Exhaust Installation

This blog covers the muffler installation after repair.

Overview
In a previous blog, the issues with the selected exhaust system were covered in detail. What I was not prepared for was the total lack of support from Akrapovic.

After the initial contact, their Australian agent forwarded my simple request for the material type to the factory. As it was manufactured from titanium, my welder wanted to know the material to allow the most suitable filler rod to be used - simple, eh! - no!

My request was greeted with a weasel-worded corporate reply or "We don't want to know."

"Project for Rotax 912 has been concluded directly with the producer. And therefore the nature of the project as well all related conditions of the product, as well as agreements with a partner, are strictly confidential, and we are not allowed to share any info. And since the product is used in particular conditions, my high recommendation would be to contact the seller of your product directly and place the question to them directly.

I apologise that we cannot give you the information you need.

I thank you for your understanding of the situation."

Milan Hernaus

Aftermarket Country Manager 

Repair

The builder decided that the most likely material was Grade 2 Titanium due to the amount of fabrication with a Grade 2 filler rod was purchased. Peter Goard welded the muffler after modifying the internal pipes to the specification outlined in a previous blog.

Poor support..!

Installation

The modified exhaust system was fitted to the engine fresh from a Marwen zero time rebuild and installed onto the engine.

As seen in the attached photo, it meets my specification allowing the radiator and oil cooler to be installed as planned.

For detail of the installation follow the link to my Vlog

https://rumble.com/vw44ju-tucano-r-at-rylstone-vlog-.html

Comment

If it all goes well in service, I will then be happy.

         

Throttle Body Injection

This blog covers the design criteria used to select the Rotec Throttle Body Injector for installation onto the Rotax 912 used on this aircraft.

Overview
The Bing Carbs along with the inlet manifold used on the Rotax 912 are a practical compromise but far from ideal, there are many aftermarket EFI systems but all share a flaw - single channel.

The Rotax 915 features dual-channel electrics/electronics or in plain language a redundant system with two means of fuel/ignition, while ideal, its complex and adds weight with the 915 tips the scales at 84 kg plus extras. 

Aftermarket EFI systems have no reported history of failure, most pilots will never in their flying careers use any of the dual redundancy incorporated into a typical certified aircraft engine but this only means there is a very small statistical chance of a failure but when it is required its 100% significant to that pilot at that point in space and time.

Regardless of which EFI is used, they share one common requirement, that's for the Rotax's regulator to keep working and it's the one item incorporated into a Rotax engine that is considered a weak link. The electronics operating an EFI system use's 5 - 8 amps, leaving only 10 amps available from the Rotax alternator to maintain the battery and panel electric's so a larger alternator may be required, more weight/cost but at least there is a backup available. 

The need to have an operating electrical system also means you have to have a larger [heaver] battery and the 1 kg battery that is installed will not provide the necessary flight endurance to an alternative airfield.

Note: In the event of total electrical failure there is a high drain on any battery and at 11V a battery is considered dead flat. 

Dog Aviation review on the RV12 and the Standard Ducati Regulator

 Photos are taken from Dog Aviation images investigating a series of 
RV12 regulator failures

SDS EFI  "Aircraft engines are essentially constant rpm load devices, spending the majority of their lives at fixed power settings for long periods of time. Once a power setting is established, the injector on-time and ignition timing remain the same until power is changed. 

For this reason, we feel that 3D mapping offers no useful benefits, it merely complicates understanding and operating the system for most people"

An alternative was not available until Joe Newman from Marwen discussed with Pual from Rotec that the TBI should work with a supercharger as the new Mk2 version incorporated an internal pressure reference, at this point both agreed that they could not see a reason why it could now not operate under positive pressure, it was unproven but now worth a look, Joe had with one in his bag on his return to Rylstone. 

Note: The Mk 2 Rotec TBI now an upgraded version of the proven Ellison TBI

Installation of the single Rotec TBI onto the Tucano engine was the only option as the dual TBI setup would not fit.

Service kit - it's that simple

A suitable TBI manifold would require flat runner exits, equal length runners and large volume. 

At this time the FAA approved plastic Ultem 9085 was selected to manufacture all the necessary parts using FDM printing.  A lot of time was put into to optimising the design with FEA to obtain a feel for how the plastic would perform. FEA can create an unreliable results with plastics so the design parameters used were at 140 degrees C to analyse a single state, while not a 100% accurate it's better than a guess. 

A Rotax 914 engine cannot be operated at greater than 88 degrees C and therefore 140 degrees C was selected as the structural design point with 100 C as a maximum operating temperature. A Rotax cam has little overlap so pressure waves from the opening of the inlet valve have been ignored as a design load.

