1/2A Free Flight Models

[Jez Wilkins]

Hi all.

I said in my post about the engine starting stand that I would post some details of the 1/2A free flight models that it was constructed for.

The first one is 'Cuddy'.  Published in the October 1973 edition of the 'Aero Modeller' magazine (which I think I got delivered every month by the local newsagent) and I only got around to building one last year - although I'd fancied doing so ever since I first saw it.  I put an auto rudder on it (although the plan doesn't show one).  Power is an 0.051 cubic inch Cox Tee Dee - bladder fuel tank.   Esaki tissue over clear mylar for the wings, silver mylar for the tail and black esaki tissue for the fuselage.  The 'high viz' paint on the wing tips and fin is Montana spray cans.  Fuel proofer is Aerokote (50:50 mix gloss and matt).  This was the model that I managed to cut the glow plug lead wires with!!  It wants to go left on launch - which resulted in some slight tissue damage on the wing.  Now fixed, auto rudder adjusted a bit and ready to go again, once the weather improves.

The other one, I have no pictures for.  It was a swapmeet buy and has a VA 0.8cc(?) glow in it - but not the version that has a horizontally split crankcase casting.  I don't know for sure - but by looking at the fin shape and wing construction and outline, it is a 'Zeus' - 40.5 inch wingspan.  I managed to put a split in the pylon of this one, when a wing tip caught in the 'Keil Kraft grass' at Buckminster, when giving it a test glide!!   Also now fixed, etc., etc..

Cheers,

Jez Wilkins

[martynk]

That brings back some memories. I was always puzzled why Tony never went for a rear fin that was far more fashionable at the time.

It will be interesting to see how consistent it is when you get it sorted

--
Martyn

[Jez Wilkins]

Hi Martyn.

Thanks for the post and comments.

The combined fin and tailplane caused me some head scratching when it came to fitting an auto rudder - which I wanted to do, rather than relying on tail tilt.  In the end, I went for an 'underfin' - but taking the dimensions from a plan that I have for the 'Dubloon' and creating a triangular sheet fairing, to suit.

Cheers

Jez Wilkins

[ffkiwi]

Nothing wrong with a Cuddy-it was my first 1/2A power model....40 years ago...i still have it, still in one piece, though the tailplane is looking rather ratty after 40 years. the fuselage is still fairly pristine as I painted it with 'reaction lacquer'-2 part polyurethane...which is proof against anything you care to throw at it. Have built two more since then-the second I sold in a major clearout I had on 2000; the third resides as yet uncovered, down in the garage....just to be different this one sports a Webra 1.5 for our Kiwi Power class. I note that Tony Cordes mentioned in his original article that the Cuddy was sized at the upper end the 1/2A range....as befits its intended use as a 1/2A trainer...and this made it suitable for a 50's era diesel with about the same output as the TD 049/051-albeit at 2/3 of the revs on a significantly bigger prop!

 Funny-or perhaps serendipitously coincidental that Jez' other picture shows the 'Zeus'....sitting downstairs is a recently completed Zeus-again intended for Kiwi Power-with an original Taifun Hobby up front.....and you will look long, and hard-and IN VAIN-to find a lighter 1cc diesel of similar power (even lighter than a PAW 80 or 100!)....and as a small bonus-it also meets our NZ 1/2A rules...thanks to our 1cc limit for 1/2A. [as for Kiwi power-the rules specify a 1.5cc max plain bearing diesel-but no minimum-I appear to be the only one here going down the smaller route....which offers some possibilities in terms of dual usage-such as 1/2A power/Kiwi Power or Mini vintage/kiwi power.....with the right choice of engine and airframe.  [I note some of my Australian colleagues-notably Roy Summersby-have taken an alternative approach-basing their Oz Power (same general class rules) designs on existing F1J designs-simplified]

 ChrisM
 'ffkiwi'

[ffkiwi]

Following on from my post above here are some pics-the original 40 year old 'Cuddy'-still intact-though in need of a wing recover!  The uncovered wing and fuselage for the Webra powered one-the tailplane-not shown- has been modded to allow for a removeable fin to facilitate transport and storage [I hate 'fin on stab' designs with a vengeance....] retained by two small machine screws from the underside of the tailplane-fortunately the amount of negative tail packing raises the underside of the tailplane far enough above the rear fuselage to allow clearance for these screw heads; and finally the recently (late 2023) completed 'Zeus'-still awaiting final DT line and fuel shutoff line rigging.  On taking the photos of the assembled model it struck me how similar it was to a KK Gaucho-which appeared a year or two earlier. I built one of those not long after the first Cuddy....but never had much joy of it at the time..

