Has anyone got a VW engine installed in their a/c that has a priming device fitted to the inlet manifolds?
The type of device I'm specifically interested in is the SAF push type drain valve that allows a syringe full of fuel to be squirted directly into the manifold as part of the starting procedure.
If you do have this or very similar type of device fitted and it was installed as an authorised mod to the engine, would you please contact me as I wish to fit this priming system to my a/c's VW engine.
I've contacted LAA engineering and they have advised that such a mod may have been approved in the past but they do not currently have the resources to locate it in the mainly paper files however, if I can let them know of an aircraft that does have the mod fitted as an approved mod, the search will be easier.
Failing this, I've got to go through the small mod approval process which is not a real problem but will be a real annoyance if I subsequently learn that it was approved all along.
Thanks in advance for any assistance given.
VW engines with priming device fitted to inlet manifolds
Moderators: John Dean, Moderator
VW engines with priming device fitted to inlet manifolds
Roger Callow
033963
033963
Sound like an odd arrangement.
What problem is it designed to address?
Are we talking about an aircraft with no electrical system? If so, doesn't pulling the prop through 16 or 20 blades prime the engine before the 'mags on' swing?
If an aircraft with an electrical system then why not fit an electric fuel pump, and then just pump the throttle a few times? This rather assumes a Stromberg or similar, I suppose: if not the case then what about a proper aircraft hand primer to proper nozzles in the inlet tract(s)
Or am I missing something?
Also, wouldn't a push type drain valve in an inlet manifold open with the suction of the engine when running, leaning the mixture?
What size of syringe? Sounds like an awful lot of fuel to me. It would surely just sit in the manifold un-atomised waiting to catch light in the event of a backfire on startup!
Just realised I'm sounding very negative! Sorry about that. I hope to be enlightened.
What problem is it designed to address?
Are we talking about an aircraft with no electrical system? If so, doesn't pulling the prop through 16 or 20 blades prime the engine before the 'mags on' swing?
If an aircraft with an electrical system then why not fit an electric fuel pump, and then just pump the throttle a few times? This rather assumes a Stromberg or similar, I suppose: if not the case then what about a proper aircraft hand primer to proper nozzles in the inlet tract(s)
Or am I missing something?
Also, wouldn't a push type drain valve in an inlet manifold open with the suction of the engine when running, leaning the mixture?
What size of syringe? Sounds like an awful lot of fuel to me. It would surely just sit in the manifold un-atomised waiting to catch light in the event of a backfire on startup!
Just realised I'm sounding very negative! Sorry about that. I hope to be enlightened.
Rob Swain
If the good Lord had intended man to fly, He would have given him more money.
If the good Lord had intended man to fly, He would have given him more money.
Rob. The general idea is to ease starting on an engine fitted with a carb that doesn't have an accelerator pump with which to prime the engine.
As you know the Stromberg 150 relies on a choke and loads of pull throughs of the prop before sufficient mixture has been drawn into the combustion chambers.
I'm not getting any younger and pulling a prop through 10 to 15 times before throwing the switch is getting more difficult, so a priming device is a good option for me.
I do know the device is fitted to VW powered a/c elsewhere in the world (and possibly even in the UK) but no official mod exists (or can be found) in LAA engineering's records.
Having spoken to them about the use of SAF valves as a priming device they share the concerns about the valve being opened by the negative pressure in the inlet manifold but if that were a problem a stronger return spring could be utilised to overcome that particular issue.
If I can find this device (or similar) in use on a VW installed in a permit aircraft on the UK register, the information I could gather on how the installation had operated safely over a long period would be very benificial to my plans to seek a minor mod approval.
Thanks for your input.
As you know the Stromberg 150 relies on a choke and loads of pull throughs of the prop before sufficient mixture has been drawn into the combustion chambers.
I'm not getting any younger and pulling a prop through 10 to 15 times before throwing the switch is getting more difficult, so a priming device is a good option for me.
