You have seen me mention my new engine on other posts, and you have probably seen my advice on the considerations involved when you want to increase your Fournier's engine power, particularly those involving cooling.

In Australia, with an Experimental airplane, we can go ahead and do this stuff without involving the authorities.
HOWEVER, we must still exercise 'due diligence', consider all the relevant aspects of such a conversion, take responsibility for our actions and, most importantly, document it.

In Britain and Europe, further steps are required, to satisfy the voracious bureaucrats and to keep them in employment.

I intend to satisfy the first set of requirements, and I shall attempt to satisfy the second (British) authority.
To this end, I have spent four years researching and fulfilling all the likely requirements.

Here follows the documentation I have generated so far, plus, later, a few photos and the flight test results.
I hope the documentation following should satisfy the British Light Aircraaft Association ( the governing body for such things in Britain) and I have made my submission as detailed as possible, so it should also satisfy the EASA authorities, but of course I can give no guarantee.

Among the documentation, you will find a letter of 'no technical objection' signed by René, and a stress anaylysis document raised for me by aeronautical design engineer Wally Thomson of Thomson Design. For interest, this (plus copious amounts of advice and assistance) cost me $2,200. This inevitably includes a contribution towards Wally's liability insurance premium. He has said that I can share the information with you all, but that of course he cannot accept any liability for its use in any other aircraft than mine.

Please feel free to use any or all of this information if you should wish to emulate my experiment in significantly increasing your Fournier's power

Yours, Bob

The Need
The ability to maintain height during aerobatics.
The ability to fly a half upward vertical roll would be useful.
Dual ignition would give additional redundancy.
A fuel pump might allow inverted running.

In early 2010, HDO has a 1400cc engine (64 mm stroke, 83mm bore) with an 8.2 to one compression ratio. Its climb rate at aerobatic weight (with 15 litres of fuel) in WA’s summer temperatures is around 550 fpm. We lose height from 1,500 feet to 500 feet in four minutes of aerobatics, so a climb rate of 1,000 fpm would seem adequate. The biggest bore cylinders and pistons which can be fitted to a standard 1600cc crankshaft without weakening the crankcase by machining are 90.5mm diameter, giving a capacity of 1776cc. These cylinders also have the greatest cooling fin area.

Research
South Africa
Peter Goldin said: ‘Most South African RF4 motors are from 1600cc to 1800cc. Balance and blueprint, raise the compression and it performs beautifully. The 1600cc or 1700cc are of similar weight to the 1200, with about 2kgs difference. The cowl is a tighter fit, and it is best if you change the prop for a coarser pitch.’

Europe
Walter Berner has fitted a 1700cc RF5 Limbach engine to his RF4.
Patrick Faucheron, president of Club Fournier International says there are many RF4s in Europe running with 1700 Limbachs, 1835 VWs and 2100 Sauer engines. These are legal EASA-approved conversions.

America
Joe Buckner runs an 1835cc engine in his RF4D.
Charlie Webber said the original Rectimo was insufficient for his weight in the California heat and altitudes, so he fitted a 2100 cc Revmaster engine with an Ivo prop. He says ‘It can climb ~1200 fpm and cruise past 120 mph’.

Britain
The PFA’s Francis Donaldson said: ‘Several British RF4s have 1600 engines. These conversions happened many years ago, on the simple basis that no problems were revealed, so there is no structural, stability or performance data.’

Australia
There are only three Australian RF4s; all have either 1200cc or 1400cc engines.

Reference Documents
Discussion with Walter Thomson revealed the existence of FAA Advisory Circular 23-12 plus lots of useful supplementary information.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/7baf3d7c1f279645862569b2006a74c7/$FILE/AC23-12.pdf

CASA Instrument EX 06/06

The British LAA publishes a useful document: Understanding VW Aero Engines

For improved cooling, refer: Limbach Technical Bulletin 44.1 (Too High Engine Temperatures)
http://www.limflug.de/downloads/905/905.700.028.005.pdf

Great Plains produces a VW engine baffling manual, plus baffle templates.

[Edit by Bob Grimstead on Monday, October 3, 2011 @ 04:48 PM]

Reduced Pitch Stability (particularly in the full-throttle climb)
A series of flights was made to establish longitudinal stability. This turned out to be more than adequate. Details are in the Thomson Design document. If necessary, with such a wide C of G range, this range could be artificially limited. Tailplane Volume Coefficient was calculated as 0.4658.

