MJD

My Feedback: (1)

Har har, I got the cowl plug all done, the second mold layup is next on the list, as soon as the PVA is done drying as it is doing right now. So far so good.

So.. with the bench (partially) cleared, the Screamin Demon .65 project is back in the spotlight. In the meantime I fiddled with the engine mount and firewall, trimmed them to fit the engine and intake, and cut spars and ribs. And run the engine a few times, I think it will pull the aircraft okay from the sounds of things [>:]. My crude method of caging it on the front of the delta is evident here, note that at this point it's all just push-fit together to stare at. I'll tie everything together solidly after basic assembly. I'm hoping the engine doesn't just tear out the nose first time I throttle it up.

If this goes well, will it fly before the snow does..? Never know.

MJD

combatpigg

My Feedback: (3)

You're of to a flying start!
I see that there is a marine .67 for sale right now. I suppose it's OK to turn the cylinder around as long as you turn the piston with it?
Having a reasonably cheap source of props at Eliminator sure removes the excuse some guys had for owning these engines but never running them......

MJD

My Feedback: (1)

Yup, just flip the crankcase 180 degrees end for end and off you go, but you will lose your piston to liner orientation so do it new or do it bewares. The P/L set is interchangeable with the .65, but it's $165 so I don't need one that badly yet. The .67 is the "7-port" cylinder whereas the .65's are "5-port", although I did note that if you put a web in the middle of each of two boost ports on a 5-port engine you get a 7-port engine. I'm just fooling of course, AFAIK OPS does things for a reason; the .67 is supposed to have 10% more top end power so it obviously breathes better. If and when I do ugrade one of my .65's I'll put in a new rod at the same time, as apparently it is the weak link that results in redlining them at 24k stock.

MJD

Mike Connor

My Feedback: (5)

Hey Mike, I like your new signature.

MJD

My Feedback: (1)

Someone noticed..!

I hope to duplicate the feat with this contraption, then it's a club.

MJD

combatpigg

My Feedback: (3)

We really can't call it a club until the speed has been verified. I got my computer back from the 2nd shop that looked at it. He installed a program to turn video into a wave file and he was able to get a sample I gave him of another plane loaded onto Wavoscope, but the waves don't appear on the screen. You can click the icon to hear the file, but all you get is sound...no waves to analise. Eventually the screen locks up and you get the "unresponding program" message. I have WAVEoScope files that might contain instructions, but they are in PDF thatn this computer won't open. The only time I ever successfully loaded ADOBE, the user agreement didn't have a box anywhere to click on for "I ACCEPT"...so after a 3 hour download, that never got done. Right now, I'm so pissed, I can't see straight. FTS [>:]

MJD

My Feedback: (1)

Send the video to someone - I can export the audio and have a go at it if you want.

MJD

combatpigg

My Feedback: (3)

MJD, that's an offer I can't refuse!

MJD

My Feedback: (1)

Fine Talisker Scotch? Oh, not that kind of pissed.. I get it.

I just found myself cackling while I was fitting the ribs to the spars on this thing, and I've had the engine and pipe in and out of it maybe 15 times this evening, just to admire the cylinder height:wing span relationship. There's something not quite right about it..

Aha, wife's off to bed, and I'm all keyed up to build, and bonus, I already finished dry fitting everything. So now it is assemble the jigsaw time, with perhaps a little cut and try here and there. I'll take pics when there is a tangible framework with glued joints to behold. I got bored trying to "finish" the design on CAD, it's easier to build it the way it looks like it should work, take notes, then draw it if it does. Or something like that.

Uh oh, gotta pony up and order the RC RNV.

MJD

Mike Connor

My Feedback: (5)

Or just upload it to Youtube and we can all enjoy it.

Mike Connor

My Feedback: (5)

I doubt it. Here is a 1/8" ply engine mount that survived 120 flights and this crash. Beside that, I am sure you are going to strengthen the entire area with you monster engine.

MJD

My Feedback: (1)

I laminated three 1/8" ply motor mount plates with 6oz glass/epoxy between each layer and on the outsides. This made a nice 3/8"+ a bit thick and very solid beam mount. I'm tying it all together with some extra spar material and a couple of little mods here and there. I'm taking progress pics but too sleepy tonight for any more up/downloading plugging things in and out crap.. manana, manana. I think it will work, and there's room for everything too. The only big job is one more cowling plug and mold, but I'll try to make this a production prototype and therefore useable for any Demon. I didn't change the exterior envelope at all on this one for that reason.

The small block SE engine/tank cowl mold is curing overnight, then tomorrow morning I tear it apart, hopefully successfully. I get the first one, I get the first one, tra la la la laaa laa.. [sm=lol.gif]

MJD

LGM Graphix

My Feedback: (22)

Mike, how hard would it be for your laser cutter to scale this up big enough to put a 17lb thrust turbine on?

MJD

My Feedback: (1)

I do the drawing work anyhow, saves money, so no problem scaling. The guy I use right now for cutting (oh for my own machine someday soon..) only has a 24" wide platen..

Now funny you should mention this because I have already been sketching things for smaller turbines based on SD wing techniques..

MJD

Yak13

My Feedback: (17)

CP: Where is the .67 for sale?

combatpigg

My Feedback: (3)

Ebay, I think it ends today.

MJD

My Feedback: (1)

Progress pics.

