[DeltaRomeo]

From the factory FB page.

"We've had several RVator articles over the years about the perils of modifying the fuel system, but it may be time to revisit the subject.

We were recently contacted by the NTSB with regard to a fuselage fire in an RV-10 with an automotive engine installed. This had what was described as a 'standard RV-10 fuel system', but the picture below forwarded by the NTSB showed plumbing which left our technical staff's jaws hanging slack in disbelief. We counted 28 clamps on the rubber hoses, but may have missed some.

Obviously, we strongly discourage any deviation from the plans, but if a builder decides that changes must be made, it is best to use approved aviation practices for fuel systems as outlined in AC43.13. The AN fittings and aluminum line shown in typical RV plans are based on current certified airplane standards and are reliable. The arrangement as shown is potentially lethal, more so if used in high pressure systems (Lycoming fuel injection systems typically run around 25psi, some automotive types may be 60psi or higher!). The cause of the presumed fuel leak/fire in this case is not known, and we await the NTSB's verdict with interest, but irrespective of their conclusion, a fuel system like this is simply a Bad Idea.

Whilst we have great freedom to experiment with RVs, the fuel system is one area where proven aerospace techniques and materials are always the best course."​

 

[Mike S]

The cause of the presumed fuel leak/fire in this case is not known, and we await the NTSB's verdict with interest,

O.K., please folks, learn from this, but please keep the speculation to yourselves.

 

[Kyle Boatright]

O.K., please folks, learn from this, but please keep the speculation to yourselves.

This. The guy lost his plane and suffered burns in the accident, as did his daughter. I'm sure he's suffered enough without a bunch of armchair quarterbacks rehashing things.

 

[flion]

Even that was more speculation than I was willing to do.

 

[9GT]

This. The guy lost his plane and suffered burns in the accident, as did his daughter. I'm sure he's suffered enough without a bunch of armchair quarterbacks rehashing things.

I don't think Van's or anyone else is trying to make the builder look bad. Members on this forum who have been here a while know who the owner of this plane was and are sympathetic to his loss and are grateful he and his daughter were not killed in this tragic accident. I consider this to be nothing more than a good reminder to adhere to and follow acceptable standard aviation practices when building.

 

[David-aviator]

My frontal lobe tells me I should not comment on this subject but something needs to be said about the photo and the use of high pressure fuel injection hose in an airplane.

I have been flying with it since 2003. I changed the entire hose material about 18 months ago as a precaution and found the material as good as new. None of the clamps were loose, none have ever leaked. Each had to be cut to be removed. They are not screw type clamps. (I do not use hose forward of the firewall with the Lycoming, I did with the Subaru engine.)

They key here is to use proper hose and clamps. There is fuel hose and there is high pressure fuel injection hose. The only clamps to use are OETiker. Once installed with the OETiker plier they are very difficult to remove. Many, many auto installations are done this way and last forever. You see an auto fire on the side of the road now and then, they are mostly caused by an electrical problem, not a fuel leak.

Aluminum fuel line is safe and recommended as per Van's. But the flaring tools we use are not very precise and frequently the flare is not perfect. That can lead to flare cracking and a fuel leak. I happens. None of this is totally bullet proof.

The fuel system in the photo appears to have been reconstructed. I wonder if the clamps are original?

 

[DanH]

Let's move away from speculation and onward to education. Hose clamps are not forbidden in aviation, but there are details to safe use.

First, the common clamps in the photo are no longer used in auto and truck applications where long term reliability is required. They have a well known problem; the clamped rubber extrudes out through the slots over time, which results in a loss of clamp pressure.

Reliable clamps have no slots. They are either solid bands pulled with a screw or worm clamps with embossed threads rather than slots.

Small diameter hoses for high pressure fuel have their own special clamp. Not suprisingly, it is known as a "fuel injection clamp" at your local auto parts store:

Slotted band clamps are fine if long-term clamp pressure isn't critical. An example might be an accessory case breather hose or any SCAT tube.

The second problem involves fit. Band clamps tend to be treated as if one size fits many diameters. Actually the range can be narrow, and the problem gets worse as the tube gets smaller and/or the clamp gets cheaper. The screw body of the clamp is often shaped with an inner radius matching the middle of the intended diameter range. Using this clamp on a tube at the far end of the possible range results in poor clamp pressure in the areas of radius mismatch:

It's not just a slotted clamp problem; you must look closely at fit when using any clamp style.

 

[RV8R999]

Great info Dan!

Where do you get all the neat diagrams????

 

[Mike S]

Thank Dan!!

Let's move away from speculation and onward to education.

Exactly!!

One more item, this is the non pressure side of the system, as I recall.

 

[skylor]

Exactly!!

One more item, this is the non pressure side of the system, as I recall.

