Pushy Cat fast electric pusher plane build

[simonh]

This will be a proper build....

It will be built from a plan by Ron Laiden. It's a fast sports plane designed for a 400 size motor. Mine will use a Mega 16/15/3 (3000kV) and something like a 4.7 x4.7 prop. I'm going for speed rather than the vertical accerleration capability of my stryker. It should be good for 120MPH +. I struggled to find a pic of a completed one on line - this is the best I could come up with......



I have neither experience or the necessary skills to build a plane from plans (well not one that would actually fly!) so letting me loose on my own with some drawings and a pile of balsa would not be a good idea 

So  - two of these will be built side by side - one by me and one by Gareth - with me learning as I go.  Mine will be as per plan with a prop with 3S 2200 pack and 40A ESC.  Gareth's will be modified from the plan to take a ducted fan - with a bigger battery, a totally insane 4400KV motor and a 60-70A ESC to power the fan. That's nearly 50000 rpm - will it be the first electric model to be noise checked??  The idea is to maiden these together at the patch in a few week's time.

I'll write this from the point of view of a total beginner and Gareth will add stuff as we go - especially on the mods to his version to make it more interesting for the more experienced model builders.

Copies of the plans were made and a copy stuck to the wall for reference.



Another copy on the table to act as a guide for cutting. With a kit, I'm used to starting at step one and finishing at the final step. I can follow a recipe so this is not a problem. With plans there is no obvious starting point.  We started by cutting out the wing and tailplane sections first and glueing the wing panels together.
 
The balsa was cut using medical scalpels - and something that looked a bit like a bone cutting saw (ouch!) - cant remember what it's called. The scalpels had a variety of blade shapes. The saw was used when cutting across the grain. The scalpel blade was curved for all the cutting I did. Basically, I was given the appropriate cutting tool and did what I was told  For some of the sections, we measured from the plan and translated the measurements to the balsa. For the more complex shapes, the section was cut out of the plan and used as a template.

Wing panels cut to size and stuck together lengthwise using 5 minute epoxy. With 2 of us, we could mix, apply the epoxy and assemble the joint quite quickly. If doing this solo, I'm guessing a slower epoxy might be needed. The two sections placed together (with a strategically placed finger  ) just to give an idea of the completed wing size.



Wings after some more cutting......


Tail fins cut and laid out. For these, we cut the relevant section out of the plan to use as a template. I seem to remember doing all the cutting for these (there are 2 more for the other plane not shown) Apparently it was to give me plenty of practice 



And finally the tailplane and elevators cut out.

[Mike S]

This is looking good. I've seen the motor Gareth's going to be using and yes its not a plane its a rocket, does slough have a speed limit .

This should be built very quickly and I am looking forward to see this fly (sorry Gareth couldn't help it ).

[lionawa]

Hi Simon
              Best of luck with your Pushy Cat! I dont mind hand launching it  as long as it has no paws!!
              Cheers!
                         Lionel

[Gareth]

ok, just to add to simons post.

The build has gone well so far, we have 2 wing shapes and the parts rough cut for the tail. The elevator is all cut out so that will not take long to get sorted.

The next jobs are to make the wing tips, sand the profile on to the wing and then ensure they both fit to the plan. Once we have the wing shape we can then final shape the booms, I might end up modifying mine slighly to remove the elevator from the current thrust line.

On the motor setup i have i have a couple of options:
Simon:
Mega 1615/3, 3000KV, 3s (10v Nominal) 30,000RPM.
4.7x4.7 prop at 30,000rpm. this should give about 120mph on the flat.

Gareth EDF:
HET EDF-2w, 4750KV, 3s (10v Nominal) 47,500RPM
WemoTech 480 Details.

Gaerth Prop:
HET EDF-2w, 4750KV, 3s (10v Nominal) 47,500RPM
4.7x4.7 prop at 47,500rpm should give about 180mph on the flat (if the amps hold up).


Based upon website suggestions these are the figures that get returned by a motor calc for each of the prop setups. Link. The EDF should produce about 450w of power on 3s, and about 700w on 4s  .

[Gareth]

I have a couple of questions to go out to the general population about thrust and servos.

Thrust:
Looking on other build threads for this model if you put the motor on the top of the wing you will induce a load of air on the underside of the elevator meaning it will create lift and cause problems at different power settings.
I was thinking of mounting the lugs just above the wing so the fan will sit below the tail and partly below the wing, can anyone see any probelms with this? (I plan to build up the model so the fan cant get caught on the ground)

servo:
At the moment the servo is going to be just in front of the motor, this isn't a problem for a pusher but might interfere with the airflow on the EDF, I was thinking about moving it to the front of the wing and running snakes through the wing, as its only 6mm thick i was worried it might weeken the structure but if it will filled with epoxy it would be just as strong?