Engine Power
The RF-4D has a 1200cc Rectimo 4AR1200 (Volkswagen conversion). This produces a nominal 39hp at 3,600 rpm in ISA at sea level.

Mike Ellinas of Heliptera Propellers says he reckons to get 9.2 hp per litre per 1000 rpm. That would mean my 1200cc Rectimo would give 39.74hp, the 1400cc would give 46.36, and the 1750cc Aeropower/JMR engines should produce 58-59 hp (in ISA, at sea level).

1st February 2005 1200 Rectimo dynamometer run. OAT 24°C
9.75 x 3,600rpm = 35.1 hp.

12th January 2005 Aeropower 1750cc engine dynamometer run. OAT 30°C
BHP = No x RPM/1000, so: 14.5 x 3,600rpm = 52.2 hp

So, a 1400 engine should produce around 40.9 hp at 3,600 rpm

Several JMR 1776 Stuska dynamometer runs in November 2009 gave max
54 bhp/98 ft lb at 3,600 rpm in ISA.

Powerplant weight
The Rectimo 4AR1200 weighs a quoted 136 lb (61.5 kg), with a single Bendix magneto and a Zenith 28 RXZ carburettor. I weighed mine at 66.7 kg with exhausts & baffles.

An 1800 cc Rectimo with 90 mm Nikasil cylinders is said to be 3,5 kg lighter than a comparable original Rectimo/VW engine.

My British Rectimo (No123) weighs 55kg/121lb with magneto & mount, spark plugs, baffles and prop flange.

My British JMR 1776cc engine weighs 54kg/119lb with magneto & mount, spark plugs, baffles and prop flange.

My Australian Rectimo (No 198) weighs 66.7 kg with oil cooler, full sump, carburettor, intake manifold, exhausts, magneto, harness and spark plugs, baffles etc, but without the manual starter, its cable and the drive cog (propeller back plate) propeller or spinner. Its C of G is close to the central upper crankcase cross bolt.

My new Aeropower engine weighs 60 kg without oil, intake or exhaust pipes, hand starter kit, propeller, spinner, back-plate or baffles, but with oil cooler, magneto, HT harness and spark plugs.
or 67.2 kg, with oil cooler, full sump, carburettor, fuel pump, intake manifold, exhausts, magneto, electronic ignition, harnesses and spark plugs etc, but without baffles, the manual starter, its cable and the drive cog (propeller back plate) propeller or spinner. So, the new engine is currently 500 gm (one pound) heavier than the old one with all equipment attached. However, the new cowlings are 500 grams lighter than the old ones, negating this difference.

Old Hoffman propeller weighs 2.3 kg.
Heliptera 52x36 prop weighs 2.6 kg.

Ignition Timing

My Aeropower (Australian) engine produces maximum bhp with its timing set at 32°BTDC. John Maher says that a standard 1776cc VW engine is likely to produce maximum horsepower with a similar timing advance.

To be conservative, to prevent overheating, and to harmonise with the magneto’s 28° impulse mechanism, the timing will be set to 28°BTDC.

Improved Cooling
A 50% increase in capacity means 50% more heat to lose. Solution: better baffles, curved outlet lips, a 5° chamfer on inlet lips, a fixed lower cowl flap, opened up exhaust pipe outlets, reduced spinner size.

VW fan-induced cooling airflow is 26 cubic feet per second, or 1,560 cubic feet per minute, or 2,695,680 cubic inches per minute.
So, a 1750cc motor will need at least 2,300 cubic feet (or 3,989,606 cubic inches) per minute at 70 mph or 60 knots to keep the engine reasonably cool in the climb. I make 70 mph 6,160 feet per minute, or 73,920 inches per minute, so cooling intake area needs to be at least 54 square inches.
Standard Fournier cowling intakes are 52 square inches.
Outlet area should be at least 130% of that.

As measured:
Standard cowling intake area was 320 sq cm
Smaller spinner should increase this by 54 sq cm at the sides.
So total new inlet area is 374 sq cm = 17% increase.

Standard cowling outlet area was 251 sq cm
Increased outlet area by 125 sq cm = 376 sq cm = 49% increase.
Sides of outlets are smoothed by semi-circular fairings to improve exit flow.

This demonstrates that the added bulk, complexity and weight of a separate carburettor heat system is unnecessary.
Fuel Flow & Consumption
Rectimo says ‘Consommation d’ essence maxi 13,5l’. A graph suggests that the full throttle fuel flow is nearer 14 litres per hour. Dividing by 12 and multiplying by 18 suggests the 1750cc motor will use around 20 lph at full throttle.

