Actual Flying Rotax Installs

[WesRagle]

Hey Rusty,

Looking good! Did you put the O'Keefe Aero landing gear on it?

Wes

[13brv3]

Hi Wes,

Stock gear. I went with the 5.00x5 tires, which gave me about an extra inch of prop clearance. Warp seems to think a 60" 3 blade will work fine for 80 HP, so that's what I've got. Prop clearance will be tight, maybe 6", but I had 4" on an RV-3B with a Mazda engine, and those gear legs were really flexible. I never hit the prop, but the guy I sold it to trimmed it a bit on the runway :-)

I'm hoping to get the wings on it tomorrow, and I'll be really interested to see how the W&B comes out.

Rusty

[WesRagle]

Hi Rusty,

Sounds good. Stay out of the gravel ;-)

Wes

[Kai]

Kai,
Murray is absolutely right.
A larger bore will decrease your overall brake pressure, a smaller bore will require a little more effort, but much more pressure. On my Sonex I’m using 1/8” line and 1/2” bore Hegars on my Sonex brakes and if I try and land short and apply hard pressure, I have to back off sometimes because my tail will rise and the plane will nose over. They are toe brakes so I am able to apply a good amount of pressure. They do provide adequate stopping power. Differential definitely makes a difference in control and stopping ability. Now I don’t need a parking lot to make a u-turn. Hegar makes a quadrant of dual masters and handles you could install. Also you could install 2 handles on the stick, I say that because my other aircraft with Hegar brakes have them set up on the handle and they work awesome. I just alternate with my fingers and I don’t have to take my hands off any controls. Only difference between the 2 planes is I have Hegar disk brakes on one, and Sonex on the other. Lines and bore sizes are all the same. I would shy away from heel brakes in my opinion. Or, just make some toe brakes!

Herraripower,

Most gratefull for all explanations given by you, Murray, and others. Should I decide to rebuild the brake system, 2 pcs 1/2” bore masters clearly seem the way to go!

I once flew some kind of Cub (I seem to recall) with heel operated brakes. They indeed took a little while to get used to. And while I don’t feel differential braking is a must operational wise (category ‘nice to have’), making up some sort of baseplate with both heel brake masters installed on them before the whole setup is secured to the cockpit floor, presently clearly seem to be the easy way out installation wise- anyhow much less physical contortions than rebuilding to toe brakes would require. And when I got this setup worked out I could perhaps install some sort of parking brake valve operated by the existing standard wheel brake lever.

But- am I missing something? It seems you probably know something I don’t: why shy away from heel brakes?

Thanks
Kai

[Zack]

Great stuff Zack. Thanks for all that. Did you manage to work out how to post the pdf file you referred to??

I would reach out to Ryan Mace at Mace Aviation for details, he could also provide you the PDF. https://www.maceaviation.com/ It has multiple 3D views, some transparent that really help you visualize the cowling. Here's one page:

[Zack]

Next week is exhaust week, I trailered the plane to the exhaust fabricator yesterday. My goal for the exhaust was equal length primaries and a 4-1 merger into a secondary, all at appropriate lengths for engine size, rpm etc to maximize power between 5400 - 5900 RPM range. I purchased a program called PipePRO that allows you to enter the engine characteristics and it would calculate the ideal pipe length, diameter etc. The end result would look like some of these systems: https://www.kitplanes.com/firewall-forw ... t-systems/

Unfortunately the space constraints won't let that happen. The biggest issue is the Sonex bed mount verses the more typical ring mount. In addition to the mount, the radiator and oil cooler are also on centerline. If I wanted to merge the exhaust from each pair of cylinders it would have to happen behind the radiator close to the firewall. This won't leave space for any length after the collector, it would have to drop out of the cowling immediately. I would need to use inline mufflers before the collector. Finally, running the exhaust along the entire bottom of the firewall would add a lot of heat where my ECU, fuel pumps, fuse box etc are mounted. Not an ideal situation.

Thanks to the wider firewall on the B-Model, I do have a lot of room on the sides. We are planning to do a 2-1 design with two exits, one on each side. I considered the sides of the cowling first, but I don't want the exhaust exiting directly in front of the leading edge of the wing, and higher up I have two of Peter's NACA vents and I don't want CO poisoning. So out the bottom it is.

Based on my research, and the PipePRO program, I should NOT step up the pipe diameter after the merger / collector on a 2-1 system like I would for a 4-1. I'll be using 1.2500 OD tubing (the factory exhaust sockets measured 1.1895 OD). The ID is 1.1300 versus the 28mm / 1.100 the Installation Manual calls for. I will try for 11th harmonic 8.8" to 11.9" equal length primaries with 7-15 degree merge angle, then an inline motorcycle style muffler and exit out the bottom between the landing gear legs and the radiator exhaust duct.