 ChrisM
 'ffkiwi'

[vintagemike]

I built a Cuddy ariund the time of the Tan2 rubber shortage, it was my first "competition" power model. Built simply with fuse DT and a DC Merlin up front  it was a case of start it up, throw it into the air and wait for it to come down. Trimming over! One flight! Brilliant model, recommended

[Jez Wilkins]

Hi vintagemike and ffkiwi/ChrisM.

Thanks very much for the posts and information

ffkiwi/ChrisM - are transport and/or storage issues the reason(s) why you 'hate fin on stab designs with a vengeance'?  If not, would you mind explaining what your reasons are?

I notice on the 'Zeus' design that you have a cylindrical fuel tank.  Any reason(s) why this is preferable to a cuboid one?

The British Model Flying Association's [BMFA's] 1/2A Power rules are pretty basic - see the attached 'screenshot'.  At a pinch, 'Cuddy' as originally drawn (i.e. without the auto-rudder that I fitted) could be used for U.K. Slow Open Power [SLOP] and the international class F1J [as mine is over the minimum total weight (less fuel) of 160 g/5.63 oz].  Mine is, however, under the minimum weight of 250 g/8.84 oz for the international class F1P, even if it met the minimum projected wing surface area criteria.

Whether using 'Cuddy' for any class other than BMFA 1/2A Power is a good idea, is another question entirely.  My experience with such models is very limited - but I am suspecting that it would not be very successful.  

I guess that it is going to happen more and more, as time goes on - but it really grieves me to see nicely built models ending up on a table at a swapmeet, following the demise of yet another aeromodeller.  I am happy to give such models another opportunity to take to the air again, if I can.  If they have BMFA numbers/owners details on them, I will include a reference to these, as a tribute to their earlier history, when 'rebranding' them.           

Cheers

Jez Wilkins        

[ffkiwi]

OK Jez-my reasons for disliking 'fin on tailplane' setups are two fold:

firstly -as you surmise, transport and storage-tailplanes with fins occupy vastly more space than a simple tailplane-which can be stacked closely together in a model box-including different spans and chords-and there is no way multiple finned tailplanes can be. I dislike subfins and tipfins on tailplanes for the same reason-and usually make them detachable if I can.

secondly-most power models-and I'm referring to high powered pylon types, not sport models, are very sensitive to rudder...sometimes to as little as +/- 1/64" ....so when you have a tailplane mounted fin there is always the risk of varying rudder-from flight to flight due to the fact that they're not usually mounted with zero slop....because you ALSO need reliable, non delayed DT operation-which in turn requires a little bit of sideways clearance on your mounting....you did note the bit in the Cuddy article about split dowel locators ?  [OK some more advanced models may use tongue type tailplane mounting (F1Cs, F1Js for example)......but you'll look long and hard and most likely in vain to find one of these with a fin on the tailplane]

Now a variation of 1/64" won't have any noticeable effect on the glide-but it MAY impact on the power pattern...and if I can avoid it I will. That being said I have a LOT of 'fin on tailplane' models.....but most of them are either sport models or vintage...and you get no choice with the latter.

 ChrisM
 'ffkiwi'

[ffkiwi]

One more thing I've just noticed-Jez' third picture in his first post-the drawing (Argentinian perhaps?)-of the 'Cuddy'-the CG range given on that drawing: 50-55% is MILES OUT -for a locked down model....whoever drew up that drawing either didn't have a clue, had brain fade or was used to flying modern 'systems' models which do have CGs in that range. Stick to the original CG as stated in the Cuddy article of 1-inch in front of the TE....84%...which is fairly typical (75-85% chord) for a conventionally laid out, locked down pylon model. A few-most notably the much loved Dixielander-have CGs right on the TE-and a few people push it even further aft, squeezing a fraction more glide performance out of it at the expense of stability.