Fuel consumption of 1,750/1,776cc engines should be 12 (twelve) litres per hour cruising, 20.4 lph max at full throttle (extrapolated from Rectimo manual).

RF5 (Limbach 1700) manual consumption figures: @ 110 mph/3400 rpm 14 lph, @100 mph/3200 rpm 12 lph, @ 87 mph/2800 rpm 10 lph.

In preparation for fitting the Aeropower 1750cc engine, we did a fuel flow test at the banjo fitting into the carb. It passed two litres in 1 min 37 secs, which I make 74 litres per hour. Flow from the needle valve (standard orifice diameter is 2.00 mm, marked 200, but mine’s drilled out to 2.5mm for the 1400cc motor) with float and needle still fitted was 20 lph. Flow out of the float bowl into the main jet socket was 16 lph.

So, both the needle valve and the exit from the float bowl to the main jet were drilled out for the 1750 motor.

The resulting fuel flow with minimum fuel in the tank was 25.7 lph at the main jet socket.

Main jets
Standard 1200cc Rectimo main jet for the Zenith 28RXZ carburettor is 1.25mm diameter.

Five years of flying experience has established that 1.32mm is better for the 1400cc engine.

Some brief test flights suggested that a 1.40mm main jet was more appropriate for the 1750cc engine.

The Limbach 6L 1700E engine (VW conversion) uses the same Zenith 28RXZ carburettor with a 1.50mm main jet, but this breathes cold air with a carb heat box.

An NGK AFX Lambda sensorwill be used to establish the correct jet for optimum full-throttle mixture.

The Conversion
Phase One
Remove 1400cc Rectimo engine and replace with 1750cc Aeropower engine.
Fit Eugenio’s bigger cowlings and comprehensive Limbach-style baffles
Utilise original Zenith 28RXZ carburettor, but with drilled out main jet socket and enlarged 1.40mm main jet.
Use original intake casting with new, 32mm ID manifold tubing.
Use original 28mm ID Rectimo exhausts.
Do not fit fuel pump or secondary ignition.
Use original Heliptera 52 x 34 propeller with small, skullcap spinner.

Phase Two
Fit Heliptera 54 x 36 propeller with small, skullcap spinner.
Test fly ditto.

Phase Three
Fit 35mm exhaust pipes & silencers.
Test fly ditto.

Phase Four
Fit Mikuni carburettor with new inlet manifold.
Test fly ditto.

Phase Five
Wire up secondary ignition.
Test fly ditto.

Phase Six
Fit cold air inlet with carb heat box.
Test fly ditto

Hoffmann 145/B/80 (57 x 31.5) propeller (weight 3.2 kg)
Identical conditions except surface temp 23°C, 1015 HPa.
Climbed 500 to 1,500 feet at 60 knots in 1:44 = 577 fpm
Rpm = 2,900, oil press = 2.8 kg/m2, oil temp = 90°C, CHT = 145°C
Max speed at 500 feet =107 kts IAS at 3,550 rpm
Max speed at 1,500 feet =104 kts IAS at 3,550 rpm

Heliptera 52 x 36 propeller (weight 2.0 kg)
Climbed 500 to 1,500 feet at 60 knots in 1:49 = 550 fpm
Climbed 500 to 1,500 feet at 60 knots in 1:52 = 536 fpm
Rpm = 2,750, oil press = 2.6 kg/m2, oil temp = 86°C, CHT = 137°C
Climbed 500 to 1,500 feet at 55 knots in 1:53 = 531 fpm
Climbed 500 to 1,500 feet at 65 knots in 1:54 = 526 fpm
Max speed at 500 feet =110 kts IAS at 3,350 rpm
oil press = 2.8 kg/m2, oil temp = 83°C
Max speed at 1,500 feet =107 kts IAS at 3,300 rpm
oil press = 2.8 kg/m2, oil temp = 83°C, CHT 137°C
RPM vs airspeed at 1,500 feet
3,650 rpm (diving) = Vne 135 kts IAS
3,500 rpm (diving) = 123 kts IAS
3,300 rpm = 107 kts IAS
3,000 rpm = 97 kts IAS
2,800 rpm = 89 kts IAS
2,600 rpm = 82 kts IAS
2,400 rpm = 74 kts IAS
2,200 rpm = 65 kts IAS