The Rotax installation manual states: "Distribution of the exhaust system into 2 separate systems is not recommended. Individual mufflers on either side cause power loss and increased engine noise." but it also says "The shape and configuration of the exhaust system is essentially determined by the free space available in the aircraft.". I'm disappointed there wasn't space for a 4-1 system. Looking back, the only way that would work is if I had ring mount and / or split the radiators, one on each side.

The graphic I shared in the previous post should help visualize this. I'll take photos this week and share later.

[Kai]

Next week is exhaust week, I trailered the plane to the exhaust fabricator yesterday. My goal for the exhaust was equal length primaries and a 4-1 merger into a secondary, all at appropriate lengths for engine size, rpm etc to maximize power between 5400 - 5900 RPM range. I purchased a program called PipePRO that allows you to enter the engine characteristics and it would calculate the ideal pipe length, diameter etc. The end result would look like some of these systems: https://www.kitplanes.com/firewall-forw ... t-systems/

Unfortunately the space constraints won't let that happen. The biggest issue is the Sonex bed mount verses the more typical ring mount. In addition to the mount, the radiator and oil cooler are also on centerline. If I wanted to merge the exhaust from each pair of cylinders it would have to happen behind the radiator close to the firewall. This won't leave space for any length after the collector, it would have to drop out of the cowling immediately. I would need to use inline mufflers before the collector. Finally, running the exhaust along the entire bottom of the firewall would add a lot of heat where my ECU, fuel pumps, fuse box etc are mounted. Not an ideal situation.

Thanks to the wider firewall on the B-Model, I do have a lot of room on the sides. We are planning to do a 2-1 design with two exits, one on each side. I considered the sides of the cowling first, but I don't want the exhaust exiting directly in front of the leading edge of the wing, and higher up I have two of Peter's NACA vents and I don't want CO poisoning. So out the bottom it is.

Based on my research, and the PipePRO program, I should NOT step up the pipe diameter after the merger / collector on a 2-1 system like I would for a 4-1. I'll be using 1.2500 OD tubing (the factory exhaust sockets measured 1.1895 OD). The ID is 1.1300 versus the 28mm / 1.100 the Installation Manual calls for. I will try for 11th harmonic 8.8" to 11.9" equal length primaries with 7-15 degree merge angle, then an inline motorcycle style muffler and exit out the bottom between the landing gear legs and the radiator exhaust duct.

The Rotax installation manual states: "Distribution of the exhaust system into 2 separate systems is not recommended. Individual mufflers on either side cause power loss and increased engine noise." but it also says "The shape and configuration of the exhaust system is essentially determined by the free space available in the aircraft.". I'm disappointed there wasn't space for a 4-1 system. Looking back, the only way that would work is if I had ring mount and / or split the radiators, one on each side.

The graphic I shared in the previous post should help visualize this. I'll take photos this week and share later.

[Kai]

……..The Rotax installation manual states: "Distribution of the exhaust system into 2 separate systems is not recommended. Individual mufflers on either side cause power loss and increased engine noise." but it also says "The shape and configuration of the exhaust system is essentially determined by the free space available in the aircraft.". I'm disappointed there wasn't space for a 4-1 system. Looking back, the only way that would work is if I had ring mount and / or split the radiators, one on each side……..

Zack,

Eighteen months ago this was me.

After intense and exhausting activity of my mental capability I came to the same conclusions as you: INCREDIBLE! I HAVE ACTUALLY DONE SOMETHING RIGHT! But there is always some nagging doubt, so thank you for this confirmation. Hence my decision not to fall for the temptation to use the easy way out and go for the Sonex bedmount. Instead I slightly butchered my Jab 6 mount, fabricated two 12mm steel adapter bars for the rubber isolators to go between the Jab mount and the Rotax ring, and went for a split radiator setup. Pictures of the installation was posted on this forum a good while back.

This setup allows more free space for the exhaust setup, but my Legacy cowling is even more restrictive than your B-type, so the selection of an exhaust system caused many sleepless nights. I finally decided to go for the Rotax 914 setup- piping, flanges, brackets, and muffler. As a replacement for the turbo I had a stainless pipe connector elbow tig welded up with inlet- and outlet turbo flanges on the exact same positions as the turbo housing. The final result is good suppression of the characteristic Rotax exhaust noise, with an aggressive, dark, undertone. Super!

The split radiator setup required some additional work, as overcooling even in high (for us) ambient temperatures could only be harnessed with the addition of tw BMW V12 thermostats, one for each radiator cirquit. Finally coolant temps stay pegged at 80C’s during operations.

