Cowl - Carburator intake curiosity

[Battson]

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.

Maybe Bob never did the math on lean of peak operating, we paid our's off in 100 hours. The fuel savings are huge, at least 15 L/h and could be as much as 25L/h if you wanted to slow down a bit. I didn't realise how good it was before I ran the engine myself. I would NEVER have a carb, knowing what I know now.

You can still hand-start a fuel injected plane very easily, you just need a small backup battery to prime it. I have such a battery because of my EI, so I am good. Modern ignition and FI go hand in glove.

Edit to add:
Reliability and maintainability wise, they are the same in my view (talking Bendix injection). Any mechanic who can only work on carbs would be retired by now, and mechanical injection is probably as reliable or more reliable than a carb in my view.

Also - the hot start thing is a hangover from various certified aircraft. My buddy and I did a fuel injected Bearhawk each, and both start dead easy (any temp) and behave exactly the same. There is no mystery to it, you just need to know one basic rule.

[whee]

Even the Beach Boys understood

[svyolo]

Battson, what type of FI are you running?

[Battson]

Battson, what type of FI are you running?

Old school Bendix, an experimental variant by Airflow Performance.

[svyolo]

I still have about 6 months to decide what route to go. EFI has a couple of advantages over the MFI, and vise versa. I do like that MFI and EI use very little electricity. The start battery will run the EI for several hours.

One of the reasons I want EFI is that it is using the same sensors and computer as the EFI. The EFI adds a few, (engine temp, Intake air temp, TPS) but those are not that vital and the engine can be run with them failed. The MAP, crank trigger, and ECU(s) have to function for the EI, but they are also used by the EFI. Same ones. The big negative of EFI is the injectors each use about an amp, and running one fuel pump takes 4 amps. For a 6 cylinder, that is an additional 10 amps. Add in the EI and the engine is using 12-14 amps. Still hopefully 30-45 minutes off the start battery, or double that if I have a second battery (I am not planning 2 batteries).

Still on the fence, and getting all the input I can. It sounds like Gami has sorted out balancing their injectors for each customer, so that eases that concern. The EFI's allow individual fuel trim at each injector. Both should run very well balanced.

This is definitely thread drift from he original. Sorry.

[Bcone1381]

I am building a Patrol, and talked with both Bob Barrows and Don at Airflow Performance Inc. today. (API rebuilds certified FI systems, and manufactures FI systems and components for experimental aircraft.) I think I finalized my engine order. Those two and this thread helped. I won't know if I will be happy with today's decision until I have 100 hours on the airplane.

Bill, Battson, Jim, Svyolo and others... thanks for your input.

Two Questions for Battson, Do you use Airflow Performance's Purge Valve? Whats "the one basic rule"?

This thread started out asking about cowlings and carbs....but it really was about carbs and FI. Working thru this, I feel like I am dealing with two very honest business men who are easy to contact and have my best interest in mind. Bob Barrows form the engine, and Don at Airflow Performance Inc for the Fuel Injection questions.

Bob will be building me an engine...an IO-360 with a Bendix RSA FI system. When he builds a FI engine, he sends the Bendix RSA unit to Airflow Performance for overhaul. The injectors will have an ability to be tuned (Like GAMI injectors) so that when leaning the peak EGT will be reached by all four cylinders simultaneously.

I asked Don "Sell me on your system compared to the Bendix that Bob is offering me." Don said "If you can get a better deal on the Bendix, use it. Both systems will do the same thing."

[Battson]

I am building a Patrol, and talked with both Bob Barrows and Don at Airflow Performance Inc. today. (API rebuilds certified FI systems, and manufactures FI systems and components for experimental aircraft.) I think I finalized my engine order. Those two and this thread helped. I won't know if I will be happy with today's decision until I have 100 hours on the airplane.

Bill, Battson, Jim, Svyolo and others... thanks for your input.

Two Questions for Battson, Do you use Airflow Performance's Purge Valve? Whats "the one basic rule"?

This thread started out asking about cowlings and carbs....but it really was about carbs and FI. Working thru this, I feel like I am dealing with two very honest business men who are easy to contact and have my best interest in mind. Bob Barrows form the engine, and Don at Airflow Performance Inc for the Fuel Injection questions.

Bob will be building me an engine...an IO-360 with a Bendix RSA FI system. When he builds a FI engine, he sends the Bendix RSA unit to Airflow Performance for overhaul. The injectors will have an ability to be tuned (Like GAMI injectors) so that when leaning the peak EGT will be reached by all four cylinders simultaneously.

