December, 2000

The correct use of prop hubs.

We have seen the discussions on Internet Groups as to why there are different prop hubs and what their individual uses are. Some ended with confusion and still left many questions. It is important to note that not all prop hubs are designed to be used with all crankshafts. The following is a breakdown of our prop hubs and the correct usage:

Shrink Fit Hub. This is the oldest prop hub design offered. The hub has a .002" to .003" interference fit on the end of the crankshaft and extends 1.5" out from the engine case. The hub features reverse threads on the engine end of the hub to "sling" the oil back in the engine. All of the hubs we offer are made from 4140 preheat treated steel. The Shrink Fit Hub is designed to be used only on a stock 69mm forged German crankshaft or the 74-78mm forged crankshafts as used in 1/2 VW conversions. Many of the early hubs made by others, allowed the prop hub retaining bolt head topass clear through the hub, relying only on the washer for prop hub retention on the crankshaft. Plus, many early hubs (from other suppliers) were made from aluminum and cracked in the prop hub key way after a few hours of operation. The Great Plains Shrink Fit Hub is the most popular prop hub sold for a stock 69mm crankshaft and 74-78mm 1/2 cranks.

3 Degree Standard Taper Hub. This prop hub is also made from 4140 preheat treated steel. The hub extends out 2.5" from the engine case. This prop hub is designed to be used with an oil seal that is epoxied onto the engine case. The crankshaft must be tapered to match the taper of the hub. With our Standard Taper Hub, the head of the bolt will not pass through the hub. The prop hub keyway it features, has slightly rounded corners to minimize the possibility of cracking. Some earlier hubs made by other companies allowed the head of the bolt to pass through the hub, allowing only the washer to retain it. The Standard Taper Prop Hub is for use on stock 69mm forged German crankshafts only.

Force One Prop Hub. The Force One Hub is also made from 4140 preheat treated steel. The hub extends out 3.675" from the end of the case. This hub is designed to be used with a bearing/seal/housing that requires the case to be machined. The crankshaft must be tapered to match. The taper extends back to the brass drive gear on the crankshaft. Our current design uses a 1/2" bolt and special washer for prop hub retention. Older designs used a stock 20mm bolt and hardened washer. This prop hub can be used on stock 69mm forged German cranks or forged 82mm aircraft style cranks as well. The Force One Prop Hub and Main Bearing setup are mandatory for use on all Type 4s, direct drive applications and Type 1 Stroker Crankshafts.

The Force One Prop Hub was designed as a result of having stroker crankshafts break while using shrink fit and standard taper hub types. Back in the mid to late 80's we replaced quite a few stroker crankshafts used by another company, (and one of our own) that had broken with the shrink fit or standard taper style hubs made by other companies and still replace 3 to 4 per year. Since the introduction of the Force One Hub, crankshaft breakage has been almost eliminated. When used in combination with our aircraft style 82mm stroker crankshaft (featuring a 1/2" bolt, etc.), to date, not one has broke. In a nut shell, torsional vibration is the culprit. Stop and think for a moment, you have a prop on one end of the crankshaft, and a flywheel on the other end -- plus combustion. Both masses are accelerating and de-accelerating at different rates and speeds. In addition, you have the gyroscopic loads being transmitted to the prop hub/crankshaft by the prop. Failure occurs when the hub and/or hub and crankshaft no longer can absorb and dissipate the different loading imposed.

For a more complete story, look at our web site.

to you and your family from Steve & Linda at Great Plains Aircraft. We would like to thank you for your continued support.

OCTANE

Their are many variables taken into consideration when calculating the absolute compression ratio of an engine so that you can determine the minimum/maximum octane fuel to use. We are going to just keeping it simple, by doing math only. We are not considering variable timing, camshaft duration, camshaft overlap on the intake and exhaust strokes etc... We are simply looking at three variables:

1. The Deck Height. The distance from the top of the piston to the top of the cylinder when the piston is at Top Dead Center.

2. The CC volume of the head.

3. The displacement of an engine divided by 4. (Our engine assembly manual goes into great detail of how to calculate the compression ratio out, so we won't do it here.)

The reason you need to know the compression ratio of your engine is simply to prevent the engine from detonation caused when a low octane fuel is used in a high compression engine.

Octane in simple terms is a fire retardant, it slows the combustion process down. In effect it allows more heat to be absorbed by the piston and thus produce more work.

In our catalog engine statistics list, we show a compression ratio of 8.0:1, the use of 100LL avgas and a certain HP the engine produces at a given RPM. These are all valid known numbers. But that doesn't mean you have to use 100LL avgas. Shims are used to lower the compression ratio of any engine. When installed under the cylinder they produce more deck volume. Greater deck volume will yield a lower compression ratio.

100LL avgas is needed in many VW powered homebuilts. In our opinion any VW that has a compression ratio of 8.0:1 or greater needs 100LL avgas. Like wise, we feel that even lower compression engines that use a POSA type carburetor should use 100LL avgas unless the owner has sufficiently tested 92 unleaded auto fuel in high heat (outside air temperature) conditions. We have found that auto fuel in many VW powered homebuilts will work fine in gravity fuel systems until it gets hot outside. In part, this is simply due to the fact the auto fuel evaporates (boils) at a lower temperature than 100LL avgas does.