The assembly in the picture has two fuel injection pumps plumbed in parallel with each other and rubber hose with worm screw type hose clamps are clearly visible on both sides of the fuel pumps. The rubber hose and hose clamps are definitely used on the high pressure side of this particular assembly.

Skylor

 

[Bavafa]

Let's move away from speculation and onward to education. Hose clamps are not forbidden in aviation, but there are details to safe use.

First, the common clamps in the photo are no longer used in auto and truck applications where long term reliability is required. They have a well known problem; the clamped rubber extrudes out through the slots over time, which results in a loss of clamp pressure.

I am learning as much here from good friends as I have building the plane. Much appreciate all the good technical info provided here.

 

[DanH]

Where do you get all the neat diagrams????

I draw them in a CAD program and post a screenshot.

 

[TSwezey]

The assembly in the picture has two fuel injection pumps plumbed in parallel with each other and rubber hose with worm screw type hose clamps are clearly visible on both sides of the fuel pumps. The rubber hose and hose clamps are definitely used on the high pressure side of this particular assembly.

Skylor

This is probably one of the many iterations of just trying to get 100lbs of **** in a 10lb box. I don't think there was a picture of the final assembly but if I remember everyone of those fittings came from the auto racing industry and are used extensively in auto racing. The clamps used were what was supplied with the barbs that were used and as far as I know they really served very little purpose as you could not remove those hoses once they were put on the barbs. They had to be cut off. The only two places we ever had leaks was in the area underneath the seat following and using Van's methods and we did have a leak were the fuel line connected to the rail. Tom fabricated us an excellent fitting and hose that solved this problem. The fuel lines were rated to 175PSI. I have tried to keep out of this but I can't anymore. I believe I know what happened to our airplane and could happen to ANYBODY'S airplane certified or experimental. I believe the way we built ours actually saved my daughters and my life. I am trying to stay civil with this. I have not talked to the NTSB since a couple days after the crash I will have to get in contact with them and I would be shocked if the true cause was ever publicly released.

 

[IowaRV9Dreamer]

I would be shocked if the true cause was ever publicly released.

In the spirit of safety and education, I hope the above isn't true. Please find a way to help us improve our aircraft and save lives by somehow releasing the true cause.

I've learned a lot about fuel clamps from this thread.

 

[Ron Lee]

I believe I know what happened to our airplane and could happen to ANYBODY'S airplane certified or experimental.

And that possible cause that has me at risk is.....?

 

[RV7Guy]

Enlighten us

I have not talked to the NTSB since a couple days after the crash I will have to get in contact with them and I would be shocked if the true cause was ever publicly released.

Todd,

I study every helicopter accident I can because of my medical helicopter flying job. I also study every RV event I can. I do this in an effort to learn so I can be as safe as possible.

Others have alluded to how important this issue is. Since this is a matter of public record please fill us in on the "true cause." I'm sure we will all learn. Especially those who are building/flying the 10.

Nobody has passed any judgement and I'm sure that will continue if the cause is released.

We are all very thankful there were no fatalities.

 

[Dennis_I]

Sorry to hear about the loss of an RV-10, but im glad ure still with us today... How is it in the US, do the Experimental Aircraft need to be inspected by a lincesed Engineer or something similar during building process?

/Dennis

 

[aarvig]

I have tried to keep out of this but I can't anymore. I believe I know what happened to our airplane and could happen to ANYBODY'S airplane certified or experimental. I believe the way we built ours actually saved my daughters and my life. I am trying to stay civil with this. I have not talked to the NTSB since a couple days after the crash I will have to get in contact with them and I would be shocked if the true cause was ever publicly released.

Todd,
I am glad you are all OK and that you have the luxury to discuss with us your point of view regarding your accident. But with all due respect...please don't make a post that makes the rest of us flying certified or experiment aircraft, as you mentioned, feel like our planes are going to explode at any minute and then leave us hanging without an answer. If you have a reasonable argument please present it to us.

 

[pierre smith]

Hi Dennis..

Sorry to hear about the loss of an RV-10, but im glad ure still with us today... How is it in the US, do the Experimental Aircraft need to be inspected by a lincesed Engineer or something similar during building process?

/Dennis

The airplane doesn't HAVE to be inspected during the build process but it's recommended. The EAA has tech inspectors that look at your airplane for free and make suggestions as to improvements and/or safety, during the build process.

We have DAR's (Designated Airworthiness Representatives) that do the final inspection for pay. They may or may not isue an airworthiness certificate, depending on what sort of faults they discover. Once these issues are corrected to his satisfaction, an airworthiness cert will then be issued.

Best,

 

[Bob Axsom]

The Company "Design" ?

