Help needed with SSDRs

[Richard Mole]

As an aside to the search for SSDR types, it is perhaps worth mentioning that David Cook's Shadow ('D' series I think but don't hold me to that!) had an empty weight of 150 kg and 15 m2 of wing for a TWO seater with very respectable performance, decent handling and admirable general robustness.

I am surprised that some bright spark has not set about scaling the general arrangement of the Shadow back down to an SSDR type; it would seem a very promising starting point. The whole design was a good example of using quite a wide range materials so that maximum benefit is obtained from each one ie matching the particular material properties to a particular structural requirement. The range of affordable materials today is probably even wider than was available to David Cook.

Its a pity about the relative lack of well proven small engines - any one offering a half decent and sensibly priced 4-stroke in the 25 to 35hp range might find the world beating a path to their door.

[G.Dawes]

The original jabiru engine was I believe a twin and they enlarged it to four and six then eight. I remember something last year where they rebuilt the prototype as an exercise for the trainees. maybe they should try a production as the modular design is ideal.

[Brian Hope]

Whilst the idea of a twin Jabiru has been suggested by enthusiasts, I have never heard that one has ever been built. The Jab engine was built because the company's engine of choice for its new aircraft - the Italian KFM - ceased production. My understanding is that the company then decided to build its own engine and a 1600cc four cylinder unit was produced. This was found to lack sufficient power so capacity was very quickly upped to 2200.
If indeed a twin was to be put into production it would fit very nicely into what is currently a vacuum in the small aero engine market - the 40hp four stroke.

[David Calvert]

http://hubpages.com/hub/Copyright-free-aircraft-plans

This site has links a number of interesting yahoo groups. The Texas Parasol is worth a look

http://www.home.earthlink.net/~cavelamb/parasol.htm

but as always the problem is the engine. A pity that the LAA has ignored the SSDR in the engine design competition. 40hp/39kg is too big. I think we need 30hp/30kg.

[Brian Hope]

I'm sorry David but I disagree that we have ignored SSDR. The 40hp/39kg is to try and generate an engine to compete with the Rotax 447, an engine that can be used in a number of SSDR types. To lower the power requirement to 30hp effectively restricts the engine solely to SSDR, or ultra light single seaters like the Luciole, and we wanted 40hp so that it would offer an affordable engine to future developers of ultra light two seaters, based on Luciole or eGo type technologies. 39kg is of course the maximum weight limit, there is every possibility that somebody will come up with something lighter. Personally I hope it generates at least one good 40hp four stroke as such engines are sorely lacking at the moment.

[NickChittenden]

David, why don't you go ahead and develop a 30hp/30kg engine? The whole point of this competition is to encourage members to head out to the shed. I have been messing around with a light car engine conversion for some time, it should weigh in at 37 kg but whether it can develop 40hp remains to be seen. The engine is being developed for my own SSDR project.

It is my earnest wish that the competition be free to enter and as many people join in as possible. A whole range of engines from the sublime to the ridiculous (mine) should provide a great deal of interest, amusement and debate amongst the judges and membership. Members should not be discouraged from entry even if the conversion does not meet the power/weight requirements, the sheer practicality and some recognition for the effort involved matter just as much.

Is Mr Cantrell joining in?

[Brian Hope]

Thanks Nick, that is just the attitude we want the competition to generate. It is indeed free to enter and the rules have been kept pretty simple so as not to stifle ideas. It is open to all, member or not and from anywhere around the world. The article is currently being translated into German and French and being sent to foreign homebuilder organisations. I hope that technical colleges and university engineering departments might take up the challenge too. Let's get some ideas flowing that will hopefully lead to a few more affordable engine options for the amateur builder.

[David Calvert]

Thanks Brian and Nick for your comments which highlight the choice availble to the SSDR designer and builder. It seems to me that there are two routes I can follow.

Firstly I can take the e-go route and use high tech materials and advanced design and building techniques to produce a beautiful sleek aircraft. I admire their achievement but it's taking years to build and is neither simple nor cheap. If I had £25k to spend on an aeroplane I would have plenty of choice. It seems to me that this route does not take advantage of the freedoms that the SSDR format offers.