 ChrisM
 'ffkiwi'

[Jez Wilkins]

Hi ffkiwi/ChrisM.

Thank you very much for both of your posts and the information and advice contained therein.

+/- 1/64" is very little!!  I can certainly agree with you about the additional space taken up in a model box, by a 'fin on tailplane' arrangement.  

I cannot quite remember how long ago I bought it - but I have been using the building jig from the Sun Lane Engineering Company [SLEC], based in the U.K., for all my builds (control line and free flight) for a good few years now.  Please see the attached 'screenshots' of the jig itself and a further one of the 'Cuddy' fuselage on the jig.

I have found the SLEC jig to be extremely useful when using slow set epoxy to glue wings and tailplanes into the profile fuselages of control line team race models and also to ensure everything is aligned/level on free flight models, before marking and then gluing small pieces of 1/32" balsa (or split dowels, as you mention) to ensure that they are always assembled consistently thereafter. I do, however, acknowledge your point that, with a fin on tailplane arrangement, varying rudder and reliable D/T operation are unhappy bedfellows.

With regard to tipfins on tailplanes I bought (from a swapmeet) a lovely (wooden) model box containing five nice rubber powered competition models.  These turned out to be 40 gram Wakefield models (as per an email conversation with Mike Woodhouse - during which I provided him with details of the owner and models). Three of the five models had (detachable) tip-plates on the tailplanes and these were banded on, using small hooks on the leading and trailing edges of the tailplane.  I did not like this arrangement - so I 'jigged' the tailplanes and tip-plates into correct alignment and glued them in place.  I then used suitable lengths (and thicknesses) of balsa and 'velcro' to secure the three tailplanes into a suitably sized plastic storage box.  Yes, I now have to remember to pack two boxes, in order to fly these three models - but, to me, this is a worthwhile chore - and much better than the alternative of possible inconsistent trim.

Regarding the CG range shown on the 'Cuddy' plan - I built from the original 'free plan' from the Aeromodeller magazine - and the CG of my model is as per that plan.  The only reason for attaching the version of the plan that I did, is that this is the only version I have, which I could convert into a format that the HPA site allows!!  

Cheers,

Jez Wilkins                          

[ffkiwi]

Jez-the best advice I can give you when it comes to building pylon models is....if at all possible....use a design and/or structure (if your OD) that allows you to move the pylon back and forth to set the final CG location....this is infinitely better than needing to add tail weight (not that often!) or horror of horrors-having to move the engine forward due to too heavy an aft end...the latter has you running out of options very quickly-especially if the design uses engine bearers....of course the Cuddy does do this-but not all design do....even some with a slotted in sheet pylon can be arranged to have a bit of fore and aft movement.

 ChrisM
 'ffkiwi'

[Jez Wilkins]

Hi again ffkiwi/ChrisM.

Thanks for the further post , information and advice.

Balancing models and (particularly) having to add lead to them, must rank as my two least favourite jobs to do, when building model aircraft!!

Slightly off topic (but with a purpose in mind) with control line models (particularly profile fuselage ones) the usual method is to leave the engine mounting until last - when it can be moved fore (or aft) a bit - subject to bearer length and wing position, to get the CG in the design position.  It's also possible to fit a heavier (usually brass) safety spinner nut - to move the CG even a bit further forward, if needs be.  Moving the CG rearward with lead is a bit more problematic - as there is (like with FF competition models) not much fuselage width to play with.  I've known some suggest leaving a 'square' centre section on a solid balsa team race wing, cutting a 'slot' in a profile fuselage, temporarily banding the engine in place and sliding the wing, to get the design CG.  The problem is that glass cloth/laminating epoxy does not conform well to the change in wing section (even if using a 'wing press') and there is, potentially, another issue - which I will refer to later.