Things have changed no doubt but in my documentation for building our RV-6A there was only a little minimal sketch of a fuel system that did not satisfy the needs of our airplane and proposed some things that were unacceptable to me. The disclaimer of design responsibility for everything other than the basic airframe was very clear - I wouldn't want it any other way actually. The fuel system is a special deal and it was not enough to "follow the company direction and call it good." There are many threads in this forum presenting and debasing various fuel system approaches so you have to know there is no standard fuel system that will be found in most RVs. They address filters, gascollators, fuel valves, bulkhead fittings, solid lines running through rubber grommets in fuselage skins, distributed tanks without individual controls, venting, fuel quantity sensors, gauging, aux. pumps, primer systems, fuel/primer line selection, calibration, testing, etc. You have to think through the operational requirements as well as function, performance, long term reliability and maintainability on your individual airplane and make individual choices. The pitfalls are many and not every resulting system is going to be the same or perfect. It is not an easy task so calling attention to it for sensitivity purposes is probably a good thing but dictating design or restricting personal choices is not in my opinion.

Bob Axsom

 

[rv6ejguy]

This is an interesting discussion. I'm frankly somewhat surprised at Van's comments about this matter since the NTSB has not released their findings on the cause of this accident and secondly they imply that since the design of this fuel system is not the same as what they recommend it is not as good. They go on to say the usual things about recognized aircraft materials and procedures which are usually a good thing but let's face it you don't see things like nylon brake lines and rivets used for static ports on certified Pipers and Cessnas yet these are deviations which Van's finds acceptable to recommend on their aircraft. Why? Because they've been proven to work just fine if done correctly over the hundreds of thousands of flight hours that RVs have accumulated. Makes perfect sense to me.

Vans puts out amazing designs at amazingly fair prices but nobody is perfect and we can all learn from proven past practices, experiences and failures. I can think of a couple things in particular about Van's designs which anyone with practical mechanical or engineering experience would not find acceptable and in fact did not work out and had to redesigned.

I see many people cringe at the sight of hose clamps and barb fittings in aircraft. I can only assume that this is because it does not 'look' right. I've been working on fuel injected vehicles (thousands) as a business for over 30 years and virtually every OEM uses barb and hose clamps with rubber high pressure fuel line. Why? Because it is a very reliable system proven over billions (trillions?) of hours of use with virtually no maintenance ever being performed in a far more corrosive environment than aircraft experience. They are not affected by vibration, metal fatigue or bad flare issues like aluminum tubing/ flare connections.

IF DONE CORRECTLY, they are more reliable IMO than what is recommended by Van's. By correctly, I mean proper, high pressure fuel injection hose, the proper type and size of barb fitting and proper clamp tension. Many people tighten clamps too much, not understanding the mechanics of the joint. You don't crank these down tight to get the rubber spilling out. While the clamps Dan shows are preferable to standard clamps, for our world where things are inspected and replaced frequently (every 5 years say in the case of rubber hoses), I've never seen a problem using standard clamps with these connections yet. Certified Rotax engines have many hose clamps and they work just fine. They recommend simply to replace all hoses at regular intervals which makes sense for these materials exposed to high heat and various types of fluids.

Does Van's think that one of these hoses slipped off? Not likely as I always have to slit the hose with a knife to remove them even after the clamp is removed. These just don't fall off if done right- not ever. Let's wait for the full report before condemning something that has an immensely proven reliable track record.

 

[bkthomps]

Todd, did anyone inspect the flare angles on the fuel fittings? I was searching a while back for flare tool info and came across this thread- it seems that nobody is able to find a true 37degree flare tool at home depot yet that is where you were able to source one, could it have actually been 45degree?

http://www.vansairforce.com/community/showthread.php?t=20924

I'm also trying to be civil, I want to be absolutely certain I'm learning all I can while I build and I just didn't know if anyone had given this detail any attention?

I am glad that both you and your daughter are safe and that everyone is here to discuss and share knowledge of the subject.

 

[Mike S]

Well, I guess it is time for me to jump in here with a bit of information.

I spoke with Todd about this in the past, and again today, and have received his blessing to post this.

It is Todds opinion that the explosion, and resulting fire, was not caused by the fuel system at all, and that there were no leaks, but that is was caused by something that was being carried on board---------and that until the NTSB is through with the investigation, he is not planning on disclosing any more. The investigation is still ongoing, and the final determination is still unsure.

Bottom line, who knows????

We will have to wait and see.

 

[aarvig]

Well, I guess it is time for me to jump in here with a bit of information.

I spoke with Todd about this in the past, and again today, and have received his blessing to post this.

It is Todds opinion that the explosion, and resulting fire, was not caused by the fuel system at all, and that there were no leaks, but that is was caused by something that was being carried on board---------and that until the NTSB is through with the investigation, he is not planning on disclosing any more. The investigation is still ongoing, and the final determination is still unsure.

Bottom line, who knows????

We will have to wait and see.

