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It's almost a prop plane, at least it ought to be fast.

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

It's almost a prop plane, at least it ought to be fast.

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Old 03-24-2009, 12:48 PM
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MJD
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Default It's almost a prop plane, at least it ought to be fast.

Okay, further on my declaration that I would focus on two worthy and hopefully fast flying projects for this year (nothing like starting early) I have been researching and sketching and designing and homing in on the design for a pulsejet powered Fi103R. No, it's not really a prop plane, although the Veeder-counter driver on the nose of the unmanned exploding versions is certainly a propellor (see photo!). But it will be noisy, and if it flies, it will be fast. What else do you gearheads need anyways?

Most of the work has been how to massage the design to work as a RC model. The biggest fundamental problem is nothing to do with aerodynamics - the airplane is little more than a bloody great Stick with a streamlined body for a fuselage instead of a box! The stab area is generous too as is - percentage wise.

The rub is this - the real aircraft had a stall speed of what must have been close to 200 mph. I need to work out the wing loading and projected stall speed sometime, there's enough info around - it should be good for a giggle. But remember this tiny thing weighed just over two tons, was launched at over 200mph from a steam catapult, and its only requirement for landing was to hit roughly nose first with the controls jammed hard over! Stall speed? Don't care about no stinkin' stall speed so long as we toss it fast enough!

Therefore, faced with the problem of desiging one that can actually land slower than cruise speed and be launched without a steam catapult or rocket sledge (meaning, I don't have to use them that is..), one has to choose between a fuselage the size of a dirigible with tiny wings, or scaling the wings up somewhat. I chose the latter, fattening the wing chord and increasing the span a bit. The next issue is balancing the engine - the engine I have weighs 850 grams and the CG is at the dot on the drawing. With the wing moved rearward as shown, I'll need maybe 650-700 grams of weight at the nose to match that (I'm not considering the final reality here, just the moment arms at this point) and with the layout as is, I think the airplane should come out close to balanced sans engine as is, so most of that ballast factor could be accounted for with useful payload such as big Rx batteries and all that. The 3 pounds of fuel will be centered on the CG of course.

Check out the wing mounting detail in the sketch - looks like one of the common contemporary model wing mounting schemes to me.

As to details and looks - just yesterday I read that there are 5 surviving Fi103R's in the world - or were at the time of writing - and one of them is 4-1/2 hours away at the Ottawa War Museum... pant pant drool drip. Time to call and speak to the V-1 polisher and protector for some quality time with a camera, measuring tools, and a notebook! Road trip.. road trip.. and my brother lives 20 minutes away.

Just to let y'all know there is a semblance of reality to this project. Apart from all this, I am working on a test stand setup for the engine - I haven't even run it yet! What a freakin' loser, eh?

Maybe I'll screw an .010 to the nose to qualify.. I don't wanna hang out on the jet forum..[&o]

MJD

Edit: in summary, I slimmed the fuselage down, it's only 7" OD now (), scaled the wings up to 14" chord and 24" half panel span, adjusted the stab area a bit, have not worked on the vertical stab area issue yet (you noticed how little there is too, huh? Check out the Dutch rolling in some of the archive videos of air drop launching. Or gyro hunting, whichever.. looks wiggly is all I know!).

As it is now, over all length is about 6 feet plus tailpipe extension (or lack of it.. yes PJ fans, I know about the turbulence back there and am suitably worried too!), wing span a hair under 5 feet, aiming for dry weight between 10-12 pounds ann that will take some care to achieve! 12 is more realistic. At that figure stall speed will be around 45mph wet, 40 or so dry. Good enough.. bungee launcher is part of the plan anyways. Unless one of you wants to hand launch it?

p.s. Oh yeah - that thing I drew on the side view, to the right of the the note about wheels, isn't what it looks like it might be if you were thinking along those lines. It's supposed to be a front view of the buried wheels..
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Old 03-24-2009, 01:10 PM
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Default RE: It's almost a prop plane, at least it ought to be fast.

If there are guys already doing this in Europe, I'd seek out information there. I think the biggest obstacle is how to integrate that red hot firecracker into the airframe without having a lot of bulk hanging out and without cooking the airframe.
I would build a fiberglass covered foamie in the Class A size range with elevons and tip fins. Maybe sweep the wings to give dihedral effect. There are a couple of guys selling ARF wings [Treneff and Seaholm} in the combat forum that would make good starting points for a project like this. Foamies are easy to alter [at the field even] if you are seeking the smallest package that will get the job done....then once you are satisfied build a "keeper".
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Old 03-24-2009, 01:18 PM
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Default RE: It's almost a prop plane, at least it ought to be fast.


ORIGINAL: combatpigg

If there are guys already doing this in Europe, I'd seek out information there. I think the biggest obstacle is how to integrate that red hot firecracker into the airframe without having a lot of bulk hanging out and without cooking the airframe.
I would build a fiberglass covered foamie in the Class A size range with elevons and tip fins. Maybe sweep the wings to give dihedral effect. There are a couple of guys selling ARF wings [Treneff and Seaholm} in the combat forum that would make good starting points for a project like this. Foamies are easy to alter [at the field even] if you are seeking the smallest package that will get the job done....then once you are satisfied build a "keeper".
There are a couple of sport scale EDF models around, they all look more massaged in proportions than this. But the only large gonzo model with a PJ I know of was built 20+ years ago by Jorg Vogelsang or his machine shop crew at least. No model data of similar issues to refer to.

