Important notice
Please remember that people from all over the world read and post on this forum, and that every country has its own rules, regulations and standards. This forum is based in the USA and so much of the information posted here is for the benefit of people who operate aircraft in the experimental/exhibition or experimental/racing categories. Advice given on this forum may be region specific. A person from Europe, for example, may make suggestions perfectly appropriate for a U.S reader, although not acceptable in his home country!

Please take this into account and carefully consult the authorities, standards and approved documentation where you fly.
Fournier Forums Upload picture | User Cp  |  Register  |  Members  |  Search  |  Help
    |- Fournier Aircraft > Aerobatics Post New Topic   Post A Reply
Inverted fuel system printer friendly version
next newest post | next oldest post
Author Messages
jb92563
Second Lieutenant

Gender: Male
Location: Lake Elsinore, CA, USA
Registered: Mar 2007
Status: Offline
Posts: 583

Click here to see the profile for jb92563 Visit http://picasaweb.google.com/jb92563 Send email to jb92563 Send private message to jb92563 Find more posts by jb92563 Edit or delete this message Reply w/Quote
Posted Wednesday, July 1, 2009 @ 03:59 PM  

I was wondering why no one seems to have been using an all position fuel system for Aerobatics.

I came across an article on the Rev Master Revflow floatless carb and thought this would be a perfect fit
as it is designed to be fed fuel at only 1.5 psi and can utilize an electric fuel pump, gravity feed or the mechanical fuel pump on the VW....good redundancy.

Since its made for VW engines I would think this would work out pretty well.

Down load the article here after you "Skip the Ad"

http://www.fileqube.com/shared/KrvgF1478500

Ray

[Edit by jb92563 on Wednesday, July 1, 2009 @ 04:07 PM]

Bob Grimstead
Captain

Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2027

Click here to see the profile for Bob Grimstead Visit http://www.redhawksduo.co.uk Send email to Bob Grimstead Send private message to Bob Grimstead Find more posts by Bob Grimstead Edit or delete this message Reply w/Quote
Posted Thursday, July 2, 2009 @ 04:59 PM  

Hi Ray,

Many guys at my local club keep telling me I should use one of these.

But then a Chipmunk owner I know said his caused an abrupt engine failure at 100 feet after take-off due to an air bubble in the fuel line and the carb having no float bowl.

Another guy I know fitted one to his Pulsar and had an in-flight fire. Before that, he also had all kinds of mixture problems and an unexplained engine failure. He's dead now.

Another guy I know had a bad crash in his BD-5 with one of these carbs, again probably because of over-heated fuel, getting a vapor lock and instant engine failure with no warning. He'll never walk again.

The makers never tell you these things.

First you need a flop tube in the tank, but the tank's very thin-walled, so the weight on the end of the flop tube will probably bash its way through. Fancy flying with the cockpit swimming in fuel? Not me!

Like so many of the other guys on this forum, I reckon Rene knew what he was doing, had the best brains around to help, and his airplanes have been flying fine for forty years.

If you want full-on aerobatics, fly a Pitts or a Christen Eagle, or even just a Decathlon. Any of those will fly upside-down for minutes on end, so you can make your head feel like a pumpkin and your eyes look like blood oranges.

A Fournier's great for gentle, evening, positive G aerobatics.
I demonstrate a little more, just to show the ignorant it's not merely a 'toy' nor a feeble motor-glider, but I'm pushing the envelope all the time.

Last display (last Sunday) I inadvertently stopped the prop on a stall turn (hammerhead) from which I usually make a negative G pushing recovery. Trying to get the prop going, I pulled the lever so hard, I pulled the circlip out of its groove. The small cog jammed against the big cog. Eventually the prop turned and the engine started, ripping the teeth off the little cog (the last known one in captivity). I recovered much lower and going in the wrong direction (by pulling, not pushing). I managed to salvage four minutes of aerobatics and most of the crowd didn't know anything unusual had happened, but my display pilot buddies all had a good laugh at my expense. What I do is far more than the airplane was designed for. I do it as a challenge, but I would never suggest anybody else copies me.