Todd and I have exchanged emails regarding this as well. Let's give Todd and the NTSB some room to investigate this fully. Todd's thoughts as to what caused the accident need to be played out and are quite reasonable considering the information I have been given. I will concur with Mike and say that Todd's concerns are regarding an item that was brought on board and I believe they are very valid concerns.

 

[Ron Lee]

The possible cause is NOT one that could happen to anyone. I can't comment on the owners possible cause, but pilots need not worry that their aircraft fuel system is a ticking time bomb.

 

[Bavafa]

After learning about this accident and another RV10 that had a broken fuel line in the FFW some months ago, I started doubting my flares and decided to pull all the Vans supplied lines which are 3003 aluminum and replace them with the 5052 aircraft grade lines. Pulling the old lines and inspecting the flares on them showed all near perfect flare with no sign of any issues but no regret as I feel some what better with the stronger fuel lines in my plane and having double checked my flare.

 

[rv6ejguy]

After learning about this accident and another RV10 that had a broken fuel line in the FFW some months ago, I started doubting my flares and decided to pull all the Vans supplied lines which are 3003 aluminum and replace them with the 5052 aircraft grade lines. Pulling the old lines and inspecting the flares on them showed all near perfect flare with no sign of any issues but no regret as I feel some what better with the stronger fuel lines in my plane and having double checked my flare.

A good precautionary measure. In the RV10 with fuel system components and flap motor in the same tunnel, even a small seep could be hazardous.

 

[ScottSchmidt]

Some thoughts on this thread...

I know Todd and we have talked on the phone when he was building and when he brought his plane to Oshkosh. I have no idea why "the real reason" is not being discussed here, I did not talk with Todd after the accident or anyone else here that apparently knows what is going on, but we can all guess that insurance companies and lawyers are doing something and the NTSB is still doing their investigation which has a huge bearing on the outcome.
Now maybe Van's comment was early but then again maybe not. The NTSB contacted them to discuss the issue since the combination of the fuel system in the picture or something he was carrying in combination with an RV-10 caused an explosion. It just sounds like they are all doing a good job finding out what happened and gathering as much data as possible. The problem is that Van's showed us all only one piece of the puzzle that has many many pieces.
Maybe no one should post anything until the NTSB finishes their investigation. Obviously no one can talk right now about what they think the root cause or combination of problems or issues were. It is not fun to have a post deleted and it does not seem fair that some comments are allowed that cause us all to ask questions and when the question is asked it is deleted. As a moderator I would just recommend both sides stop posting. I think we can imagine the emotion involved with an event like this.

I don't think there is any reason to be concerned though with the number of hours on RV's and the rarity of an explosion like this. In fact this is the first one I have heard of and I sure felt bad for Todd and his daughter. I really enjoy this forum and would hate to see anyone not openly share their thoughts and comments unless they violate the rules.

 

[David-aviator]

I know Todd and we have talked on the phone when he was building and when he brought his plane to Oshkosh. I have no idea why "the real reason" is not being discussed here, I did not talk with Todd after the accident or anyone else here that apparently knows what is going on, but we can all guess that insurance companies and lawyers are doing something and the NTSB is still doing their investigation which has a huge bearing on the outcome.
Now maybe Van's comment was early but then again maybe not. The NTSB contacted them to discuss the issue since the combination of the fuel system in the picture or something he was carrying in combination with an RV-10 caused an explosion. It just sounds like they are all doing a good job finding out what happened and gathering as much data as possible. The problem is that Van's showed us all only one piece of the puzzle that has many many pieces.
Maybe no one should post anything until the NTSB finishes their investigation. Obviously no one can talk right now about what they think the root cause or combination of problems or issues were. It is not fun to have a post deleted and it does not seem fair that some comments are allowed that cause us all to ask questions and when the question is asked it is deleted. As a moderator I would just recommend both sides stop posting. I think we can imagine the emotion involved with an event like this.

I don't think there is any reason to be concerned though with the number of hours on RV's and the rarity of an explosion like this. In fact this is the first one I have heard of and I sure felt bad for Todd and his daughter. I really enjoy this forum and would hate to see anyone not openly share their thoughts and comments unless they violate the rules.

Scott,

The original message of this thread implies what caused the event.

Perhaps the entire thread should be deleted or locked down until the NTSB completes the investigation as the implication may be completely in error.

