Re: PROs and CONs of Engine Choices
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Originally Posted by
nyrikki
I am moving closer to family in SW Wyoming, thus my obsession with head winds.
It dumping boost during takeoff is the concern, thanks for the feedback.
Not so much on takeoff as imitial climb. I know another guy with a non-intercooled 914 in Albuquerque that draws air from u deer the cowl with no cool air inlet. He's occasionally on the forums. I'll ask him if he's observed anything similar, as his should be the worst case scenario for airbox temps.
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Re: PROs and CONs of Engine Choices
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The max continuous HP is 80, can you provide any documentation that shows differently?
X340 liine card: Attachment 16333
The "340CC" manual was written to meet LSA requirements - the engine is stillcapable of the x340 specs (there are no limiters". You were refering to the x340 NOT the 340CC "manual".
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But these engines are also not sold as a normally aspirated, mags, fixed pitch so that is what you call a straw-man.
The 340 CC you are now refering to IS carburated AND fixed pitch - so it is not a "straw man".
Please don't insult my intelligence and tell me that CC buyers are spending north of 200k and running them per the manual. They are sham numbers.
The x340 does 166/180 CONTINUOUS and 75% is way north of 5.5 GPH.
Greg
Re: PROs and CONs of Engine Choices
I should have some numbers for all in a couple months. I am running a “modern” 340 with the efii system.
Re: PROs and CONs of Engine Choices
Re: PROs and CONs of Engine Choices
I asked forum member BobRS, who operates a normally-aspirated, non-intercooled 914-equipped S7 out of Albuquerque about the high airbox temperature. He says that he has not experienced his TCU limiting boost for high airbox temp.
He does report that hot starting is difficult, and he needs to let things cool down for 45 minutes or an hour prior to attempting a start, and believes this may be due to a hot airbox.
Re: PROs and CONs of Engine Choices
A 914 is not normally aspirated. It’s turboed.
I flew Stuck and Rudders 914. We didn’t start losing power until we did an extended climb for 5+ min. That was without using over boost. He also had a NACA duct that threw cold air on the filter that was directly on the turbo.
Re: PROs and CONs of Engine Choices
Dur... I meant carbureted.
Why would you mistake what I said for what I meant? ;)
Re: PROs and CONs of Engine Choices
A big factor that I'm not hearing about in this discussion is wing loading and power loading. While the power loading generally will be better with the bigger engines, many times the increased wing loading due to all the extra weight minimizes the extra power, resulting in similar, or even less overall performance. And almost always the lighter wing loaded airplane will be more fun to fly.
I like to fly seaplanes, amphibians specifically. And in that realm l have seen guys putting large engines in their seaplanes only to learn the smaller engined, lighter seaplanes will outperform them. Land planes are less effected, but the same general rule applies. Especially with small aircraft like the Kitfox that have small wing areas compared to something like a SuperCub.
But even in the SuperCub world big horsepower doesn't always help. A guy recently put a 260 hp 540 with a constant speed prop on his SuperCub floatplane. Yeah it was kinda cool, and made all kinds of noise...but it only marginally performed better than a 160 hp SuperCub. I call that the point of no return: Where the extra hp doesn't really offset the extra weight to the airplane, and the extra weight of the fuel needed.
This summer I was hanging out with the Just Aircraft gang and one of of them now has a couple hundred hours on his 340 powered Super STOL XL. He said he really loved all the extra torque of the 340, but that it also burns about twice as much fuel as his previous 912 equipped Super STOL. When I asked about performance differences he said a light 914 powered Super STOL is nearly as good on half the fuel. Now take that all with a grain of salt as that is only one mans opinion. But I think it is likely a realistic perspective of what to expect if going the route of the 340 on a Kitfox SS.
I personally would go for the 914 or 915 with the constant speed prop. Big bucks, but overall best performance IMHO. Again, I know it will be pricey, but you only go around once ...;)
Re: PROs and CONs of Engine Choices
As an update I am targeting the 912is Sport right now.
As most of you know the bing carburetors do do a fairly good job of altitude compensation until you hit main jets at high power levels which are not compensated and will be more rich.
With EFI this is less of an issue and even with the Bing carbs you could fly for a lifetime without having this be an issue...but we all have our own personal minimums and levels of acceptable risk.
Technical reason for those who care.
Bing CV carbs are almost certainly altitude compensating better than most pilots but only to about 50% of the optimal mixture due to Bernoulli's equation. So the higher you fly richer the mixture will get even at power levels below 75%. I am conservative on this topic but it is important to remember that on Bing CV carbs altitude compensation do not change the mixture the main jets.
With the warning that you should take these following numbers as examples and not as set in stone:
idle to ~ 25%: Idle Jet
15% to ~ 80%: Needle Jet
65% to 100%: Main Jet
Note: As the main jet is not altitude compensated on the Bing 64 CV carbs the mixture will be richer above ~75% than below
(IIRC).
If we choose those random numbers of 100 % at 100' MSL and 75% at 7000' you will be producing somewhere around 60-65% or less at full throttle with a sea level sized main jet. The important part is that you should expect more power loss at takeoff power in any Bing CV equipped engine than you see lower in the power band.
To be honest isn't a huge concern if you plan for this additional drop in power on the top part and/or an occasional visitor.
The Bing CV carbs are probably safer than the problem of pilots failing to lean the engine for maximum RPM at altitude with a mixture control. But remember that a nice idle or acceptable if larger cruise fuel burn doesn't mean you will have the same performance at the top end when the main jets are the largest source of fuel.
The additional weight for FI and x340 is what drove my decision when I cataloged what I would want to typically take on a weekend trip. While the x340 would have more than enough power even rich I think that trying to lean to maximum RPM at full throttle during runup with 180HP on the front on the carb version would be a bit past my comfort zone in a light taildragger too. I am making no claim as to if there is actually at risk of a nose over but it is beyond my personal comfort levels.
As a reminder, this post is opinion and very specific to my decisions, desires, and wants so once again take all of this with a grain of salt. Hopefully this will help others decide to look into this themselves or possible remind people that they need to leave some head room for larger power losses at high DA with Bing CV carbs at high power settings.
Obviously if you only fly at altitude changing the main jet would also be an option as long as you remembered to be careful at lower altitudes where you will be too lean.
For the vast majority of people using Bing CV carbs a small increase in fuel burn is probably the only result of this behavior. For those with engines and a mixture knob remember to lean for RPM during runup above 5K MSL or AD.
Re: PROs and CONs of Engine Choices
I am assuming that all who prescribe to the economy of the Rotax as the best choice for our aircraft, all drive a Prius...:D:eek: I kid... I kid...
All kidding aside, I am not interested in the best fuel economy. The Kitfox flies just fine with a 340. Otherwise Kitfox Aircraft would not have shown the world what it was capable of with this engine.
I don't drive a Prius nor do I worry about what my MPG is at any given day. Does a 340 burn more gas? I am sure it does. Will it out climb a 912 is? I am sure it will.
To each his own, I choose a different path. Catch me... if you can! :cool: