Discussion in 'Wood Construction' started by Victor Bravo, Apr 5, 2017.
Got it. Makes sense. I had no idea that was his design.
Pete owns the prototype Cracker Jack, so the initial acquisition cost for that was zero. Pete and Pat Panzera got the second Cracker Jack (plans built #1) at a price lower than they could have bought most other similar airplanes. So the cost was lower there too.
Because the O-100 weighs a lot less than the A-65 or the 4 cylinnder VW, starting with an existing airworthy homebuilt (Baby Ace, DA-5, Volksplane, Bebe Jodel) would have resulted in a tail heavy airplane that needed major components moved around and re-engineered. Long engine mounts designed and built, battery moved several feet forward, etc. So just bolting the engine on an existing Baby Ace would have added time and effort to redesign parts of the airframe... and this time had already been put into making the Cracker Jack correct.
Pete is going to be offering plans and eventually kits for the Cracker Jack, so there is that motivation in the mix too.
If I remember correctly, I think the O-100 came about because Pete was looking for a better engine for the new and improved Cracker Jack.
Yes that is 100% correct as far as I understand. The entire project began 5 or 7 years ago because Pete realized that an updated version of the CJ would be relevant to the (then-new) LSA niche, and he remembered that there was no really good, reliable, affordable 4 stroke powerplant in that size/weight/HP range. He had gone through three or four different engines, and realized (when gas prices skyrocketed) there was an even bigger niche for a good economical engine.
Dave's Cracker Jack, the first "Beta test" version 2.0 now under construction, is a thing of beauty. You can't believe how much cleverness, engineering, common sense, ease-of-building, and safety-thinking has gone in to this re-design. Fuel tanks out of the fuselage for added safety. New airfoil for added performance and handling. Increased cabin dimensions for added comfort. Features for improved control authority and "feel".
I have been petitioning Pete to develop laser cut kit parts for this, so that the builders will have the option of true "scratchuilding" or faster/easier build. As much as I like aluminum, the experience of building a classic style aircraft in wood will appeal to many builders. And the Cracker Jack definitely will have to look and feel of a classic light sportplane that deserves to be crafted in wood. The structure and shape of the airplane will easily justify the translucent "clear" antique linen look for those who want to do it.
I think this would be a popular option. This would be ideal for many first-time builders who may not be confident in their wood working abilities. Also, faster build times = more completed projects.
That is partially correct, but at this stage all of us who are involved to one degree or another agree that the engineering (actually mechanical) aspect still has to come first..... for just a few more moments. It is still in development phase, albeit at the very last stage, but it's not quite in the sales stage yet.
I have quoted Pete's words before and I'll say it again... nobody wants this engine to be available for sale today more than Pete Plumb. As soon as the production demonstrator crankshafts come back from testing with hard data, if Pete can stomach it I'll put my Rayon Leisure Suit (with white patent leather shoes) salesman outfit on and help Pete start taking orders post haste.
The engine is not going to be sold... whether experimental, ASTM, or FAA certified... before an independent university lab has completed the torture testing.
You know I have nothing but complete respect for Pete and his project. I've met the man, sat across a diner/cafe table from him and talked about the project, been to his office and hangar, helped in whatever miniscule way with a day of early flight tests of the engine in the original Cracker Jack, and am generally about as big a fan and cheerleader of the O-100 as he has, possibly excepting yourself, of course.
But the time comes eventually to shoot the engineer and release the product. It has been said here before, and by far more qualified "engine people" than I, that Pete would learn more, faster, about potential hidden issues with the engine by getting several in the air in the hands of a small cadre of carefully-selected homebuilders. The testing would be more realistic, the exposure of unexpected variability in the various manufacturing processes, etc. more complete. I'm glad he's decided to limit the university testing to the crankshaft, and agree that that's worthwhile testing work.