Ultem 9085 plastic was chosen for its superior Izod number and heat deflection temperature [HDT] and strength at elevated temperature.

Material Specification

A 3D model estimated an assembled weight of 1.8 kg for the throttle, body/manifold/primer which is 1.2 kg lighter than the Rotax assembly it would replace.

Proposed Manifold/TBI/Inter-cooler
3.5 kg as shown [design weight 4 kg]

Elevation

Plan

Note: A Rotax engine MUST NOT exceed 88 degrees C, so a temperature probe is to be installed at the inter-cooler outlet allowing the temperature to be monitored.

The biggest issue at this time is this may not work, why, the Mk 1 Rotec will not operate under positive pressure but the Mk2 may because of a major design change Joe from Marwen noted at Oshkosh.  

To prove the design a 3D printer will be purchased early next year to manufacture a working prototype and it up to both of us to prove it works as a system. If it does work it will be 2/3 the price of an injection system and lighter - worth the look.

If it does not work back to the drawing board and on go the Bings.

Meshing basic manifold

Stress at peak [red] about 4 Mpa with 20 Mpa on Z axis allowable at 140C
Simple manifold used as this is within the limits of the package available
The model has a 3 mm thick wall, a wall thickness of 2.5 would be acceptable 

Comment

What if, what if?

Radiator - Oil Cooler Mount

This blog covers the manufacture and installation of the radiator mount

Overview
There are no details on mounting the radiator and after peering at it for a while a email was sent to the factory, a series of photos showing the factory mount were received but more importantly the mounting points on the engine shown - problem solved.

A 2D drawing for a Rotax 912 was located on the net and then a profile was developed and sent out for laser cutting in aluminium.

It was decided to mount the radiator in a flexible mount - to do this the four mounting bolts were secured through 6 mm OD grommets secured with flanged M6 bolts and large S/S washers. The grommets were mounted in seperate angle brackets with the top pair riveted and both lower brackets secured with M3 cap head screws fitted into rivet nuts - this allows easier installation.

The frame was assembled over the radiator, offered to the engine and secured using M10 Titanium bolts just to save a little more weight.

A good feature is that once the lower bolts are removed the assembly hinges forward on the upper bolts.

Oil Cooler
The installation of a Silent Hektik oil cooler removed the need to cut another opening into the cowl allowing better control the air flow in the long run.

Oil Cooler Schematic

Engine Cooling Schematic

The location for the oil cooler is behind the radiator mounted off the arm supporting the radiator. 

Radiator / Oil Cooler bracket hinged forward

The bracket was fabricated from aluminium sheet 0.030 and 0.020'' to provide the mounting points and stiffeners respectively. 

Construction was dictated by the folder but a satisfactory bracket was created within these limits and the cooler mounted using four [4] M6 x 20 screws through 10 mm spacers onto the base plate. 

All assembly was done using 3.2 pop rivets.

Oil Cooler Bracket

Radiator / Oil Cooler / Picture frame seal installed

Comment
The choice to install a duct from the inlet to the radiator precluded installation of a oil cooler under the nose and the water cooled option seemed to fill the need. The advent of the Vixen from Foxbat confirmed my decision has some solid ground, this aircraft is 20 knots faster than its predecessor the Foxbat on the same wing and motor. 

The air for the oil cooler is collected under the top lip of the inlet and ducted over the radiator to the oil cooler at 90 degrees to the radiator.

The primary difference apart from a different fuselage profile is a extreme upgrade of the air flow through the cowl including a radiator that is effectively ducted from the inlet. This is not the sum of the changes but may explain some of the speed boost.

The next task is the duct this will have a overall length of 175mm and will seal on the picture frame shown on the photo above with the biggest problem just plumbing all the hoses and this has thrown a few plans into a spin.

The good news the muffler, oil cooler and radiator fit into the area allocated, hoses are another issue as already stated.

Muffler Fix

This blog covers the work to fix the muffler as outlined in a previous blog.

Overview
The muffler has to be rectified as the installation needs the compact design and the weight saving that is more than welcome. 

Rework
The first problem was to remove the side plates with the inspection opening showing that this was possible. After a number of different approaches with the best using a 4'' grinder with cutting disk to remove approximately 50% of the flange and finishing with a grinding wheel. A few blows with a soft hammer and the flange broke free.

The penetration from the bead weld is better than a mm and the standard of workmanship from the welder / fabrication is without fault - design is another issue.