The 'Cuddy' plan and/or build article refers to a 'Tatone engine mount'.  I didn't have one of those - so I had to use beam mount bearers (beech).  I took the bearer size and length dimensions from the 'Dubloon' plan (attached) and positioned an extra former in the front end of my 'Cuddy', to accommodate the bearer ends.  I also divided up the interior of the fuselage a bit - to create separate compartments for the timer (port side) and the fuel bladder (starboard side). These I built (and fuel proofed well) before adding the fuselage top skin - which I also selectively fuel proofed (to avoid any areas which would subsequently receive glue).

The 'Cuddy' build article does not mention moving the pylon, to achieve the correct CG.  Fortunately, before starting on 'Cuddy', I had built a Spencer Willis' kit of his Sweet "P30" P30 rubber design.  In the build instructions for the kit, he mentions banding the wing to the pylon and then moving this along the (very nicely made) rolled balsa tube fuselage - to find the correct CG.  Then the pylon glued in place and strengthened with doped on silk strips - all very dainty!!  

Anyway, for 'Cuddy' I did something similar - engine temporarily banded in place, as far back as possible on the bearers and move the pylon, with the wing banded to it.  The fuselage was already tissue covered (maybe even fuel proofed) at this point - so I marked the pylon position and then carefully removed the fuselage tissue - to allow a 'bare wood to bare wood joint' for gluing (as the pylon is not 'built in' to the fuselage, for this design).  I used 'slow set' epoxy [Araldite] and jigged it up in the 'SLEC' jig, until cured.  Seems strong enough - as it survived the impact which caused the slight tissue damage to the wing - mentioned in my first post.

I must confess that I am not very 'aerodynamically minded'.  The distance between the trailing edge of an aircraft's wing and the leading edge of it's tailplane (aka 'horizontal stabiliser') is known as its 'moment arm', I think.  Moving the position of a wing, in order to achieve a design CG, could be lengthening (or shortening) the moment arm.  I've tried (internet) searching - but all the results that I've found relate to muscles and joints!!

Anybody care to enlighten me, please, as to what effect change of length of moment arm/moment arm length, has on the flight characteristics of a model aircraft?   Thanks very much, in advance.

Cheers,

Jez Wilkins

             

             

[Slowmatch]

Anybody care to enlighten me, please, as to what effect change of length of moment arm/moment arm length, has on the flight characteristics of a model aircraft?   Thanks very much, in advance.

Hi Jez, hope you are well.

Strictly speaking the tail moment arm (known as 'ℓh' or 'lh' for 'length to horizontal') is measured from the CG to 25% of the tail chord.

The tail moment arm is the length of the lever at which the tail creates lift in order to provide a stabilizing force. Reducing the lever length means slightly less stability. You might need a hair more decalage for the same balanced trim and the CG might need to move a % or two forward on the wing chord. Dynamic stability - the ability to damp out oscillations in pitch over time - will be reduced a little too.

Increasing the length of the nose will slightly increase the inertia of the model in pitch, which also harms dynamic damping a little.

However, with a small change in moment arm these effects will be very minimal - and on a power duration model you already have excellent stability from a long tail arm, large tailplane and short nose. In other words: while the effects I mention are present, they will hardly be noticeable. If the model design was already close to the limit (eg a scale model with a short and small tail) then shortening the tail might be more significant. But your model has a large margin of safety in this kind of stability so it's not likely to be an issue.


Jon

[Starduster]

 The distance between the trailing edge of an aircraft's wing and the leading edge of it's tailplane (aka 'horizontal stabiliser') is known as its 'moment arm',
             

Well, sort of...

In a full size airplane, the designer will specify a fixed point on the aircraft. This point can be rather arbitrary, and indeed can be forward of the nose of the airplane. This point (known as the Datum or Datum Line) is used to determine the center of gravity of the airplane when  loaded.

You may ask, "why not just place the datum at the center of gravity?". The reason is that the CG can move depending on where the load is located. The CG in a full size airplane is a range. That is, the aircraft must be loaded so that when the aircraft is fully loaded for flight, the resulting CG must be between the forward and aft limits of that range. This CG envelope is different for each type of airplane. Airliners, for example have a much wider CG range than, say a single-engine light airplane.

