Cowl - Carburator intake curiosity

[Bcone1381]

Just ran across some photos that I took during a random walk at Oshkosh last summer. How do you think the builder of this experimental Cub variant with an O-320 engine eliminated the external carb intake? Do you think that the cupped and screened air intake (on the aircrafts right side of the cowl inlet) leads to the Carburator?
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[Battson]

That's easy

You simply install a 95 degree (or 110 degree) elbow where the carb body normally attaches, and bolt the carb to that. You then install a filter housing, possibly a custom-made one, and run a SCAT duct to the intake point of your choice.

We did something similar with our Bearhawk, after a LOT of research and thinking about a lot of designs like this one you've mentioned here.

We thought about an intake in the cooling air intake, but we didn't like it for two reasons:
1. You are robbing precious cooling air pressure from the engine. Especially when you need full power and full cooling at once, like every time you climb!
2. The -540 engines need a LOT of air at full power, and we didn't want to starve the engine with a small SCAT duct with twists and turns. Better to have ram-air straight from the prop to the induction.

Here's a photo of what's under our cowl, to give you an idea of what I am trying to describe.
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[Bdflies]

Could be that he used a forward mounted carb system:

http://shop.aeroinstock.com/p-39640-cold-air-sump-kit-o-320.aspx?_ga=2.176415202.674716979.1513310174-919016800.1452568087

If that scoop is his carb air intake, I'd like to see his WOT manifold pressure. MAP translates directly into power. Any induction restriction reduces MAP. I'd guess he has at least 18" of 3" SCAT tubing, leading to his filter, then to the carb. Not ideal, if that's what we're seeing.

Bill

[Bcone1381]

I am on the fence about weather to go with a Carb or Fuel Injection. I thought I had my mind made up (FI) then I called and talked with Bob.

Cleaning things up on the lower cowl is one of my goals. A vertical carb w/Carb Heat Box sticking out the bottom of the cowl appears standard. I understand the 90 degree elbow, or the forward mount intake. Up to now I had thought those were systems specific for FI. I wasn't aware of horizontal carburetors and wonder about their availability... They don't seem widely used to me. The Cub variant was the first I had seen with a carb with no intake out the bottom of the cowl.

Bob's main argument for a Carb was better in the back country, and economics...that one will never recoup the extra cost of FI due to fuel savings. The Simplicity of No Carburetor Heat, No primer, ability to fine tune individual cylinder fuel delivery for lean of peak ops, elimination of carb ice....I am on the fence. saving .5 gallons an hour in fuel is about $2.20/hour = $4400 every 2000 hours.

Enlighten me. Maybe I dont understand the advantage of a carb in the back country. Sell me on the Carburetor if you think its better. Tell me why you chose what you did.

[Bcone1381]

Additionally, My goals in this decision is simplicity, safety, and making the build easily achievable. Its not an improvement if those values are compromised. I don't want to be in a position where a decision I make an improvement results in a plethora of complex issue to solve that I could not have envisioned. I want it to be well thought out.

And I kind of think I should stop thinking and asking questions. If I do, I think Bob will build meet my goals of this build which is Safe, Simple and Achievable.

[Bdflies]

OK Brrooks, you asked for it! I have an O-360 A1A. Got a black cast iron Marvel Shiebler updraft carb, just like the ones on old Massey-Ferguson tractors and Lincoln welding machines, hanging on the bottom. I did install a plunger primer, but have used it exactly one time. That was the first start. Didn't really need it. Hot, cold, warm, sunny or cloudy, one stroke of the throttle when I hit the starter and she lights right up. No engine mounted diaphragm pump and no airframe mounted (expensive) boost pump. No breaker, switch or wiring to the boost pump either. If there's gas in the tanks, gravity gets it to the ugly old Marvel Shiebler. When I say she lights right up, I don't think I've ever seen 3 blades before starting.
Injected engines are a bit different. Cold, there's one procedure. Hot, you do it different. Kinda warm, well, you learn what works most of the time. If you have a big enough battery, don't worry abot it....you'l probably start it on the third or fourth try... Lately, I've been flying an R-44 with an IO-540. Cold starts are a breeze. Stop about 15 minutes and visit with friends...and it's kind of a coin toss. Good thing is that the Robbie has a HUGE 24v battery and I think it could hover on the starter alone! If you're not installing a HUGE battery, I'd install a ground power port. But, does that beautiful back country strip have a start-cart? Bendix style injection systems, on Lycomings, are archaic, to say the least. Not as archaic as carbs, but close. Constant flow port injection might be better than an updraft carb, but only slightly, at best. The biggest issue is the placement of the gas distributor (spider) on top of the hot engine! Can you say 'vapor lock? Who ever thought that was a good place to put it? Yeah, I know, that location makes it easy to have equal length injector lines... I recall that there's a Patrol flying, with the new EFI / EI system. Maybe we could get an update on that system?
OK, so you learn how it likes to be started and you say Bill's full of bull. Are you gonna install a fuel pressure gauge? Is your boost pump gonna have high/low boost switches? High boost on takeoff and low boost in flight? Or no boost in flight, but a low pressure warning light on the panel? So, in addition to the boost pump circuit(s), don't forget the fuel pressure gauge/light circuits.... I think I'm getting a headache... Wait, how much gas is injection gonna save?
Do injected engines run well? Yep! Carbs do good, too. If you want an opinion (which is what this forum is all about, isn't it?), save the injection $$ and install an electronic ignition unit. Now THAT makes a difference!
Remember, opinions expressed here are guaranteed to be worth what you pay for them! Now let's hear from the pro-injection guys...