Modifications shown in red
After modification it will become only a resonator box

Once the modifications were done the components were bundled up and set out for re-welding.

Comment

Me Too

Muffler Cluster @%#^

This blog covers what called a Cluster !#% begin supplied as a muffler system.

Overview
It was decided to save some muffler weight by selecting a titanium muffler manufactured by Akrapovic. Though expensive it carved two [2] kg from the total weigh and was very compact in design so on its arrival it was found to be of a first class construction and fitted like a glove and confidence was high.

Later examination revealed a rather small perforated inlet to the exhaust side of the muffler but a internet search yielded no bad reports but it was put on the to look at list. A recent Facebook Post created a reply from Thomas at Edge Performance indicated that this was indeed a problem so it moved up my to do list. 

Examination of the inlets and exhaust with a torch showed a perforated inlet of at least four times the length of the outlet with the areas begin larger than the inlet/outlet pipes based on a 50% open area. However Thomas comment concerned me so the decision was made to open up the outlet for possible modification and this is were the reason for the failure of the design became slowly apparent.

Exhaust outlet - No I am not kidding
that's all there is

With the access the builder decided to grab the torch and look up at the inlet and that is when another issue revealed its ugly head, that 100 mm perforated tube had only 50 mm of exposed area as 25 mm was mounted in a flared slip tube to reduce thermal stress.

At this point the logic of the system escaped me totally - OK I am not that bright but this just left me lost for why..!

A - the slight shadow id the end of the flared mount
B - Is the 50 mm of open tube
C - The end of the inlet tube

A lot of time was spent on the internet with no comparable concept found until a clip on why a turbo muffler can flow more gas that the classic hot dog straight through. Classic turbo mufflers form a looped path with the inlets and outlets offset from each other - So why are they more efficient that a straight line of the hot dog?

The answer lied in the fact that the perforated material of the legs inside the muffler had a ever increasing boundary layer even though some gas escaped via the perforated leg until it exited to the next leg creating an increase in gas velocity.

So in a previous life I had been involved with piping systems and it just hit me - this fool has effectively coupled up both headers [inlet 1 /2 image below ]. Let me explain - fluids all have weight therefore inertia so the concept of stopping a discharge in 50 mm while turning 90 degrees before the next charge arrives is not plausible in any world.

Looking at one cycle with unequal header lengths feeding the muffler, the first charge [short header] enters the muffler with a balance of the gas accelerating past the perforated tube up the long header until the inevitable collision occurs. Now the cycle is repeated in the opposite direction with evacuation more of a result of the pressure build up in the headers.

I tend to never criticise other peoples designs but this is a total cluster stuff.

If this description is true there is only one solution and that's a 1970 hot rod muffler gutting. The edge is bead welded so I will try to grind off the bead and then the ends should be removable allowing the guts to fall out. Stubs will be welded to each inlet and the inlet cut at 30 degrees to create a smoother acceleration as it enters the exhaust wit the jury out on the inlets.

As this aircraft will fly as experimental in Australia it is in Phase 1 testing all its life so no noise restriction applies other than a social one. 

Proposed design - bit rough but a first cut

Comment
None - I am at a loss unless some one can explain this to me in simple terms

Engine - Reservoirs

This blog cover the mounting of the oil reservoir for the supercharger and engine.

Overview
After searching there are no details on a stand alone mounting bracket for the Rotax 912 oil reservoir so this meant there were no ideas to use but after some thought using weight as the guiding principle a simple U bracket with band clamp was developed.

Installation Oil Tank
The bracket was fabricated from 25 x 3 commercial aluminium flat bar with bands created with two [2] x 100 mm OD worm drive clamps. The clamps chosen were purchased at a local auto store featuring a long length of un-perforated area. To prepare the bands one had the worm drive cut off with the other cut at the start of the perforations, finally both bands overall length were trimmed to start at the fold placing the worm drive about the center of the assembly

Both bands were drilled to place a two [2] x 1/8'' pop rivet at 10 mm from the fold line and the end of the bracket with the holes matched drilled through the bracket. All holes for the lower mount were drilled to suit M4 screws in the bracket with both holes placed at the edge of the clamp and at the edge of the fold.

Note: These locations selected for the rivet and screws in the void created by the interface with the oil tank. 

Both brackets were alodined then bands riveted to both bracket ensuring that they closed up before riveting.

Oil tank moved to other side to avoid fouling sensor on supercharger
Note relocated to the starboard side

The Adell clamps were fitted to the engine mount then the lower mount fixed to the engine mount via the clamps. With this bracket in position, the tank was now installed the band tightened, next the top side was wired to the engine mount. 