 

[N395V]

Below is a lengthy article that will require 4 sequential posts to fit. It is a long read and I cannot remember where I lifted it from. The author is attributed at the beginning and end. I have found this article quite useful over the years.
Part 1

Fuel Systems for Homebuilt Airplanes
by Lyle S. Powell, Jr.
117 El Camino Corto Walnut Creek, CA 94596
I'm one of those people who reads accident reports, and subscribes to several publications where they're featured. Over the years it keeps re-occurring to me that fuel system related accidents are by far the most frequent single type of non-pilot-error accidents, especially the serious ones, and especially in homebuilt airplanes. Many fuel system related accidents also involve pilot error, such as inaccurate knowledge of fuel quantity and mismanagement of fuel selector valves. However, it is my feeling that these are chiefly system errors more than pilot errors, because such systems often invite pilot error.
There are essentially three types of fuel system emergencies. The first and most important are those occurring on take-off or initial climb, when there is insufficient time, however well managed, to correct the situation. The second can best be called running out of fuel. Some of these are also system-invited by such things as having tanks whose capacity varies with the attitude of the airplane when fueled, or gauging systems of poor accuracy. The third major type are those that occur on approaches and go-arounds. Most of these are definitely system related.
On take-off and initial climb, sudden engine stopping or serious power loss occurs more frequently in homebuilt than factory airplanes. This is probably a reflection of repeated experience and standardization by the factory airplane builders. However, some of these employ antiquated systems and non-ergonomic practices, fuel selector valves being the most prominent. It is absolutely amazing how often fuel selector valves are mismanaged under stress by even the most experienced pilots. Another frequent one is the vapor-lock incident or accident. Almost all of these are system related. One of the many causes is the engine driven fuel pump which is such a good 'teapot" for boiling fuel. When the boost pump is plumbed in series, rather than parallel, and when the engine (and pump) is hot from waiting for take-off, or from lean cruise followed by descent many "carburetor ice" accidents occur, both on approach or go-around, and on liftoff. The only reliable thing that carries the calories out of that hot fuel pump on the engine is the flow of fuel itself. When the throttle is at idle (for descent or waiting for takeoff) there is precious little flow, so bubbles form and have a hard time getting through the small openings into the carburetor needle valve orifice or fuel injection servo unit.
When power loss occurs on go around or take-off, even it proper and immediate valve switching is done (if that is what is needed), the time required for reestablishment of sufficient flow into carburetor or servo unit is often too long. Part of the problem is due to the tremendous demand of the engine for fuel at full throttle . . . it's usually 2-1/2 to 4 times

 

[N395V]

Part 2
the usually thought-of cruise flow, and catch-up in this circumstance is hard to accomplish. Also, this is a time when boost pumps cavitate from air inhalation from an empty or near-empty tank.
Homebuilt airplanes have a tendency to have fuel system accidents early in their careers, during the learning and sorting-out phase of the pilot/builder as well as the airplane. Fuel system accidents include not only outright failures of devices in the system, but things we rarely think about, such as:

• Not knowing how much fuel you can put into a tank because of attitude sensitivity or venting.
• Small vent tubes easily obstructed by a single drop of water or an insect.
• High pressure boost pumps cavitating with interruption or surge in flow.
• Fuel selector valves sticking or not having clearly defined detent positions.
• A leaking gascolator gasket admitting air bubbles into the system, yet leaks little or no fuel.
• Vibration-induced cracking and leakage of spare fuel tanks.
• Split flares in metal tubes producing leaks, or inlet of air into system.
• Inadvertent flap valves in fuel hoses produced by improper insertion of connectors.
• Foreign bodies in the tank jamming boost pump piston or breaking carbon vanes of high pressure pumps.
• Inadequate sized elbows or other fittings in the system producing bubbles in the flow of fuel.
• Foreign bodies obstructing finger screens, gascolator screens or filters that are too small.
• Leaky carburetor floats.
• Leaky fuel injector servo diaphragm (beware of the shelf life).
• Leaks in diaphragms and edges of diaphragm in engine driven pumps.
• An unsupported vibrating fuel hose that partially obstructs flow.
• Worn or grooved connector fittings that leak air or fuel.
• High pressure systems (fuel injection) are considerably more critical with respect to leaks and obstructions than low pressure systems, for obvious reasons, and experience bears this out. Also fire hazards are greater with high pressure systems due not only to the higher pressure but because of the increased footage of plumbing and larger number of connections in the engine compartment. Boost pump failures and pump priming failures are also more prevalent here.

Gravity fuel systems, while seemingly simple and reliable, are plagued by very small supply pressures and ease of interruption. For instance, the minimum pressure required by most current carburetors is 1/2 lb./sq. in. This requires a gravity column of 18 inches -not counting any losses for tubes, filters, valves,

 

[N395V]

Part 3

• elbows, connectors, etc. - or the occasional sticking of a float needle valve. For small engine applications only, where small flow requirements prevail.
• Air being sucked into the flow of fuel can be as obstructive as vapor lock bubbles. This is another reason to have little or no suction component to the fuel system. Fuel leaks are much easier to find than air leaks because air leaks don't always leak fuel.

