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Astro Hog

Plans, engine, build advice

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Nick Holmes-Mackie13/08/2007 21:46:00
17 forum posts
There's an article discussing low wing trainers and one of the contributors recommended the Astro Hog (not SIG) as a suitable build. Pics on the web persuaded me - a lovely retro look to the model - looks timeless to me :-)

So.... I researched, and found a couple of plans. One's the Berkeley models plan (looks just about suitable to build from, although it's a set of kit drawings) and there's another set "Uncle Willie's Astro Hog" that's clearly derived from them. So, I have plans (returning to building after 30 years...)

I'd appreciate advice from anyone who's owned or built one of these - what engine would suit (4-stroke, or glow, for example - and what sice for each)? Why is the SIG kit not recommended? It looks to me better to use a tail-dragger u/c, but is there a good reason to fit a tricycle u/c? Any recommmended (or not recommended!) mods? (for example, the 'Uncle willie' plan includes flaps, but I've seen the model described as one that 'floats' to a landing, which indicates to me that flaps are probably a waste of effort). The original has a single servi for both ailerons - I guess it's probablt more straightforward and probably better to use 2 with a 'Y' lead? Oh, I could go on and on. Also, the plan doesn't include recommendations for control surface throws - and recommendations? (yes, I know it's early days, but I figured I can use any advice anyone has!) I thought I'd update with progress as I go - or is this terminally dull for regular forum readers?

Thanks in grateful anticipation...

Nick
Evan Pimm 214/08/2007 08:50:00
51 forum posts
Cor Nick, thats heaps of questions, but having built a `Berkley' clone with help from the `Aeromodeller' drawing for some of the sections, I will attempt to answer some of them. The mods done were only for the use of modern gear, so the removeable top was made fixed. Keep the tank hatch as drawn, it's quite useful for maintenance. The tailplane was fixed, using the external doublers as a fairing, and I added a bit more incidence (L/E up) to give about 1 deg diff. between wing and tail, we have elevator trim now, you see. The dihedral braces were extended out to the outboard end of the L/G blocks and the blocks themselves scarfed at the centre, and glued to the ply brace, really strong. The rear braces were extended only one extra rib bay. The balsa spars are more than adequate, don't change them. I used 5/32 wire for the L/G instead of the two bits of 1/8 as shown on the plan. Otherwise it was built`as per'. I use a 1/8 ally engine plate and just make up another one for whatever engine I'm using in it at the time. As for power, anything from an old FP.40 to a K&B .60 has been used, gentle with the .40 and grossly overpowered with the .60. As a guide the flying weight with a TT.46 was 5.5lb and it would do the full 1970's schedule with it, so it don't need a lot of power to do the necessary. As for radio stuff, I use one servo in the centre with old fashioned bellcranks etc, but it's up to you. Keep it a tail dragger, it's lighter and better for you, it really is a lady on the ground but it will help with learning to use the rudder for torque control. Flaps definitely not required, nor strip ailerons, and the Sig version has the tailplane in the wrong place, looks all out of shape. It is an old fashioned airplane, but if you build it straight, with perhaps just a smidgeon of washout, you will discover that there are lots of models out there that could do with a bit (lots?) of what this model has. I use mine as an `ab initio' trainer these days and it still teaches them quicker than any of the modern high wing ARF boxes. We have not learnt much in the last 40 odd years...
Evan.
Nick Holmes-Mackie14/08/2007 19:56:00
17 forum posts
Thanks Evan, that's really useful. And I feel pleased that it looks like I've made a good decision! Reading what's available on the Web about the Astro Hog, it sounds like everyone who's had one feels a great affection for it - always a good sign, I think.

Am I odd, or does everyone have a whole list of models they'd like to build? I already know what I want to build after the Hog - a scale Chipmunk.. Did some lessons on one in my early days. I know it's very popular - there's a reason for that, I suspect.....

When I was last modelling, there were very few 4-stroke engines around - and they were all pretty large. If a 4-stroke is much less noisy that a 2-stroke, I'd like to consider that for the Hog - any suggestions? Or, given that 2-stroked are so very much cheaper, should I be content with that?
Evan Pimm 215/08/2007 06:05:00
51 forum posts
Nick,
It all depends on whether you can get it to balance. Any 4S from .45 up to, say, .70 will be ample power, the limits will be engine weight and how far you can move the flight battery to compensate. As for the noise thing, there isn't much difference between a 2S and 4S, only the perception of the listener. As for models we would like to build, well there comes a time when you realise that you are gunna havta live considerably longer than most, and with all your faculties intact...
Evan.
Allan Jordan15/08/2007 10:33:00
495 forum posts
Hi Nick, The Astro Hog by David Boddington is still available from the Plans Service . Plan No. RM283. Hope this is of some help to you. Regards Allan J..TTFN
Nick Holmes-Mackie15/08/2007 19:45:00
17 forum posts
Aha - thanks, Allan.

I'm not sure whether I need that one - I've two already - one from the Berkeley kit and another from the original American magazine article from 1958... Is it worth looking at the Plans Service as well? (and where are they? Are they on the web? Could you post the URL?)

