These angle-things for the firewall required massive trimming. They all needed to be straightened up because the angle was off on either side, then lots of trimming of the edges. When that was done they fitted perfectly.
Tuesday, July 29, 2014
Monday, July 28, 2014
Received stuff from Great Plains
Ordered a "toolkit" and an engine stand to mount the Aerovee and an oil cooler. Also ordered some books about the VW. A manual is included with the Aerovee, but some extra literature won't hurt.
It will take at least 10 weeks before I receive the engine and propeller.
Looked a bit closer at the engine/propeller calculations, and that equation is a bit simplistic. It is perfectly valid, but only with the same propeller blades, that is the blades only changes pitch and length, they do not change the length of the cord. With an increased diameter it is natural that the cord also increases. Different propellers can be completely different regarding cord and diameter. To chose a propeller just gets more complicated, and I am happy I chose the AeroVee.
I am also going for a completely "stock" engine with the AeroCarb. Then I know everything will work as it should, and I will found out for myself if modifications are needed or not. To make modifications with no basis in the actual status is not the correct engineering way to do things, and I am an engineer so :-)
It will take at least 10 weeks before I receive the engine and propeller.
Looked a bit closer at the engine/propeller calculations, and that equation is a bit simplistic. It is perfectly valid, but only with the same propeller blades, that is the blades only changes pitch and length, they do not change the length of the cord. With an increased diameter it is natural that the cord also increases. Different propellers can be completely different regarding cord and diameter. To chose a propeller just gets more complicated, and I am happy I chose the AeroVee.
I am also going for a completely "stock" engine with the AeroCarb. Then I know everything will work as it should, and I will found out for myself if modifications are needed or not. To make modifications with no basis in the actual status is not the correct engineering way to do things, and I am an engineer so :-)
Tuesday, July 08, 2014
Fwd fuselage
Got the new countersinking tool and finished dimpling and countersinking the fwd fuselage sides.
Sunday, July 06, 2014
Engine - Conclusion and order
The order was sent today for an AeroVee :-)
Even though it comes in pieces and has to be built, the completion log of Onex'es clearly shows what is the certain path to a flying aircraft. About 95% of completed and flying Onex'es has AeroVee. What in the end became the deciding factor for me was the propeller. The propeller supplied by Sonex was is the best of several dozens they tried. A fixed pitch propeller has to fit the engine and the aircraft, and for another engine with different RPM range, to get this right has to involve lots of trial and error.
I have decided to use a Rotec TBI. But, depending on how the rules are implemented here in Norway, I may actually have to use the Aeroinjector initially, and then modify the engine later. The rules say an engine conversion must be used with the same ignition and fuel system as the "original" conversion, or bench testing will be necessary. A modification later on is not that strict. The thing is however, thousands of VW conversions are run all over the world with all kinds of ignition and fuel systems. After all this is a VW, just like any other VW.
The reason for a Rotec TBI is it has a pressure regulator that is essential for correct mixture during different g-loads, and is otherwise essentially an exactly like an Ellison TBI. A Rotec TBI does however require more fuel pressure than the Aeroinjector, so a pump or two will be required.
Even though it comes in pieces and has to be built, the completion log of Onex'es clearly shows what is the certain path to a flying aircraft. About 95% of completed and flying Onex'es has AeroVee. What in the end became the deciding factor for me was the propeller. The propeller supplied by Sonex was is the best of several dozens they tried. A fixed pitch propeller has to fit the engine and the aircraft, and for another engine with different RPM range, to get this right has to involve lots of trial and error.
I have decided to use a Rotec TBI. But, depending on how the rules are implemented here in Norway, I may actually have to use the Aeroinjector initially, and then modify the engine later. The rules say an engine conversion must be used with the same ignition and fuel system as the "original" conversion, or bench testing will be necessary. A modification later on is not that strict. The thing is however, thousands of VW conversions are run all over the world with all kinds of ignition and fuel systems. After all this is a VW, just like any other VW.
