the ambient temperatures.

All RV's fly pretty close to Vne, so allowing higher speeds with turbocharging might not get you much within the envelope. Starting with a 120hp turbo, now that is a different story.
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  #7  
Old 06-25-2017, 05:27 PM
weissfamily97 weissfamily97 is offline
 
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Default

Well, Continental does also have the CD135 (135hp).
Maybe that would be a better (more fuel efficient and less expensive) option?
I suppose that's kind of what I was implying in my original question.
Could you achieve similar/better performance with the CD135 vs an O-320?
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  #8  
Old 06-25-2017, 05:55 PM
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N941WR N941WR is offline
 
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Default Cost and weight

Take a close look at all the numbers.

I have an O-360 in my -9 and can cruise at 150 to 155 knots while burning around 7 GPH +/-, depending on the conditions, at 50 to 60% power.
75% cruise is right at 175 knots, if I want to pour that much fuel in it.

Up high I have seen as much as 159 knots while burning 5.2 GPH. While I would really like a diesel, at this time, I don't see the advantage of having one.
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  #9  
Old 06-25-2017, 06:45 PM
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Mike S Mike S is offline
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Default Welcome aboard!

Adam, welcome to VAF.

Any idea of the weight difference in the engines? Seems that could be a big factor....
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  #10  
Old 06-25-2017, 09:39 PM
weissfamily97 weissfamily97 is offline
 
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Default

Thanks Mike!
As near as I can tell, the diesels are about 20lbs heavier than a Lycoming O-320.
So, not too big of a deal.

Bill R. - thanks for sharing your numbers.
I was wondering if you could put an (I)O-360 in a -9/9A, as it's not shown on the website, and they specifically have a "why can't I put in a bigger engine" section.
Your 75% cruise (175kts, 201mph) puts you over the Vne.
Isn't that a concern?
I'm really new to Vans aircraft, so I'm really curious.
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