Again, absolutely respect and admire Pete and what he's accomplished here - the engine is exactly what we need for light aviation and not only that, it's a great engine to boot. But history is absolutely littered with projects that were never released because the very talented engineer/inventor insisted that it be "absolutely as good as possible", meaning "perfect in his eyes" before he would sell any of them. Babbage is the classic example. I'm hearing those kinds of phrases reflected in your reports from Pete, and I'm honestly starting to become a little concerned. If, as you say, there's any question that Pete can't "stomach" releasing the engine for even limited sale to homebuilders for testing after the crankshaft testing is completed (successfully, of course), then I'll honestly say that I'm becoming concerned that he's falling into that trap.
The engine will never be perfect. There will always be room for improvement. At some point, no matter how much development or testing is done, one of them is going to fail and somebody might get hurt. Nothing Pete can do will stop that, unless he never releases for sale at all.
I'm probably wrong. I hope and think he's just waiting for the crankshaft testing results to come back, and then he'll start selling engines to a limited pool of homebuilders for real-world experience. Pete is a great guy. I like him personally, respect his skills and the obvious care he puts into both the O-100 and his airplane woodworking company (amazing work there!), and his vision for this engine. The engine itself is an absolute gem, and I have no worries or concerns whatsoever about its ability right now to be a very successful, safe, and well-performing engine. He's done absolutely beautiful work, which seems to be the norm for him. I have no doubts about Pete's capabilities, his engine, or his business plan. I'm just hearing repeated expressions that, in other people, might hint that he's having trouble "letting go", stopping the development and "improvement" process, and releasing a product for sale. That's all.
I and others have strongly supported the concept of taking orders as soon as the crank testing is done. At this stage I believe that is what Pete is planning to do.
Recently I made an arrangement to bring a very highly qualified research scientist, from a major US research facility frequently dealing with engines, to visit up there. This is a pretty heavy duty lab testing and data guy who also happens to be "one of us", a homebuilt enthusiast, model airplane guy, a fabric/tailwheel guy, and an outside the box thinker. For whatever it is worth, this researcher agreed that the quality of the parts, and quality of the thought process, was excellent. He supported the notion that lab testing the crankshafts was very worthwhile.
All of us involved with this project on any level realize that no engine, airplane, or component is going to be perfect. I agree 1000% that he will never get it perfect. But everyone needs to accept that Pete is not off on a wild academic goose chase demanding perfection. This engine will never be sold as "perfect", or claimed that it will run forever, or claimed to never have any problems. That is absurd, even for a certified PT-6.
All that's going on here is that he is not willing to have the one largest and most critical moving part of the engine go into anyone's flying airplane based on theoretical calculations and what "ought" to be safe.
Fair enough, and I'm glad to hear it. Just expressing a concern. Very happy to hear that it's unfounded.
Looking forward to this.
I think the original Cracker Jack used a Dutch built DAF 2 cylinder engine converted for aircraft use. There were some problems with it and that may have led to the Pegasus project.
As for CJ 2, does it have a monospar wing? I'd wonder about torsion issues.
The Daf engine flew the original crackerjack, but was underpowered. The other plans built crackerjack (80's version) saw dramatic climb and cruise speeds with the prototype 0-100 engine. The latest CrackerJack that I am building has "D" Box construction. the front section of the wing from the top of the spar to the front spar, (leading edge) and back to the bottom of the spar is fully sheeted. This construction allows the spar to handle the curving forces while the D box handles the twisting forces. There are new pics with descriptions just posted. http://flypegasuspower.com/wp/davescrackerjack/
Thanks! Victor Bravo Things are moving quickly now. I am pretty close to varnishing fuselage. I got parts for the torque tube zinc chromated today. Have to make a few bellcranks, brake/rudder pedals, cabane structure all welded, pretty close to building that turtledeck (as in picture posted.) I will keep pics updated weekly, and check messages here !
Glad that you are here on HBA. Amazing report; the photos should be useful as a “how it is built” guide for future builders, as well as a general guide to wooden light airplane structures.
Thanks for the reply!
I was also wondering about the ailerons - if there's no rear spar what do they attach to?
Hi Guys! Dave told me about this thread. I've enjoyed reading through it. You guys are SO supportive and I really appreciate it. After I answer a couple questions here, I'll head over to the Pegasus thread and give you an update. A quick look at Barnstormers on the Biz Op category will give you an idea of where the engine is though. Topaz, don't shoot me yet - the design is FROZEN and production units are in production! Nuff said here about that.
