What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

What isn't stock in this pic?

seagull

Well Known Member
There are several mods I have done but one should stand out.

I have 75 hours 3 1/2 months on this configuration. Went through a 50 oil change and conditional. I see no harm only good results.

balance tube_s.jpg
 
Looks like safety wire is missing for left carb air filter.

No safety wire on either air cleaner.
They fit in such a way the clamps would have to loosen for them to come off. If they were safety wired in the tang it would not stop them from coming off, only falling to the bottom of the cowling.
 
Everything looks California normal to me :rolleyes:, except that loose wire connector lying next to the #3 upper spark plug cap...

Jes kiddin! Why the jumbo crossover pipe??
 
“Loose wire” is connected to coolant temp sensor.

Oversized balance tube works at a much higher RPM than the OEM one. Very smooth running at all speeds. I haven’t noticed any negatives.
 
It also has two gps antennas.

I have a Dynon on the pilot side and Garmin 696 on the co-pilot side. They each have their own GPS and ADS-B receivers. I like the redundancy and that sometimes one will report an aircraft the other won't.
 
OK, I'll play: Right-side carb retention spring is not attached at forward end to modified crossover tube.
 
If you're looking for non-stock items, I noticed that crossover tube as well... but I'm surprised no one has mentioned the blue silicone water hoses yet. :)
 
Oversized balance tube works at a much higher RPM than the OEM one. Very smooth running at all speeds. I haven’t noticed any negatives.

I am skeptical that this would make any difference in the smoothness at higher RPM's... (but I haven't ever done any tests so it is just an opinion based on the design philosophy of what it is supposed to do)

When at WOT (wide open throttle) or nearly so, the potential imbalance between the two carbs is miniscule. I.E., a small difference in throttle plate position will have little if any difference in flow area of the carb throat.

It is at idle and just above idle that the cross-over tube has much influence. That is why after reconnecting the crossover tube after doing a carb synch, it is not uncommon for the engine to feel even a bit smoother on idle than it did while finishing the synch procedure (during the synch procedure, the balance tube is effectively not connected, so is not having any influence on engine smoothness).
 
I had heard a larger crossover tube, how much larger than stock I’m not sure, helps equalize carbs better than the stock tube. Your mod looks good. Please report any data points you notice during your operations.
 
When at WOT (wide open throttle) or nearly so, the potential imbalance between the two carbs is miniscule. I.E., a small difference in throttle plate position will have little if any difference in flow area of the carb throat.

I agree what you say about WOT. I am only at WOT when climbing. I cruise between 4800 - 5200 unless I am in a hurry. Descents are below that. These lower RPM’s 3000 - 5000 are where it makes a difference.

The stock tube looses its influence above 3000 RPM.
 
I agree what you say about WOT. I am only at WOT when climbing. I cruise between 4800 - 5200 unless I am in a hurry. Descents are below that. These lower RPM’s 3000 - 5000 are where it makes a difference.

The stock tube looses its influence above 3000 RPM.

I am still skeptical, but maybe you are smarter than the Rotax engineers ;)
 
That wasn’t necessary, especially from you.😞

MAYBE, they they had constraints like cost, average use, or a new design on the horizon 912is.

If you took that as a personal dig, I apologize. It wasn't meant that way at all, which was why I included the ;).

I think it is pretty much a universally accepted premise that the 912 Rotax has some pretty high level engineering and 35+ years of evolutionary development time behind it.

The context of my thought was just that.
 
Alright, Walt... I know this isn't a discovery, because you told me about it... long ago, I'm just surprised I still remembered it.

You have lines of some sort, going from the carb vents to the back of each K&N air cleaner, much like on a Factory Rotax air cleaner box.

You'll have to explain how that's working out with the lowered fuel consumption per hour.
 
Alright, Walt... I know this isn't a discovery, because you told me about it... long ago, I'm just surprised I still remembered it.

You have lines of some sort, going from the carb vents to the back of each K&N air cleaner, much like on a Factory Rotax air cleaner box.

You'll have to explain how that's working out with the lowered fuel consumption per hour.

Yup, there is that also.
The air above the fuel in now at the same atmospheric pressure as the air going into the carburetor. This is important because a difference in pressure will cause a rich or lean condition in that carburetor.
The turbulence inside the cowling causes variable pressure on that vent tube when it is left under the bowl bail.
Fuel consumption is down about 12% and plugs look much better.
carb vent.jpg
 
The hose clamp on the hose from the radiator seems to have washers under the nut, I have never seem that configuration before. Also what is the 90* pipe inside the yellow hose into the air filter?
 