I do know the device is fitted to VW powered a/c elsewhere in the world (and possibly even in the UK) but no official mod exists (or can be found) in LAA engineering's records.
Having spoken to them about the use of SAF valves as a priming device they share the concerns about the valve being opened by the negative pressure in the inlet manifold but if that were a problem a stronger return spring could be utilised to overcome that particular issue.
If I can find this device (or similar) in use on a VW installed in a permit aircraft on the UK register, the information I could gather on how the installation had operated safely over a long period would be very benificial to my plans to seek a minor mod approval.
Thanks for your input.
Roger Callow
033963
033963
Wouldn't an aircraft primer just do the job?
The mega cheap option:
http://www.aircraftspruce.com/catalog/a ... merkit.php
The somewhat more expensive option:
http://www.aircraftspruce.com/catalog/a ... primer.php
By the time you've been round the houses with a new mod etc. the above is likely to be quicker and cheaper. OK it still needs a mod form, but it would probably be quite quick, being a pretty conventional solution.
There are other priming options on the ACS site too.
I have one other question: Avgas or Mogas?
If Mogas then it might be that when you come to start up the float chamber is close to empty, the fuel having evaporated in the engine heat after last shutdown. All those blades to get the engine going might just be pumping fresh fuel up from the gascolator, through the fuel pump and into the float chamber. Is an electric fuel pump a possibility? That might sort some of the problem. You could run it off a small 12v sealed lead acid battery.
Avgas suffers such evaporation in the same way, but nowhere near as bad.
The other issue with Mogas is it 'goes off' much more quickly than Avgas, which makes starting more difficult.
I sometimes resorted to detaching the fuel line from the carb and injecting fuel in with a syringe to fill the float chamber, put the hose back and give it a swing. It would often go first swing (admittedly with electronic ignition).
The mega cheap option:
http://www.aircraftspruce.com/catalog/a ... merkit.php
The somewhat more expensive option:
http://www.aircraftspruce.com/catalog/a ... primer.php
By the time you've been round the houses with a new mod etc. the above is likely to be quicker and cheaper. OK it still needs a mod form, but it would probably be quite quick, being a pretty conventional solution.
There are other priming options on the ACS site too.
I have one other question: Avgas or Mogas?
If Mogas then it might be that when you come to start up the float chamber is close to empty, the fuel having evaporated in the engine heat after last shutdown. All those blades to get the engine going might just be pumping fresh fuel up from the gascolator, through the fuel pump and into the float chamber. Is an electric fuel pump a possibility? That might sort some of the problem. You could run it off a small 12v sealed lead acid battery.
Avgas suffers such evaporation in the same way, but nowhere near as bad.
The other issue with Mogas is it 'goes off' much more quickly than Avgas, which makes starting more difficult.
I sometimes resorted to detaching the fuel line from the carb and injecting fuel in with a syringe to fill the float chamber, put the hose back and give it a swing. It would often go first swing (admittedly with electronic ignition).
Rob Swain
If the good Lord had intended man to fly, He would have given him more money.
If the good Lord had intended man to fly, He would have given him more money.
Roger,
My Colibri has a primer fitted that deposits fuel into inlet manifold. Ask the LAA to look at G-HRLM. It's been there as long time so could have been part of the original build. I still have to wind the prop to ensure the carb is full, else it just runs on the prime and then stops.
The primer is a ki-gas type and dumps too much fuel in if you use a full stoke of the plunger.
Like all VW's, you have talk to it nicely before trying to start it, or it won't play.
Hope this helps
My Colibri has a primer fitted that deposits fuel into inlet manifold. Ask the LAA to look at G-HRLM. It's been there as long time so could have been part of the original build. I still have to wind the prop to ensure the carb is full, else it just runs on the prime and then stops.
The primer is a ki-gas type and dumps too much fuel in if you use a full stoke of the plunger.
Like all VW's, you have talk to it nicely before trying to start it, or it won't play.
Hope this helps
027411