With the lower Adell clamps fitted the upper one was slipped into position and its mounting point marked onto the upper bracket. The bracket was removed and the hole was drilled and tapped M4 and a screw fitted with thread locker.

The assembly was reinstalled and all points tightened.

Note: Ensure there is space for the engine mount rubber to pass the clamp for the oil reservoir

Instillation Supercharger Oil Reservoir
Two spreaders were fabricated to use the factory mounting points using 25 x 3 aluminium bar with 20 mm extension past the tank mounting to accommodate the Adell clamps. The lower bracket uses two [2] Adell clamps  with the upper one scalloped to clear the reservoir inlet. The bars were fixed using S/S M5 x 10 cap head screws with the Adell clamps fixed with M4 screws.

Relocated to the port side

Comment
All the mounting holes would be tapped for ease of installation if doing it again. After a trial installation with a dummy engine and cowls both reservoirs were swapped to opposite sides with the oil reservoirs on the starboard side and the supercharger reservoir on the port side.

Another job finished..!

Update
A trail check using a dummy engine proved that all the parts with fit as intended. This engine will be used to manufacturer all the necessary brackets etc for the final installation of the converted engine.

Trial install - note final location of oil tank [crank, pistons are removed] 
This engine was removed and was found to be close to failure.  I was flying behind this few hours before my L2 noted the issue after flying the aircraft back to its base
over the Blue Mountains....!

It will all fit....!

Engine Upgrade

This blog covers status of the work to convert the Rotax 912 into a supercharged engine.

Overview
The factory has undertaken a period of testing that has validated the FlyGas Supercharger upgrade, this modification has proven safe but remains an experimental engine, so for those seeking more power with a proven record the factory is recommending the proven Rotax 914 or maybe a Rotax 915 when available.

The existing 912 mechanical fuel pump does not cope with the extra fuel flow demanded by the supercharger and requires the installation of two [2] electric fuel pumps. The 912 pump will cope once the power is reduced to below 100 hp so this does provide a mechanical backup in the event of a total electrical failure [i.e. regulator] but is messy requiring two pumps and their electrical demand with a limited alternator output.

A product known as a "Billet Pump"  was marketed in the US using a piston pump for engines up to 400 hp using carburettors or low-pressure fuel injection but appears to have been removed from sale by the supplier. Robert Borger's Europa has a conversation and had other pilots interested but the supplier would not respond but is happy with the performance of the pump. A single electric pump will be fitted and operate in a similar manner to any low wing aircraft.

Robert Borgers Billet pump installation

Robert has provided all the information on his pumps 
construction aiding the design of a new installation

After a lot of research starting with the patent number, it was discovered this was a modified automotive product so it was decided to replicate the original design intent and this will be covered in a later blog. This is a proven concept so its anticipated there will be no operational issues and once proven I will make available all the drawings and STP files for the machining as an educational package once I work out how to remove the existing adaptor. When done a 3D model will be developed to mount the pump on the Rotax and sent out for CNC machining. 

Another upgrade is the installation of a Silent Hektik regulator that allows an output of 20 amps from the existing alternator, additionally, a water-cooled oil cooler from the same company is to be incorporated to tidy through the air flow through the cowl.

Reference: DOG Aviations RV12 - interesting reading

Note:  I have found the VANS RV 8 / 12 an excellent source for information and validation.

To assist in creating a more directed air flow a top mounted cooling hood used on the VAN RV12 is to be installed, this was selected over the same item from Rotax, it's a 1/4 of the cost. It will be feed from a 2'' NACA duct located on the lower port side of the cowl.

RV12 Air Hood
It will be fitted to the rear to gain as much
clearance as practical but can be modified

Engine
The installation of the supercharger requires the installation of decompression rings lowering compression to 8: 1 preventing detonation at a boost of 6 psi. All this work is to be undertaken by Joe Newman an RAA L2 as I am time and skilled challenged in this area and Joe has an engine mount at his hangar at Rylstone, it is now hoped the work can begin in July. 

Joe will be keeping a photo log that will be published in this blog with any of his notes on assembly issues. The manual from FlyGas is very comprehensive as is the kit so these notes will fill the gaps.

Comment
Finally redesigned the intercooler and now has all its detail drawings prepared and will be sent out for manufacture locally. Once complete and installed it will be included in an update but it's smaller and a LOT lighter by mounting directly on the engine mount.

Other items - there a lot of jobs at various stages but there is a long wait for parts coming from mainly the USA creating increasing time between the posts, regrettably in Australia it's an industrial wasteland....!