Test Flight 19th April 2008 Heliptera 52 x 36 propeller
Take-off weight 379 kg (20 litres of fuel aboard)
OAT 27°C, 1014 HPa Wind 270/10 Serpentine Runway 23
Max static rpm (cross wind) 2675 rpm
Unstick speed 40 kt at 2750 rpm
Climbing cross wind, over the sea at 60 kt IAS, 2750 rpm
Start climb 0 minutes 0 feet oil temp 51°C press 2.9 bar CHT 120°C
1 minute 680 feet oil temp 58°C press 2.9 bar CHT 120°C
2 minutes 1230 feet oil temp 64°C press 2.9 bar CHT 130°C
3 minutes 1700 feet oil temp 69°C press 2.9 bar CHT 130°C
4 minutes 2300 feet oil temp 75°C press 2.9 bar CHT 130°C
5 minutes 2830 feet oil temp 79°C press 2.9 bar CHT 130°C
Average = 566 fpm
Level flight at 1,500 feet, 3300 rpm = 108 kt IAS
Level flight at 1,500 feet, 3200 rpm = 104 kt IAS
Level flight at 1,500 feet, 2200 rpm = 63 kt IAS
Throttle fully closed dive to 135 kt IAS (Vne) rpm = 2900

Test Flight 23rd November 2008 Heliptera 52 x 34 (blue) propeller
Take-off weight 377 kg (17 litres of fuel aboard)
OAT 25°C, 1006 HPa Wind 230/10 Serpentine Runway 23
Thermic and windy. Climbing cross wind at 60 kt IAS

Start climb 0 minutes 500 feet
1 minute 960 feet
2 minutes 1500 feet
3 minutes 2010 feet
4 minutes 2540 feet
5 minutes 2940 feet
Average = 488 fpm

Flight Tests of WGN’s 1400cc motor with Heliptera 52x36 prop
28 May 2009 Spinner fitted, 20 lit fuel aboard, OAT 23°C 1031 hPa
Time Alt tot alt IAS RPM
0 -300 70mph 2900ind (2600 true)
1 270 570
2 800 1100
3 1290 1590
4 1700 2000
5 2130 2430
WOT @ 2,000ft 117KIAS @ 3400rpm (3100true?)
Average = 486 fpm

[Edit by Bob Grimstead on Wednesday, May 26, 2010 @ 09:45 PM]

New Aeropower 1750cc VW engine specifications:

Original 'universal' magnesium alloy VW crankcase
Standard VW forged 1045 steel crank No 201X
Big end bearings are standard size
Main bearings are bored out 10 thou
Extra 2-inch front thrust bearing behind prop hub
Oil pump with tacho drive.
Limbach 2000 aluminium cylinders, bore 90 mm, stroke 68.8 mm
Dual-plug, dual-port heads
Head volumes 51cc
Capacity 1750 cc
Compression ratio 8.02 to 1
Top quality German Mahle BMW pistons
CAD/CAM Computer-cut H-section Scat con rods
Stainless steel inlet and exhaust valves (diameters 35 mm and 40 mm)
1.1 to 1 lift rockers
Special Aeropower cam, optimised for high torque at low rpm, opening 10° before TDC, and closing 15° after TDC.
Magneto: Lycoming rubber cushion pads driving Slick 4016 with RH rotation, 28° dwell firing upper plugs REL 37 B
Hall effect fixed-timing electronic secondary ignition firing lower plugs
Cold air inlet 36 mm (1½ inch). Exhaust ID 32 mm (1¼ inch).

Cowl -- I assume you are using one on Eugenio's new cowls, correct? How is it fitting?

Intake -- How does the new intake clear the cowl? It looks like the Aeropower plenums over the head intakes might interfere. How about the placement of the carb? Does it interfere with the fuel system?

Exhaust -- The new engine is wider and it places the stock pipes 2"-3" away from the sides of the fuselage. Are you making new exhaust or just letting them stick out?

Prop -- It looks like the extended prop hub moves the prop out a couple of inches. What are you going to do about a spinner?

Starter -- are you keeping the pull starter? Will it fit with the extended prop hub?

These are just some of the issues I've been wrestling with. Are you finding the same issues?

--------------------

It's good to hear from somebody else facing exactly the same problems as me. I'll post some photos later, when I get the time.

Sometimes I wonder whether it's worth spending hours typing at the computer and posting photos, but when I get a query like yours and know somebody else out there is facing all the same problems, it's suddenly worthwhile.