Bill

[Bcone1381]

Bill,

What kind of ignition system are you running?

Do the Marvel Shebler Carbs require seasonal adjustments? Are Carbs less demanding of maintenance and servicing than a Bendix style mechanical FI system?
__________

The FI system I lean towards is AirFlow Performance FM150 kit. Its mechanical, not dependent on an electrical system. It has One mechanical engine driven pump, one simple electric back up. No need for fuel pressure indication. But, will Airflow be servicing these in 15-20 years, if not who will....probably no one because its a small specialty item for our market that is ever changing and improving. So, its back to a Bendix system.

The electrical dependent FI has benefits, but it is not something I want to pursue.

My desire is to have this topic produce valuable information. I know folks will feel strongly one way or another. Like Bill, pass along the information as you see it.

I change my mind every time I listen to someone. The lean of peak thing was witchcraft back when I was leaving the reciprocating engine arena. Information is not as good as experience.

[Bdflies]

No carburetor adjustments required. I'm running one Emag 114 and 1 Bendix mag.
I'm probably mis-remembering something, but I think I recall that Continental was happy with LOP ops, but Lycoming does not approve such.

Bill

[JimParker256]

Bill,

I've made the decision that I will follow Bob's advice and go with a carbureted engine on my Patrol. I read very similar advice over on the Back Country Pilots forums. I understand the carburetor's operation and failure modes, and pretty much any mechanic anywhere can help you out with one – not to mention that odds of finding the part you need are a LOT higher with a carburetor than with one of the experimental fuel injection systems. Then there's the whole "don't fly behind something you don't fully understand" aspect... The factory systems are complex enough, but some of the experimental ones are... well... challenging to understand. The ones that are well-engineered tend to be poorly documented – at least to this retired IT guy...

Then there's the whole "starting issue" discussion... Having lived with an IO-540 engine (Commander 114), I grew to really dread having to start the engine back up after a fuel stop... Cold starts were fairly straightforward (most of the time, anyway – but every once in a while...). But both warm-starts and hot-starts were a royal PITA. I have tried every "sure-fire" trick people suggested to me, but NONE of them worked 100% of the time. I always prayed that I would find the right combination BEFORE I ran the battery down... Succeeded more often than not, but it's not something I want to experience out in the bush somewhere... I won't miss THAT aspect of factory fuel injection at all...

They tell me that the 3rd-party experimental fuel injection systems don't have the same issues as the Lycoming systems, because they run fuel back through a return line, ensuring that vapor-lock is minimized. That's all well and good, but then you've got to deal with either return lines back to the fuel tanks (doubling the plumbing issues), or using a "header tank" somewhere in the cabin. Reading through NTSB reports quickly soured me on that idea – the risk of post-accident fire is significantly higher with ANY fuel tank in the fuselage, and I don't like that prospect at all...

So I will follow Bob's advise, and keep it simple with a carburetor. The fact that I'll save some money up front is not too shabby, either.

As for Lean-of-Peak operations with a carbureted engine: It IS possible, if you can get the fuel/air mixture distribution a bit more even. The Grumman Traveler I owned a few years ago could be flown LOP at about 65% power, by opening the carb heat just a little bit – just barely cracking it open. Somehow, the airflow into the carburetor changed just enough to even out the fuel/air distribution to all four cylinders, making it possible to run at about 50º LOP. That trick doesn't work for all aircraft, but seems to work on "most" of the 180s that use carbureted O-470s. (Learned that trick at the Advanced Pilot Seminar – best value in aviation education!)

But experimental aircraft have other options: a friend of mine installed a simple X-shaped "flow divider" just upstream from his carburetor. It's just a piece of tubing with an x-shaped sheet-metal insert (aligned with the airflow) that basically causes the airflow to "straighten out" before entering the carb. By changing the alignment of that flow divider a few degrees at a time (like 30º initially, then splitting the difference to optimize), he was able to have all six of the cylinders on his engine reach peak EGT within a pretty narrow mixture range, so LOP operation was possible. That's something I will definitely try when I do my engine install...

[MitchG]

I'm waiting for the release of this system.....It checks all the boxes for me! Their new "System 32", a more polished version of a proven package.

