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Feb 25, 2018, 06:22 PM
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Hi Fuzz--Hope you're feeling better. I've been tip-toeing through this winter in hopes of not getting pneumonia like I did last year that kept me sick, like you, all the way through summer. I'm not so much into jets, but I do like the L-39. Is there a trick with the CG on jets, like the Guillow display jets that you mentioned? Am I hearing you say that you don't follow the usual swept-wing measurements for locating the CG? I would be interested in designing an L-39 hand-launch-size stick-and-tissue model, which would be about four designs down the road for me (which means I may or may not get it done in this lifetime ).
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Feb 25, 2018, 07:11 PM
Big gov never Works
St. Martin's Avatar
Thread OP
Hi Jay, and welcome my friend! The L-39 has the advantage of the standard mono-plane configuration, similar to the P-80. Figure your CG at 25% MAC or forward as much as 22%. This dependent upon the airfoil. Airfoil has so much to do with the center of mass for static balancing. Then you have the final dynamic balancing from flight. better to be nose heavy than tail heavy. The L-39 is a good choice for a stick jet. Basic design, and a bifurcated intake that allows a lot of area for batts and equipment.
But... then will try your building with the ducting. But...(I love buts) You do not need to have a 100% efficient ducting to be successful. Nothing wrong with properly designed cheater holes. As long as the fan has a good Clark-Y lip, and the cheater is properly placed. But,(another but) cheaters improve static thrust, not dynamic. So, a "dirty" frame may be improved by not having a ruled area ducting because of drag.

So, Take the plunge, Jay .Everybody dreams of having a jet. When I fail, I learn!

Fuzz
Feb 25, 2018, 07:25 PM
Registered User
Hi Fuzz--Thanks for all the "but" hints in design. You were talking about going from the inside out with the design, and I can believe that one! It seems everything is dependent upon the duct as well as the motor/fan selection.
Feb 25, 2018, 07:46 PM
Big gov never Works
St. Martin's Avatar
Thread OP
Yes, Jay, the internal design is important for efficiency of the flow for dynamic thrust(high efflux). But most stick jets will be very light weight. And the static thrust achieved with a cheater, will not require a duct system capable of high efflux velocity. As with prop planes, the best performance enhancement is power to weight ratio. The whole object of a stick and tissue type construction, is static thrust, and slower flight. Sure, area ruled ducting is of a positive. But not 100% required. I have jets that fly with cheaters. They are lighter but are not fast. You cannot have the best or both worlds. Decide on static or dynamic thrust. Or, a happy medium to suit the airframe. It depends on how you want to fly it. Fast or slow. No difference than a prop plane.

Fuzz
Feb 25, 2018, 10:55 PM
Registered User
It is true about the either-or aspect of high performance planes not being able to fly slow. I designed and built a 1/12th scale 1958 C-310b that one of the guys at the field when I maidened it said it flew as fast as a jet. I was standing at the pilot's station leaning forward just to keep my mind connected with this plane, as it was going way faster than anything I had ever flown before. But I was mostly flying it at 1/2 throttle! Granted it had plenty of power, but that airframe is known to be slick in the full-scale version. Now to just apply that slickness to the inside in the form of slick ductwork to match an equally slick outer airframe!
Feb 26, 2018, 12:47 AM
Registered User
Speaking of a slick airframe, here's some pix I found on AeroFred that might help me or anyone design a nice size RC stick and tissue model.
Feb 26, 2018, 11:47 AM
Big gov never Works
St. Martin's Avatar
Thread OP
That is a pretty design, Jay. Thank you for finding. On the downside, I have had a head cold since saturday. I went to an orthopedic this morning. He told me I have advanced arthritis in my spine. Of course I have it in my hands, legs and hands, Too. He said he could prescribe a pain killer, or I could wait till the weather warms to get relief. The weather around here has been damp and cool. Not good for the back. I layed on a heating pad most of the nite and morn, so, I'm good now. I'm tired of just turning my neck and hearing "creaking". I think it's getting close to the time when I take a bottle of Wild Turkey out fishing and let them find me with a smile on my face. Only kidding.. I'm so tired of not being able to function as in the past.

I need Arizona or New Mexico/Texas climate.

Fuzz
Feb 26, 2018, 04:06 PM
Registered User
Quote:
Originally Posted by St. Martin
I'm so tired of not being able to function as in the past.

Fuzz
I hear you, buddy. You're not alone. Hang in there, Fuzz!
Feb 26, 2018, 05:44 PM
Big gov never Works
St. Martin's Avatar
Thread OP
Thank you, Jay, I'm doing a conversion of the old Jetster design. Called the the Fantansia by Bob Reynolds. I'm designing a power pod to make this assembly into a builder friendly construction. It's not easy. But, doable.

fuzz
Feb 26, 2018, 05:45 PM
Registered User
Kevin Cox's Avatar
Nice Fuzz!
Feb 26, 2018, 06:41 PM
Registered User
Quote:
Originally Posted by St. Martin
I'm doing a conversion of the old Jetster design. Called the the Fantansia by Bob Reynolds. I'm designing a power pod to make this assembly into a builder friendly construction. It's not easy. But, doable.

fuzz
I'm not familiar with the Jetster. But I hear you on it not being easy to convert something so that it's user friendly. I've been working on someone else's plan that was full of errors, trying to correct everything so that it can also be user-friendly. A lot of work, although I think the design is great and deserves more audience. I'm building it with my corrections right now, which will be the proof of my initial work. Do you have a link to the Fantansia or an example of a power pod?
Feb 26, 2018, 06:43 PM
Registered User

My hat is off


My hat is off to you old stick builders. I too started with Comet kits etc back in the olden days and loved stick building. Give me a razor blade and those printed balsa sheets and I was in balsa bliss for days. I still remember ruining my Grandmother's new card table slicing thru the balsa into the fancy cardboard top on her table. I never knew I did it until it was too late. I did not know what an exacto knife or a razor saw was back then.
Reading those plans and building those planes unknowingly provided me with manufacturing common sense that lead me to a 45 year long career with General Dynamics/Lockheed Martin as a Reliability Engineer building the F-16 .
You gays have me looking for a jet to build! I'm thinking the MB 339 "Freece Tricolori" just might be my jet of choice.
Thanks again and good luck with your projects,
Rob
Feb 26, 2018, 06:57 PM
Registered User
Fuzz--I found your link to Dick Sarpolis' Jetster 20. I get it now about the power pod. Looks like a really easy way to get into EDF!
Feb 26, 2018, 07:05 PM
Watch out for that planet....
Shane McMillan's Avatar
Hi Fuzz,

Just read through the thread here, more temptations!

Stumbled across the old Berkeley Temco Pinto plan this morning, downloaded from the net. probably could work well with some 'Inside Out' duct design.

Here it is.

Shane.
Feb 26, 2018, 07:09 PM
Diver-driver
meatbomber's Avatar
there is a whole list of stick jet plans here (at least small ones )
http://www.stickandtissue.com/cgi-bi...m=1394305340/0


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