TCONROY

TCONROY

Well Known Member
I'm an RV-7A builder with the emp complete and wings on order. I know I'm at least a year and a half away from needing a fuel pump, but I'm trying to educate myself now so I know what to buy later with the fuselage. Can someone explain why the Andair pump and filter being offered in the group buy is better than the one from Van's? I've seen pictures of all the tubing that must be bent in the "tunnel" to connect the Van's fuel pump, selector, injected return line..etc. Does the Andair assembly eliminate all that fuel line that must be bent for the various items in the tunnel?

Any input would be appreciated.
 
TCONROY said:
I'm an RV-7A builder with the emp complete and wings on order. I know I'm at least a year and a half away from needing a fuel pump, but I'm trying to educate myself now so I know what to buy later with the fuselage. Can someone explain why the Andair pump and filter being offered in the group buy is better than the one from Van's? I've seen pictures of all the tubing that must be bent in the "tunnel" to connect the Van's fuel pump, selector, injected return line..etc. Does the Andair assembly eliminate all that fuel line that must be bent for the various items in the tunnel?

Any input would be appreciated.
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The Andair pump does reduce plumbing complexity by offering an option of going with an internally regulated pressure system. Instead of requiring a return line (or external loop) for fuel by-passed by an external regulator, the new Andair does all this internally. The electric pump currently used is not internally regulated and will produce over 100 psi if not regulated.

The problem I have with the concept is heat. Fuel circulated back through the pump, be it through a loop or internally within the pump, is going to heat up, the heat being generated by a the pump motor and pressure. That is not a good thing. As the temperature of fuel goes up, its vapor lock thresh-hold goes down.

I prefer to send by-passed fuel back to the tank where it has a chance to dissipate its heat. Yes, it is a pain in the butt to do with the 6 hole selected and an extra line to the tank, but it is a better system.

The increased temperature of fuel does not matter a whole lot so long as the pressure is up but when the pump is turned off, that warmed up fuel will be sucked forward by the engine driven pump and that's where it becomes marginal. If Andair is run continuously, it may not matter.

Just my 2 cents worth, or maybe worth less than 2 cents.....:)
 
Trevor,

One other small detail that has not been mentioned. You only need these fancy, high dollar pumps if you are going to install fuel injection.

If you are going with a carb, then you can use the $42 facet pump.
 
Good thread as I'm ready to buy a pump and filter. A guy brought this Andair setup to our last EAA meeting and it sure looks sweet. Very simple, clean, and a lot less fuel connections. Maybe even quieter?

I'm interested what everyone's comments are on this one as I am still on the fence.
 
Here's what Andair was showing off at OSH09. A much simpler install then the AFP pump IMHO. You do however still have to order a few of the pump housing parts from Van's.

IMG_2865.JPG
 
easier retrofit??

Looks like the Andair setup will make for an easier retrofit if one were to go injected from a carb setup. No returns to the tank to install, fuel valve reused, etc.
Not to worry about internally regulated pump technology IMHO. Gazillions of miles in recent automotive applications have proven these pumps to be every bit as reliable as bypass type systems. As for hot fuel at the injector on a restart, well I see concern, but the fuel pressure in the line forward of the pumps impeller is under substantial pressure, precluding vapor formation.
That's what I kinow, now for what I don't.
I am an auto mechanic for a living, and fly a carbureted RV, and I am not too familiar with aircraft injection system specifics. None the less, I wan't to learn more.
My question is, don't most FI systems need pressurized fuel to the injector body over and above that delivered by a diaphragm engine driven pump? If so, it would seem a backup electric pump is in order. I have seen installations that use parrellel pumps for redundancy, and some that use just a single roller vane pump to supply pressure. Looks like the AFP setup uses a backup pump, and I am familiar with how fuel is metered in this type of system.
What are the basic differences in the systems, and their fuel requirements?

Thanks a million,
Chris
 
carguy614 said:
What are the basic differences in the systems, and their fuel requirements?

