Snice-Mitar Pusher Jet - possible Need for Speed ?

[solentlife]

As known - I've been searching for a replacement for the HK Parkjet - the main stay of the Need for Speed campaign. An immense amount of data has been accumulated for such a machine .. launch techniques refined, power levels pushed to incredible levels ... such a pity for it all to die for want of a PKJ.

The Snice-Mitar is slightly larger at 28" span but has similar overall form. It has a fuselage shell that should help accommodate our LiPo's etc.

Initially I was concerned about overall strength of a 6mm Depron machine and also not a follower of the KF aerofoil regime. Modifications to the overall design while building are normal for me - so that's the route I'm taking.

I'm posting the build thread here and not on Scratchbuild listing due to the Need for Speed and Parkjet demise.

First the plan was printed up ... taped together .... and as found with most - the tiling does distort certain aspects no matter how careful. Sorted by cutting plan to each piece and correcting each.



Wing form cut from Depron ...



Then onto my cheap floor foam for additions ..





Wing calls for a beam to be fixed underneath to stiffen ... so I use 6mm dowel and then my modification to have 5.5mm floor foam beam alongside ..



mmmmmmm not so happy with this... wing is still flexible ... needs overall stiffening.
First glue in fuselage sides and some doubler pieces ..



Decided only way to stiffen up wind without using CF and other - is to double up the foam wing itself ... using the floor foam - this is light and easily done ...









Glues used so far ... Hot glue for fuselage sides to wing and then fillet run along joint. White PVA for large surface areas as in the wing doubling sheets.

It's now waiting for the PVA to set and I can move onto other areas.

To continue ...

Nigel

[solentlife]

Sorry about the long wait for next instalment ... work got in the way ....

At present in Texas - Houston awaiting flights to Bahrain and then after complete assignment - home hopefully to complete this baby.

Few details ... Motor intended is a 3800kv 250 heli motor and 4.75 x 4.75 prop ... with 3S and 4S LiPo's .... ESC probably a 50A job ... 9gr servos ...

Nigel

[crxmanpat]

Nigel,

I must have missed your initial post. At 28" wingspan, this baby is just screaming for a 2212-6 2200kv motor, 30A ESC and APC 6X4E prop. I would have definitly used a CF spar and foregone the doubling up of the foam.

EDIT - Found the plan:

http://www.rcgroups.com/forums/showthread.php?t=1499635

I may just have to do one myself and use the setup I posted above.

[dahawk]

Pat,

I have a Grayson Super Mega V2 looking for a new home. Looks interesting. Meanwhile, I'm going to order the Red Arrows T-45 airframe to replace the one I just retired. Loved that plane.


Nigel,

Know of a good site I can download RAF decal images to go with the T-45 ?

Cheers,

Hawk

[crxmanpat]

Hawk,

Check this thread for decals, it might have what you need:

http://www.rcgroups.com/forums/showthread.php?t=359029

[solentlife]

Originally Posted by crxmanpat

Nigel,

I must have missed your initial post. At 28" wingspan, this baby is just screaming for a 2212-6 2200kv motor, 30A ESC and APC 6X4E prop. I would have definitly used a CF spar and foregone the doubling up of the foam.

EDIT - Found the plan:

http://www.rcgroups.com/forums/showthread.php?t=1499635

I may just have to do one myself and use the setup I posted above.

The doubling up of the Depron with my harder floor grade foam made a huge difference. Even with the spar fitted - I didn't like the flex on the wing ... and I'm hoping to push this baby to limits unheard of ...

The wing is now stiff and I reckon will take the speed buffeting it will experience in my hands ! She will have over 3000kv motor, 4.75x4.75 and possibly 4S stuffed into her ... reason for the extra underbelly fuselage strakes to create a cooling duct for ESC / Battery etc. without hanging out in the breeze to get damaged.

As you can appreciate - the plan is a foundation for me to work on my additions / mods to get her up in the high-speed market.

I also have to say that CF is not easy for me to source - so pine spars etc. are order of day for me.