The hose clamp on the hose from the radiator seems to have washers under the nut, I have never seem that configuration before. Also what is the 90* pipe inside the yellow hose into the air filter?

The OEM hose clamps are "spring" type to keep a continuous clamping force as the parts grow and shrink with temperature. I was unable to find spring clamps that fit the 1" silicone hose. These clamps use belleville washers stacked under the screw to maintain the clamping pressure. Another feature is they don't have an exposed screw track on the band that eats the easily cut silicone.
https://www.mcmaster.com/hose-clamps/clamp-type~worm-drive/constant-tension-clamps-for-soft-hose-and-tube/


I wanted the hose to turn sharp coming out of the air cleaner without collapsing. I put a stainless 90 degree tube inside the Tygon vent hose. There is a nylon tie on the hose 1" from the end to set the distance inside the air cleaner. The tie would normally collapse the Tygon without the stainless tubing. The stainless tube has a slight flare on the end inside the Tygon tube. The tie is before the flare so the tubing can't slip out of the Tygon.
 
Last edited:
Yup, there is that also.
The air above the fuel in now at the same atmospheric pressure as the air going into the carburetor. This is important because a difference in pressure will cause a rich or lean condition in that carburetor.
The turbulence inside the cowling causes variable pressure on that vent tube when it is left under the bowl bail.
Fuel consumption is down about 12% and plugs look much better.
View attachment 14637

If you do a longer trip, say, pick an altitude, at 4500 ft, at 5200 rpm, what's your burn rate of fuel per hour?

And what would it be at 8500 ft altitude?
 
I was at Apple Valley for breakfast and saw this question. I climbed to 8500 on the way back, set autopilot for KREI then adjusted for 5200 RPM.
You only asked for that speed but later thought about other RPM's, the reason for the other screen shots.

8500_5200rpm.jpg

8500_5410rpm.jpg

8500_4580rpm.jpg
 
Just wondering out loud how close that is to fuel consumption for a 912IS motor? At least .5 gal /hr better than what I see in my RV-12.

Still running Costco Mogas? Complete with close to 10% ethanol?
 
Last edited:
The other NON Stock things are teh 1st design AS Flightlines teflon hose assemblies for the fuel sytem. These were before we made the 8m banjo fittings for th teflon hose. Nevertheless----their teflon and have no service life.

Tom
 
The other NON Stock things are teh 1st design AS Flightlines teflon hose assemblies for the fuel sytem. These were before we made the 8m banjo fittings for th teflon hose. Nevertheless----their teflon and have no service life.
Tom

Shouldn't that be "unlimited service life"? Sorry, couldn't resist!
 
Hi Mel! Yep---please excuse my grammar and writing ability---my mind and typing skills arent what they once were-

Tom
 
Walter---I did notice the 5.2-5.4 psi fuel pressure readings. I'm assuming this is pretty standard for you since you changed to our teflon hose package?
Tom
 
Just wondering out loud how close that is to fuel consumption for a 912IS motor? At least .5 gal /hr better than what I see in my RV-12.

Still running Costco Mogas? Complete with close to 10% ethanol?

My 912iS is currently cruising 4500 MSL @ 5000 RPM burning 4.7 GPH while cruising 105kt.

I do not yet have wheel pants and I just picked up from paint shop yesterday and have not installed the gap fill (beveled weather strip) between the wing end and fuselage. I'm hoping wheel pants and weather strip will net me a bit more speed and a bit lower fuel burn.

As for fuel I have two FloFast 10-gallon fuel containers and I stop at Southern States Co-Op and put 5 gallons of 90 octane non-ethanol in each then stop at Shell and fill the rest of each container with 93 octane premium. My thinking is this nets me 91.5 octane with less than 5% ethanol. I'm not a petroleum engineer and didn't stay at a Holiday Inn Express last night so I ask: Am I wrong?

Jayson
 
We (semi) officially consider the entire fairing set (3 wheel fairings and nose gear leg fairing) to be good for a 3 kt speed increase.

Top cruise without fairings - 117 kts
Top cruise with fairings - 120 kts
 
A friend of mine installed the RV12 wheel pants on the main gear of his fixed gear Glasair. He saw 3kts increase in cruise on his first test flight.
 
Back
Top