Here are a few new photos of my twin engine project. More to come shortly at www.homebuiltdirectory.com.
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Here are a few new photos of my twin engine project. More to come shortly at www.homebuiltdirectory.com.
Newest photo as of today (bottom photo)! Engines being built shortly.
That is a very interesting project! I have been toying with the idea of designing a light twin for some time now, given the rapidity with which engines are growing more efficient, airframes are getting lighter and stronger, etc...
Looks like you've adapted an RV-7 or something(?)
Would love to see more photos! Keep up the good work. Can't wait to see that fly!
Thank you for the kind words! I will be adding more pictures very shortly. I am currently finishing the instrument panel/center console installation, minus avionics for now. Used to be a RV-6A. Now it is called a Twin JAG.
More coming soon.
Jim
Here are some more recent photos. Trial fitting the burlwood panels on the center console. More pics coming soon...
What engines are you planning on using?
I am building custom 120hp Corvair based flight engines. They are direct drive 6 cylinder air cooled and are very smooth running engines. They contain a fifth bearing to handle loads imposed on the crankshaft by the props. My engines will use the following brand new custom parts:
1. 4340 billet ion-nitrided crankshafts
2. Custom pistons & cylinders
3. 4340 connecting rods
4. Falcon machine heads
5. High volume oil pumps
6. Weseman 5th Bearing
7. ...much more!
I will begin building these engines in the next few weeks.
Jim
Very nice project!
.
Your Dec 17 post included a picture of your console with the #1 & #2 PROP BRAKE controls. I had only seen passing reference to brakes in obscure texts. A recent forum thread regarding the Bally B-17 replica had pictures of those powerplants and some folks thought the brake drum looking things aft of the props were freewheeling devices. There were some opinions expressed that a free wheeling prop on a shut down engine was desirable.
Could you bring us up to speed regarding the relative drag of a feathered prop vs a braked prop vs a free wheeling prop. I can't wait to see pictures of your brake system. It could turn out to be lighter than a cs feathering prop. As if there were one even available for a 120 hp Corvair. Can't go wrong with the Corvairs.
Bob
Thanks Bob!
As you know, a constant speed prop is both heavy and complex. It is also a failure point and it's weight puts stress on the crankshaft. My concept of a prop brake is a simple one...I will install a mechanical brake caliper, identical to a bicycle's, which will stop the windmilling prop using the machined surface of the flywheel (just under the teeth where the starter meshes with).
Here are a few of my thoughts for this setup:
1. A feathered prop, using a constant speed prop, effectively reduces drag approximately 97% compared to an unfeathered windmilling prop.
2. A stopped unfeathered prop, using my proposed braking system, effectively reduces drag approximately 93% compared to an unfeathered windmilling prop.
3. I feel that with a simpler and lighter setup, I would be willing to live with the 4% degradation in performance. I can makeup the difference by setting limitations to the operation of the aircraft (ie. minimum runway lengths).
These are just some generic thoughts of mine that describes why I am choosing this route. It is much more in depth than I can describe on this forum. Hope this helps.
Jim
Attachment 3646
Panel shot...
interior pieces just in place temporarily.
Panel with Dynon templates taped in place...
Here is a pic of the left motor mount. Due to the shallow geometry of the firewall hardpoints, a truss style mount is required. Weighing in just under 10 pounds, I over-engineered the mount but am confident in the strength. It passed a 6 g load test.
Recent photos with engine mounts installed. Powdercoated pearl color.
Just fabricated and installed landing light enclosure. Also streamlines upper portion of nosegear leg. Landing light is Aveo LED...very bright and low amps! Airframe just about complete...just waiting for engines and avionics. I am just starting to build the engines now and hope to have them installed late summer or early fall. Also taking advantage of the warmer weather to finish the filling and sanding of all the fiberglass work.
Made my night, Frank! Too funny...that movie is most excellent
Filling & sanding....about 80% complete.
Painted cases bolted to mounts for sizing purposes. Building shortblocks very soon...
Both engines have cases closed with ARP case studs with cam & crankshafts installed. Should have both shortblocks complete within next 2 weeks. Fifth bearings installed on both cases last week. Virtually everything other than the cases and head castings will be brand new parts.
Attachment 4163Attachment 4164
http://eaaforums.org/attachment.php?...tid=4266&stc=1
Right engine almost finshed. Left engine also in same stage of completion. Bringing both engines to Corvair College first week of November to test run and break in.