But really, other than the noise and plumbing problems, the layout here is textbook Hershey bar wing sport plane, 19.5% stab at a sensible moment arm, and a fuselage to hold it together = I have little fear of the flying characteristics. Aw, I dunno, I may toss together a subscale something or other. I do have a Wattage fan lying around that would push around a 30-36" foamie fast enough to hold it in the air I think. As to foam wings, I have a Feathercut gizmo and can whack out wing cores in no time.

Come to think of it, I could make the fuse for a foamie from lightweight rocket parts.. it's a tube with a nose cone and tailcone.. dead nuts easy to do. I have 3" and 4" stuff.. hmmm. Make an easy-squeezy fuse plug at least.

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Old 03-24-2009, 02:09 PM
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Default RE: It's almost a prop plane, at least it ought to be fast.

The new avatar is quite apropriate for this project!
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Old 03-24-2009, 02:22 PM
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Default RE: It's almost a prop plane, at least it ought to be fast.


ORIGINAL: RocketRob

The new avatar is quite apropriate for this project!
Why thank you! I quite agree to be honest..

I made it last night with the "help" of my 16 yr old son..
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Old 03-24-2009, 04:02 PM
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Default RE: It's almost a prop plane, at least it ought to be fast.

I've got an old Q-500 with a V-tail that would take about 4 hours to convert. I would remove the engine and build a nose cone to house all the gear forward of the firewall.
The owner of our LHS stuck one on a Ringmaster when he was a kid and flew it at a local school yard on 60 foot lines.
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Old 03-24-2009, 04:36 PM
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Default RE: It's almost a prop plane, at least it ought to be fast.


ORIGINAL: combatpigg

I've got an old Q-500 with a V-tail that would take about 4 hours to convert. I would remove the engine and build a nose cone to house all the gear forward of the firewall.
The owner of our LHS stuck one on a Ringmaster when he was a kid and flew it at a local school yard on 60 foot lines.
An 8 oz bladder tank will fly a Dynajet around reliably for mebbe 3 minutes on naptha, you'll have about 4-1/4 lb thrust. 2-1/3rd oz/minute IIRC? Might need a bit of a subfin to bump up the area with the extended nose and all that gobbledygook hanging out up top.

Some aluminum lithoplate on the inside of the fins and on the fuse top might be a good idea. And have the tailpipe exit as far clear of the airframe as possible, keeping CG in mind of course. It's nasty air near the exit plane, beats holy bejeebers out of tail surfaces that get too close.

One of the mags had a blurb about a couple of guys who figured they'd build a moon rocket by mounting a Dynajet underside a Playboy old timer. Check out the climb now, suckers! Problem is, a Playboy can easily generate 4-1/4 pounds of drag and do so at surprisingly low speeds and suck up all that power in a blink.. so they ended up with a nice flying Playboy that went about as fast as a glow version and made an earth-shattering racket and sucked over two ounces of fuel a minute in the process! Still fun though. Let one rip in something clean though, different story!

CP, got a Dynajet kicking around? Go for it! My small pj is Dynajet sized, but the head is extremely heavy so the total engine weight is about a pound. More of a show piece than a go piece. The big one weighs less than twice that and is rated at 18lb thrust.

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Old 03-24-2009, 06:50 PM
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Default RE: It's almost a prop plane, at least it ought to be fast.

Your observations are why I think a flying wing would be the best all around airframe. Most GO for the least amount of work. I would sneek in some dihedral to offset the jet's location. Could easily be built in a week out of balsa and spruce sticks and some balsa sheet. Cover it with 3/4 oz glass and epoxy paint. I don't have a jet, probably never will unless one falls in my lap.
Once I get done with my yard work, then I'll be able to fathom building a speed plane someday. []
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Old 03-24-2009, 08:28 PM
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Default RE: It's almost a prop plane, at least it ought to be fast.


ORIGINAL: combatpigg

Your observations are why I think a flying wing would be the best all around airframe. Most GO for the least amount of work. I would sneek in some dihedral to offset the jet's location. Could easily be built in a week out of balsa and spruce sticks and some balsa sheet. Cover it with 3/4 oz glass and epoxy paint. I don't have a jet, probably never will unless one falls in my lap.
Once I get done with my yard work, then I'll be able to fathom building a speed plane someday. []
That's why I live on 1/4 acre next to the community hall - the town keeps the strip mown and tidy for me.

The Europeans in general seem to have settled on deltas for pulsejet hijinks. Lots of area, lots of room for fuel at the CG, stall resistant and tolerate desperate 180 turns back to the field without snapping into the swamp.

I have an older AAM (I think..) with an R/C Dynajet powered F-4 model. Quite lot of real estate to haul around but apparently it still got up in the 160 range or so - and it didn't exactly have a super thin airfoil. I don't think undercambered polyhedral wings on pylons are quite suitable for pulsejets though.

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