Thanks a million,
Chris
Click to expand...

A basic difference is the aircraft system will operate without electric power. The engine driven mechanical pump is all that is needed and it provides a head of pressure to the controller, from there through the flow divider and to the injectors the pressure is very low, like 1 to 3 psi. It is not like pulse time injection in an auto which is high pressure right up to the injector. These injectors are a fixed open orifice.

The electric pump (Andair or whatever) is a back up if the mechanical pump fails. Unless the electric pump is on, fuel is literally sucked by the mechanical pump from the tank through selector valve and the electric pump plumbing . Fuel can not be sucked through the electric pumps offered by Vans or AFP, they need an alternate route and have it.

What provision the Andair has for fuel flow through it when it is not operating is unknown. It must have a by-pass feature when it is not powered or it would not work. There always is a pressure drop across a check valve of any type when fuel is sucked through it and it is potential point of fuel vaporizing if it is hot.

So far as fuel type is concerned, all I know is the AFP system will run on anything. But I don't know about the innards of the mechanical engine pump. It has seals that go back to when dirt was invented and may well dissolve if some ethanol hits them.
 
carguy614 said:
snipped
Not to worry about internally regulated pump technology IMHO. Gazillions of miles in recent automotive applications have proven these pumps to be every bit as reliable as bypass type systems. As for hot fuel at the injector on a restart, well I see concern, but the fuel pressure in the line forward of the pumps impeller is under substantial pressure, precluding vapor formation.
That's what I know, now for what I don't.
Click to expand...

Chris,
The Bendix designed fuel injection used on Lycoming engines only uses about 25 psi, so it is not as resistant to vapor formation, when compared to the latest automobiles [40 to 60 psi]

carguy614 said:
I am an auto mechanic for a living, and fly a carbureted RV, and I am not too familiar with aircraft injection system specifics. None the less, I want to learn more.
My question is, don't most FI systems need pressurized fuel to the injector body over and above that delivered by a diaphragm engine driven pump? If so, it would seem a backup electric pump is in order. I have seen installations that use parallel pumps for redundancy, and some that use just a single roller vane pump to supply pressure. Looks like the AFP setup uses a backup pump, and I am familiar with how fuel is metered in this type of system.
What are the basic differences in the systems, and their fuel requirements?

Thanks a million,
Chris
Click to expand...

I'm also an auto mechanic. 95% of the time, a Lycoming is using ONLY the 25 psi mechanical fuel pump. The electric pump is for added safety [during take off and landing phases] and also as a redundant pump.
The Basic pump used by Airflow Performance [and sold by Vans] was originally used on GM's first electronically fuel injected vehicles. Specifically, the 1975 to 1979 Cadillac Deville and Olds Toranado. The only variant of these cars to be fuel injected used the Olds, 350 V-8 engine. The system is very similar to the port fuel injection system GM put into wide spread use in 1986. The earlier injection system was open loop [no oxygen sensors or catalytic converters]
The Bendix [and Airflow Performance] fuel injection systems are purely mechanical. The closest automotive equivalent is the mechanical Rochester fuel injection used on late 1950s Corvettes.
If you are interested, I can supply you with lots of literature [including manuals] on the Bendix injection. Just drop me an email or send me a private message with your email address. I'll send the tech literature I have to you.
Charlie Kuss
PS Bosch CIS fuel injection [early style] is not to far off of what a Bendix FI system is.
 
Injection priciples.

Charlie and David,
Thanks so much for the info.
I am familiar with the CIS type of fuel injection that the aero systems use, but was unsure about what the pressures are. It is basically like Bosch K injection, except Bendix and AFP types use a differential diaphragm as opposed to a vane plate that weighs the incoming air. I now realize that the engine driven pump delivers adequate pressure to operate, and does not need the backup vane pump at cruise settings. There are some systems out there that operate a pad driven pump (Eagle maybe) and have an inline for backup.
I am still a bit confused as to why some installations have paralleled vane pumps. Seems a bit excessive to triple redundify the thing, although that may be the case.
As for pressures against fuel vapor formation, I see that AFP uses a diverter valve to clear vapor from the fuel line to assist hot starting. Must not be enough pressure residual in the line to keep the fuel from vaporizing.
Anyway, thanks so much for the help in understanding the fuel flow issues. I'll spend some time noodling around the net to glean more..