Yes, the Cracker Jack is a design I came up with in the mid 70s after seeing a cut-in-half VW engine on a card table at the Chino Airshow in about 1977. That thing inspired me to design a "Cub-like" single-place and since I had established my Wood Wing Specialty repair shop at Shafter Airport a year or so earlier, I thought I could build it out of wood for nearly nothing. Well, 5 years later when it flew for the first time, I had enough money in that thing to have purchased 2 Cubs! That's how it goes, right?
Admittedly, I didn't know a lot about engineering an aircraft at that time - no wait - I didn't know Jack S*** about engineering an aircraft at that time but I was working daily with brilliant minds on the Gossamer Condor and was mentored by the best of the best. With a basic knowledge of model aircraft structures, I was able to build and fly a pretty nice little airplane. Although the design was inspired by a 1/2 VW, it ended up with an engine I bought from the Sorrells of HyperBipe fame. Originally powering a little car called a DAF, the twin-opposed engine did work well but was the plane was under-powered and parts availability was a problem. I flew the prototype Cracker Jack with the DAF screaming at 4000 rpm for about 200 hours between 1982 and 1986 and during that time, I sold about 100 sets of plans. The first plans-built example of the Cracker Jack flew in 1986 with a 1/2 VW and it is on that very aircraft that we are now testing the Pegasus DP-1 with great success.
About the single spar wing. I credit John Lake with giving me the idea for the single spar wing. I was very familiar with compression member and drag wire construction but not "D-Tube" construction at the time. John was able to show me the benefits of it for a light weight airplane and I went with it. There is another small spar along the leading edge to which the 1/16" ply D-Tube sheeting is attached. Many glider wings are built this way as was pointed out earlier. I used a 4415 on the original so the double benefit of using that thick airfoil was the 6" deep spruce main spar to carry the bending loads and the area within the D-Tube section to handle the torsional loads. The drag and anti-drag loads are also dealt with efficiently with the D-Tube. In flight drag loads are not the concern - it is the high-G, high alpha angles that really test the D-Tube's ability to resist anti-drag loads. The resultant force is acting forward (chordwise) and with the distance between the two spars at 13" the COMPRESSION on the front spar fittings in a 6 G, max CL pullup is about 3200 lbs! The wing and center section are designed to handle it but it is something to be aware of. Any of you novice designers out there needing help with that let me know.
The aileron spar. Yes there is a structure to which the aileron attaches. On the original it was a piece of 1/4" x 3" spruce that spanned about 6 of the outboard ribs a foot from the trailing edge. Since it doesn't run all the way inboard I used some 1/2" x 1/2" spruce diagonals to keep it from shifting laterally. I worked okay, I guess, but the new set-up in the "B" model is much better. Lateral movement will be controlled by sheer panels instead of diagonals. There is a spar but it is only there to form the well. The support structure for the aileron well and its attachment to the ribs carry the loads from the aileron into the D-Tube via the 7 trussed ribs to which it is attached. It is much better structurally and very light weight..
Well, I better go. I'm slammed in the shop right now. Thank you for all the nice comments and support you guys! And kudos to Dave for the fantastic job he is doing on his airplane. He comes out everyday and works on it. Soon we will get back on his wings and you can see more detail of the structure. Tail feathers too!
Bye for now! Pete Plumb
Music to my ears! Thanks for the update, Pete! SO looking forward to this! :grin:
There are a few more pics added to the list. This past week I have been working on the control stick, waiting for a piece of chrome moly for the short push/pull tube to the elevator bellcrank. Today I was making brackets for the aileron pulleys, building support structure for the seat. Hopefully I can get things together for pics by end of week (before everything gets taken apart for zinc chromating !)
I have some new pics posted. I have the pulley brackets and seat/lap belt attach brackets temporarily installed. I intentionally left out the washers and used non locking nuts in areas where I have to locate holes and then go back and drill them out for bushings. I also have to zinc chromate all metal parts and silver varnish all wood that will be covered by brackets. Looking forward to getting fuselage on gear, my back needs the rest !
What is “silver varnish” and what is it used for?
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