Flitzer Sport Flying Association

Flitzer Goblin

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for Robert Nillson's spectacular model Goblin images.

August 17, 2003 Update:

The #1 UK Goblin is taking shape on my bench at present. I have heard that Willy Gruhier in Paris is just as enthusiastic as ever for the Goblin he commenced last Christmas holiday, but has been extremely busy as chief instructor with the Marcel Dassault Company flying club, and has not found time to work on it for several months. Gary Steadman supplied all the metal work for his project, which uses almost 100% of the Z-21 metal parts. With luck I should catch up with Willy in terms of his progress in about six weeks, assuming he is still busy elsewhere, and if I can concentrate the number of hours on the project that I'd like to.

The RHS fuselage frame is on the bench awaiting the cluster-blocks at the longeron/upright interfaces, and the firewall jig is complete as are most of the rudder parts, carry-through members, etc.

I'll keep you posted.

Best wishes,

Lynn

Goblin Stability

From a May 28, 2003 post to the Flitzer-Builders group:

Hi Darren,

You've raised some very good questions which I'm happy to answer, as follows:

> Greetings group,
>
> While evaluating the Flitzer line, I've become interested in the
> Goblin. While appearing to have
> been simplified in design, ie., lack of motor mount and an all flying
> rudder, I was wondering how
> the shorter length and the lack of a fixed vertical stabilizer will
> affect its stability relative to the
> Z-21.

It's very early days yet for the Goblin, with the only fuselage currently nearing completion (sadly the prototype's rudder was stolen recently from a communal workshop).

In the past I have built small-scale stability models (as small as 1/12 scale) which have proven the basic stability of the design to my satisfaction, with, in the case of the Z-1 (basically a Z-21 with the 'small' horizontal tail), R/C models of 1/5, 1/4, and 1/3 scale having been built (subsequently) which have enabled spin characteristics of the full size to be evaluated, the models being close dynamic models of the real thing. All these machines mimicked the characteristics of the full size aeroplane as closely as possible.

It does not follow that an unstable model, especially to very small scale, would prove that a full size aeroplane which was based on it would also be unstable; but the reverse seems to be true.

The increased tailplane area (6%) on the 'plans' machine was incuded to satisfy a test pilot comment that he felt that the aeroplane might be 'elevator limited' when flown by a lightweight pilot with full fuel. I disagreed with this, and was able to prove that a light pilot could flare the a/c with full fuel at close to Vs.

However, certification was not forthcoming until the tailplane was re-rigged at a large negative angle, which would have ruined the hands-off cruising capabilty (add a trimmer!), or reduced Vc to below 60 mph., or whatever. Stalemate was avoided when I modified another 64" tailplane into a 69" facsimile of a deeper (projected) tailplane, which reduced the 'trimmed' approach by 5 mph, to 55 mph. without any adverse effects on the handling. The deeper (stronger) tailplane is now shown on the plans, and only this tailplane (still rigged at zero) is approved for the design, now identified as a Z-21, and the aeroplane exhibits the same hands-off stability as the prototype at Vc, with the elevator 'in trail'.

>Is the wing area the same as the Z-21?

No. The wing area of the Z-21 is 97'sq. gross. The wing area of the Z-1 Type K is about 90'sq. gross (ie, calculated thro' the bottom of the fuselage 'carry-thro'). However, the bottom wing is only 30" chord, and the stagger is less than on the Z-21. Despite the apparently 'short-coupled look' in side-elevation, the tail arm is quite normal, and this is assisted by the slightly higher aspect ratio of the horizontal tail, which, at 72", is of greater span than the 64" of the Z-1 prototype, and the 69" of the Z-21. The tailplane chord of the Goblin is only 12", with a 13" elevator chord (these measure 16" each on the Z-21), tailplane being a ply-covered stressed-skin, semi-cantilever unit on the Goblin, strut-braced from below, on the rear spar. Although these chords sound frighteningly short on the Goblin, in context they appear quite normal, the horizontal tail area of the Goblin having only 49" sq. less area than that of the Z-1, (which is only 7" x 7", ie. not much different!). This matches the wing area reduction perfectly for the tail arm provided, all on a basic fuselage length of 9'9" (ie. 13' total length with engine and rudder attached).

>In essence, what I'm asking is the Goblin is identified as a sport plane, but will this mean it will also be more
> of a handful than the Z-21 or is it a more basic version with similar stability?