To your question: "What is a moment arm?" It is actually two different things, "moment" and "arm". Though in most operators handbooks, there are charts that you can use to determine the CG of an airplane, I always preferred to use the equation - Weight X Arm = Moment. For example, if I have a bag that weighs 75 lbs, and, according to the handbook, the rear cargo area is at 275 inches (arm) 75 X 275 = 20,265. I calculate the moment for each load (fuel, passengers, etc.) to get total moment for the flight, then I take the total weight and divide by the total moment to get the resultant arm ( Moment / Total Weight = Arm). This resultant Arm must fall within the CG range set by the manufacturer.

Check this out for a better explanation:

https://www.faa.gov/sites/faa.gov/files/12_phak_ch10.pdf

How does this relate to a model airplane? It's actually simpler, as we do not (typically) define a CG as a "range" or "envelope", so we can just use the desired location of the CG as the Datum. We use some method to determine (hanging by a string, using our finger tips under the wing, etc) whether or not the airplane is balanced at the desired CG. If it is not, we have to do something to solve this. On a small, light airplane, a simple lump of clay on the nose (or tail) may do the job. On larger airplanes, some lead may be needed.

The distance between where the weight is being added and the desired CG is the "arm". As you can surmise, the further the distance, the larger the moment, and, hence the larger the effect on the CG.

Another option is to lengthen (or shorten) the arm. This is why, typically, power models have their fin aft of the stab and rubber ships forward of the stab. Besides an aft fin has more effect than a forward one, in the old days, power ships tended to be nose heavy, so they could afford to lengthen the tail.

In my case, I've converted quite a few power ships to electric, and I struggle with the CG. I always have trouble getting enough weight on the nose. I could just simply lengthen the nose, but that would affect the moments of the design. I usually add weight to the nose to compensate. But that's a design choice I made.

Clear as mud?

[vintagemike]

I must have been really lucky when I built mine, I found an R/C moulded engine mount for the front end, the Merlin fitted perfectly! and I could shim the mount to fuselage joint if it needed any thrust adjustments. It didnt, just flew straight away

[Jez Wilkins]

Hi Slowmatch/Jon and Starduster.

I'm good Jon and thanks very much for asking.  I trust that you are, also?  With a bit of luck, we will meet up again at Buckminster on a 'Free Flight Priority Monday' - once the weather improves a bit!!

Thanks to you both for taking the time and trouble to post your explanations of 'moment arm'.  It was 'as clear as mud' - now it's 'as clear as crystal'!!  

I must have been really lucky when I built mine, I found an R/C moulded engine mount for the front end, the Merlin fitted perfectly! and I could shim the mount to fuselage joint if it needed any thrust adjustments. It didnt, just flew straight away

Hi vintagemike and thanks for your further post.  I at first thought that I was going to be O.K., so far as engine mounting was concerned, using one of the SLEC 0.049 cubic inch mounts ('screenshot' attached). I already had (more than) one of these 'in stock' - must have been impulse buys at the Nats., or similar, at some points in the past .  However, when I tried a Cox Tee Dee 0.051 cubic inch motor in one, it was clear that the gap between the bearers was too narrow for the width of the crankcase (it splayed the ends of the bearers, when the engine mounting lugs were seated flush on the top face of the bearers).  It could have been made to fit, by shaving material off of the bearers (I forget exactly what now, but maybe a 'triangle', from the top inside corners).  I was, however, not happy about doing this - so went with the beech bearer alternative - which has worked well, I think.

Cheers,

Jez Wilkins  

[ffkiwi]

Jez-the SLEC 049 mount is ridiculously small for the engine size it is supposed to take-ie 049....I have a couple and they're an excellent fit for my DC Bambi 0.15cc! You might squeeze a Frog 50 into one as well -with a bit of a stretch!   There ARE good mounts available for the TD 049/051 and the Dave Brown ones even distinguish between 049s and the slightly larger 061s...ie they do an 04-05 version, and an 05-06 version of what is essentially the same mount-the difference being about 1/16" more gap between the arms on the 05-06 one...to suit Norvels and the like which tended to have slightly wider crankcases than the Coxes....even if the mounting hole pattern was identical.

