combatpigg

My Feedback: (3)

Hey, look what just showed up on my workbench!

It looks like a very well thought out design. The parts fit is right on the scribe lines.
I've got a 5.5 oz tettra tank for it and a Nelson .40 for power.

My question is...I've never used plywood to mount a speed engine, only maple or aluminum. I'm wondering what kind of special treatment the plywood should get so the engine doesn't burn into it or so that the mounting hardware doesn't crush the wood and constantly loosen up?

MJD

My Feedback: (1)

Well, if you're concerned my advice would be to think aboot a nut plate for underneath, i.e. a 1/2" wide strip of 1/8" Al or whatever with the holes drilled and tapped to fit, or nuts and washers underneath a clearance drilled plate. For the top surface, two strips of that 1/64" CA'ed to the top surface and running longitudinally would harden it up somewhat.

On my # 1 model, which so far has securely (really) held the West .50 and Jett .50 and been bounded on the nose once from a few feet up with no harm, I used the laminated mount plates as per the directions, filled in the lower area with scrap fill and blended it all in. Then I marked and drilled to clear a #6 machine screw, holes through the top of the bearers and straight down through the filler block material, and through the lower airframe skin (intentionally). The sheeted and filled areas had already been glassed already at this point. From the bottom, I then drilled 1/4" until I hit the plywood bearers, then I inset 1/4" dowels with thin CA in each hole. Then, once again from the top I drilled those right through, then around the bottom I drilled larger to accept T-nuts. I can reef right down on that and it seems to hold up fine. The short version: I bushed the holes with hardwood dowel and used T-nuts underneath.

Hopefully others will now chime in with their ideas. Does the nose ring deal and the two plates makes sense?

MJD

p.s. I see blue painter's tape. I love it! Use it all the time. I find it handy for the LE sheeting too. I found laying a metal rule along the LE against the forward edge of the rib, allowed me to pen a line along the LE back face where the sheeting glues and helped keep it straight as I moved along with fingers and glue. I also added extra 1/8" sq AFAIK, since I've grown fond of laminating the LE, tip, and TE.

combatpigg

My Feedback: (3)

Thanks MJD. I think the vertical dowels should be plenty strong. IIRC, didn't Speedy Gonzalez laminate C/F cloth to the top of the mount, too?

Mike Connor

My Feedback: (5)

I don't have that many flights on a Demon but the Dust used the same 1/8" ply and I got almost 120 flight on one of them with a Jett 50 on it. I just use 1/64" ply top and bottom where the engine mounts and fuel proof it well with thinned epoxy. I usually use aircraft locking nuts with washers and tighten once each flying day. The first pic is a current Demon engine mount. The second pic is the 120 flight Dust after flight 120. The engine mount is the only thing that survived almost.

combatpigg

My Feedback: (3)

Thanks for showing that Mike. Amazing what works, to me it looks like something that a hot engine could tear up, but obviously I'm all worked up over nothing......[X(]

MJD

My Feedback: (1)

It looks like the rear spar made it - or did it lose some off the one end?

Mike D

freakingfast

My Feedback: (3)

The D Dust uses 1/8" ply for the engine mount and I don't have any problems with the wood's integrity whether it's a DF engine or a YS 45.
After the engine is fitted and the mounting holes are drilled I wick in some CA in to the edge of the cut and into the mounting holes, this helps fill the grain of the wood and make it more dense and less likely to compress between the mounting lug and washer. I like to than seal whole mounting area top & bottom with finishing epoxy to protect the CA joints in the area from fuel.
After the first flight I re-tighten the mounting screws and check them from time to time thereafter. Ive had some hard "landings?"[sm=red_smile.gif] and hundreds of flights on several Dusts, and the engine mounting area never needed repairs. I did Kevlar lay-ups and found it's a waste of time and added weight. The Demon and Dust design are fine as they are but a few little strips of .007"carbon in some places does make me feel better. Sometimes you do need to supply your own mount if you stick an odd ball engine in there.

Mike Connor

My Feedback: (5)

Actually both spars made it but the leading edge was a different story.

