Another Parnall Elf

[Greyhead]

Techydave

I agree it looks as if it’s got nice proportions for a RC model. I was interested to see the photo of the floatplane; our flying site at Redmarshall is in a dip and is prone to flooding so that conversion might come in handy!!

Grahame

[Guest]

A very useful site. Pity other manufacturers didnt have something similar for modellers. See Dave Platt`s "Kingfisher" magnum opus in this month`s RCMW (Jan 05).

[Greyhead]

It has been pointed out to me that the method of building the wings is not very clear. This from my brother who has seen the finished article so I’m surprised nobody else has commented! Having gone through the thought processes to devise the method it seems fairly straightforward to me but hopefully this will clarify things a bit.


TYPICAL WING SECTION





Remove shaded section from ribs and make additional sections for “riblets”. Stack together and drill 1mm hole in approx. the marked position.


Make the balsa web by gluing together strips cut from sheet balsa (approx. 2” x the width of the sheet).


The assembly sequence is:


1. Thread ribs onto rear spar, pin into position over plan and glue.


2. Glue 1/8" x1/4” spruce spar in position.


3. Glue 1/16” balsa web in position, NB grain direction from LE to spar.


4. Glue 1/4" x1/4” spruce spar in position.


5. Thread removed rib sections and any “riblets” onto a length of button thread to form a “necklace”.


6. Glue rib sections and “riblets” in position.


7. Glue upper and lower LE sections in position.


8. When dry fix one end of thread to a solid point, tension the thread and fix the other end.


9. Soak the thread with thin Cyano.

[Greyhead]

I got talking to another modeller recently about the pros and cons of adjustable tail incidence, basically is it worth the trouble? Here are my thoughts on the matter and a couple of photos to prove the point.


If the mechanism is “out in the open”, as is the case with the Elf, then I’d say as it needs to be modelled for scale authenticity the small amount of extra work involved in making it operational is well worth it. If it is hidden and you’re not worried about perhaps having a fair amount of elevator trim on show why bother?


The full size is adjustable in flight but I thought that was a step too far!





The tail is mounted on brackets made from thin steel and attached via ball joints to allow for the fact that the brackets are fitted to the tapering fuselage sides.


The adjuster consists of a 2mm rod threaded at both ends with a nut soldered at one end. The rear of the fuselage has a dowel, with a length of snake inner down the centre, into which the adjuster is screwed in or out to alter the tail incidence. A lock nut goes the other side of the rear tail brace to keep things solid.


The braces are attached to the tail and fuselage by steel brackets again using closed loop adaptors and 14BA nuts and bolts. There is very little movement at the fixing points as the tail incidence is altered and the bolts don’t need to be slackened.





In this shot you get a good view of the tailskid, moulded using epoxy and carbon fibre and the elevator operating arm. The closed loop for the rudder goes in the space between the fuselage and the tail plane. EDIT can't find the photo but this shows the brace from tail to fin which is virtually the same.

[wonwinglo]

Grahame,now this idea I really like and approve of,it has always been my contention that more models fly badly due to incorrect tail incidence,the problem is as we all know that fixing the tailplane is very much an hit and miss affair,a few thou can make such a very big difference to the trim of the model in flight and more often than not we continue to fly our models out of longitudinal aerodynamic balance,by incorporating such a feature as you have here the aircraft can be made to perform to its peak in terms of aerodynamic efficency.Incidently the late Howard Boys once wrote that it was very doubtful if any model had its tailplane set correctly on its very first flight ! so who are we to argue this very valid point froma true pioneer of scale model aircraft.

Incidently in flight tailplane trim would not be impossible to achieve just as the full sized counterpart.

[Greyhead]

Further to the adjustable tail incidence (post No. 79 above). Having had a few sessions with the Acrowot to get my thumbs up to speed again after the winter recess, I got the Elf out for it’s pre-flight checks.