First: I flew it yesterday for the first time, for 2:10 to check consumption as well as performance. Consumption was 12 litres per hour exactly at 3050rpm & 90 knots/105mph approx, plus half a litre/quart of oil. Performance details in a later post.

Yes, I'm using Eugenio's cowlings, and they fit OK except:
Over the Great Plains inlet castings, where they're very tight.
I cut down the castings to make them shorter, and ground the outsides to make them more nearly circular.
That was a full day's work there alone.
Then I added two layers of glassfiber inside the upper cowling at the tight spots to act as rubbing/ablative strips and I'll see how they go.

No problem with the Zenith carb, there's plenty of room, thanks to that kinda fixed cowl-flap outlet on Eugenio's cowls. Ditto with the Mikuni, but I had to ditch the originally planned Stromberg CD150 because it stuck out too low below the engine (but it has altitude compensation, and that's a sad thing to lose).

I did have to modify my original intake up pipes. At first I simply used a Great Plains ninety-degree bent tube, sawn off at the intake manifolds to abut tight against them under the rubber hose. They were a little short at the lower end, so there was an 8cm (3-inch) gap between them and the original carb casting, over which I simply used a 16cm (six-inch) length of rubber hose. That was fine until 1:40 into the two-minute full-power ground run, when I noticed a gradual 100 rpm drop (from 3,000 rpm).

I hate doing that two minutes run at full power on the ground, but it's a British requirement, and it's also a good idea, because any fuel flow problems (the most common first-flight problem) should show up. It will also reveal any overheating problems. I suspected the engine was beginning to seize, but stuck with it because the oil press & temp were OK and there were only 20 more seconds to go.

Turned out that the actual problem was a collapsed left intake hose. It was very wet inside from fuel, and quite warm & squishy. So I simply cut a couple of 8cm/3-inch lengths of steel pipe to fit the gaps inside the rubber tubing. Problem (temporarily) solved!
I guess that's another reason why we do that two-minute full-power run.

No problems with the extended front bearing. I simply mounted the cowlings so there was minimum overlap on to the fuselage at the rear, and accepted a small gap behind the spinner at the front. See photos later.
I made an extension bracket and tube for the hand-starter.
Even the electronic ignition Hall-effect sensor fits, because the cowls are an inch or so forward.

You'll see all this in the photos.

I'm currently just using the old, slim exhausts for the first test flights, but I'm making up new ones of the correct larger 32mm internal diameter (from Great Plains tubing, because I could not get thin-walled tubing of the correct diameter locally). Not an easy task, but satisfying when it goes right. I'll go into more detail when they're done and tested.

After landing I found the right forward exhaust pipe was touching the lower cowl and had burnt a patch about the size of a postage stamp, although it had not burned through. No problem, those exhausts are coming off soon to be replaced with my new ones which, although wider, fit tighter under the engine (I hope).

More when I have the time.

Yours, Bob

[Edit by Bob Grimstead on Wednesday, May 26, 2010 @ 10:14 PM]

[Edit by Bob Grimstead on Thursday, May 27, 2010 @ 07:04 AM]

However, the Great Plains oil cooler adaptor just put the oil cooler a little too high and a little too far forward.

Maybe with a little more time and patience I could have made it fit, but in the end I simply reverted to the Woolard adaptor off my old Rectimo.

The rear baffle was also easier to make air-proof this way.

You can also see some detail of the cut-down Great Plains intake castings and my long GP intake tubes, plus the mod to move the hand-starter forward. There is an extension tube, but you can't see the joint, because it's hidden under the electronic ignition loom.

Here's another intake detail.

Sorry, I don't know why, but today ImageShack has decided to swivel all portrait-format photos to landscape. I can't change it, so you'll just have to tilt your head.
I do wish these bloody geeks wouldn't fiddle with their sites!

You can see (if you twist your head) that the exhaust pipe nuts are tight under the intake tubes, which means you have to remove those tubes if you want to remove the exhausts.
I've probably done this a dozen times already, and although it's annoying, it's not a real hardship.
Maybe the radiated heat from the pipes helps with fuel atomisation & evaporation? Who knows?

Yours, Bob

[Edit by Bob Grimstead on Wednesday, May 26, 2010 @ 10:52 PM]

[Edit by Bob Grimstead on Wednesday, May 26, 2010 @ 11:02 PM]

[Edit by Bob Grimstead on Wednesday, May 26, 2010 @ 11:04 PM]

This is pretty much where I started a month ago.
Old engine still in place, new engine mounted on dummy firewall to get everything properly fitted and in place.
Right! Like that worked okay!
Well, it kinda did, but there was still a huge amount of fiddling and adjustment to get it all working right once the engine was in place on the real firewall.