Cheers
Nigel

[JetPlaneFlyer]

Nigel,

If you want something really fast did you ever consider a 'proper' pylon racer type design? Something like the Slipso400 might be a cheap route to a genuinely fast model (160mph+): http://www.rcgroups.com/forums/showthread.php?t=418625

Adding more and more power to what is basically a quite un-aerodynamic airframe has it's limits. A nice 'clean' design like the Slipso will go much faster watt for watt so don't end up being overweight with huge motors and batteries which lets you preserve decent flying characteristics and low speed handling.

[solentlife]

Originally Posted by JetPlaneFlyer

Nigel,

If you want something really fast did you ever consider a 'proper' pylon racer type design? Something like the Slipso400 might be a cheap route to a genuinely fast model (160mph+): http://www.rcgroups.com/forums/showthread.php?t=418625

Adding more and more power to what is basically a quite un-aerodynamic airframe has it's limits. A nice 'clean' design like the Slipso will go much faster watt for watt so don't end up being overweight with huge motors and batteries which lets you preserve decent flying characteristics and low speed handling.

Will look at the later once I'm quiet at work ...

The intention is to find a replacement for the HK Parkjet that has been discontinued .... the Need for Speed groups main machine. Design criteria : Pusher prop with power train set-up etc. in line with the PKJ. Given that the PKJ was about $14 a kit - it's hard to find a suitable candidate of similar pricing .... therefore my trial of this scratchbuild. To be honest - we could probably use the Rarebear if it wasn't a Tractor prop !!

I know from many years ago when a F15 flat plate plan was reviewed in UK mag ... the flat-plate machine was good but not fast. I knew a guy who took that plan and added a second level to the wing form, created a thin aerofoil shape and the change in speed was dramatic. Maybe it was luck - but my thoughts are whether that may occur here. Plus stiffening the structure as I have with little weight increase.

Cheers
Nigel

[JetPlaneFlyer]

Ahh.. the Slipso is a tractor prop so possibly doesn't fit your requirements. But maybe a departure from the Parkjet formula is called for in order to further fullfill the speed lust? The park-jet design really isn't inherently that fast anyway, at least not compared to a proper pylon race design of similar power... Though more than fast enough to be terrifying I'm sure!

[solentlife]

The Need for Speed group have invested a lot of time and effort in achieving speeds / power levels that make the mind boggle on such a frame. Many are averaging over 200kph ... my own best being 222kph. The standard PKJ is about 120 - 130kph and that is quite a handful on such a small model.

It's not so much achieving just high speed - it's the solution to making a type of airframe do it ... in this case the PKJ Pusher. Would be a shame to change model and specs too much now and lose all that data collected. My aim is to find a frame that can replace the PKJ and use directly the data collected ... whether we get 200kph or not is not really the factor ... it's again doing the seemingly impossible.

The pusher detailed at start of this thread is similar in a lot of ways to the PKJ except for the flat plate fuselage and wing ... something that I think will evolve as I and maybe others catch on to.

It's an addictive avenue ... and hopefully one that can carry on ... but it really needs a One-Design concept as we had with the Parkjet.

Cheers
Nigel

[solentlife]

Thought it time to show a few pics of my mods to the Snice-Mitar ....(excuse the tape - GG drying .... )...

General top view ...





HK Funfighter 1950kv motor + 5x5 prop



Servos half set into wing top - direct link.



General underside view



Doubled up under fin skids ....



Cooling duct and also hand-hold for those hand-launch days ... all servos etc. are top mounted to allow bungee launch and snag free on landing.



Battery bay is set for a 4S 1600 ....



Starting on paint scheme .... nice and vivid to see ...



Nigel

[solentlife]

Finished ....





Went to field and fired up ... ESC failed before I even got to launch ...

Wind has been terrible since - so replacement made ... now wait better weather.

Nigel

[solentlife]

Launch failed ... even with CioG on plan position - this thing stood on its tail and that was it ! I shut throttle ... let her flop down ... ESC disconnected from motor ... and that was it ...

I have now moved battery more fwd and RX back ... altered CoG 20mm in front of plan position and wait weather to try again !