Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

6 year old Demon resurfaced

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Old 11-10-2015, 08:17 PM
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MJD
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Default 6 year old Demon resurfaced

Seems to have aged well. Only took three paper towels and some IPA to clean it off, by the way CP.

Back when I built the SD .65 I built a second stock airframe, and set the motor mount up for the West .50 that I had used in the prototype. I covered both in Ceconite dacron fabric, heavier than Coverite, this was full size ultralight grade, 1.7oz IIRC. The fins are 1/8” balsa, one layer each .5oz carbon mat, 3.2 oz glass, really light finishing cloth of some weight. These materials extend around the tip fin base to the tip and up to the tip rib.

You have no idea how tough this airframe is with the heavy dacron covering, yet it’s going to finish up around 52-53 oz. The torsional strength is immense, no freaking way this will flex or flutter or come to any grief in the air. The West will challenge the SJ50 for top speed, they are real close
.
The elevon servos are HS5665 digitals, and an HS85 for the throttle – they are all just Gooped to the floor, though the elevon servos are elevated at the forward end to bring the arms up out of the sheeting better. They are Gooped to a piece of Ό” x 1-1/2 TE stock which is Gooped to the floor.

I am fiddling with adding inflight mixture control, it rocks if you use it but don’t abuse it.

Pushrods are 4-40 rod, horns are Sullivan steel 1-1/8”, the clevis connects ½” out on the servo, middle hole. No slop. The elevon hinges are continuous prefab hinge – prebevelled balsa/hinge/balsa laminate – from Foremost mebbe? I bought it in the ‘80’s I think. Nice stuff, darn tough.

I fit it with a glass cowl, which seems almost pointless with the side exhaust, but I had one so why not? Now to add cooling inlet/outlet, clean up the plug and needle holes. Add trim. Done. 1400 LiFe opposite the pipe beside the tank - pipe plus the heavy covering pulls the CG back.

https://www.youtube.com/watch?v=QWhahZdRxfw

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Old 11-11-2015, 10:48 AM
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It would look good with Grande Prix paint scheme.
I should give IMC a try with the one I'm working on. Not because it needs it, but to go through the motions of setting it up and using it.
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Old 11-12-2015, 09:59 AM
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I realized I don't really have any idea how much inlet area is needed. I have a rectangle 3/8 x 7/8 drawn on the front, maybe I better open up my Andy Lennon book..
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Old 11-12-2015, 04:51 PM
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I always ask myself what the difference will be between what looks right to me and what the current thinking is about what works best.
Bear in mind that the current thinking is constantly evolving anyway.
The most surprising part about running FG cowls on high revving, high speed models is how quickly the attachment points can wear out.

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Old 11-13-2015, 07:43 PM
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Look at the sexy work here.



http://www.f2aspeed.org/gallery/models
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Old 11-13-2015, 09:58 PM
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Dont forget this one a near cover up

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Old 11-14-2015, 05:59 AM
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I think the air inlet is bigger than the cooling inlet. That square inlet is kinda the deal I'm going for. On this it is more a practice/bling exercise, wot with the bloody great side exhaust header and pipe not tucked behind the engine where they should be. But why not? What I really need is a scale plastic Holley air scoop for the top of the cowl.
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Old 11-15-2015, 02:08 PM
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Originally Posted by MJD View Post
What I really need is a scale plastic Holley air scoop for the top of the cowl.
Hahahahahaha! Wow, that was the best laugh of the day!

Dave
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Old 11-15-2015, 02:29 PM
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Those cowls are really a great example of what you can do with wood...[and some artistic ability].
SIG used to sell a heavy paper called Rhino hyde and I'm wondering now if it was used to form cowls.
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Old 11-17-2015, 02:30 PM
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Regarding the intake If your going fast Andy's book isn't going to address it fully. HP has posted many example of intakes and they are a lot smaller than Andy Lennons setups. Look at the German stuff the intakes are tiny slits. As far as the size of the inlet vs outlet the outlet needs to be (at least) 140% the size of the inlet to work. Nice work on the CL cowling!
CP I saw both rinohide and canvas used over the years, along with thin plywood or vernier wood.
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Old 11-17-2015, 08:00 PM
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Ironically I learned the 140% rule from my own website. It was part of the tech stuff, and I had never seen it until I posted a question about air outlet area, and Mike Connor posted back "you should read your own website!".

Derp..