Of course the Laser fired up “first flick” and ran faultlessly but when I checked the nut on the tail incidence adjuster it stripped the thread with only slight torque on the spanner. It was actually the rod that had stripped; it was one of the 2mm rods from the model shop with a thread at one end. I needed a short rod; about 50mm long, with a thread at both ends so I’d tapped the extra thread. When I investigated the problem I found that the rod as supplied has a “rolled” 2mm thread but the rod itself is only 1.7mm diameter. All had seemed OK when it was made but obviously with vibration from the engine and the load when elevator is used, the undersized thread wasn’t good enough for the job.

At least I found the problem before anything disastrous happened and it re-enforces the need for regular checks and especially before the first outing of the season.

[wonwinglo]

Further to the adjustable tail incidence (post No. 79 above). Having had a few sessions with the Acrowot to get my thumbs up to speed again after the winter recess, I got the Elf out for it’s pre-flight checks.Of course the Laser fired up “first flick” and ran faultlessly but when I checked the nut on the tail incidence adjuster it stripped the thread with only slight torque on the spanner. It was actually the rod that had stripped; it was one of the 2mm rods from the model shop with a thread at one end. I needed a short rod; about 50mm long, with a thread at both ends so I’d tapped the extra thread. When I investigated the problem I found that the rod as supplied has a “rolled” 2mm thread but the rod itself is only 1.7mm diameter. All had seemed OK when it was made but obviously with vibration from the engine and the load when elevator is used, the undersized thread wasn’t good enough for the job.

At least I found the problem before anything disastrous happened and it re-enforces the need for regular checks and especially before the first outing of the season.

*** Grahame,you were indeed very lucky to have spotted this failure,once I was doing a pre-flight on my old Leopard Moth and found a broken aileron horn hidden underneath the wing,it just goes to show that check,check & double check especially after a period of lay up where hangar rash can set in.Anything to do with flying controls is prone to fail,in full size practise anything like this gets two inspections,by two different people ! I know that this is not practicle in our case but there is certainly a lesson learned here.Never take anything for granted,it cost you a model at the least.

[Glider Guider]

Anyone who reads RC Model World will get a case of Deja Vu when they arrive a page 102 and see a four page spread featuring the construction of Grahame's Parnall Elf. It's looks as good in print as it does on screen.

[Greyhead]

Techydave

Glad you enjoyed the write-up; the original copy sent to RCMW included “ For a more in-depth review see www.scale-models.co.uk/showthread.phpt=708” but unfortunately the editor removed the address from the article before publication.

I think this is a great pity, as anyone who found the article of interest would surely find the thread even more interesting and informative!

Grahame

[wonwinglo]

TechydaveGlad you enjoyed the write-up; the original copy sent to RCMW included “ For a more in-depth review see www.scale-models.co.uk/showthread.phpt=708” but unfortunately the editor removed the address from the article before publication.

I think this is a great pity, as anyone who found the article of interest would surely find the thread even more interesting and informative!

Grahame

*** I wonder why he removed the address Grahame ? unless he considers Scale-models a threat to RCME & E,I find that a bit odd.

[Greyhead]

Barry

I have no idea unless there is some sort of copywrite on the address, but if so you would have thought that they could have contacted John to OK it, as you say, very strange!

Grahame

[Greyhead]

Well it’s took some time but at last I managed to get myself, photographer and weather all to co-operate so here are 3 flying shots. Hope you think it’s been worth the wait!


Take off





Banking right





On finals





This is what it’s all about, a scale model flown in a scale manner.


There won’t be anymore flying (with the Elf) for a while, but that’s for the another post!

[John]

Good to see al lthe hard work paid off Grahame, very impressive :respect1:

[Guest]

looks real !

just sums hope the whole project greyhead, well done . she looks stunning in the air.

[wonwinglo]

Grahame,superb and exactly how a scale model should be flown,keep the wild aerobatics for the pattern ships,I know which type of flying that I would rather do ! scale circuits beautifully judged,touch & goes just like they do in full size practise,just looking at a model like the Parnall Elf in the air gives me a buzz,brilliant.