Do you like my dollie?

[Bruce Richards]

I have been thinking about something like this for my Hawker Hunter. However, I have just realised it will not work with a pusher prop. 

What thought process did you go through on Mk1 and MK 2. Please keep us posted on how well it works.

[Former Member]

[This posting has been removed]

[Tim Mackey]

And incidentally, isn't that nosewheel spring reversed?

[David Ashby - Moderator]

Guess it goes front two wheels first?

[Bruce Richards]

 I think that is the tail wheel it travels with the single wheel at the rear. I think.

[Bruce Richards]

Too slow!!

[Tim Mackey]

David Ashby - RCM&E wrote (see)

Guess it goes front two wheels first?

Ah....gotcha.

[Doug Ireland]

Excuse me for being a bit slow... what is it?

[Tim Mackey]

A dolly - for allowing a model without undercarriage to R.O.G.

[Doug Ireland]

Ah ok, thanks for that. How do you keep it from bouncing about on the take-off run?

[David Ashby - Moderator]

You pray Doug.....

[Tim Mackey]

I well remember around 20 years ago or so, acquiring a 56" span Mirage 2000, with a Rossi 90 rear induction and tuned pipe set up beast. I made up a dolly from hardwood strip into a similar shape as the one featured in this thread, but it had a nosewheel....err at the nose end ! The rudder was useless at ground run speed, so I figured out an over-complex steering setup - a servo and tiller onto the wheel, and the servo was connected to a standard size stereo Jack Plug that was mounted vertically at the apex of the triangle, and corresponding socket was fitted into the underside of the model. The socket was connected to the rudder channel output of the receiver and therefore supplied steering until the model lifted off the dolly and got away. It worked of a sort.....

Erratic connection, a reluctance to unplug itself, and general mechanical unreliabilty meant it only lasted around half a dozen "exciting" runs. The plane was an absolute missile, and the prop tips were reaching supersonic speed in a dive.

Awesome machine in its day, one of those that was guaranteed to make everyone else at the strip land and pit when they saw me prep it!

Ah fun days.....

[Former Member]

[This posting has been removed]

[001]

Is that a spare receiver, battery and servo on the dolly shown? With the same frequency as the model of course.

[Peter Miller]

Back in the control line days there were two good systems that were used.

For normal small stunt models we used a drop out U/C, this was just a normal two wheeld U/C that plugged in to two tubes in the model As the model lifted clear the U/C just dropped out. Never failed.

For speed models we used a tricycle U/C , single leg trailing. This had two arms which locked over the top of the wings, these were held in place by a simple trigger mechanism held by a trailing wires.

The model lifted the dolly off the ground, the tailing wire dropped and released the trigger and the arms flew up and the dolly dropped away. This was called the "rat trap" dolly. There is a good illustration in "The Control Line Manual." I don't have a copy at the moment.

Ours were pretty heavy because we were using very powerful engines and the models weighed a fair bit. I imagine that for an electric powered model they could be quite a bit lighter. No sure how you would use the drop out system on a model with a pusher prop

[Peter Reay]

The problem with the type of dolly shown is that you cannot get rotation to increase the angle of attack to lift off.  The 'secrect' is to angle the frame at about 10 deg to give a static angle of attack then the model will just lift off when flying speed is reached.  The only small problem is that the pilot cannot choose when to lift off as the elevator is ineffective until the model is airbourne.  with the flat dolly the model and dolly rip up the field, much to the amusement of the spectators, but won't lift off.

Another solution is to make up a mini trike dolly with a layout similar to a trike undercarriage on a fixed U/C model, then the model will be able to rotate in the normal way and fly off the dolly.

 Good luck with the ideas.  It's what makes this hobby so much fun.  I made an angled dolly to launch my Mini Tigershark as it was difficult to get some one to give it a decent hand launch.

[David Whitehouse]

Hi guys

Mark 1 and 2 both had a fixed wheel arrangement, and caused problems on the flying field (not exactly a bowling green where I fly) and as soon as it hit a small bump would start to veer off with no means of correcting, (Take off aborted)

My fun fighter not having a rudder and hand launching seems only a matter of time before it bites the dust.

I decided to build the mark 111 with a stearable-trailing wheel, there is a receiver attached to the underside along with a batt and servo, utilising the rudder channel.

Hopefully will give it ago this weekend if weather permits, will post results (good or bad) and some pics, thanks for the input and will include some of the design features mentioned in the mark 4, if this doesn’t work.

Dave

[Former Member]

[This posting has been removed]

[Doug Ireland]

If I remember correctly, the target drones used at the Aberporth Missile Range for RAF Valley used a "dolly" on a circular track. Never saw it used but it must be a bit hairy!

[Peter Miller]

Back in the 50s I sawa film of a full size Piper Cub taking off from a circular track. IT was held by a cable at the wing tip until it took of, then the pilot released the cable. IT was on a Newsreal of the day.

[Peter Costello]

I need a really light weight dolly for a 48" EP mossie - I only trust a small number of members to chuck it for me!  The drop out tube types sound good but the wings are veneered foam and probably not that strong for this type of  set up - must be other ideas out there. I have no rudder at the moment - perhaps this would help for ground control?

Pics or good description would be great.

[Peter Miller]

Rudder would help with ground control.

 The plug in U/C is normally fitted to the fuselage, The tubes are bound to a former with wire and then soldered. Alternatively they could be held with saddles, or even just drilled into hardwood blocks.

The U/C legs are joined with a cross brace and the prongs should be about 2" apart. Making them wider would run the risk of hanging up. The wires need to be a loose sliding fit in the tubes and be very free so they drop out. On the other hand really sloppy is not good as the under carraige could fall out if the model just bounces.

 The prongs should be about 2 inches to 2 1/2" long.

[Matt Hackers]

Sounds like a catapult and a ramp might be safer.

[Tom Sharp]

or get some one to hand launch it out of a tree

[leccyflyer]

Peter

My pal and I knocked up a lightweight dolly suitable for electrics some years ago, making use of plastic tubes and connectors from a demolished Wendy House and commercial model wheels.

If I can make the picture attachment thingy work I'll put some pictures up. The dolly works well on short grass and I've used it with electric funfighter sized models both with and without functional rudder. Without the rudder it;s reliant on the dolly tracking straight or the model naturally weathercocking into wind, but TBH the model doesn't usually stay on there for long enough to have made it a problem except in one failed attempt to use it to launch a pusher flying wing.

The model on the dolly is an electrified Cambrian Spitfire, weighs about 3.5lbs, no rudder servo fitted and takes off from the dolly with no problem. My Cambrian 109 does have a functional rudder, so in theory could be used to steer the dolly, but in practice the dolly tracks pretty straight with the tailwheel set for midships and the loud-quiet lever advanced to "All Ahead Full"