 There is no real drama about filing the top inner edges of the beams of such mounts to ensure a good fit-I was contemplating this exact thing yesterday when pondering over a mount to fit the Russian OTM Striz 1.5 diesel....which an earlier moment of curiousity had prompted me to weigh....a surprising 75g...lighter even than the Allbon Javelin-generally considered to be the lightest 1.5 diesel- and that makes the Striz the lightest 1.5 plain bearing diesel i've ever encountered....and that in turn opens up some interesting possibilities for Kiwi power-a class where power to weight is usually more important than absolute power. A glow 09 mount is a bit narrow, and a 15 a bit wide, but the 09 can be filed along the top of the beam inner edges for clearance...

 As vintage Mike notes-with these radial mounts, thrustline adjustments are easy-if required, and the other advantage-in light of our earlier discussions is-if needs be-in terms of nose weight-you can simply slap on another firewall-either 1/8" 3/16" or 1/4" ply should you need to move the balance point forward. I use this method quite a lot-sometimes deliberately if planning to try the model on more than one engine-and it is rare to find two different brand engines of the same size weighing even close to the same weight-or in some cases, where I have no choice, as the model has come out tail heavy on completion.

 ChrisM
 'ffkiwi'

[Jez Wilkins]

Hi again ChrisM/'ffkiwi'.

Thanks again for the further post and information.

DC Bambis are really cute, aren't they?  Never owned one - having given it some thought, I cannot remember having seen one for sale at any of the swapmeets that I've been to, for quite a while.  The price tag on any that I have seen in the past has always put them out of the depth of my pockets!!

Thanks for the advice about 'shaving' the top inner edges of such mounts.  I would be more inclined to do so, in the future - for the advantages of ease of thrustline and CG adjustment that you and vintagemike have mentioned.

The Dave Brown mounts are a new name to me.  I did a quick internet search for them, before doing this reply and, unfortunately, there does not seem to be much U.K. supply.  Sometimes, with small light items, such as this - the postal rates in the U.K. these days are more than the item itself!!  I also found a couple of 'hits' on eBay - but in the U.S.A..  The postal rates shown there, to the U.K., really are eye watering!! Anyway, it's a name to look out for in the 'rummage boxes' at swapmeets.

Thanks, once again, for the assistance.

Cheers,

Jez Wilkins

[ffkiwi]

Jez-the Bambis are cute eye candy-but not terribly practical-I have two of the originals and they are little horrors to actually start-you have to belt the prop in 'team race pit stop fashion'-and that's just on the bench! On an engine of 0.15cc that's a fraught experience-and I would not dream of trying it in a model. The Dave Banks VA Bambi replica sold in the late 90s and early 00s is a different kettle of fish-being quite well made and having quite nice handling-I had two but lost one on the highway when a roof box lid blew open.  Sadly you have to grab these sort of things as and when you can-whether an original-or a replica-the originals were largely a vanity exercise for Davies Charlton-giving them bragging rights 'worlds smallest' etc-right up till when the Cox TD010 appeared in 1961....at which point it became hair splitting time-0.15cc vs 0.16cc?  'actual displacement vs physical size?'............and coincidentally DC stopped making them then (1961)-but after 7 years (1954-61) you'd expect to find a few of them lying around-unless actual production was merely a handful a month....which could well be the actual case. The VA's of course were a limited run of replicas so probably only a few hundred were produced.   

The take home lesson being if something like this hits the market and lights your fire-then grab it while you have the chance-as will near certainty they won't be around long. it certainly lit my fire-and as a result I have a fairly enviable collection of micro diesels-admittedly acquired over a lifetime of effort. not all is gold that glistens of course-the Clan .24s and .48s, and the AE .1s and .2s are not viewed with much affection by those who've tried to use them....and even the VA .25 and .4 Mills replicas have a chequered reputation-especially the 0.25cc model

The other lesson is that these micros are not for the occasional dilettante-you have to know what you're doing, treat them gently, and learn their individual foibles-and at that size they seem to have individual personalities when it comes to starting and handling.....a lesson first learned in the early 1950s when the .5 diesels first appeared in quantity-and even more relevant when you drop down in size...