Take it easy out there guys, these are old airframes. Ever tried to snap an old, dry twig?

Have fun, but please fly the airplane within its limitations.

Yours, Bob

jb92563
Second Lieutenant

Gender: Male
Location: Lake Elsinore, CA, USA
Registered: Mar 2007
Status: Offline
Posts: 583

Click here to see the profile for jb92563 Visit http://picasaweb.google.com/jb92563 Send email to jb92563 Send private message to jb92563 Find more posts by jb92563 Edit or delete this message Reply w/Quote
Posted Friday, July 3, 2009 @ 06:15 PM  

Theres nothing like real world experience to prove something out.

You completely answered why and now I would not use one either as it obviously has
not been proven safe and reliable.

Ray

Bob Grimstead
Captain

Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2027

Click here to see the profile for Bob Grimstead Visit http://www.redhawksduo.co.uk Send email to Bob Grimstead Send private message to Bob Grimstead Find more posts by Bob Grimstead Edit or delete this message Reply w/Quote
Posted Wednesday, February 24, 2010 @ 08:32 PM  

Hi Guys,

Hi Guys,

Some of you may know that I have a small modification to my standard Zenith carburetor which helps the engine to run for a second or two while inverted. In essence it is simply a matter of getting the fuel from the float bowl to trickle into the intake while you're upside-down.
As always, the devil is in the detail, and it has taken me years to get an occasionally reliable system.

Sam, you're running the Mikuni carb.

I have at last had the time to take a good look at the one your uncle Jon sent me, and first I must say what a superb job he has made of the modifications to enable me to use it on my new engine (going in this month, I hope).

The float bowl vent comes out of a 3.5mm hole at the top of the carb, so it should be fairly simple to open out that hole a little (to 5/32"?) and run a tube forward from it into the air filter.

Provided you roll to the left, fuel should easily flow through the carb drillings and down that tube to get sucked into the manifold to keep the motor running.

The tricky bit is likely to be calibrating just how much fuel flows through the tube. You could either solder over the end and gradually drill it out until you get enough fuel, or else put smaller diameters of tubing inside that one to reduce the flow.

Happy experimenting.

I should be able to do all this when my new motor's up & running, but I just may not have the time this year.
My diary reads:
March, install new motor.
April 1 to 16 test fly, practice and work up.
April 17 & 18 fly for Red Bull Air Race Perth.
April 19th Inhibit aeroplanes & cars, close down house.
April 20th, go to Europe for the summer display season.

Yours, Bob

Bob Grimstead
Captain

Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2027

Click here to see the profile for Bob Grimstead Visit http://www.redhawksduo.co.uk Send email to Bob Grimstead Send private message to Bob Grimstead Find more posts by Bob Grimstead Edit or delete this message Reply w/Quote
Posted Tuesday, March 22, 2011 @ 00:41 AM  

Inverted fuel system? My British buddy Barry Smith is now retired, so he can’t help. He it was who devised and refined an all-attitudes fuel-injection system for aerobatic aviation Volkswagen conversions (including an all-attitudes dynamometer!)

Sooo..... From time to time, my Rectimo does run (on & off) for a few seconds while inverted, but I found it very hard to replicate reliably the occasions when it does. Mostly it seemed to be when I half-loop to the inverted, rather than rolling. Mostly it belched black smoke (indicating richness).

I tired various things to improve the situation and to lengthen the time it ran continuously – waggling the stick fore-and-aft, waggling it from side-to-side, flying with a slight bank or slip/skid left or right, nose high or nose low. Sometimes things were better, sometimes not. Nothing seemed predictably repeatable.

Matthew Hill had told me that Mike Dentith’s motor in NY always continued to run, whatever its attitude, so I figured there must be some variable in these carbs that could be adjusted so that they could all run when inverted. All carburettors have a float chamber vent, to equalise pressures inside and outside the chamber, so the jets work properly, and I suspected Mike’s inverted fuel might be coming from this source.