Yours, Bob

300 hours at full throttle, three Red Bull Air Races, three state competitions,and dozens of displays, I owe this engine a huge debt of gratitude. It ought to go on a plinth in our lounge, but I don't think Karen would accept that (indeed I know she would blow a mushroom cloud).

Yours, Bob

Where the templates need enlarging, I use masking tape (lots of it, as you can see) to make the templates as near perfect as possible, so there's miniumum aluminium cutting and trimming to be done.

Yours, Bob

[Edit by Bob Grimstead on Wednesday, May 26, 2010 @ 11:32 PM]

As you can see, I've cut down the spinner and its back-plate to allow a bit more cooling air into the front of the cowlings.
I have not yet finished trimming and fitting the spinner, so my first flight was made with the little skull-cap spinner I've been using for the past couple of years. Not so pretty, but quick and easy to fit.

Yours, Bob

[Edit by Bob Grimstead on Wednesday, May 26, 2010 @ 11:29 PM]

Thanks to master-VW-builder John Maher of Scotland I've bought an NGK AFX lambda sensor to check I've got the correct mixture, rather than simply flying, checking the spark plug colours, opening out the main jet a bit and flying again.
I know that method works, but it's not scientific and it could result in a broken valve, melted piston or damaged head if there is serious overheating from a weak mixture.
I had already empirically established that a 140 (1.4 mm) main jet would be about right in that little Zenith carb.

The lambda sensor fits into a boss welded into an exhaust pipe.
It measures millivoltages and displays a number relating to mixture.

You can read the manual at:
http://www.ngksparkplugs.com/pdf/AFX_Tuning_Manual_REV_06.pdf

Since the sensor has a heater, drawing 2 amps and my Fournier, like most, only has a 3.5 amp/hour battery, I suspected that the voltage would not be sufficiently stable to get a steady, true reading.

I thought about this long and hard.
Do I take a second battery up with me, run the heater for five minutes and then swap batteries for the readings?
Awkward in that cramped little cockpit and not necessarily likely to get a reliable result.

How about I fully charge the battery, run the sensor for an exact time on the stopwatch and then take a reading? The reading might not be exact, but comparison should be possible if I always run the sensor for the same time from a fully-charged battery.
But I still didn't like that idea.
It was not sufficiently accurately repeatable.

Then I realised the test did not have to be done in the air.
The aeroplane's brake holds it against full power, even from the new, bigger engine (if yours doesn't, see my brake post) so I can do all this on the ground.
Why not park a car alongside the aeroplane, connect the sensor to the car's battery, run the engine, so the alternator provides a stable power source and take the readings that way?

That's what I did, and I got the following results.
The first readings are with only 9 litres in the tank, to ensure I get the leanest possible likely mixture at full power (I won't fly aerobatics with less than ten litres in the tank, because the outlet becomes uncovered so often the engine keeps stopping).
The second readings are with a full tank.

NGK say the perfect stoichiometric ratio (mixture) for maximum power is between 12.5 and 13.
For minimum fuel consumption it's about 16.
To keep an air-cooled engine below melting point, a figure of 10 to 12 is recommended.
Ideally, the result would be around 11 for full power, but a higher number, closer to 16 for cruise power at half throttle or around 3,000 rpm, and then a lower number again for idling.

The readings seemed to vary around half a unit, but the average was (with a low fuel head)
At full throttle 11.7, cruise (half throttle) 12.3, at idle 14.

With a full tank these all reduced slightly (became richer, as you would expect) to
At full throttle 11.3, cruise (half throttle) 12.5, at idle 13.2.

But they all look in the right sort of ball-park.

However...
I made one obvious mistake.
These readings were taken without the cowlings, but as you know, the RF4 normally breathes hot air from the lower cowling, so they may be erroneous

Also, the next day I talked to design engineer Wally Thomson. He explained that the dynamics for flight and propeller loading will probably vary both the intake and the manifold pressure, which can affect the mixture readings.
He recommended that I do it again with the finest pitch propeller I can find and compare the results.
I still have the most excellent prop that Steve Thompson carved for my Turbulent, so if I have time I'll try that, with the cowlings in place, to see if there's a significant difference. It's very fine for the RF4 in flight, even with only the 1200cc engine, but should work nicely for this test.