The middle spar will be cut out in the center bay to make tank space. The rest of the gobbledy gook is mostly to recover that lost strength, add a bit more, and add solidity to the front end. So far I am happy with it.

MJD

combatpigg

My Feedback: (3)

That looks great!

If you limit the flying to big, open, back and forth passes, there isn't that much stress. It's absorbing the vibrations and sending those bad vibes out the wing-tips, giving that junk the path of least resistance. I believe it works something like electricity, same goes for the shock waves of impacts.
I think applying some FG to the spar / rib intersections is worthwhile, and also to FG the ends of the spars to the perimeter of the frame. I just did a post mortem of an old DD and those areas were still mostly intact.

MJD

My Feedback: (1)

You're right, I'm not building this one to play flying circus. I have no intentions of trying full deflection elevator tricks or the like at speed, with the possible exception of fast rolls by accident or intent. So my biggest concern was integrity around the engine mount (that is an awful big chunk of howling, thrashing metal up there) and a means to distribute the engine loads/vibes about the framework somewhat fairly.

Since I have an abundance of arrow shafts I made a cradle you can see in the prev pics, and wrapped the intersections with carbon tow and epoxy. One shaft runs outside the center ribs and aligned with the engine mounting plate, rearwards between the two short spars behind the engine, and ties in to the front half-spar. This is epoxied and glassed to the ribs though that does not show up in the pic too well. These short lengths of CF tube are very light and the stiffness is tremendous, plus the tensile strength is off the scale. The engine plate is a 3/8" thick laminate, and well trapped within the rib structure. If it comes apart I think the piece that hits the ground will be the engine and the center rib assembly as an intact unit, with Dacron bags of shattered parts flapping in the breeze on each side.

I plan to cover this with Stits fabric, so the whole airframe will be cocooned in a drum tight skin, and in addition I will epoxy-laminate the fabric to the exposed sheeting for skin toughness and abrasion resistance. It will be one tough little bird when together, I think. The torsional strength and stiffness should be impressive, it barely flexes as it is and also based on my #2 bird results. The fins will be carbon/glassed sandwich of 1/16" balsa - 1/64" ply - 1/16" balsa. The airframe in the last pics is up to 325 grams, and I weighed it a bit eariler with the engine and pipe together for a reading of 1050 grams IIRC. So even if I added a kilogram with tips, covering and radio, tank etc., which I think is pretty unlikely, it would end up at about 4.5 pounds. I know it will fly at that weight, launches notwithstanding, and land at reasonable speed. So I'm encouraged so far, and I hope to come in closer to my original 4 pound or so fantasy. Curses, just had an hour break to clean the kitchen and get started on dinner, and all I wanted to do was get back at it. I do enjoy those fleeting times when a project is interesting enough to me to be that absorbing. Two 2:30am nights are taking their toll though, I really should shut it down earlier.. And dinner seem lately to be chosen exclusively from our list of fast-fixeruppers for some reason.

Criminy, this thing might be done within a week at this rate. I better order my RNV now!! Dummy!

Oh yeah btw, dumb question, I've never owned an RC RNV and I know you have one CP - does/can the RC RNV completely replace the existing needle, as in act as the primary needle valve, or are they meant to modulate an existing needled assembly? And are they free enough for a strong micro or a mini servo? I probably can find this out on their website but hey, I'm here and I bet you read your instructions already.

MJD

combatpigg

My Feedback: (3)

A stand alone RNV is all you need, then send the metered fuel from the RNV into a spray bar on the intake that has no needle.
It's interesting to note that the Nelson spray bar channels the fuel into a spigot that dumps direct over the intake window of the crank, it practically rubs the crank. This is done to get the best possible fuel draw from an engine with an over sized [13 mm] venturi.

MJD

My Feedback: (1)

Cool, then that means I have lots of room near the carb for the RNV. Now I can relax a bit having, in my building enthusiasm, already closed in on top beside the tank bay where something might have had to go.

Does the RNV need much servo torque? I'd like to plan for a suitable servo while mine is on the way.

This is getting exciting, I can feel the project coming together now. The first launch will be one hell of a show no matter what happens.

Mike

edit.. p.s. I forgot to add.. watch it end up 10mph slower than yours in the end!

combatpigg

My Feedback: (3)

MJD, you are talking about a MCV, not RNV. The RNV is manually set just like if it was mounted at the carb. The MCV is the gizmo that is servo operated. The ones I have don't take any torque to control, but you still [I'm guessing] don't want fast linkage, you want fine control. Use a servo that can take vibration from just being onboard.

MJD

My Feedback: (1)

Okay I guess I got my acronyms messed up. I am talking about an R/C mixture control, so that's an MCV. Can those serve as the primary mixture control, i.e. as the needle, is that what they are meant to do? Or is the regular needle still fitted and these just vary conditions ahead?

MJD

EDIT: looking at the Perry site, it seems it has a manual adjustment for the mixture range, or midpoint if you will, so yeah I guess it can do all the RNV/MCV work.

MJD

My Feedback: (1)

So far today:

- all sheeting done, exception last part of radio compartment but that waits for a bit
- elevon assemblies made including CF TE insets, continuous hinging, center section filler. Not mounted yet.
- cut out center of spar for tank compartment.

Tomorrow morning - drink 2 pots of Earl Grey tea, make fins, attach elevons and center filler, maybe glass them in if time permits.

MJD

combatpigg

My Feedback: (3)

Looks like it'll be done by lunch tomorrow! [X(]