MJD

My Feedback: (1)

On a different note I just set #2 aside for the night with big smears of epoxolite-type fairing compound in the inner corners of the tiplets. Not too much left to go before committing flight. I wish I had a RIRE .45 or .50 though. I keep eyeing my one toy boat.. up on the shelf with a fairly fresh OPS .45 poking it's head out. Bad thought, leave it alone.

Mike D.

combatpigg

My Feedback: (3)

FF, thanks for taking the time to show me those mounts. 10,000 happy customers can't be wrong, and I've known in the back of my head this is how it's "officially"done. This is my 1st "official" delta, all the others have been cheap copies [8D]

evan-RCU

On my DD I put some carbon fiber sheet across the whole mount plate after I fininshed building it. Some sheet I got from a balsa distributor, had a western name not Balsa USA, sorry i don't remember the name. Anyway that and self locking nuts under the plate with big washers worked well for me.

combatpigg

My Feedback: (3)

Thanks Evan... ya, one of those balsa suppliers sells other materials like that, like Sig or Lonestar.
If I get careless with my money I'll go through AeroSpace Composite or AirCraft Spruce.

MJD

My Feedback: (1)

Good info!

One area where the Demon is different I notice, is the extra material in the ply ribs around the engine mount area due to the airfoil shape. Also, although the instructions don't mention this yet, I really like filling in the lower engine mount area with scrap balsa and dremelling it out to clear the crankcase, then glassing over the bottom - I think this helps absorb nasties and distribute loads smoothly.

I have only run lowly Jett and West .50's in mine so far, but I don't see fretting or other problems yet with the mount, knock on balsa.

And yeah on the epoxy clear coat everywhere in there. I sometimes hit the area with a heat gun a bit to lower viscosity and encourage seeping and wicking - without cooking the resin that is. Don't use CA, it's not nitromethane proof.

Mike D

evan-RCU

Lonestar!!! That's where I got it... yeah western name.... or sci-fi

freakingfast

My Feedback: (3)

Good point Evan, Always use a self locking nut (nylock). By the way, if they get a bit loose from use, you can tap on the crimp side with with a hammer and keep using them many times.

combatpigg

My Feedback: (3)

Here's some progress. I made a couple of nut plates on my poor old drill press as it chattered away. The blocks to fill around the nut plates I made from fir. Reasoning is, there won't be much wood left after shaping and I was out of large balsa block. I used the poor man's mill to cut the filler blocks, too.
To mount the servos further outboard I doubled the balsa ribs with plywood and made a couple of plywood platforms for the servos.
I called BVM today to buy a servo operated needle valve and they don't make them any more.
It might be possible to modify a Nelson remote needle?

MJD

My Feedback: (1)

http://www.perrypumps.com/prod03.htm

?

vicman

My Feedback: (10)

No chance of that one leaving the airframe behind.[X(]

combatpigg

My Feedback: (3)

MJD, that valve is perfect and very reasonably priced. Hopefully the airplane operator will be able to use it correctly.

Vic, gotta remember to safety wire the mount bolts, too.

MJD

My Feedback: (1)

It will still be a b- to find when the entire wing vaporizes behind the engine. At least the engine will be wired to the mount though.



MJD

evan-RCU

Nice motor, do you have a nitro head on that thing? Is it the F3D one with a huge venturie? If so what prop ar eyou going to run and where are you getting them? I broke the special one I had this weekend and I need a source, it was a custom one around 6.7X8.6 good for around 28.5k on the ground....

evan-RCU

Who will be the operator?

Mike Connor

My Feedback: (5)

And no throttle!! You and CP have more guts then me.

RANIERY

My Feedback: (3)

combatpig, you can use a nelson remote needle. my FAI nelson has it.

combatpigg

My Feedback: (3)

Even, IIRC the prop I tried so far is APC 7.4 x 8.2. 29,000 on the ground. When Henry came out here to fly some combat a couple years ago I asked him to set a FAI engine up for 15% nitro.....so this engine might have a nitro head, or it might not..I never asked.

Mike C, a good working fuel shutoff might actually be as safe as having a carb...depending on the operator's ability to hit the switch in time. The throttle lever on the TX will be pre-occupied with working the mixture control valve. I'd like to figure out how to combine the 2 functions on 1 lever or switch.

Rainery, I was thinking about soldering an arm onto the NVA that a servo could operate. The Perry FCV looks like a good thing to try.