I think I'll do the 3/8 x 5/8 and put some baffling beside the lower cylinder. The stupid head makes it rather difficult to fit the baffles to the cowl sides. I'll try to shape it nice and blend it in all purty and aerodynamic.
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Old 11-21-2015, 11:44 AM
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As long as you keep the airflow as tight as you can to the engine it should work fine.
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Old 11-27-2015, 08:19 PM
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3lb 0.7oz as it sits here. Rx is installed, so is a 1400mAh LiFe 6.6V pack in the bay opposite the pipe for an attempt at lateral balance. Cowl in progress on right. Filler is epoxy, lots of balsa powder, some cabosil. Tough, light, sands really well with wet 120/220/400.

Final weight will be this plus what's missing.. 1/16" ply hatches, Al pipe bracket, trim. Maybe 3-1/4lb dry weight then.

The side exhaust pretty much cancels out all the streamlining efforts, but this was also a practice effort.
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Old 11-27-2015, 09:51 PM
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What APC prop is that one Mike?
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Old 11-28-2015, 07:47 AM
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That's a sport 8x9 on there at the moment. I was running this setup on 8.8x9.25 and 8.8x9 props trimmed to about 8" previously, but will check out the sport props again.

Next grafting job is the cooling exit back of the teardrop section.
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Old 11-28-2015, 08:14 AM
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Even with the side exhaust it should be better than the cylinder sticking out.
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Old 11-28-2015, 08:24 AM
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I played around with epoxy and sawdust years ago and it surprised me how little epoxy it takes to make a nice putty consistency.

These guys would like for you to build them a cowl when you get done with this one.
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Old 11-28-2015, 11:40 AM
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I actually have an ancient container of SIG "powdered balsa" in the shop still half full. I noticed that the dust in the collector bag of my orbital sander is perfect, so I know how to make more. I added cabosil to stop sag.
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Old 11-28-2015, 05:31 PM
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Hey look, he really is building a Holley scoop for that thing.

And believe it or not, I've also got an ancient box of SIG powdered balsa. I came across it while working a late friend's estate and I had to have it. I'd never heard of it before.

And you betcha, that cowl is going to do plenty for you even with the side exhaust. Every little bit counts. Shoot, style points alone will let you add 10 mph onto your readings!

Dave
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Old 11-28-2015, 11:14 PM
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The West .50 V1 with the open pipe sounds great too, it should have a bit of attitude as a whole. Dave glad you're tuned in, I wanted you to see the cowl mods. I cut the air intake from 1/8" basswood, okay yeah I laser cut it with locking tabs. 3/8" x 5/8" ID. Before gluing, I profiled each piece with sandpaper, bonded the box together, then fit it to the cowl. I tacked it in place with CA, then puttied in the epoxy filler.

The air exit is next, choices are so far:

- piece of .950" ID rocket tube grafed into the rear of the cowl like a minipipe
- trimming off the rear of the cylinder teardrop until the slot has sufficient exit area
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Old 11-28-2015, 11:44 PM
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A slot would do a better job I'll bet.
I got something like 160-170 out of my Webra .50 / Demon so the ball is in your court...!
[no pressure though, not from me...]

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Old 11-29-2015, 07:58 AM
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I have no clockings of my Jett or West 50 powered Demons.. only experienced - and surprised - witnesses. One F3D flier said in a thick accent "that must be sree hundred kilometers per hour" and a jet flier said "that's got to be 170".

The slot will be a heck of a lot less work too..
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Old 11-30-2015, 07:03 PM
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Just remember to make a shape like you added the profile in your intake on the sides and top of your exit slot in the cowls interior so it has the venturi effect scavenging the exit airflow for you.
I am curious when you added the cabosil what type of proportion was it, how is it to work with? I found microballoons are a great to thicken filler but it is still subject to sag even using balsa dust and talc. I had heard of cabosil but have no idea of how to use it properly (I like to be able to do some sculpting like you did on that cowl) and am looking for any advice you care to offer.
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Old 12-01-2015, 04:23 PM
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A shot of aluminum paint to show up all the rough spots for more sanding and touchup, coming along. I went for the rear exit slot and added some crude ducting. Still have to make the header opening look less grotesque and make the needle valve hole prettier as well. Think the cowl might have to be bright aluminum with clear coat.


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Old 12-01-2015, 04:28 PM
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Oh yeah IE - I typed a long reply about using cabosil, then the browser crashed and pissed me off. I'll retype it in word and paste it here to avoid that. In fact it crashed on this reply a minute ago and this is the 2nd try to say why I haven't answered yet..
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