• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

Fuel Injection. Which one?

stewartb

MEMBER
Does anyone have experience or first-hand knowledge of the Precision Silver Hawk AND Airflow Performance Inc's fuel injection systems? Is there a preference or advantage of one versus the other? Given a choice with no price difference which would you choose?

Thanks.
 
I have the Silver Hawk, Bart recommended that injection system when he built my engine in 2010, I have 450 hrs on it with no problems.
 
Thanks. I have a similar pirep from a friend that uses API. I'm hoping somebody here has hands-on experience with both.

Can you balance the nozzles with the Silver Hawk system? If so, have you done it?
 
Airflow Performance overhauled my Bendix system and modified the nozzles so that they could be tuned by changing orifice size. After doing a flight test they worked with me in fine tuning the fuel flow between cylinders. I recommend them for their good customer service.
 
Yes, API is known for balance tuning the injectors. It's supposed to make for a very smooth engine. They describe it as doing the GAMI thing at 1/10th the price. Their restrictors cost $17 per injector. What got my attention is their 200A servo on a horizontal induction makes more horsepower than their other fuel servos. More fun thanks to the experimental category. Superior offers the Silver Hawk and API injection systems on their XIO engines so I was hoping for some comparisons between the two.
 
Last edited:
I have the Airflow Performance with 275 hours. Great--outstanding--customer service. No problems with the system. I also have their Purge Valve installed--nice option.
 
Yes, I have an alt-air "gate." Never have had to use it. Purge Valve guarantees no (even minor) fuel leak at idle cut off, which is possible (normal?) without purge valve. Also helps as I understand it with hot-starts. Easy to install; easy to use.
 
What is the purpose of the purge valve in this system? I could only find it on Airflow's price list, without any mention of it's use. I do not have one on my Cub and have no troubles. Granted the Precision systems on Lycomings do make air in the fuel injector lines on a hot engine on a hot day when the engine is shut down. This is not a problem. Sometimes in hot weather while on the ground the engine does get air bound and can shut down. This situation is alleviated by turning on the fuel boost pump. This is also more of a problem with low wing airplanes.
 
What is the purpose of the purge valve in this system? I could only find it on Airflow's price list, without any mention of it's use. I do not have one on my Cub and have no troubles. Granted the Precision systems on Lycomings do make air in the fuel injector lines on a hot engine on a hot day when the engine is shut down. This is not a problem. Sometimes in hot weather while on the ground the engine does get air bound and can shut down. This situation is alleviated by turning on the fuel boost pump. This is also more of a problem with low wing airplanes.

I was told by API that the purge valve was to address hot start problems and that the servo has zero-leakage at idle cutoff (just repeating what I was told). My first question to them was regarding a fuel return line to see if their system required one. Without the purge valve the answer is no. Coincidentally the Silver Hawk system does not require a fuel return either. I prefer the simple plumbing with no return line and can't say whether there's any merit to adding one. I'd like to know more if somebody out there is willing to school me.
 
Last edited:
Here is overview paragraphs from Airflow Performance' Purge Valve manual:

Modern light aircraft fuel injection systems are of the low pressure constant flow type.Fuel is metered and is delivered to air bled nozzles which atomize and spray the fuel ateach intake valve. Airflow Performance and Bendix fuel injection systems meter fuel tothe engine based on engine air consumption. The fuel regulator in both these types ofinjection systems do not return any fuel to the tank, therefore only the fuel that is used bythe engine flows through the fuel controller. Vapor in these types of metering systemscauses the fuel regulator to operate erratically and poor engine performance will result.This is usually evident during hot restarts. Hot restart problems are a typical complaint ofpilots operating fuel injected engines. After engine shut down heat in the cowling andengine tends to boil the fuel in the fuel control, fuel pump and related fuel meteringcomponents. Some of the fuel expands in the nozzle lines and gets forced through theinjection nozzles and into the engine. This leaves hot fuel and fuel vapor through out thecomplete fuel metering system, engine driven fuel pump included. During an attemptedstart under this condition usually results in the engine starting for a moment then quitting.The pilot is then faced with decision of how to proceed with the start procedure.Flooding the engine then cranking the engine until it starts is usually done. Thisprocedure is dependent upon battery life which sometimes expires before the enginestarts. Engines which use the high pressure diaphragm fuel pump, experience anotherproblem which influences the ease of restarting the engine. By their design thediaphragm fuel pump acts like an accumulator when the engine is shut down. This keepsfuel pressure on the fuel controller, and leakage in the idle cut off circuit of the fuelcontroller will allow the fuel to bleed off into the engine. This can cause run on in idlecut off and flooding of the engine initially after shut down. 3All Airflow Performance, Inc. fuel injection systems come with the purge valve asstandard equipment typically installed as an assembly on the flow divider or purge valve.In addition to the above operational issues with this type of injection system, AirflowPerformance fuel controls incorporate a rotary mixture control valve. Due to the inherentdesign of the rotary valve the device does not give zero leakage at ICO. Therefore eventhough the engine may shut down using the mixture control the purge valve will give aclean ICO under all circumstances.
 