I hope that's all of interest.

Yours, Bob

[Edit by Bob Grimstead on Sunday, March 11, 2012 @ 04:35 AM]

Those were all photos I took last week.
Can't find my camera this morning; it must still be down at the hangar.

Performance figures.
Rather disappointing.
Here followeth the details of yesterday's test flight

Conditions
VH-HDO at max weight of 390kg, with full fuel and a mid-range C of G.
Aeropower 1750 VW engine, Zenith 28RXZ carb with 140 main jet, Heliptera 52x34 prop, skull-cap spinner.
Max static rpm 3,000
OAT 16°C, QNH 1013 -- 29.92"

Flight profile:
Take-off, five-minute timed full-throttle climb at 62 knots (presumed new, higher speed for best climb rate), Vne dive, two-minute full-throttle run at 1,500 feet, ten minutes cruise at minimum cruise power (2,600 rpm/75 knots), 1:40 at normal cruise power at 1,500 feet (3,050 rpm/91 knots), five-minute full-throttle climb, glide approach and land.

Be warned. This is a very dangerous first flight profile.
The first flight with a new powerplant should only be a single circuit, then check for abnormalities, leaks or loosness of all nuts, bolts & fittings.
Then a timed climb, cruise portion and land, ditto.
Then the two-hours consumption check.
But, I have limited time here, and atrocious weather was forcast for my last few days in Australia. They weren't wrong, we had 5cm (two inches) of rain last night and local homes were hit by tornadoes. It's still raining today.
So I risked my life for impatience...

Time altitude alt gain
0 300 340
:30 640 700
1:00 1000 1040
1:30 1340 1380
2:00 1680 1700
2:30 2000 2050
3:00 2350 2350
3:30 2650 2660
4:00 2960 2960
4:30 3260 3270
5:00 3570
Climb rpm was 3,100, oil temp rose from 63°C to 94°C (as you would expect); oil pressure dropped from 3.2 bar to 3.1 bar (not bad!)

I make that an average climb rate of 654 feet per minute, which ain't impressive.
However, this is a brand-new engine, not yet broken-in, and very stiff, with lots of internal friction.

Max speed after two minutes of level, full-throttle flight at 1,500 feet was 109 knots (125 mph/202 kph).

The second full-throttle climb at the end of the flight suggested that the piston rings had bedded in a bit, although the engine was still very stiff the next day.

Time altitude alt gain
0 300
:30 730 430
1:00 1100 800
1:30 1460 1160
2:00 1760 1460
2:30 2120 1820
3:00 2450 2150
3:30 2790 2490
4:00 3130 2830
4:30 3470 3170
5:00 3800 3500

That's 700 feet per minute, which is obviously better, but still far short of my target of 1,000 fpm.

Total fuel burned in this two-hour flight was 24 litres, equating to a rough 12 litres per hour.

Last year in Europe I made a test flight of a very similar engine with a similar propeller, similar standard Zenith carburettor with identical main jet, standard intakes, small exhausts etc.

Conditions
at max weight of 390kg, with full fuel and a mid-range C of G.
1776 VW engine, Zenith 28RXZ carb with 141 main jet, 52 x 36 prop, standard spinner.
OAT 5°C 1013 hPa (29.92"
Static RPM 2,800
Time Alt tot alt IAS RPM
0 -200 72 3100ind (2800 true)
:30 250 450
1 640 840
1:30 1060 1360
2 1470 1670
2:30 1880 2080
3 2240 2440
3:30 2640 2840
4 3060 3260
4:30 3450 3650
5 3800 4000
Average = 800 fpm

In comparison with that Euopean Fournier, you can see that mine has a big performance shortfall.
Unfortunately, I do not have time now to investigate and fix these issues, so it will all have to wait until I get back to Australia after the European display season.

I hope that what information I have given is at least of interest, and possibly of assistance to some folks.

Yours, Bob

[Edit by Bob Grimstead on Thursday, May 27, 2010 @ 09:38 AM]

[Edit by Bob Grimstead on Thursday, May 27, 2010 @ 09:42 AM]

[Edit by Bob Grimstead on Wednesday, August 25, 2010 @ 04:28 PM]

[Edit by Bob Grimstead on Wednesday, August 25, 2010 @ 04:30 PM]

What kind of baffle seal material are you using between the baffles and the cowl? A huge amount of air can leak out there if the seal is not perfectly tight, but still allow for engine movement. My stock RF4 did not seem to have a very good sealing system. When I built the RV6A, I worked out a system to trim the baffle strip material so it conformed very tightly with the cowl. You can see some pictures and commentary in this gallery: http://picasaweb.google.com/dannsparks/BuildingAnRV6AN786DB Maybe this will be of some help. I plan to do the same with the RF4.