Thx
Kai

[Zack]

Kai,

You made a sound decision. My philosophy on this project is to take things one step at a time. In this case my previous decisions have limited my exhaust options. Looking back, I think I'd still chose the Sonex bed mount simply because I'd want an engineered ring mount, I don't have those skills, and finding others that could engineer and fabricate the ring mount would be expensive. I do wish Sonex would ditch the bed mount though, it's been a source of frustration.

The 2-1 design should have some advantages, it's simple, light, and easy to install. The PipePRO program identifies primary and collector pipe lengths based on the harmonics. Like a trombone changing length for different notes, you can tune your exhaust lengths to give you a negative pressure pulse as the exhaust valve opens, to improve airflow through the cylinder head. Here is the output of the program for the 2-1 header (Rotax 912 engine specs but for a 2 cylinder instead of a 4). Caveat: the inputs I supplied to the program were to the best of my ability!

--- Primary Tube Specs : Race Header • Single Tube diameter size ---
Peak TQ Diameter Range = 1.213 -to- 1.338 Best Length = 32.524 -to- 34.924 inches
Best Mid-Range Diameter = 1.338 Best Length = 32.524 -to- 34.924 inches
Peak HP Diameter Range = 1.338 -to- 1.463 Best Length = 32.524 -to- 34.924 inches

--- Primary Tube Harmonics --- ( One-End-Closed Tube = Odd Numbered Harmonics )
1st Harmonic = 97.573 to 99.973 inches long ... typically never used ( too long to fit any Vehicle )
3rd Harmonic = 32.524 to 34.924 inches long ... highly recommended , best Torque and HP Curve
5th Harmonic = 19.515 to 21.915 inches long ... shortest recommended ( Shorty or very Hi-RPM Header )
7th Harmonic = 13.939 to 16.339 inches long ... shortest recommended ( Shorty, Hugger, or Log Style )
9th Harmonic = 10.841 to 13.241 inches long ... shortest recommended ( Log Style or Cast-Manifold )
11th Harmonic = 8.870 to 11.270 inches long ... shortest recommended ( Log Style or Cast-Manifold )
------------------------------------------------------------------------------------------------------
--- Collector Specs : Straight Tube Collector • or Straight with a slight Merge shape ---
Peak TQ Diameter Range = .923 -to- 1.048 Best Length= 21.312 -or- 42.624 inches
Best Mid-Range Diameter = 1.048 Best Length= 21.312 -or- 42.624 inches
Peak HP Diameter Range = 1.048 -to- 1.173 Best Length= 21.312 -or- 10.656 inches

--- Collector's Harmonics --- ( Both-Ends-Open Tube = Odd and Even Numbered Harmonics )
1st Harmonic = 170.494 inches long ... longest recommended with Mufflers and TailPipes
2nd Harmonic = 85.247 inches long ... longest recommended with Mufflers and TailPipes
3rd Harmonic = 42.624 inches long ... greater Low RPM Torque -to- Peak Torque RPM
4th Harmonic = 21.312 inches long ... highly recommended , best Torque and HP Curve combination
5th Harmonic = 10.656 inches long ... reduced Peak Torque , higher RPM HP gains possible
6th Harmonic = 5.328 inches long ... reduced Low RPM Torque , even though Tuned Length

Best TQ + HP Tuned Collector Lengths= 5.328, 10.656, 21.312, 42.624, 85.247, 170.494 inches long
Worst TQ + HP Loss Collector Lengths= 7.992, 15.984, 31.968, 63.935, 127.871, 255.741 inches long

Collector definition: from the Primary Tube's ending inside the Collector -to- Atmospheric exit point
Note : all Tube Outside Diameters are based-off your Header Tube Thickness choice's value

These lengths are similar when calculated for a 4-1 system, but the collector diameter is larger. 33 in / 84 cm primaries and a 21 in / 53 cm collector would never fit in a Sonex cowl. Even if that large exhaust header fit, it would be heavy and put off a lot of heat to be managed. That squashed my dream of an ideal tuned 4-1 system and made my compromise 2-1 system easier to accept. We're targeting 5th Harmonic = 19.515 to 21.915 inches long primaries right now. Once we tack that up today or tomorrow we'll figure out the collector.

We were planning to use an inline motorcycle style muffler as part of the collector. Has anyone had experience with straight pipes on a Rotax, are they really loud or obnoxious?

[Kai]

Zack,

Depends a little on what kind of straight through muffler you are planning to use.

We have experimented a little with what Tony Bingelis defines as a ‘swiss muffler’. It’s a fairly long outer tube, a perforated inner tube, the space between inner and outer filled with absorption material.

This layout was not a success for the high revving Rotax. To tame the Rotax bark we needed a very long (almost as long as the fuselage) unit. It worked so-so to start with, but after a short while the thing got louder and louder: the absorption material disappeared out of the muffler!

We came to the conclusion we needed something with chambers/deflectors.

Thx
Kai