There are many benefits to using auto fuel when combined with a lower compression ratio, a fuel pump and a carburetor that can handle the fuel pressure. "Getting the lead out" of the engine almost eliminates exhaust valve seat erosion and valve sticking problems. The engine usually runs cooler (lower compression ratio) and the service life of the engine is extended (lower compression ratio = lower horsepower).

Mathematically you should be at 7.3:1 to use 92 unleaded non-alcohol auto fuel. In actuality, we find that you can run 7.8:1 and still run without detonation. So a half point seems to be the merging point between math and reality.

Our 2180cc VW engine we sell is set up for 7.8:1 using .177" shims. I have this set up in my own VW powered aircraft. I use an Ellison EFS-2 mounted on top of the engine with a fuel pump. It drinks a steady diet of 92 Unleaded Amoco and it runs great. I can run it on auto fuel or avgas with a minor cockpit adjustment to the mixture.

Sonerai Ribs - Available 3 Ways!

Great Plains Aircraft now manufactures our own Sonerai Ribs. All Ribs are precision laser cut from 2024T3 .025" alclad aluminum. The ribs are available 3 different ways. The price of ribs will change according to the cost of aluminum at the time the material is purchased. We currently have 10 complete sets in stock!

First, laser cut only. We supply you with a full size wooden pattern, you cut out. You flange the lightning holes, add the rib stiffeners and bend the airfoil. No further cutting or trimming is needed. Cost for ribs this way is $18.00 each or $396.00 per set of 22, plus $10.00 for wooden pattern.

Second, we supply you a full size wooden pattern, you cut out. We flange the lightning holes and add the rib stiffeners, you simply cut the pattern out, make a duplicate and bend the airfoil surface, top and bottom. The ribs cost $23.50 each or $517.00 per set of 22, plus $10.00 for wooden pattern.

Third, the ribs come completely finished. Lightning holes and stiffeners are installed and airfoil formed top and bottom. They just need to be fluted. The ribs run $29.50 each or $649.00 for a set of 22.

Note: A set includes 22 nose ribs and 22 center section ribs. Ribs can be made left or right hand.

2001-2002 VW Catalog Is Ready!

Our 2001-2002 VW Catalog has been revised with many new pictures and includes the Front Drive, Rear Drive and Reduction Drive. Order your new catalog today!

The Great Plains On-Line Shopping Cart should be complete very soon! Updates to the Product Catalog have been completed on the web site also.

Wanted - Pictures of projects & planes!

Send us a picture of your project or flying aircraft. We are building a New section on our web site to highlight the many different VW projects/planes. You can e-mail a picture (gpasc@earthlink.net) or send it snail mail. Include your name, address, telephone number, e-mail address and if you have a web site, we will link to that too!

Sun & Fun: 2001 Engine Forum

We will once again be conducting the VW Workshop at the EAA Sun & Fun Convention 2001! This will include disassembly in the morning (by Keith Brown) with assembly and test running of the VW engine in the afternoon (by Steve Bennett). The workshops will begin on Monday and end on Thursday. There will be no VW workshops on Sunday, Friday or Saturday. Simply attend a workshop to learn more about the VW or stop by the booth. Our booth is in building "A".

Customer Appreciation BBQ!

Don't forget to stop by the booth and say HI! Also sign up for the "FREE" BBQ on Monday, April 9. Or send us an email before you leave for the Airshow (gpasc@earthlink.net). The BBQ is held on the field and the festivities start around 5:30 P.M.

Rear Drive Intake, Mount & Exhaust Ready!

Although they have been available for about 8 months, most of you have not seen the newest additions for the RDS. The intake manifold is now available, along with the engine mount and exhaust system.

The intake manifold has been flow tested. It comes powder coated, with gaskets, hardware and connecting hose. It is designed to fit the Ellison EFS-2 only. It allows you to use a stock mechanical fuel pump and electrical boost pump in series for take off and landing. Priced at $219.95.

The engine mount (as shown) will fit a KR-2 or KR-2S. We have made our jig so it can accommodate many other firewall dimensions. We have a photo of it on the web site by itself. Stock motor mounts come powder coated and we can powder coat custom mounts once final fit is insured. We currently have them for both the KR's and the Sonerai II or II Stretch for $249.50. Custom mounts will be quoted upon receiving your drawing.

The exhaust system is a universal system designed to fit a wide variety of current airframes. The only real change that may need to be made to it, is the angle of the 2 exit exhaust tubes. They can be rewelded to clear the bottom of most firewall's. The current design as pictured, will fit the KR's. The exhaust is a 2 Into 1 System and is very compact around the engine. Cost is $294.95.

Some have asked us about dual ignition for the RDS. If you really need a dual electronic ignition, a secondary system can be purchased from Electroair in Chattanooga, TN.

To place an order: Call us at 1-800-922-6507
Questions at 1-402-493-6507
Fax us at 402-493-3846.
Inquiries can also be directed to:
gpasc@earthlink.net