'ello Dolly

[Tim Mackey]

I hate bungees, and refuse to fly a jet with dangly bits hanging down

So, I am pondering the design of a lightweight, simple 3 wheel dolly made from a piano wire frame for my 30 oz foamy F18 Hornet. Simple short upright plastic sleeved wire pegs would retain the main wing until flying speed was reached.

Now I've done dollys before in the dim and distant past, wooden, plastic plumbing pipe, servo operated steering tillers etc, etc, but want this one to be small, light, easy to fit in the car, and above all simple.

Grass strip, some small divots, and the odd weed, but generally in pretty good shape - do you think I could get away with no steering ( no rudder either on the F18 ).

Any fag packet / superduper CAD design sketches welcome

 

[Biggles' Elder Brother - Moderator]

Mmmm, interesting project!

 

never flown an EDF (will do one day when I've run out of bipes to build!) do they exhibit much torque reaction? If not I guess you could get way with tricycle undercarriage without steering with the main wheels "toed-in" to encourage straight tracking. The problem of course is that if you do loose direction there wont be much you can do about it!

 

BEB

[Chris Bott - Moderator]

Hi Tim

 

Leccyflier had a great dolly at the RCM&E Fly in.

I now have one just the same.

They are for prop driven warbirds mind you, but I can't see the principle being any different.

 

On these the tailwheel is manually adjustable so it is set for whatever a particular model requires. Mind you, if a bump sends it off course there's a problem. The models rudder does work to some extent still though.

 

 

My biggest problem was with the thrustline being higher than the wing. This meant a tendency for the nose to pull downwards.

To counter this, I now have the model sitting further back and lower on the dolly. 

[Tim Mackey]

BEB - there is no torque reaction with an EDF, and as for directional stability, the toe-in / toe out argument is bound to start now lol

Hi Chis...when you say the tailwheel is adjustable...for what exactly - tracking?

I guess the plastic tube version is actually gonna be lighter than an all piano wire one, although it kinda looks a bit bulky and clumsy IYKWIM

[Chris Bott - Moderator]

It is very light yes, you may be better off with something smaller for an EDF though.

 

I can manually steer the tailwheel then it stays pointing that way.  Needed if the takeoff continually veers one way..

[Chris Bott - Moderator]

Put Dolly in the forum search, there's a number of threads..

[Romeo Whisky]

When I wanted a dolly for my Ripmax P51 and Overlander Tucano I started with an idea using polypipe.  However this proved to be a bit too heavy for reliable take-offs when the grass was wet or a bit long so I redesigned it using light dowel to replace the polypipe.

 

The Mk 1 version was fitted with a castored tail-wheel but it careered all over the place on take-off, so for the Mk.2 I did away with the castoring in favour of a fixed tail-wheel and was interested to learn recently that some WW2 aircraft had to lock the tail-wheel in centre position for take-off.

 

Here's a pic of the latest version of my dolly and I haven't had a failed launch with this version.  The big wheels cope with longish grass on the football field quite easily.

 

There are more pics from different angles in my album.   By the way, I found using just stubby foam front restraints didn't work as the model would bounce over the restraints on rough ground before reaching take-off speed.  Hence the longer sheathed wire restraints shown above.

Edited By Romeo Whisky on 22/10/2010 15:48:03

[Mowerman]

If fitted with its own rx, servo and battery the dolly could be steerable.

The rx on the same channel or bound to the same tx/model as the aircraft.

After takeoff just get a 'fetchermite' to pick the dolly up and switch it off.

Could be expensive if using Futaba 2.4 gig.

[Martin Harris - Moderator]

Ideal use for one of the new cloned receivers?

[Biggles' Elder Brother - Moderator]

Be cheaper to buy a low cost RC car fit it with a "roof rack" and have a mate drive it in a straight'ish line

 

BEB

Edited By Biggles' Elder Brother on 22/10/2010 21:43:36

[BB]

Posted by Mowerman on 22/10/2010 16:27:54:

If fitted with its own rx, servo and battery the dolly could be steerable.

The rx on the same channel or bound to the same tx/model as the aircraft.

After takeoff just get a 'fetchermite' to pick the dolly up and switch it off.

Could be expensive if using Futaba 2.4 gig.

 Or, just land it back on the dolly:  And taxy to the pits

[Tim Mackey]

This is most odd...I posted a reply to the point about the receiver for steering, hours ago - and its disappeared!

The gist of it was, the cost would not be an issue as I would use the cloned "orange 4 channel job" -  I can bind as many receivers as I like to any one model memory, but only one model memory to any one receiver.  That would mean I could only use the dolly with one particular model which would be a shame.

I also thanked you guys for the responses so far, and would maybe go for something like RW shows, possibly using C/F rather than wooden dowel.

Edited By Tim Mackey - Administrator on 22/10/2010 22:32:40

[TonyS]

Hate's a strong word Tim but I know what oyu mean about bungees. There's something wrong with a technique that stores a whole load of energy then once you let it go you have absolutely no control over it until it's spent...

I had both a bungee and a Dolly for my Yak - it  did work though (shame the plane didn't..) 

 

Because the plane and the wheels are both towed by the bungee then it just 'sits' on the foam with no need for any wing restraints....

 

[leccyflyer]

Posted by Tim Mackey - Administrator on 22/10/2010 15:21:35:

BEB - there is no torque reaction with an EDF, and as for directional stability, the toe-in / toe out argument is bound to start now lol

Hi Chis...when you say the tailwheel is adjustable...for what exactly - tracking?