I was also aware of ‘Miss Schilling’s Orifice’ on the Spitfire’s later Merlin engines (actually, she was Mrs Schilling, but no matter, she was a genius who helped to win the war). And my former editor Nick Bloom had posted an informative document on Stampe carburettors entitled ‘Froggy Tricks’. All these helped spur me into a little practical research.

I removed HDO’s carburettor to look at it more closely; dismantled it and discovered a vent above the float chamber which exits into the top of the air filter casting (it’s hidden behind the choke plate). Aha! As I suspected, that might allow fuel to trickle into the venturi when the carb’s inverted.

So I blocked that vent with a filed-down tiny self-tapping screw. But the float bowl still needs a vent, so I drilled a small hole in a similar place, but on the rear of the carb, outside the air filter casting, and fitted a small-bore 10cm length of copper tubing bent ninety degrees down to exit below the bottom of the carb to ensure fuel does not trickle out.

Now I fly inverted, and whatever I do, I cannot get the engine to run. As I had suspected, I figured it was tending to run thanks to that trickle of fuel from the inverted float bowl into the wide-open venturi (I always left the throttle wide open while inverted, so the engine would burst back into full power as soon as I had positive G).

Sooo... I removed that screw I had fitted to try again. Now it runs more predictably upside-down, but still hiccupping and burping. I figure putting in and removing the screw must have opened out the original vent hole a little. But the engine only runs for a few seconds, 'cos the float bowl is so tiny. Using a syringe, I established it holds 20cl of fuel, which my calculator tells me should be enough for 13 seconds of full-throttle running. That’s OK, I’m unlikely to be upside-down for much longer than that.

When I unbolted the carb and turned it upside-down, I also got a trickle of float-bowl fuel from the little air jet immediately below the venturi. I could not fiddle with that, or the engine would not run properly, but I figured I could augment its flow and produce better atomisation than the dribble from the original float bowl vent.

I reckoned I needed to meter the fuel going into the engine when upside-down, and I needed to get that fuel into the middle of the venturi. So, from the local model shop I got several short lengths of brass tubing of various internal diameters around the size of the main jet and/or the existing vent hole (or, by trial and error, one that would pass around 12-15 litres per hour). I bought a set of small-diameter tube bending springs from the same place.


I then drilled into a cast indent in the carb just below and off to one side of the venturi. That goes into the float bowl, towards the top of it, but not at the very top.

I bent several bits of tube through ninety degrees and one by one fitted them into this hole, with their outlets bent up into the air filter casting and exiting approximately in the middle of the carb's venturi. This trickle of fuel combined with the fully open throttle butterfly should give me steady power for maybe a quarter-minute.


[Edit by Bob Grimstead on Sunday, December 20, 2015 @ 10:10 AM]

--------------------
Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Bob Grimstead
Captain

Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2027

Click here to see the profile for Bob Grimstead Visit http://www.redhawksduo.co.uk Send email to Bob Grimstead Send private message to Bob Grimstead Find more posts by Bob Grimstead Edit or delete this message Reply w/Quote
Posted Tuesday, March 22, 2011 @ 00:45 AM  

I made a series of test flights (actually very many, over a period of three years) until I had established which tube was the best size. During these flights, it became apparent that my original air vent tube’s internal diameter was too small, so I had to go with a bigger diameter air tube. That improved the situation, but affected everything else, so I had to start again with the test flights.

The air vent inlet tube is now 2.25mm ID (No 43 drill bit) and the spray beak tube is 1.4mm ID (No 54 drill bit)

Finally, I got the right combination, but the engine only ran for one or two seconds. Looking inside the carb, it was evident that the inlet tube was so far below the roof of the carb, a lot of petrol/gasoline was just staying in the upper carb. So, I filled the space with fuel-resistant epoxy resin, shaped to slope down towards the tube inlet when the carb was inverted. And bingo, I now get four seconds or more of more-or-less steady inverted running.