I asked Don "Sell me on your system compared to the Bendix that Bob is offering me." Don said "If you can get a better deal on the Bendix, use it. Both systems will do the same thing."

I didn't order a purge valve, and neither did my buddy here with a FI Bearhawk. Neither of us missed it. I'll give some background about our planes.

Both our engines start exactly the same, despite being slightly different fuel systems firewall forward (layout etc). I have run both quite a bit. In my view, the vapour lock problems only come from certain variations on the basic fuel system design, variations which put large heat-sink devices firewall forward. Particularly, designs which put fuel transducers or backup fuel pumps near the hot parts of the engine or firewall. Many certified planes do this. It means a decent volume of fuel could get hot enough to vaporise.

We put all our pumps, transducers, filters, gascolators, etc aft of the firewall. Our fuel lines enter the hot side of the firewall at the LOWEST possible point, so cold fuel sits there under a head of pressure, and does not vaporise or drain back too far. The run to the engine pump, RSA servo, and to the spider has NO big metal parts, only hose. They have fire sleeve over them too, from the engine driven pump onward. We prime using the electric fuel pump, which is under the pilot's feet. We both also have a horizontal air induction, so primed fuel doesn't drain away, it sits in the intake for the start.

Given that setup, both planes have NEVER vapour locked, and both start every single time.

The underlying cold start is:
Start full rich, prime for 5 seconds.

Hot / warm / tepid engine start - the CHT doesn't really matter, provided it's above ambient air temp AKA hot start:
Always start full lean.

Here's my hot start rule:
Prime for at least one second. Add one extra second for every 30 minutes cooling time, up to 3 seconds max.

Here's an example of the rule:
0 minutes since shutdown, 1 second
30 minutes since shutdown, 2 seconds
60 minutes since shutdown, 3 seconds
90 minutes since shutdown, 3 seconds

A very hot engine needs only 1 seconds priming just to re-pressurise the fuel system, nothing more. A tiny amount of fuel will have collected in the air intake with that short blast of the fuel pump, so you don't want to over-prime and flood it. If you flood it, you will have to crank for about 10 seconds to clear it. But it will start eventually. Rest the starter motor every 6 seconds.

On a day with 30 degree Celsius (85*F) ambient temp, even if the CHTs are only at 40*C (105*F) I will still use the hot start. It's reliable, more reliable than assuming the engine is ready for a cold start.

[svyolo]

Battson. Great post. I took a screenshot and will archive it.

[Bcone1381]

Battson,

Great post is right! Thank you so much for documenting your well thought out measures to mitigate hot starting. That is probably my main concern with FI, and it build confidence by helping me understand what the causes are, and your wise remedies, both physical remedies you made in your design, and operational procedures you shared.

What type of ignition are you using?

[Battson]

Battson,

Great post is right! Thank you so much for documenting your well thought out measures to mitigate hot starting. That is probably my main concern with FI, and it build confidence by helping me understand what the causes are, and your wise remedies, both physical remedies you made in your design, and operational procedures you shared.

What type of ignition are you using?

Thanks - I just hope it's helpful.

I have been using Bendix mags, with L mag impulse coupling. Not my first choice, but affordable.
My buddy has Slick Mags maybe, I think, but definitely with shower of sparks starting (does Slick do that, maybe he's Bendix too?).

By the by, I just changed to Surefly SIM mags (which is actually EI). I will report back.

[schu]

I did extensive research on this years ago, and came to the same conclusion as Battson. The Airflow Performance Setup is the way to go in my mind. Here is what convinced me:

1. You don't have the hot restart problems as other FI systems because you can install the purge valve which when combined with the boost pump puts cold fuel back on top of the engine.

2. You can still hand start the engine if you can just get it primed, which doesn't take much battery. I'll probably install a small solar cell in my windshield, or keep one in my kit. I figure I can charge the battery enough to run the boost pump for 2-3 seconds in an emergency and get it going again.

3. LOP operations save a LOT of fuel. Like 25% or more. Aircraft engines are air, fuel, and oil cooled. At 65% and at altitude, you don't need the fuel cooling. LOP with a carb is a roll of the dice. You might be able to make it work, but you might not.

4. A carb setup that is gravity fed has been known to not flow enough fuel with a fuel transducer, so even if I had a carb, I'd almost certainly still need to have a fuel pump. I'm not interested in building a new airplane without a fuel computer, and if I'm going to run a fuel pump, I want an electric and mechanical pump. I bought an Andair, it's really really nice.