Front view of engines mounted temporarily.
It seems very hard to believe that just stopping an unfeathered prop cuts 94 of the drag, or else it would have been used in other planes, cheaper, simpler than feathering.
Obviously, once you get to flight testing you can, at a safe altitude, shut down one engine, brake the prop to a stop and try it, and you will know how it flies on one engine. A premium would then be on getting the brake off and restarting.
It may work, but I'd sure wear a chute and be able to get out. A chute won't help if an engine is lost on takeoff,though.
You sure have put some work into it.. Good luck.
Note, I am not any kind of expert on this, and don't even have a multi rating.
Having studied some twin conversions (I'm on the board if the organization that actually holds the TC on one of the twin Navion conversions), did you increase the size of the tail? Rudder trim?
Yes, the tail is aproximately 30% larger than the original tail. No rudder trim.
Bill, you are correct. It is not truly 94%...I was just trying to quantify in simpler terms the reason for my thinking. A feathered prop is more streamlined than a flat blade. Stopping the prop does make a huge effect on drag although my props will probably stop on their own due to low inertia below 100kts. It is just a simple way to reduce drag if the crankshaft broke just behind the prop hub for example.
Some engine details....still fabricating intake, exhaust, baffling, oil cooler, etc.
Attachment 4701
Designed & carved this 62" x 74" test prop. I will use this prop to test run my engines. I will then tweak it for flyable props. Hope to run the #2 engine on the aircraft before Airventure. I will run the #1 engine shortly after I return from Oshkosh later this summer.
You may see a baggage shelf, and you did a nice job of designing and fabricating it, but I see a rumble seat! I'm not sure how a "light" person would affect the W&B sitting up there, but with a little bubble canopy on the nose cone, instead of just the door on the side, that would make a cool perch!
Aerodynamically speaking, a spinning prop has the same flat plate area as its entire disc area. This was confirmed by Fred Weick of NACA in the 20's, which is why the feathering prop was developed, as props have little tendency to spin much when feathered. Yes, the blade presents more flat plate area in cruise configuration than when feathered, but only if if it's not turning. What if you have a severed crankshaft, a compression ratio of 20:1 won't keep the prop from turning in flight. If you feather the blades so there's minimal aerodynamic forces acting upon them, you won't have the drag of the entire disk, just "6%" of it. Feathering props are wicked complex and heavy. Jim has created a simple, lightweight system here to help minimize some of the yaw problems associated with an engine-out condition.
I appreciate other homebuilders posing questions to those showcasing their projects here: it's how we all learn lessons from those who tried and learned something new. The only stupid question is the one that hasn't been typed...that said: what color will she be painted after flight testing?
Hi Crusty...I'm leaving the paint up to the wife lol. We are going to use a pearl basecoat vs white though.
Photo right after successful first run of right engine on the airframe. I fabricated a cooling baffle to direct air through the cylinders. I could not be happier with the first run. The Ellison TBI performed flawlessly! I will be fabricating the subsystems for the other engine over the next few weeks now that I know there are no major issues with the right engine. I will be doing many more hours of engine runs on both engines over the next several months. Back to the hangar...
Attachment 5055
Here is a link to first start of right engine...
http://youtu.be/pcImWpnbb2M
Sweet!
That had to be a rather momentous occasion after all the work to that point, sounds strong.
I have heard of issues with the Elison TBI providing unequal mixture to both banks in the split intake scenario. Have you compared head temps? I heard the spray bar should be fore-aft instead of cross ways. I know of someone who balanced theirs with a "Tornado" insert. Also, is one engine reverse rotation?
Hi Dave,
Both engines turn the same way. Too many cons vs pros in having counter rotating props. I made my own swirling device similar to the "Tornado". I feel they should swirl the air fuel mixture downstream of the Ellison so when it reaches the "y" in the intake, there will be even distribution. All the builders who have done this report very good results. I don't have all of my engine instrumentation yet so the verdict is still out. The Ellison can be mounted in any attitude. You should avoid having the spray bar vertical as g forces can affect the diaphragm thus affecting fuel delivery.
Jim
I see you have done your homework, then again, I already had that impression. Will you be using a Plenum system like M Langford? ( http://www.n56ml.com/corvair/phoenix/ )
Dave
Links to videos of left engine's first run on airframe...
https://m.youtube.com/watch?v=UcaaDl3ch2U
https://m.youtube.com/watch?v=xx1iTqUEXnU