I’m working on a new exhaust system too. In an earlier post you mentioned putting “silencers” on the new exhaust. Are you thinking of a more effective muffler system, or just making a larger version of the original perforated tubing tips.

I had planned to use Great Plains 1 3/8” diameter tubing for the new exhaust system but am having trouble finding some thin aluminum tubing that fits snugly over the 1 3/8” exhaust pipes to make the perforated tips. I have also been looking at some motorcycle mufflers and Supertrapp mufflers, but have not hit on anything that I think will work. What did you have in mind?

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Dan, nice to hear you are still tinkering with the exhausts. I got mine welded and so far they are holding out fine.

I had a nice little commuter flight today with good thermals that I exploited. A local police chopper passed the area and I decide to loose some height so as not to disturb them. Very useful, those Aeros are.

May the 4's be with you/ Jörgen

My baffle rubber sealing material is Aircraft Spruce part No 05-01300
http://www.aircraftspruce.com/catalog/appages/uchannel.php

But I also bought two larger sizes of a similar-shaped moulding, so that if I inadvertently cut the aluminium baffling to short, they would fill the gap.
All voids were filled with Loctite black high-temp RTV silicone sealant ('Black Maxx', I think?)

Yes, I used Great Plains exhaust flanges and 1 3/8" tubing for my exhausts.
The rear ones are easy, just a flange and a length of straight tubing.
The front ones use a flange, a 180-degree bend and two cut-down 45-degree bends.
The flanges are welded to the tubing both inside and outside the flange, for strength.
Rather than weld the pipe joints, because I wanted the smoothest possible pipe interior plus strength, I cut 3/4-inch sleeves from the next size up of tubing (a very tight fit outside the 1 3/8" and then brazed the whole lot together.
Everything was then painted with high-temp black paint.
Of course, this is a three-dimensional jigsaw puzzle and it took me several days to get right.
I should know by the end of today whether they fit properly or not.
The silencers are shorter versions of the originals, made from Great Plains 'slip tubes' with one end cut off
http://www.greatplainsas.com/scexhaustparts.html
I have drilled three rows of small holes, rather than one row of large ones.
Time will tell whether this was a good idea or not.
I am not sure that aluminium tubing would satisfactorily withstand the exhaust heat, especially on the rear pipes.
My new pipes are much heavier than the originals, but I could not get any thinner-walled tubing.
Thin-walled 1 3/8" stainless steel would be best, but there's no chance of getting that in lil ol' Aussie.

Good luck, I must dash off and fit those exhaust pipes.

Yours, Bob

[Edit by Bob Grimstead on Sunday, May 30, 2010 @ 10:58 PM]

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Here are the pipes, unpainted & painted.

Yours, Bob

Yesterday I flew it with these new wider exhaust pipes, but without silencers because I had been led to believe this would result in improved breathing and greater power.

However, there was no measurable improvement in performance. Same climb rate (within 10fpm, which is experimental error) and same top speed. Plugs were a nice colour on landing, which suggests the mixture was still good.

Another intriguing aspect of the comparison between my Australian engine and the near-identical European one I flew is that the Aussie one has dual-port heads, while the other one (which performed much better) had single-port heads.

These two factors (no performance improvement with wide, un-silenced exhaust pipes or with dual-port heads) suggests that the gas mass flow at our rpm (3,000 to 3,500) is just too slow for any improvement in breathing to show up.

So it's not worth changing to dual-port heads if you already have good single-port ones. And that means you don't have to frigg about for days making up a new inlet manifold etc.

More info in six months, when I get back.

Yours, Bob

Now I've had/made time to scan it, here's that stress analysis. It is for engines up to 60 hp.
Since we only got 52hp out of my Aeropower engine, and John Maher only got 54.4 hp in ISA out of a similar one at 3,600 rpm, I reckon this analysis would indicate it's safe to use engines up to 1835cc.

Wally Thomson says you can read this, but he takes no responsibility whatever for its contents, since it was written for me and only my aeroplane is thus covered by his liability insurance.

If you read and use it, please feel free to buy me a drink next time you see me.

Yours, Bob

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