The reason for a Rotec TBI is it has a pressure regulator that is essential for correct mixture during different g-loads, and is otherwise essentially an exactly like an Ellison TBI. A Rotec TBI does however require more fuel pressure than the Aeroinjector, so a pump or two will be required.
Engine and propellers
I think I have decided on the engine choice now, but some additional "brainwork" regarding engine and propellers makes the engine choice almost a "no brainer". The reason for this is that finding the right (fixed pitch) propeller for an arbitrary engine must be very difficult. Theoretically you must know the full performance graph of the engine, that is torque vs rpm for all power settings, at least at WOT and max continuous. Then you must know the performance of the aircraft (speed vs thrust) and the performance of the propeller (efficiency vs advance ratio). I don't know any of this, so if I should chose a "non standard" engine, I would have to get at least a ground adjustable propeller, or a CS propeller to have any chance of hitting it somewhere right. For a fixed pitch I would probably have to try several different ones, 10-20 maybe.
For instance. The power needed to drive a propeller is (for one single arbitrary air speed):
P = k * rpm³ * D⁴ * pitch
P is power, k is a constant depending on units and D is diameter.
Great Plains has in the catalog at page 39 a nice note about this. Their 1835 cc engine has a known horsepower of 60 at 3400 rpm. The propeller used for this engine has D = 52" and pitch = 42". I can use this as a base and plug in the numbers for some other engines and propellers. There are more to a propeller than pitch and diameter, but without advance ratio and efficiency this will have to do. The actual numbers here may be off, but the principle is right.
The Aerovee with the Sensenich propeller will output 73 HP at 3400 rpm according to this. This is probably about right, because the larger GP 2276 cc shall output 76 HP, and will do so by slightly more pitch. The Revmaster is a different setup because it is designed to output 80 HP at 3000 rpm. With the recommended Prince propeller, it will only output 52 HP at 3000 rpm, so obviously Prince is wrong. A more "correct" propeller would be 55" diameter and 65" pitch. With the Sauer and ULPower, a usable propeller would be difficult to get right without also extending the landing gear/larger wheels due to their much lower rpm which requires larger D, or by adding more blades.
Regarding "propeller difficulties" the AeroVee is no problem. Sonex has done all the testing. The larger capacity GP and Hummel should also be relatively easy I guess. It is only a matter of adding some pitch. The Revmaster could be much more difficult. It is designed to run on lower rpm. The Sauer and ULPower would be even more difficult, and probably would need new landing gear to get a larger diameter propeller.
For instance. The power needed to drive a propeller is (for one single arbitrary air speed):
P = k * rpm³ * D⁴ * pitch
P is power, k is a constant depending on units and D is diameter.
Great Plains has in the catalog at page 39 a nice note about this. Their 1835 cc engine has a known horsepower of 60 at 3400 rpm. The propeller used for this engine has D = 52" and pitch = 42". I can use this as a base and plug in the numbers for some other engines and propellers. There are more to a propeller than pitch and diameter, but without advance ratio and efficiency this will have to do. The actual numbers here may be off, but the principle is right.
| Engine (at max continous rpm/HP) | HP | rpm | D | pitch |
| GP 1835 | 60.0 | 3400 | 52 | 42 |
| GP 2180 | 70.0 | 3400 | 52 | 49 |
| AeroVee 2.1 | 73.1 | 3400 | 54 | 44 |
| GP 2276 | 76.4 | 3400 | 54 | 46 |
| Hummel 2387 | 79.7 | 3400 | 54 | 48 |
| Revmaster 2300 with recommended Prince propeller | 52.5 | 3000 | 54 | 46 |
| Revmaster 2300 with "correct" propeller | 79.2 | 3000 | 56 | 60 |
| Sauer 2400 UL | 79.7 | 2700 | 58 | 72 |
| ULPower 2600i | 81.8 | 2800 | 57 | 71 |
The Aerovee with the Sensenich propeller will output 73 HP at 3400 rpm according to this. This is probably about right, because the larger GP 2276 cc shall output 76 HP, and will do so by slightly more pitch. The Revmaster is a different setup because it is designed to output 80 HP at 3000 rpm. With the recommended Prince propeller, it will only output 52 HP at 3000 rpm, so obviously Prince is wrong. A more "correct" propeller would be 55" diameter and 65" pitch. With the Sauer and ULPower, a usable propeller would be difficult to get right without also extending the landing gear/larger wheels due to their much lower rpm which requires larger D, or by adding more blades.