Inverted lubrication is provided by the molybdenum disulphide in my oil (se my separate post), and I am trying to wear out this engine so I can fit the new one. If it won't wear out (and it doesn't seem to want to) I can assume the molybdenum disulphide is doing its job, and will do just as well in the new engine. This old engine has now flown more than 1,300 hours in 43 years, the past seven years and 300 hours almost exclusively flying full-on aerobatics with lots of vertical and inverted stuff, but the power, compressions and oil pressure are still good.

That was the situation in January 2009, but it’s still not quite good enough for me. Nowadays I can’t use the choke, so I enrich the mixture for starting by blowing hard into my aerobatic fuel cap inlets, counting three seconds and loosening the cap to let out that compressed air. That’s enough to depress the float by fuel pressure on the needle valve, allowing a trickle of fuel into the venturi and fuel filter plenum chamber, and that’s quite sufficient for reliable starting.

I could make a smaller choke plate (or file down the existing plate) to cover three-quarters of the venturi, and that might be better, but I can’t be bothered, since I soon hope to have the new engine and its Mikuni carb, which should easily lend itself to the inverted conversion (see above).

A few words of warning and amplification...

You do not need this mod to fly inverted manoeuvres. There is so little drag that the Fournier keeps going fine.
My English (red) RF4 does not have this mod, but I can still fly all my usual manoeuvres in that one too.

This is not a reccomendation to incorporate this mod on your engine.
If you do so, obviously it is at your own risk.
Have fun and happy Fournication.

Yours, Bob

[Edit by Bob Grimstead on Sunday, December 20, 2015 @ 10:11 AM]

--------------------
Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Bob Grimstead
Captain

Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2027

Click here to see the profile for Bob Grimstead Visit http://www.redhawksduo.co.uk Send email to Bob Grimstead Send private message to Bob Grimstead Find more posts by Bob Grimstead Edit or delete this message Reply w/Quote
Posted Sunday, December 20, 2015 @ 10:14 AM  

This is the result. A fifteen second inverted run I made in Perth a few weeks ago.

https://www.youtube.com/watch?v=DPLlqaazUpg

--------------------
Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Jorgen
Captain

Gender: Male
Location: Lund, Sweden
Registered: Apr 2007
Status: Offline
Posts: 833

Click here to see the profile for Jorgen Send email to Jorgen Send private message to Jorgen Find more posts by Jorgen Edit or delete this message Reply w/Quote
Posted Monday, December 21, 2015 @ 05:38 PM  

Thanks Bob,
that was really interesting. Did you have the same mod when you shot the slow roll clip too? If I were to find a replacement Zenith carb I might try your mod too. After hibernation through this winter that is.....

May the 4s be with you/ Jörgen

Bob Grimstead
Captain

Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2027

Click here to see the profile for Bob Grimstead Visit http://www.redhawksduo.co.uk Send email to Bob Grimstead Send private message to Bob Grimstead Find more posts by Bob Grimstead Edit or delete this message Reply w/Quote
Posted Sunday, December 27, 2015 @ 09:10 PM  

I have a spare carburettor, and probably some of the tubing left Jorgen, if you're interested in buying it, but I'm sorry, I don't have the time to make the conversion.

--------------------
Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Post New Topic   Post A Reply Jump to:
Contact Us | cfiamerica.com | Privacy Policy All times are GMT -4 Hours.
Welcome to The Fournier Forum, Guest!  
Login
Username :
Password :
In order to fully utilize the abilities of this board, you are required to register as a member. Registration is free, and allows you to do lots of things including turning on or off certain features of this board. Register now!
Forum Rules & Description
Who Can Read The Forum? Any registered user or guest
Who Can Post New Topics? Any registered user
Who Can Post Replies? Any registered user
Who Can Edit Posts? Any original author
It can never be said too often: Get professional instruction before you even read this section!
Currently Active Users: 85
There are currently 0 members and 85 guests on the boards. | Most users ever online was 822 on 08-01-2020 10:15 PM
Search This Forum
Search Keywords: Search From:
Powered by CuteCast v2.0 BETA 2
Copyright © 2001-2003 ArtsCore Studios