Any thoughts, suggestions or answers would be great.
Gareth

[simonh]

Heres a link showing a couple of these being flown. Looks like they are going to be a lot of fun.

Pushy Cat

[Mike S]

I have to say that looks very nice in the air. I'm very intrested in seeing these flying at the patch as I could be tempted at building one in the future

[andyb]

...thinking about moving it to the front of the wing and running snakes through the wing, as its only 6mm thick i was worried it might weeken the structure but if it will filled with epoxy it would be just as strong?...

I think the groove for the wire and the epoxy will cause a weakness because it's a structural discontinuity, however, it's all a matter of degree. I suspect that if you use thin snakes (i.e. 0.7 mm wire running in Kavan snake inners) and cover the wing in something like glass/epoxy or glass/acrylic resin, it'll be fine.

...I was thinking of mounting the lugs just above the wing so the fan will sit below the tail and partly below the wing, can anyone see any probelms with this?...

Depends  . If the fan sits partly below the wing then its efficiency will be reduced because you're effectively choking and adding turbulence to the intake. Also, you'd need something like a 1/4" x 1/8" spruce spar to carry bending loads from one wing half to the other and would have to make sure that twisting loads at the root were adequately catered for.

Personally, I'd go for mounting the fan on top of the wing, so that the wing's structural integrity is preserved, angle the fan downwards a couple of degrees to give a bit of downthrust and move the stabiliser to the top of the fins to keep it out of the way of the fan efflux, as on a Boomerang or Tazor EDF. If you have to, you could always make the fins a bit taller.

A.

[Gareth]

Ok,

I ran a test last night on the built fan unit, hooked up to the watt meter it was pumping out 530w to start with settling to about 480w. 480w should be enough to get the model flying, now i just need to workout the best way to mount the unit.

Thanks Andy for all the advice, i think leaving the servo as it is will work best and this will allow me to make it in to a ducting for the motor. I will have to bring the plans over you to to talk about the options of fan locations.

Gareth

[simonh]

Just a quick update from my beginner's perspective....

We did some more work on the wings last night. I managed to round off the wing tips pretty nicely with a Permagrit sanding block. These arent cheap but are a great tool. I'm not a natural 'craft' type person but even I managed to get a nice rounded edge with it. I'll post up some more pics and update after the next session.

[andyb]

I concur about the Permagrit, mine have lasted for years...

A.

[Gareth]

I concur about the Permagrit, mine have lasted for years...

I also agree, I have just given mine new life by running it under warm water (to remove any loose particals) and attacking it with a wire brush. Its now as good as new, im going to have to take it easy first couple of times i use it as its going to work a lot better then it used to.

[Mike S]

My first experience of using a perma grit block was when building the Whizzza. Having never used one before I had to learn fast. Great tool to have for model working.

[simonh]

Here's where we are at with the 'cats after a few more sessions. The wings are done (aerofoils sanded into shape etc). The ailerons need to be cut out. The fuselages are coming along. Almost everything has been cut out for these and the formers are all glued in place.

The first pic shows how the planes are starting to diverge in their design. Mine is sticking excactly to the plan and is the larger of the two fuselage's with the squared off tail. This contains a motor mount for the Mega Motor. Gareth's has a more tapered tail to allow air to be more efficiently funnelled into the fan unit.


My battery tray is in the middle of the fuselage. Gareth's will be further forward to compensate for the insane fan unit and the fuz has been modified and strengthened to allow for this.

The second pic shows where we have started to glue balsa blocks to the top of the fuselage's. These will be cut and sanded to form the shape of the top of the fuselages.


From my perspective, just getting these planes to an 'ARTF' stage - which is what you would find in an ARTF kit, is very time consuming. All the pieces have to be cut exactly to size and sanded etc to form the correct shape. Even if I did have experience with this type of build, having someone to work with while doing the build is definitely a help - to keep up interest and motiviation for the project. Two pairs of hands and eyes are definitely a help to make sure everything is aligned properly and fits etc.

The next stage will be to shape the fuselages and to get the servos and linkages etc fitted. I beleive the motor for mine can then be test fitted as well.

At our current rate of progress, I'd estimate we will be ready to maiden these in a couple of months.

[Ali]

wow i missed this build   been meaning to scratch build one @ around 150% after buying gareths old one!  Bought the plans, matts and everything else, just never found the time!  oh well.

Hopefully by the time you guys are ready, i'll have found some time to join you all at the patch with gareths old one.