This is only a partial list of potential problems, but it is a sufficient list to illustrate the character and magnitude of the problem. Often the homebuilder (and the homebuilt designer) gives the fuel system inadequate consideration, or simply follows one of several standard production examples. Too often they don't realize the pitfalls of small variations from specific applications, or lack an overall understanding of the problems, and/or the shortcuts that homebuilders are likely to take for their own convenience. I believe that the underestimation of the critical nature of the fuel system is the largest single source of poorly designed or fabricated fuel systems.
Following is an outline-type summary of fuel system items to observe when designing or building your fuel system.
Fuel Tanks
Into which a known amount of fuel can be put each and every time (not attitude, tilt or vent sensitive). Of reliable mechanical construction, unlikely to develop leaks with time and vibration and unlikely to present an unusual hazard in a crash landing. This requires substantial resistance to rupture on impact or deformation. Must not have low spots behind baffles and in comers for collection of water. Vibration is worse in 4-cylinder airplanes than others, and must receive generous respect as a destroyer of structures and producer of leaks.
Fuel Tank Caps
Must not leak fuel, air or water. Expensive, but available and necessary. Look at those caps - take them apart and examine them. Small details are important here.
Sump
Adequate depth and size, with screen and drain valve as necessary. Do not tolerate a main tank without a real sump. Auxiliary tanks, with good lowpoint drains and a "no take-off" restriction 0. K. without sump.
Unporting Protection
Prevention of fuel being thrown away from sump outlet by uncoordinated flight or turn just before take off, by use of slosh gates or check valves and baffles in tank. Necessary.
Vents
3/8" tubes or larger to prevent a frozen drop of water from obstructing. As short a run as possible, especially if horizontal (because of water droplet precipitation), with non-icing opening (any one of several types). Backup second vent highly desirable.
Valves
As simple a system as possible with all on or off if possible. An amazing number of accidents occur from pilot misplacement of valve handle or valve sticking, even from handles breaking off. Also even when properly changed, a long interval is required before engine starts. Selector valves are inherently dangerous and should be recognized as such. One alternative is a separate ball-type valve for each tank, arranged so that the handle position is obvious. Also these valves are more reliable and don't stick.
Boost Pump
Must be inside sump or have short gravity-fed inlet, otherwise very often will not reprime if run dry, especially fuel injection boost pumps. Do not try to suck fuel uphill or forward. It pulls bubbles into the fuel inviting cavitation. Acceleration occurs forward and upward on take-off and climb for a sustained period of time and fuel moves backward and down, and that's where the inlet of the boost pump should be if it is not in the sump. Protect inlet of pump with screen or filter adequate to protect the pump from jamming due to foreign body. Such filter must be inspectable and cleanable. These are often provided in the pump body by the manufacturer.
Fuel Routing
Should be direct from boost pump through filter to carburetor or fuel injector servo. Have engine driven pump plumbed in parallel, not series, so that possible vapor lock in engine driven pump will be bypassed. A check valve may be necessary, depending on pump type.
Engine Driven Pump
Requires shroud for positive-pressure ventilation to cool it, thus minimize fuel boiling (due to accessory case and oil temperatures which heat it).
Fuel Lines and Devices
Should not be exposed to heat anywhere, for two reasons:
1. To prevent vapor lock (bubbles whose surface tension make them resistant to going through small holes).
2. To prevent fire in case of accident, or fuel leak in flight
Particularly avoid proximity of fuel lines or carburetors to exhaust pipes radiated heat is more intense than most people imagine. This heat acts as an ignition source in case of accident, or a fuel leak, or a crack in an exhaust pipe in flight. Metal heat shields are often necessary because most heat transfer in cowling is by radiation, not convection or conduction. Examples are the metal shields between an exhaust pipe and adjacent hoses or wires seen in many factory airplanes.

 

[N395V]