[Mark Goldberg]

Their system looks interesting. But it does take some courage to be an early adapter of an aircraft fuel system. Mark

[Zzz]

I'm waiting for the release of this system.....It checks all the boxes for me! Their new "System 32", a more polished version of a proven package.

This is what I am using, and have the system partly integrated from the fuel plumbing design standpoint. You will learn that the technology invites a lot of naysayers. I often don't volunteer this detail because of that reason.

[Bdflies]

NAAY! NAAY!

Just kidding.. I think a fully integrated electronic ignition / fuel controller is going to be the ultimate solution. The automotive industry certainly had it's teething pains, but that's all sorted out. Hopefully, the EFII system has taken advantage of lessons learned in cars. I'd ABSOLUTELY like to upgrade to a FADEC system, at some point in the future! It's the guys who take the first leaps who'll pave the way for the rest of us. Please keep us informed about all the little details, when you start flying!

Bill

[Bcone1381]

I am a Nazarene, my Brother is a Presbyterian, my Father in Law is Catholic. I love them dearly, and (I think) they Love me. An attitude of Grace, Humility, and a hunger for knowledge gives a great foundation for our group to learn and gain knowledge and wisdom. I know people have strong feeling about Fuel Delivery and they have spent a lot of time and money to apply there decisions on their aircraft. Thanks for chiming in.

If I can run 50 degrees lean of peak at 65% hp, get equalized fuel delivery to all cylinders with a cracked throttle, or carb heat, or a flow divider, then a Carb is fine with me. Its simple, safe, and makes the build achievable. But "IF" means uncertainty.

I admire and eagerly watch builders like Zzz. I am an optimist regarding this kind of Tech. But I want my aircraft to have a simple fuel system with a L-Both-R fuel selector. Unfortunately, EFII injection system requires fuel return lines or a header tank so it doesn't fit well with my personal design goals. Airflow Performance's system seems pretty straight forward to me.... Is anyone running that system?

[Mark Goldberg]

It has been around a long time and has good reputation. MG

[svyolo]

Early FI's, both mechanical and electrical were a giant PITA. From about the early 90's on, it is ridiculously simple and reliable. It is more complicated in a car, as a car engine interfaces with a bunch of other things including the transmission and EVAC. On an airplane, it gets real easy, real quick.

The only reliability issue is wiring, connectors, and keeping the juice flowing to run the whole thing. Every car on earth has one battery and one alternator. That has been sorted out for decades. But properly installing the wiring, and using good quality automotive style sealed connectors is what makes it run reliably.

I really, really, want to run an EFI, but I might start out with a carb. IMHO, an airplane is about the last application where a carb makes sense. Airplanes run at fairly high power, steady rpm. With mixture control you can do pretty good.

Fuel injection can actually be done fairly cheap. I have done it once from scratch once on a single cylinder motorcycle. But SDS and EFII have a couple of features that I will gladly pay their price.

Modern cars run so clean their spark plugs last 100k, the engines run forever, and you don't even have to change the only but every 10-15k. SDS and EFII both use a lot of automotive parts, including injectors, ignition components, coils. I would bet a well sorted Lycoming with one of their EFI systems will run way past TBO, and save 3000 gallons of fuel between TBO's. And I would bet the engine is in a lot better shape when you do rebuild it, saving more. Personally I think the EFI pays for itself. It will also start on the first blade or two, hot or cold. If you have an electrical system to start the engine, that same one will run the engine. Running LOP is like adding 7 or 8 gallons to the fuel capacity of the BH or Patrol.

All that being said, my Bob engine is coming with a rebuilt carb. I am still on the fence if SDS and EFII are well enough sorted out for me to trust my life with them.

But modern EFI and EI are vastly more reliable than carbs and distributor ignitions. I just don't know if the ones on airplanes are.

FADEC? Add an electronic throttle, and you have a FADEC. That is it. You can pull one from a car of similar horsepower, and the gas pedal sender. SDS and EFII aren't offering that, but there is no reason they couldn't do it in the future. Many cars have used them for over 10 years.

I had an engine conversion business for about 3 years. I put Subaru motors in VW's. Install it, plumb it, and when you plug in all the sealed, gasketed connectors, turn the key, they started when the first cylinder went past TDC. Every time. And they ran perfect, without tuning anything. For me, that is simple.

I think I am talking myself out of using the Carb. LOL

[svyolo]

I am definitely still on the fence. I will try to make it to Sun n Fun and get some hands on. I could still end up with a carb.

[old pete]

i had a bendex fuel injection on my little toot biplane with a 360-a1a and never had any issues with hot starts or any problems starting in general. i had over 350 hrs of trouble free use out of it. it will be going on my bearhawk as well. I flew it a lot in Michigan and again when living in Texas and never had any issues with starting. and yes i did fly an open cockpit biplane during the winter in Michigan but that was when i was in my 20s.