Regarding "propeller difficulties" the AeroVee is no problem. Sonex has done all the testing. The larger capacity GP and Hummel should also be relatively easy I guess. It is only a matter of adding some pitch. The Revmaster could be much more difficult. It is designed to run on lower rpm. The Sauer and ULPower would be even more difficult, and probably would need new landing gear to get a larger diameter propeller.
Saturday, July 05, 2014
Corrosion tests
I made a rivet corrosion test plate just before winter. What I did was to spray it once with salt water and then just lay it on the veranda. It has laid there during the winter and spring in rain and snow and sun and I took some pictures of it now before fastening it to my boat to see how it handles marine atmosphere. It will stay on my boat the rest of the season.
The primer used is aluminum pigmented vinyl. The rivets are stainless steel and ordinary AN aluminum. The yellow "gue" is Duralac. Duralac is a special compound made particularly to prevent galvanic corrosion between dissimilar metals. Typically this is stainless steel and aluminium in marine applications. Duralac was originally made for aerospace applications, but is today mostly used in sail boat applications where they often use stainless rivets on aluminium, just like Sonex does. I use Duralac on all my stainless steel rivets for the Onex. I was a bit too generous with the duralac here, before I got used to it.
The aluminium rivets looks like new. Nothing is going on there. The SS and Duralac also look like new, primer or no primer, so this is good. Bare stainless rivets on bare aluminum shows signs of corrosion, particularly on the "shop" side. What is more troublesome is that bare stainless rivets on primed aluminium also shows signs of corrosion, even under the primer. The reason for this is probably that when the rivet is set on the dry primer, it widens and create small cracks in the primer that allows water to enter. This is obviously prevented when using duralac, but I hoped the primer alone would stop it. Maybe if the rivet was set "wet" with primer, all would be good, but I didn't make such a sample (didn't think of it).
Conclusion so far:
The primer used is aluminum pigmented vinyl. The rivets are stainless steel and ordinary AN aluminum. The yellow "gue" is Duralac. Duralac is a special compound made particularly to prevent galvanic corrosion between dissimilar metals. Typically this is stainless steel and aluminium in marine applications. Duralac was originally made for aerospace applications, but is today mostly used in sail boat applications where they often use stainless rivets on aluminium, just like Sonex does. I use Duralac on all my stainless steel rivets for the Onex. I was a bit too generous with the duralac here, before I got used to it.
The aluminium rivets looks like new. Nothing is going on there. The SS and Duralac also look like new, primer or no primer, so this is good. Bare stainless rivets on bare aluminum shows signs of corrosion, particularly on the "shop" side. What is more troublesome is that bare stainless rivets on primed aluminium also shows signs of corrosion, even under the primer. The reason for this is probably that when the rivet is set on the dry primer, it widens and create small cracks in the primer that allows water to enter. This is obviously prevented when using duralac, but I hoped the primer alone would stop it. Maybe if the rivet was set "wet" with primer, all would be good, but I didn't make such a sample (didn't think of it).
Conclusion so far:
- Bare stainless on aluminium will make the aluminium corrode.
- Duralac stops all corrosion, primed or not primed, this makes me happy.
- Pre-primed (and dried) aluminium does not prevent galvanic corrosion. Maybe another primer works better, or "wet" setting works ?
- Aluminium rivets on aluminium does not corrode, primed or not primed.
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