Part 4


Fuel Lines
Should be of well engineered type and size and protected by fire-sleeve in engine compartment.
Fuel Filters
Gascolators are not sacred devices, not even very efficient ones. They were really designed for use with fuel tanks without sumps or sump drains. With sump drains they become unnecessary, or at best supplementary. Often they are sources of fuel leaks and air leaks into fuel systems. Also they are sometimes vulnerable to rupture in case of accident. Where tank sump drains are provided, good fuel filters of several types are better than gascolators and are safer, less prone to leaks and damage. Must be of adequate size and accessible to inspection, draining, cleaning or replacement. Beware of very small automotive filters which could obstruct in flight from a slug of dirt in the fuel. I am using a FRAM HPG-1 fuel filter in my Glasair. It is commonly used in racing cars and boats, has an excellent service experience. It has a 13 ounce capacity, a steel case into which you can put a drain valve. Expensive and bulky, but a good example of what is needed.
Water Detectors
Two brands are currently available (Wag-Aero; A.I.R. Corp., Oakland). A very good idea - either in sump or filter can.
Gauges
Reliable, backup simple mechanical type gauge or sight-tube gauge advisable for last few gallons in addition to standard gauges. Float switch with warning light is another good alternative (Aircraft Spruce). Fuel gauges are justifiably mistrusted, but they are also usually of low quality. Reliable separate gauging of the last 1/10 or so of fuel can be very accurate. Flow meters and totalizers are not a substitute for fuel gauging because they are so dependent on accurate knowledge of how much you start with. Be sure to have some back-up gauging or warning system beyond standard gauge system, or a reliable spare tank.
Spare fuel Tanks, Header Tanks, Etc
All have definite problems, including selector valve hazard, but they are a reasonable alternative it designed well. Using a vibrating firewall as one wall of header tank is a questionable practice unless it is specially reinforced and stiffened. (Touch that firewall in flight sometime.) Again think of a survivable crash landing or an in-flight fire. A VW-like standpipe in the main tank is one alternative to a spare fuel tank - or a separate tank within the main tank that fills automatically -or a spare tank that transfers into the main tank. Outer wing panels are the best location for spare tanks, for structural as well as safety reasons.
Air Inlet System To Carburetor or Fuel Injector Servo
Must be of adequate size and especially not obstructed by a too-small air filter. Better no filter than an obstructive one, because the obstructive one can seriously disturb fuel mixture and produce erratic throttle-mixture correspondence. Air filters are highly desirable but must receive the same design consideration as any other system and not simply yield to what is convenient (frequently seen in homebuilts). Be sure filter will also act as flame arrestor in case of start-up backfire - it can save your whole airplane. This is done by containing the filter in a blow-out and suck-in proof container. A curved elbow type of air entry into a carburetor is poor practice because of inertial lamination of airflow into the carburetor. A plenum, horn or diffuser entry is much better, and removes those dead spots at some throttle settings also higher power.
Overflow Drains
From engine pump, inlet spider, inlet plenum boxes as well as drains from filters and gascolators, must be overboarded in a safe place away from exhaust. A manifold collector and single drain often useful here.
Carburetor Heat Source
Standard and necessary. Can be easily combined with cabin heat. Pulling carb heat cable turns off cabin heat with two-way flap valve. Be sure to overboard any unused carb or cabin heat so there's a constant airflow over shrouded exhaust pipe. Otherwise that segment of pipe will bum through and become an early carbon monoxide and/or fire hazard.
Belly Protection
In case of gear-up landing, or gearcollapse accident in fixed gear aircraft. Any exposed or vulnerable fuel-containing structures such as sump, filters, drains, gascolators, etc., should have mechanical protection. No drain valve or such structure should project where it can be easily broken off in a belly landing. Longeron-like braces in belly pan is an example of a mechanical protective structure. A strong belly plate under this area is another.
Fueling
Putting fuel into aircraft tanks deserves some thought. The flow of fuel through a hose and nozzle creates static electricity, and a discharge arc sometimes occurs to the filler neck of the airplane - explosion. So, in fiberglass or other composite airplanes, it is desirable to ground the metal fuel filler cap ring. This is true because any mass of metal plus adjacent semi-conductor fluid (gasoline with some moisture in it) has some capacitance. As such, it becomes the target for a static electric arc from the fuel hose nozzle (which may or may not be grounded) or the pouring spout of a jerry can.
This filler-neck grounding should be done with a wire (18 gauge or so is enough) attached with a good AN plated bolt and washer through the ,aluminum ring to a good plated crimpon fitting. These details are to minimize dielectric corrosion of the dissimilar metals. Aluminum bolt or rivet and wire could also be used. However, the experience with aluminum wires and connectors in the presence of moisture is poor. The wire should be mechanically supported properly into the cabin area where it is attached to the ground buss through a resistor (approx. 1 meg OHM 1 watt). This resistor limits the power of any static discharge. What it actually does is spread out the time of the discharge from instantaneous to several micro seconds. This then replaces the arc with a corona-like discharge which is probably below ignition temperature for gas fumes. In any case, when fueling, it is good practice to keep the nozzle in contact with the filler neck. If both the filler neck and the nozzle are grounded, there should be no problem. But you can't be too sure about some gas hoses and nozzles or ground connectors to airplane from the truck or pump. Finger screen in sump should be grounded - by grounding aluminum line or connector.