I guess the plastic tube version is actually gonna be lighter than an all piano wire one, although it kinda looks a bit bulky and clumsy IYKWIM

 

The dolly pictured - which Chris built up from some bits that I'd given him after he'd seen mine  - has successfully launched lots of prop-driven models, including even pushers like the venerable Zagi- with some extra care needed (like not trying to steer!).

 

It'll track straight as you like, or the adjustable tailwheel could be set up to counteract any P-reaction in the case of a prop driven model without a rudder. However in my experience of the design I've just gone ahead and launched the models whether they have had a rudder or not - they tend not to be on the dolly for long enough for it to be critical.

 

The only problem that I've encountered has been recently, due to trying to be too clever and avoiding having my helper having to go too far to pick up the dolly, resulting in dragging a model off far too early and belly-flopping in front of the advancing dolly. Lesson learned there.

 

For a model fitted with a rudder it's quite possible to taxi the model with this particular dolly.

 

I'd have no qualms in using the dolly with an EDF.

Edited By leccyflyer on 23/10/2010 12:40:29

[Former Member]

[This posting has been removed]

[kc]

A friend used a drop out piano wire u/c which looked like a normal u/c but which had vertical bits which fitted into tubes in the fuselage.  Being loose the u/c dropped out easily.  A published plan later used this  too but I cannot remember which one.

This looks more scale than a dolly. I would say a take off from a dolly which looks like a model bedsted designed for Blue Peter looks far worse than wheels dangling down in flight!

Edited By kc on 23/10/2010 18:53:29

[Tim Mackey]

Hmm, now thats an idea also - cheers kc

PS cant agree with the last bit though

Edited By Tim Mackey - Administrator on 23/10/2010 19:13:51

[leccyflyer]

Posted by kc on 23/10/2010 18:50:16:

A friend used a drop out piano wire u/c which looked like a normal u/c but which had vertical bits which fitted into tubes in the fuselage.  Being loose the u/c dropped out easily.  A published plan later used this  too but I cannot remember which one.

This looks more scale than a dolly. I would say a take off from a dolly which looks like a model bedsted designed for Blue Peter looks far worse than wheels dangling down in flight!

Edited By kc on 23/10/2010 18:53:29

 

 

 

That's a matter of opinion. A fighter swooping through the air with a pair of donuts dangling beneath looks far worse to me than a dolly that's left on the ground. It's what the model is like in the air that matters, after all, else they would all be fitted with retracts.

 

I've seen the drop-out wheels mounted in tubes featured in a magazine plan before, but, with all due respect, with the possible exception of a genuinely rocket-powered Me163 Komet they are really no more scale than a dolly.

 

There's also the small matter of what happens if the undercarriage does not drop off right away, leaving the model as being up there in te wide blue yonder with a potential hung up bomb underneath, ready to drop off onto anyone in the area. Or, if one side fails to depart, potentially leaving the pilot with the dreaded one-wheel landing. It seems a high price to pay to look so scale-like on take off as having the wheels fall off.

 

The idea of the dolly is to get the model into the air, at flying speed, whilst doing away with the need for onboard wheels - either as retracts or as fixed gear, and to avoid the heavy toll of bodged hand-launches. 

 

Then again, model aeroplanes launched by giant hands aren't exactly "scale" either.

[Steve Hargreaves - Moderator]

Just adding a post so I can be involved.....I prefer the idea of a dolly to a bungee too....

 

How big is the Spit Chris...? Just to get an idea of scale. The dolly looks a good option for both EDF & say, a Cambria FunFighter sized model (42" span)....

 

I don't know about you guys but I've found that most handlaunchers leave a lot to be desired.....the number of models I've seen trashed after a dodgy throw....well lets just say its quite a few!!!

[Steve Houghton 1]

Tim

 

This thread reminded me of a youtube clip I'd seen of a Ripmax Mustang where the guy had made a dolly of sorts. Take a look, its at the at the end of this clip here

[Romeo Whisky]

I must admit I seriously thought about using the drop-out undercarriage system after seeing it a magazine some time ago.

But it occurred to me that when it drops off, the pilot cannot see where it drops because he's concentrating on flying the model, and it might be difficult to find afterwards.

Seemed to me you need a dolly which is easy to see and retrieve at the end of the flight.  You also want to see it well enough for yourself (and other fliers) to be able to avoid it when landing, if it is still on the patch.

[Tim Mackey]

Having sat through the rather obvious "promo" film for the hugely overpriced re-badged turnigy Purple power stuff ( rant over )  the dolly in question is really more like a version of the drop out undercarriage mentioned earlier.

One problem with my F18 is that its a trike of course, so would need a full triangular frame with a nosewheel and two mains...all of which must "drop" at the same time.

 

[iawnski]

well i never, cant u just run faster my mate easy

[Tim Mackey]

I dont do running anymore Kev

[leccyflyer]

Posted by Steve Hargreaves on 25/10/2010 16:12:03:

Just adding a post so I can be involved.....I prefer the idea of a dolly to a bungee too....

 

How big is the Spit Chris...? Just to get an idea of scale. The dolly looks a good option for both EDF & say, a Cambria FunFighter sized model (42" span)....

 

I don't know about you guys but I've found that most handlaunchers leave a lot to be desired.....the number of models I've seen trashed after a dodgy throw....well lets just say its quite a few!!!

 Hi Steve

 

The dolly was originally designed for the Cambrian Spitfire funfighter and has been used to lauch a variety of funfighter models including that Spitfire, the Cambrian Bf109E funfighter, Balsacraft Bearcat and FW190,  Ripmax Spitfire, Westfield F-86 Sabre, Zagi E400, and borrowed for a few clubmates similar models.

 

It's pretty near perfect for that size of model and came about after handlauch woes and a y unsuccessful try of a catapult!