As for the engine (thanks for the comment, Evan) - I think I'll delay the decisoijn for a while, and research using a tuned pipe with a 2-stroke, as I understand that they are pretty effective at lowering noise levels. I guess a 4-stroke makes a lower pitched noise though, which is easier on the ear, even if not quieter. But I've plenty of time - there's a lot of building ahead. And I can't start until after the weekend (can't get to a decent modelling shop until then!)

And then there'll be the colour scheme to decide. I do really like the red and white scheme that is in all the pictures, but I'm looking for something a bit different and yet still appropriate for the vintage. Late 50's - what was going on ther? Warhol? Bewitched (or was that 60's?), Elvis? Flash Gordon?

Thanks for the info - I do appreciate it!

Nick
Evan Pimm 216/08/2007 08:47:00
51 forum posts
Nick,
The original (Dunn) was the same scheme (Sunburst) as the red and white one you know, only it was black and white. First flown in 1957 at the LARKS flying site in LA. So far as the photographic record shows, all the others (Dunham, Nelson, et-al) were modified in some way and the colour schemes proliferated. I have a mate who was there as a teen at the time, helped Bob Dunham after school assembling `Orbit' rigs in the back of Bobs model shop, and he still says it was the most interesting time he's had in aeromodelling. Seems all the West Coast greats were in that club at about the same time and that's when R/C really took off, if you'll pardon the pun. So really you can just go for it, Flash Gordon was alive and well, so was Superman...
Evan.
Nick Holmes-Mackie29/08/2007 21:31:00
17 forum posts

Thanks again for the helpful comments.  I've actually bought, at a very reasonable price, the SIG kit to use as a basis (it's much, much cheaper than buying the wood at my local model shop!).  I'd like to retain as much of the original design as is sensible, and I have in mind the advice in the first thread that I read that said "not the SIG version"!  So - what's the difference?  I already know that the tail-dragger is the right thing to build.  Should I include the original 'barn door' style ailerons (the kit has strip ailerons), for example?  Any advice would be gratefully received!  Nick

Evan Pimm 203/09/2007 05:54:00
51 forum posts

Nick, the `Aeromodeller' plan is still available (X plans list?) and has all the info you need to build an original. Take care with the Sig kit, replace wood as necessary, remove all the `lite ply' and use the A-M plan as a guide for replacement items. Sand it lots when complete and use plenty of epoxy around the front end to keep the oil out and you will have a model to enjoy for many years to come.

   Evan.
 

Nick Holmes-Mackie03/09/2007 17:13:00
17 forum posts

Okay Evan - thanks for that.  I'll take your advice...  Now all I have to do is get on with it.  Any more questions would just be delaying things!

 One thing - the comment about lots of epoxy.  Do you mean that I should add fillets of epoxy to prevent oil penetration of the wood/fuselage?  Or a thin coating on the firewall - or what?

Thanks,  Nick

Evan Pimm 204/09/2007 06:50:00
51 forum posts

Just some thin resin all round the engine bay, fuel tank area, and anywhere the exhaust will blow down the fuselage. You don't need much on the outside, just a bit rubbed into the wood and sanded smooth before covering. Use plenty elsewhere as you're bound to get a tank leak, split fuel line etc at some time and it's just good insurance.

Evan. 

Nick Holmes-Mackie10/10/2007 08:55:00
17 forum posts

Well, I'm getting into the build now - it's a bit slow, as I only get a couple of hours a week to spend on the Hog.  I've mostly built the wings now, and am thinking about the controls....

I think I said before that I was planning to put aileron servos out in the wings - it keeps the control run very short and seems (to me) more straightforward.   And then I wondered why people don't drive the control surfaces directly from the servos?  It wouldn't be easy to do at this stage, but it seems sort of sensible.

But more seriously - I've been thinking about the hinges and design for the ailerons themselves.  I've provided for barn door ailerons.  It seems that modern practise seems to be to hinge at the top edge, using mylar hinges, but I like the look of the original, which is more complex, having the ailerons hinged from the ends, with the centre of the hinge at the centre of the aileron andwith a rounded front edge to the control surface so that it rotates in a more 'scale' way (hope this makes sense). The original even says it uses ball-race bearings! Is there a disadvantage to doing it this way?  It seems perhaps like overkill, but on the other hand, ought to provide a very durable solutions.

Whilst I'm at it, it looks to me as though it would be sort of sensible to have a lclosed-loop rudder control.  It's easy to implement, provides more positive control and so on.  And (apart from swapping servos) why not put the servo close to the control surface?

Nick

Evan Pimm 212/10/2007 13:10:00
51 forum posts

Nick, your ideas are all sound, and I did indeed simply top hinge the ailerons. `Pull-pull' for the rudder will work just fine, a servo at the back may be ok, but I put mine all in the wing area and needed no ballast, so go easy on putting anything behind the cg. Those old drawings showing the original Friese type ailerons  (also shown on the original Orion plans) were an attempt to combat adverse yaw problems, but these days we have Tx mixing, and I had no yaw problems with the model anyway.  A servo in each wing will be fine, but very `modern'  for the old girl.

Evan. 

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