 

[N395V]

Part 5 Last part

Fueling from plastic (polyethylene) cans should never be done because these materials have a very high static electric generation potential when gasoline flows over its surface, or it is rubbed against another material. Metal cans are much safer.
The preflight ceremony of draining sumps and other fuel devices should be taken seriously because it is here that you can best prevent the most terrifying of aircraft accidents - the engine stopping on take-off or initial climb. Water is the chief enemy, foreign bodies of all kinds, second. Always use a cup or container to drain fuel, so that you can am any water or debris that you drain. If you can't see it, you don't ever know how much to drain, and every once in a while it takes a lot. Fueling from some places can produce very large amounts of water and debris - much more than a cupful - even gallons. Old buried tanks with doubtful maintenance are guilty here, even some trucks have pro: produced such events. I know first-hand of several such events.
Cessna's experience in rocking wings and tail to dislodge water from wrinkled bladder tanks should be remembered - it was successful. This applies to other airplanes, too, such as taildraggers where low spots due to attitude become pockets for water -or nose draggers with multiple baffles. Water droplets on the floor of a gas tank seem reluctant to move toward the low spot (sump) unless agitated, especially with minimal dihedral wing tanks, apparently due to surface tension.
Water is soluble in gasoline to a limited extent, and this is particularly important in winter (see article by Niel Petersen Sport Aviation, December 1986). As fuel cools in the tanks overnight, some water precipitates out as droplets. This accounts for some of the .moisture of condensation' even when the tanks are full. Also if it is cold enough, these droplets can form ice crystals or slush, which can obstruct fuel outlet screens, even to the point of collapsing them in flight In the cold winter areas this can be important not only as a pre-flight consideration, but on long flights at altitude, where the fuel has time to become cold. Jet-powered aircraft use fuel heaters or water-dissolving additives ("Prist") in their fuel for this reason. However, their fuel has a greater solubility for water, and their flight altitudes are higher - but the problem is essentially the same.
Conclusion
This list is, of course, incomplete. My emphasis has been on those items which seem to me to be most important from a safe-design standpoint. Homebuilders suffer from "ran out of room" problems just when something like a fuel filter or an air filter demands a place, then compromise occurs, and the last items on the list get the poorest design. Don't yield to this - be willing to go back and rebuild or rearrange things so that fuel priority is properly respected.
One last thing. If; you must put fuel system components in the engine compartment (where all the heat and ignition sources are), group them together and build a good metal, positively ventilated, box around them. Place the vent exit as far away from the exhaust pipe as possible.
In fuel systems, the enemies are heat, water, leaks, foreign bodies, static electricity and devices that invite human error.
ABOUT THE AUTHOR
Lyle S. Powell, Jr., EAA 38012, has been flying for 23 years (Commercial, Mulfi. Instr., 3300 hrs.). Lyle has owned several factory-built airplanes, built and rebuilt a VariEze, a Glasair (with 750 hrs. on it) and is now building a Glasair III.
He offers thanks to Andy Marshall of Marshall Consulting, George Periera (designer of the Osprey and G.P.-4) and Jim Horn (Voyager engine instrument design consultant) for their help and advice on this article.

 

[TSwezey]

I know Todd and we have talked on the phone when he was building and when he brought his plane to Oshkosh. I have no idea why "the real reason" is not being discussed here, I did not talk with Todd after the accident or anyone else here that apparently knows what is going on, but we can all guess that insurance companies and lawyers are doing something and the NTSB is still doing their investigation which has a huge bearing on the outcome.
Now maybe Van's comment was early but then again maybe not. The NTSB contacted them to discuss the issue since the combination of the fuel system in the picture or something he was carrying in combination with an RV-10 caused an explosion. It just sounds like they are all doing a good job finding out what happened and gathering as much data as possible. The problem is that Van's showed us all only one piece of the puzzle that has many many pieces.
Maybe no one should post anything until the NTSB finishes their investigation. Obviously no one can talk right now about what they think the root cause or combination of problems or issues were. It is not fun to have a post deleted and it does not seem fair that some comments are allowed that cause us all to ask questions and when the question is asked it is deleted. As a moderator I would just recommend both sides stop posting. I think we can imagine the emotion involved with an event like this.

I don't think there is any reason to be concerned though with the number of hours on RV's and the rarity of an explosion like this. In fact this is the first one I have heard of and I sure felt bad for Todd and his daughter. I really enjoy this forum and would hate to see anyone not openly share their thoughts and comments unless they violate the rules.

I spoke with my NTSB rep today. It was the first time since the explosion. He was appalled that Van's put that on their facebook and the comments they posted with it. It was extremely premature and more than likely WRONG. My theory gave my rep fuel for the fire(pun intended) and if correct like I said it will never be published! The people I have told I expect you to never publish it either! If you see me at Sun-N-Fun or Osh or anywhere else I will discuss it with you if you want. There is a reason for my secrecy on this matter.

 

[vic syracuse]

Let's close this one down.

OK. If we can't/won't tell everyone what the cause of this tragic accident was, then we need to shut this down. Conjecture isn't going to do anyone any good.

Vic


[ed. Done, and concur. Waiting on NTSB report, and hoping they educate us on how we can be more safe as a flying community. dr]