Right enough of that-returning to mounts-I don't have any great favoritism when it comes to commercial mounts-I'll use what I can find-which in practice may be SLEC (not imported to NZ  AFAIK-but I've picked the odd one up on trips to the UK), Dave Brown, BDL (a NZ brand when they were around) etc-mounts are things I tend to keep a box of assorted sizes, and add to when sales occur or you pick some up at a club auction)-another brand I find quite useful is Ernst-they do an adjustable mount in several sizes-.10, .20, .40-where the two halves slide into one another, locked by a grub screw, and you can adjust the width between the beams over a degree of adjustment-these can be quite useful in the event of 'musical chairs engines'-if you get my drift.  In theory I suppose they might be slightly less rigid than a 'solid' mount-but I've never heard any negative comments-they are well engineered. Ernst also produce 'thrust wedges'-in 1, 2, 3 and 4-degree sizes-which can fit behind the mount to add sidethrust or downthrust as required-though most of us make do with washers or thin ply to do the job.

In your shoes I'd simply do a search for 'r/c engine mounts' on the websites of various UK model shops-and see what turns up-I'd expect plenty of .20-.60-.90 sizes to show up, with fewer options in the .049-.09-.15 size range.....and the reality is, the brand doesn't matter-about the only variation betwwen brands (ignoring colour) is that some have a square fuselage mounting, some a hexagonal, but most are round.

 ChrisM
 'ffkiwi'

PS Tatone, Taibi, Cox and Mccoy also used to make tank mounts for engines-in the case of Tatone in several sizes from 049 right up to .29/35; whilst Taibi did an 049, 09 sized one and Cox and Mccoy one for their respective beam mount 049s. I would expect these to be fairly thin on the ground in the UK-they're not that common even on ebay...

PPS current Bambi project attached...a Vic Smeed 'Tom Thumb'

[Jez Wilkins]

Hi again ChrisM/ffkiwi.

Thanks very much for the further comprehensive and informative post.

As you state, a 'team race pit stop' type 'belt' on a 0.15cc motor is not good.  Unless you have a very accurate finger to 'belt' with, bent spraybars/needle valves are sure to result!!

I looked for details of production numbers for the 'Bambi' - but didn't find anything on this - although I did find more general information here https://modelenginenews.org/cardfile/bambi.html. You are probably there, or thereabouts, with the production run size for the VA Bambi replica.

The 'Tom Thumb' and Bambi look very cute.

The smallest diesel that I've owned is the AE 0.2cc.  I do not need experience of the handling characteristics of any more than this one engine to agree with you that they can be 'temperamental wee beasties'!!

I do know somebody who had a running 'Clan' (I forget whether it was a .24 or a .48) - but only after it had been 'looked at' by someone who was a control line team race engine 'guru'!!

To be fair - I've not forgotten an engineer who posted (maybe on the Barton site) that the tolerances to which model aircraft engines have to be manufactured are much closer than a full size car engine.  When you consider the machine tools with which some of the early 'post World War II' model engines were constructed, then it is maybe a surprise that any of them ran at all!!  

I take your point about 'buy it while you can' - but all my aeromodelling has to be undertaken on quite a strict budget.  So, if it's there and I don't have the money in my pocket to pay for it - then it stays where it is - and I don't lose any sleep over it!!

Thanks very much for the information on the BDL and Ernst mounts, the Ernst thrust wedges and the Taibi, Cox and McCoy tank mounts.  All things that I will look out for on eBay and at swapmeets and shows.  Regarding swapmeets - these seem to me to be a lot thinner on the ground these days than they were.  Back in the day, quite a few of the local clubs had a swapmeet during the autumn/winter 'off peak' seasons.  Now the only ones anything like local to me are the three (April, June and October) that are held at the British Model Flying Association's [BMFA's] National Flying Centre at Buckminster - an around 1.25 hours trip, each way, for me.  Maybe a number of factors at play here - COVID-19, eBay, room hire costs, catering costs, lack of a club member willing to put their head above the parapet to organise one?

Cheers,

Jez Wilkins