5. I don't want a carb heat knob, or the plumbing, or the box, or the cable control. I want horizontally mounted that's clean, easy to fab, and performs well.

6. I'm not totally sold on EFI systems. They are super expensive, require electricity, require special fuel valves, need electronics to talk to a fuel computer, etc.... The only thing they really offer in my mind is electronic ignition (which has actual timing advance.) I'm sure they run amazing and smooth, but not $3k-$4k more amazing and smooth than Airflow Performance, and you aren't going to hand prop them.

Airflow for me, and if Don goes out of business, then someone else will take over, and if not, I can always go back to a bendix or even a carb. Remember, there are a LOT of people flying airflow (like redbull air-race planes) I suspect they will be around.

[jaredyates]

I'd like to say that this thread is a great example of the fantastic contributors that we have in this community. Thank you to everyone who participates, and especially to the experienced Bearhawk operators who could just as well stop coming around once their airplanes are built. We have some high-quality people around these parts, and I really appreciate them all!

[svyolo]

We are all a product of our experiences. We all have different comfort levels based on that. I guess it comes down to what makes you comfortable when you are flying over rugged terrain, 200 miles into no where, and want to make sure you get home. For some that is a carb and magnetos. I really want an EFI, but I want to have a little closer look at what is available. I might be just as happy with a mechanical FI.

[schu]

Here is the scoop on EFI: You basically have two systems, SDS and EFII. They both have 4 basic parts.

1. The injectors which you install in bungs, or into the factory injectors holes,.
2. Fuel system which is dual electric pumps, and plumbing back to the tank because they need a loop.
3. Crank position sensor
4. throttle body
5. Spark plug coils
6. Computer box
7. Controller box to go on the panel

The rub is that you really want redundancy, and it's not that simple. Generally speaking you have multiple injectors, spark plugs, coils, and fuel pumps, so no worries there, the question is the computer box, and how to wire two of them to the same set of injectors.

The SDS system as far as I understand uses a simple mechanical relay setup to deal with that problem, and the EFII System 32 does it all solid state, with a screen that switches between the two.

So one could argue that the EFII is better engineered, but non are flying that I know of.

http://www.flyefii.com/system-32/

or

http://www.sdsefi.com/lycoming.htm

Price looks to be around $7500 for a dual CPU 540 setup, but that pays for Mags too if you don't already have them.

The system really isn't super complex, and I bet it runs awesome on any fuel, but for me, I'll stick with mechanical fuel injection. I want to be able to hand prop, at least for now.... I can always swap it out later

schu

[Battson]

That is the longest list of 4 parts I have ever seen
I know how those typos happen as the thoughts flow onto the page!

[schu]

Hahaha, yea, I meant to fix that.... I won't now....

[svyolo]

I want to hand prop as well, and Ross at SDS doesn't "recommend" it, but says it has been done. I don't have the SDS pinouts, but EFI normally has some parameters to complete to start easily. One is the "start" signal. When you crank the starter, the same 12v goes to the ECU, to tell it to start. The ECU enriches the mixture, and changes the timing, to make it easier to start. I have screwed up a wiring harness and forgot the start signal wire. It still started, but took several seconds of cranking (subaru).

Ross also said the crankshaft had to rotate a certain amount to start. I don't know how many magnets he uses as triggers on the flywheel. Maybe a couple of pulses from the crank trigger.

Hand starting should just require putting the propellor in a position to fire when you hand prop it, give the computer the inputs it needs manually, and then hand prop it. It should work very reliably. You could have a 6 foot long "jumper" that plugs into the panel, and 2 momentary switches to give the computer the right inputs before you hand prop it.

For me, my comfort zone is EFI. But, I still haven't decided. Running the engine will be 75% of the complexity of the electrical system. Sounds like some builders have sorted out the mechanical fuel system so it starts reliably. That satisfies all of my concerns with mechanical FI.

The same sensors that operate any Electronic ignition uses to function, the MAP and crank trigger, are also used for the primary control on the EFI. There a few more, but they are just "trim". The engine will run without them. You would just turn the mixture knob to rich to make sure you are running ROP. Both SDS and EFII sell an ignition only system, and the full EFI just uses the same sensors to run a 3D fuel map as well as a 3D ignition map. To my mind, if I trust the two primary sensors to run the ignition, then I also trust them to run the Fuel system. If they fail (there are 2 each), the engine doesn't run whether it is fuel or ignition.

I still have at least 6 months to decide. Learning a lot, between here and VAF forums.