Or I can do what Nick suggests and go out to the shed which is exactly what I am already doing. I want a garden shed aircraft, made with off the shelf materials, pipe bending that can be done with a tube bender from B&Q and no welding. I am working in an 8' x 10' greenhouse so the parts must all fit on an 8' x 4' building board. And I want a cost comparable with a second hand Evans VP1, say about £3k.

I am using a spreadsheet to keep track of the weight and balance, so every time I make a bit I weigh it and enter the weight on the spreadsheet which recalculates the total weight and C of G. Construction is at an early stage but is on target for an empty weight less engine of 170 lbs. This is right on the limit for the 447 and at one stage I calculated that narrowing the fuselage by one inch would save 8 ounces. It was then that I gave up on the 447 and I stand by my assertion that a 39kg engine is too heavy for my aeroplane.

I also stand by my assertion that 40hp is more than I need. I have a spreadsheet laid out as the performance matrix in the Evans design handbook which predicts that 30 hp will give me a rate of climb of about 700 fpm and a max speed in level flight of over 80 mph. Why do I need more?

I have an engine in mind. Good second hand examples are available for £800 or so, it requires relatively little modification, there is a plentiful supply of spares and it weighs less than 60 lbs including everything it needs to make it go, exhaust, carb, fuel pump, battery, starter, wiring loom and ignition switch. It will not be suitable for a permit aircraft but that is the whole point, this is an SSDR.

I am encouraged by the invitation to enter even if the engine does not meet the class requirements and as soon as you post the entry forms I will be in there.

[Nick Allen]

It will not be suitable for a permit aircraft but that is the whole point, this is an SSDR.

It did strike me when skimming the article about the engine competition in the magazine that an "SSDR engine" might have made an interesting subcategory...

[NickChittenden]

I agree an SSDR category would be interesting, however, to use SSDR (deregulation?) and then have more rules (regulation?) would be a paradox. It can't be an oxymoron because that's what I am. An idiot with a welding torch.

[Ian Melville]

Nick C
The rules would be competition rules not regulation.

Yes, it would be nice challenge

[Brian Hope]

Hi David, your SSDR sounds very interesting and I hope when you feel the time is right that you will share your project with the members via the magazine. I share exactly the same view as you re a cost effective, DIY SSDR at a budget price; that to me is the very essence of SSDR, bringing back the possibilities of minimal cost aviation. I really don't have any problem at all with the high end kits that are available today and being enjoyed by those in a position to afford them, they're great aeroplanes and I'd be delighted to own one - if I could afford to. LAA is for ANYbody who wants to fly or is interested in recreational aviation. There is room for every possibility be it a bargain basement SSDR or an RV10, and long may that continue to be the case.
My own feeling re SSDR engines is that 30hp is marginal, but I am a biggie. I'm also not keen on high revving single cylinde two strokes. The 447 is a good motor, but it isn't light for a two stroke and there are several lighter alternatives giving the same power. By setting the competition weight and power at the same as the 447 we hope somebody might come up with a four stroke alternative, but that is not the be all and end all. We generally want to encourage some more affordable options for the traditional homebuilder so whether you ideas fill the competition rules exactly or not please submit them and share your experimentation. As I said before, 30kg and 30hp would be too restrictive for the compettion, 40hp opens up more possibilities in ultralight two seat design.
The change over arrangements for magazine publication have kept me rather occupied but we'll get an entry form up on the website asap, another week will see the Feb mag go to press and allow some time to think about that in greater detail.

[David Calvert]

Thanks Brian I will look forward to seeing the entry forms. I used to be a biggie - as a Shackleton pilot sitting in the middle of four Griffons and holding 10,000 bhp in one hand. After that everything else has to be a bit of an anticlimax.

Surely 30 hp will be enough for an SSDR where the take off weight has to be less than 500 lbs, giving about 16 lbs per hp. I fly our clubs VW powered T61 Venture at 24 lbs per hp and it gets about. I share your suspicion of two strokes but I think we are stuck with them in this class. The acid test for me is - when you type the engine into ebay how many come up?

I will let you have a contribution for project news before long; just to keep your interest going the reg is G-SESA which I was astonished to find was still available.

[Dave Stephens]

does this mean you are building an SE5A?? if so, be carefull if you intend on flying in the essex area, as you might fall prey to the Fokker Scurge!!

[Ian Melville]

I think he is Dave, Saw mention of a SSDR SE5A in Dec Pilot. Reg G-SESA IIRC

Tally Ho Chaps