Exhaust - Part 1

Blog covers the exhaust selection

Overview
One of the issues that this build is facing is weight gain in the engine bay created by the installation of the intercooler with a estimated weight of 3.5 kg.

After looking for alternatives and rejecting them because of weight with one at a 5.5 kg. Searching the net resulted located CFT Trading Sweden who stock a titanium exhaust that is 1.8 kg lighter than the standard standard Rotax exhaust at 4.0 kg. 

Removing weight from any aircraft is either a lot of work or expensive - in this case it's the latter but at least it just bolts in.

Exhaust system components

Titan Exhaust System
Examination of this image in conjunction with one of the supercharged 
UK Tucano has convinced the builder that this should fit without modification

The weight of a complete system (4 exhaust pipes, 2 3-way connectors, 1 muffler, 1 exhaust pipe from muffler, connectors and springs) is 2,4 kilograms and $AU2200 - as I said not cheap.

Comment
Are there any issues - we will find out in time. This is the last major component that needs to be purchased so no excuses.

Power Plant Overview

With the ongoing success of the FlyGas Supercharger conversion on the current factory prototype confirmed my initial selection of the FlyGas conversion as the correct course. The only decision was to select either the  912UL or ULS from Rotax.

Engine:
On raw horsepower the ULS is the logical choice but this builder decided on the UL for the following reasons.

• The major difference is 140 HP peak to 120 HP peak. 
• No need to remove barrels too lower the ULS compression to 8:1
• Cheaper base price AKA poverty pack.
• Fits allow HP range for the Air Master Propeller
• Slightly lower over all weight - 1 Kg - it all helps
• Fit 2.43 : 1 gearbox & slipper clutch - 914 specification
• New motor = known history but lost warranty due to modifications
• Both motors fit the factory supplied ring mount
• Light weight package of 6.5 kg [14.2 lbs]
• Separate oil supply and pump
• Will operate with loss of supercharger but at reduced HP

Super Charger

For Flygas You Tube video - click here

Inter-cooler
The personal prejudice of this builder means that the installation will incorporate an inter-cooler. Operation in Australia require a motor to handle temperature's from below zero to 60 C. The reasons for all the electronic's on a 914 is to ensure that the inlet temperatures remain in a safe operating zone. 

Note: FlyGas have stated that the mixture will go rich in this condition to protect the engine and that they have no concerns.

Altitude compensated  Lycoming engines of the early 1960's suffered piston failure's in service with the reason begin short period low level detonation over a long period. This was the result of high temperature at the turbine outlet created by the turbines [work] adiabatic temperature rise combining with high ambient operating temperatures. All kits of this type now feature some form of inter-cooling to control inlet temperatures in all modes of operation.

A quick bash of an old text book showed that a 16'' x 5'' x 2.5'' should handle 140 HP on a 15 degree C day. Caution: Sizing of inter-coolers is as much witchcraft as formula but it's enough to give the confidence to throw money at the exercise.

Solids modeling on the CAD system resulted in the design shown opposite with an 80 mm x 1.6 wall aluminium tube welded to a Bell Inter-cooler core with an estimated total weigh of 2 kg - remember the 1 kg saved on the motor - now it helps..!

The design shown connects to the supercharger as per the FlyGas design, flow's back through the core to the rear tank and is then feed back to the carburetors. 

Air for cooling of the charge will be supplied from the existing N.A.C.A. duct located on the top side of the cowl. Air for the turbine will be from an existing N.A.C.A. duct located on the starboard side of the cowl. 

Included in the design is a larger balance tube between each manifolds  to aid in alleviating the rough running created by carburetor imbalance or loss of a single carburetor. This is available from FlyGas as a separate kit and creates a Siamesed manifold with twin carby's.

At the time of posting a order for the FlyGas equipment and inter-cooler components have been placed and will be on display at the Flying Legend Stand at Nat Fly April 2015.

Propeller
This builder has decided to fit an Airmaster Propeller. The electric  drive off the propeller means that the engine dose not require an hydraulic governor drive and governor saving about $3000 on these two items plus the weight - it all helps...!

Airmaster uses a electronic controller that allows three modes of operation. takeoff - climb - cruse thus reducing pilot workload by removing the need to set rpm / mp combinations.

This combination creates in principle a HOTS [hands on throttle & stick] with the mixture controlled  by the Bing carburetor's and the propeller requiring flight mode selection only. The supercharger is mechanically linked to the engine rpm [throttle position] and dose not  require any input by the pilot.

The proof will be in the eating and that is a meal for the future and like most decision can and may be altered with council from wiser minds.