The Postal will be to SAM 35 V20 Rules

2 rounds April 1^st – June 30^th and July 1^st – Sept 30^th.  

TOTF (Total of 3 Flights) to a 60 max with a fly-off if required. All times in each round to be set on the same day. If you achieve 3 maxes then do a fourth fly-off time.  Send your times, details of your model, timer, when and where set to webmaster@oxfordmfc.bmfa.uk

Round 1  April 1st – June 30th

Name	Model	Timer	Flight 1	Flight 2	Flight 3	Total	Location	Date	F/O
Andrew Longhurst	The Trim	J Paton	60 max	60 max	60 max	180	Port Meadow	17/4	1m 55

 

 V20 by Andrew Longhurst 

A couple of years ago I received a call from Tony Rushby, doyen of small model flying. He wanted to discuss a new competition class that SAM 35 would promote. The intention was to have a class which probably won’t outfly a small field or our capability of retrieving it a few times in an hour or two: Rules are: 

• 20ins max span (measured tip to tip on model) 
• Design published or kitted pre1951 
• Rubber power only – as much as you want 
• 7.25ins max prop diameter (180mm) freewheel or folder (need not be as per plan) 
• ROG Capable, so must have an undercart although ROG will not be used 
• Max to be 60 seconds or as per decision of the organiser 

I felt a bit dubious about allowing folding props and the apparently strange maximum diameter of 7.25ins, but Tony wouldn’t budge. 

Props 

If you think 7.25 is a strange diameter for the prop, this is the size of the excellent 1952 KK plastic prop which being indestructible, if rather heavy, are still to be found in dusty cupboards nationwide. New 7 and 8ins ultra-light plastic pops are available from the Vintage Model Co. and elsewhere. You can cut an 8ins prop down, which is what I recommend as this has the effect of increasing the pitch slightly. You can resist the temptation to carve your own balsa prop because at this size it won’t be much better than a plastic one. Folding props offer an advantage but only if two bladed so it’s a right fiddle at this size. Perhaps we can agree not to go there? 

A cut down 8ins prop with Duck tape on left blade to restore balance.

The noseblock with reverse “S” hook (you can use a semi-circle instead) and front end bending to provide the drive right-angle and winding loop in one. The shaft is 1mm spring steel wire running in bearings made from Albion Metals brass tube reference MB MBT13 obtainable from Macc Models. Standard ramp freewheel used. 

What model to build? Basically, it’s what you fancy. See my list of 28 with small scale plans in my Google album via this link: https://photos.app.goo.gl/Nz6gZ7Fgse4RoMti9 

Sixteen of them are full-size on Outerzone for free download. Print them in the free version of Adobe Acrobat using the “Poster” option and join up the A4 sheets with Prit Stick. 

If you want a kit, Rudolf Hiesbok In Czechoslovakia sells the Sparrow which is a replica of a 1940s USA design called the High Performance Sportster. It’s a world-renowned fine flyer and the original title is no misnomer. You will need to add a peg leg undercart to comply with the rules. £23 + Postage from www.Hiesbok.CZ. I have checked with Rudolph who commands good English and he can supply to the UK. I built and reviewed this kit in 2022 and it was of excellent quality. Copies of my review are available from me. 

Or there is a KK Playboy from the Vintage Model Company, but it’s a bit difficult and I think best avoided. At the time it was created there was pressure on workaholic Bill Dean and he just drew up a half size Gypsy Wake being the model he was then using in competitions. Consequently, the aspect ratio is too high. Furthermore, Bill forgot the underfin and it needs one (according to Tony Rushby). I got mine to climb all right, but it won’t glide worth a darn. 

Anyway, you don’t really need a kit for such a small model as it’s only a few sticks, a plastic prop and a dozen ribs. A spar tractor (stick) model is actually more difficult than a conventional model in the long run, so I haven’t put any in the Google Album (Hanger Rat etc.). But remember, the 21ins Cloud Tramp is probably too big unless you have built in a lot of dihedral. There is always the nearly all-balsa Veron Skylark which can give a good account of itself. 

I am told members are likely to prefer cabin models and there are three that I have built and are terrific, that is, the Wasp III, the Veron Snipe and the Skyleada Swallow. 

As always, weight is very important and your target for these three would be under 30g without rubber. The Snipe is always going to be the lightest and therefore the highest climber. 

If you have never built a stick and tissue rubber job before or can’t remember the details, there are several videos on YouTube. For instance; “TFFC: Flying Ace Moth, Tucson Free Flight Club” 

Motors 

The basic rule is that the length of the motor should not be greater than 1.5 x the distance between front and rear rubber hooks. You will probably use 4 strands of 1/8 SuperSport. If you start with 6g it should take 1100 turns. You can work out the turns per inch from this if you want a longer motor, but longer motors will knot and bunch. When winding, stretch to about three or four times the motor length and put on half turns then move slowly in toward the model whilst winding so that you arrive at the model at the max turns you have decided upon. If you end winding still some distance from the model and then march in without winding, the motor will bunch. There is a bit of an art to it. Apologies if you know this already. 