Best regards,
Chris
 
Just the facts

The definitive word on aircraft fuel injection (Airflow Performance and Bendix).

Fuel Injection 101 class.

November 6-9 2009 and March 2001 (first weekend tentative)

If you really want to learn how this stuff works come to the class. It?s no bull just facts. And you get fed and have a good time.


Don
 
Don at Airflow said:
The definitive word on aircraft fuel injection (Airflow Performance and Bendix).

Fuel Injection 101 class.

November 6-9 2009 and March 2001 (first weekend tentative)

If you really want to learn how this stuff works come to the class. It?s no bull just facts. And you get fed and have a good time.


Don
Click to expand...
Do you have a time machine :p

Where is the class going to be held?
 
time flys

Can't type; 2001, really meant 2010.

Actually the March class will be in 2010, probably the first weekend.

The classes are at the Airflow Performance facility in Spartanburg, SC. (KSPA)

Don
 
The AFP pump looks to be your standard automotive (walbo) setup with a pressure bleed off valve and a bypass valve. These are required since the pump puts out way to much pressure without the bleed off valve, and because the pump wouldn't allow the engine driven pump to pull fuel though it without the bypass valve.

Anyway here are the things I like about the andair pump.

1. It's smaller.
2. Cleaner installation with less plumbing.
3. It uses a brushless motor which should be more reliable (at least on paper.)
4. Higher quality pump.

The fourth item is a little more subjective, but I suspect that it's a higher quality pump given that the AFP walbro pump is built for cars in huge quantities and the Andair stuff is typically very high quality.

I should also note that I have the exact same system in my diesel truck (walbro pump with a bleed off valve that puts extra fuel back in the filler neck) and while it works fine most of the time, I have had it freeze up on me. When it failed it was -20F outside and I was running diesel so I doubt it had anything to do with the pump, but I did experience a failure so it did have a factor in my decision to use the andair, but mostly it was because the install is tremendously cleaner which matters to me since I'm building a bearhawk so I don't have a box to hide it in.

I'm hoping that several will jump on board, the lower prices would be great.

schu
 
KSPA to Airflow

David-aviator said:
How 'bout taxi instructions to your hangar at KSPA after landing....
Click to expand...

After you land (23 or 5) exit the active and you will taxi past the terminal building on your right. Continue down the taxi way (west) to the end of the taxi way and through the open gate , we are the last hanger on the taxi way on your right. While going down the taxi way you will see a building ahead of you with a green roof. This is off the airport property and is the city bus maintenance facility but it serves a a good land mark.

Don
 
Don at Airflow said:
After you land (23 or 5) exit the active and you will taxi past the terminal building on your right. Continue down the taxi way (west) to the end of the taxi way and through the open gate , we are the last hanger on the taxi way on your right. While going down the taxi way you will see a building ahead of you with a green roof. This is off the airport property and is the city bus maintenance facility but it serves a a good land mark.

Don
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Thanks. That's easy.

The plan is to fly to Spartanburg if I can, if not, I will drive it.

Looking forward to the course, see you next week end.
 
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I attended this class last year.

Don at Airflow said:
The definitive word on aircraft fuel injection (Airflow Performance and Bendix).

Fuel Injection 101 class.

November 6-9 2009 and March 2001 (first weekend tentative)

If you really want to learn how this stuff works come to the class. It?s no bull just facts. And you get fed and have a good time.


Don
Click to expand...

Great class, great time, great people. I highly recommend it.
 
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