Thanks, Ted. I'll quiz the API guys about why your manual differs from what they told me. I appreciate the post.
 
At one point I thought I might go the API route and I purchased their bound installation manual to learn more about it, but I decided to go another route. They charge like $70 or something for it. If you want it, I'll give it to you for half of whatever their price is.
 
Thanks, but I'll pass. I want API to issue me a manual that's matched to whatever it is they provide to Superior for my engine. What different direction did you take?

API and Superior are exception at responding to questions. I'm not used to this treatment with airplane components but I sure am liking it.
 
Stewartb

Do a search on the RV website www.vansairforce.net a lot of info on different fuel injection systems and purge valve on that site. Don Rivera at Air Flow Performance is the fuel injection Wizard and always willing to help. Bought his FM 200 FI system for my project.

Steve
 
Thank you tedwaltman1,
Now I understand the purpose. I used to have those starting troubles with the Lycoming fuel injected engines until I learned the Lycoming recommended starting procedure. Since then (1964) I have not had any issues indicating a need for a purge valve. I always start when the engine is hot with the mixture in idle cut off. Mixture rich after starting. Sometimes you need to meter the mixture until the engine is running smoothly. Remember the mixture control is nothing more than a fuel faucet. On a low wing airplane the fuel boost pump will be running. High wing airplane doesn't need the pump to be running. This is to ensure that there is a positive head of pressure on the engine pump in-port eliminating the vapor in the pump and lines.
 
Guys, API tells me their advice to me about not needing a purge valve applies to what they recommended for my engine build. My dream system includes an FM-200A servo which has zero leakage at idle cutoff. That isn't true of the earlier FM-200. Apparently some of their servos do need a purge valve.
 

Attachments

  • image.jpeg
    image.jpeg
    161.9 KB · Views: 169
Last edited:
My Pitts has an IO-360 with Bendix fuel injection and after flying it for a long time, I wouldn't even think of putting fuel injection on a Cub.
Cold starting is pretty easy and I know how to hot start it after a 10-15 minute heat soak. After an hour heat soak, I don't have enough fingers and toes to cross.
On something that doesn't fly upside down, give me a carb any day. One gas line, a little gravity and you're off and running.
 
That ship has sailed. My new plane will use modern injection. Every one of us has groaned at one time or another about flying behind 1930s technology. I may ultimately admit that 1930s technology has a place in aviation but for now I'm enjoying the 21st century and the better power and efficiency that's available.

Zoom zoom.
 
Well, I'm only wrong several times an hour and I'm overdue. The new stuff has to be better.
 
I don't know if it's better but it's what I've chosen to use.

This project is my personal aviation revitalization act and at the moment that's proving to be true. I'm sure having fun with it.
 
Update: I received my test cell report from Superior this morning. The dyno test has my engine producing 220hp with the API servo, up 5hp from the normal output with the Silver Hawk. Nothing earth shaking but at least there's some return for the $400 upcharge.
 
My Pitts has an IO-360 with Bendix fuel injection and after flying it for a long time, I wouldn't even think of putting fuel injection on a Cub.
Cold starting is pretty easy and I know how to hot start it after a 10-15 minute heat soak. After an hour heat soak, I don't have enough fingers and toes to cross.
On something that doesn't fly upside down, give me a carb any day. One gas line, a little gravity and you're off and running.
My Cub has an IO-360 and it always starts easily hot or cold. Do you have electronic ignition?
 
Back
Top