CG Position, Decalage and Thrust Line 

Before you take the model out to fly, make sure you have 4 degrees negative incidence between wing and tail. It’s not important to which surface this is applied. The CG is often not shown on vintage plans, but CG at 50% chord usually works. With a tapered wing, balance it at mid span. These models fly right on power and glide, so you should also check you have a modest amount of down and right thrust sanded into the nose. If you do these three things 

and the wing and tail are warp free, nine times out of ten it will fly out of your hand. A tiny amount of left rolling wing warp can be helpful but the opposite is doom! I find that time spent in fettling is rarely wasted. 

To DT or not to DT 

The great advantage of having a DT may not be what you think. It just makes trimming so much faster especially when you have got it gliding and are trying fine tune the thrust line, which I do with .5mm ply shims. My Snipe has a great climb but the glide is fairly steep and although I fitted a DT and set it, I didn’t really think it needed it. But one flight it found some good air and made a bid for freedom in the direction of the boat racks, but the wing pop up DT got it back…just. 

The advantage of not having a Tomy or Band Burner DT is it saves 3+grams, something like 10% and performance will be positively affected in much the same proportion. A viscous timer is much lighter but not very accurate. 

The DT action will involve the wing LE rising to about 40 degrees or the wing TE rising to about 20 degrees. Leave the tailplane alone. If the fin is mounted on it, make sure its keyed in so it can’t move. They are extremely sensitive to rudder adjustments so use half inch pieces of 1/16 square strip on the extreme TE of the fin. Use balsa cement rather than cyano as its easier to reverse. 

If anyone reading this has virgin Tomy motors stored somewhere, get them to me for conversion to single function timers. This service is free. If you don’t want them, still send them so I can distribute to others. 

Stooges 

Most rubber flyers possess a stooge to hold the model whilst winding but they can be ultra simple for such small models. I like this one, but it should be much smaller than shown, say about 2/3rds and the mounting board angled upwards. 

There is another one on: www.endlesslift.com/make-a-simple-foot-stooge. 

I can supply building and trimming notes for almost all of the red and white models displayed on the Google album. Plans on Outerzone are noted on the spreadsheet. For plans of other models contact me. 

E mail andrewlonghurst@yahoo.com 

Collated SAM 35 V20 Rules – Andy Blackburn 

SAM 35 V20 Rules (Vintage, 20”) 

A duration contest for rubber powered Vintage models. With acknowledgements to Andrew Longhurst and Tony Rushby. 

Models: Rubber powered designs kitted or published pre 1951 whose original span was 20” or under (ie, no scaling up or down.) Models must be RoG capable, so undercarriage must be fitted or added. Stick fuselages are permitted. Any quantity of rubber may be used. Prop must be 7 1/2” span or less, freewheeler or folder. 

Contests: Max to be arranged on the day, but not exceeding 60 seconds. Three flights, followed by unlimited flyoff if necessary. 

Awards: Variable, but minimum would be Certificates for top three (obvs, in our case we will award comestibles). 

 

(NOTE: The following is only relevant if you also want to enter SAM 35 V20 competitions with the same model – we’re not going to ban the model if you’ve added or moved a few spars or added a big trim tab, for example, but SAM 35 might take a stricter view). 

The way that SAM 35 do rules is that they have “general Rules”, “Free Flight Competition Rules” and then the rules for the particular class (in this case V20). This can make it quite difficult to work out what you can and can’t do unless you pay close attention. 

The following collated set of rules are an amalgam of the relevant section of the various rules outlined above. 

Construction 

Models should follow the construction shown on the plan. No major alteration should be made to structures. Minor modifications may be made as follows: 

1. Materials may be substituted for similar materials, e.g. spruce for obechi. Balsa laminated sections may replace bent cane. 
2. Conversion from a one piece to a multi piece wing, multi piece fuselage or detachable fin and vice-versa are permissible but associated changes must not significantly change the external geometry of the model. 
3. Plywood dihedral braces and local bandaging are permissible. 
4. Local sheeting to improve handling of a fuselage is allowed and also local sheeting and/or sub-spars on flying surfaces to take the strain of fixing bands and wing to fuselage contact. However it is emphasized that this is to provide LOCAL strengthening and does not extend to fully sheeting a fuselage or flying surface that was designed as a tissue covered open structure. 
5. Minor alterations may be made to enable a D/T to be fitted to a design which was not originally so fitted. 
6. Wheels must be of the same diameter as shown on the plan but the cross section may be changed. 
7. Rubber model propellor diameter sizes must be adhered to, as must the type; single-bladed or twin-bladed; free-wheeling or folding. Free wheel clutches, rubber hooks and tensioning devices may be to the competitor’s choice. The rear rubber anchorage may be moved forward slightly to assist practicality. 
8. Turbulators may be added to any component of the model provided that the type of turbulator used has been described in a publication dated prior to 1st January 1951 for vintage models, or prior to 1st January 1961 for Classic models. 
9. It should be noted that there is no restriction on the type of covering material that may be used, 
10. (but not transparent, and with no “violent colours”). However the substitution of recognised covering materials with wooden paneling in not acceptable except as described in paragraph d. above. 
11. Where plans fail to provide minor details of construction or design, then reasonable assumptions may be made consistent with the period and type of the design. For the purpose of these rules, minor details may include areas such as bracing and reinforcement of joints, but do not cover estimates of details which may affect flying characteristics such as wing profile or fin shape. 
12. Rubber model propellor diameter sizes must be adhered to, as must the type; single-bladed or twin-bladed; free-wheeling or folding