It will most probably present a greater challenge to the pilot than the basic Z-21, simply because it will have less inertia, and being so small, everything will happen relatively quicker. However, the wing loading of all the Flitzers is in the region of 7-7.5 lbs.'sq., so that the general handling will be similar, ie. light: light on the controls, with slow, safe landing speeds and powerful controls, right down to the stall, and in some cases, below it. However, if it gets out of line, it will do so more rapidly, but equally, it should be possible to regain control just as rapidly. There is no such thing as a toy aeroplane, and those types which have had their teeth drawn, have bland characteristics, and no joy in their mastery. I expect that there will be elements in the Goblin that may justify its name, and such quirks will, I trust, be considered part of its character, but that should make the aeroplane more worthwhile to master and to respect. I would not consider ussuing drawings for a dangerous machine, and the prototype will have to demonstrate acceptable stability and excellent controllability before it is provided in plan and kit form.

The all-flying rudder is a very ancient element with a great aviation pedigree, but I will not pretend that it entirely embodies the stabilising features of both fin and rudder. However, the short noses, and the slab-sided fuselages of all the Flitzers endow the designs with a natural fin-effect, none more-so than with the Goblin, with its deep profile. The Z-1/Z-21 needs hardly any rudder to balance a turn, and there is a natural directional stability provided partly by the fuselage that could almost be said to match the incredible hands-off pitch stability at Vc. I have flown hundreds of hours in Jodels, all of which had all-flying rudders, and there was never a hint of instability; and all exhibited excellent spinning characteristics and good recovery.

>What is its mission statement?

The Goblin is the smallest practicable biplane based on the Flitzer series, to share the same wing loading, and potentially (with the 80 hp. Aero-Vee motor) to dramatically out-perform the standard 1834cc VW-powered Z-21, being a minimalist (minimum-retro) design in the genre, having, in its basic version, no engine mount, no door, no fin, no trim, no brakes - in fact there is nothing else that can be left out, since everything else is absolutely vital! It is fabric-covered aft of the seat, and should be some 30 lbs. lighter than its bigger brothers, largely due to the use of Okoume ply in its construction.

Originally the very first Flitzer, the Z-1, was to have been a 15-20% smaller aeroplane, but is was 'softened up' for a more 'general pilot' capability. Initial hops proved that the aeroplane was a real pussycat, and I determined to re-establish the original minimum concept design, which first emerged as the Z-1 Type S Stummelflitzer (clipped Flitzer), but tis design was sidetracked into becoming a full-on aerobatic aeroplane, so the wings were enlarged again, fitted with deeper spars, four ailerons, balanced controls, and then the aeroplane was revised to accommodate longer installed engine dimensions, and finally ended up with a longer chord, re-profiled fin/rudder, with virtually the same dimensions as the Z-21, the 'series' designation of the basic Z-1, fitted with the slightly bigger (and deeper sectioned) tailplane.

A much simplified attempt at reviving the minimum concept emerged as the Z-1 Type M Meteor (racer), with a fabric-covered rear fuselage, the original tailplane area (but with a deeper section) and smaller all-round dimensions (span 17', length 14' 2" approx.). This was partly built by a colleague, but then sold on, unfinished.

The final evolution in this process is the Flitzer Z-1 Type K Kobold (Goblin). Even smaller, with further simplifications, it may look radical - and indeed its small size is a bit of a shock when first seen - but there's plenty of room inside, and it should have a good pilot view, like the others in the series.

>Thanks.
>
> Darren Gergel
> Edmonton, Canada

You're welcome, and thanks for your interest.

Lynn Williams

Darren,

I forgot to mention my other benchmark totem for stability and control, re the Flitzer series.

The use of the superlative and much overlooked USA 35B allows for the 15% centre-of-pressure movement, from 45% to 30% MAC, between L/D minimum (at Vc) and C/L max, at 1.6 and +20 degrees AOA, to +35 degrees at full power on the 1834cc VW. This means effectively a dual personality aeroplane: very stable in the cruise (hands-off at Vc with 'average' loading), yet with increasing AOA, the aeroplane becomes more pitch sensitive, so that in steep turns, or any pitching manoeuvres, the aeroplane suddenly becomes a real dogfighter, with a combat turn of 360 degrees flown effortlessly in 7 seconds at maximum cruising speed (Z-1 with the smaller tailplane).

The other factor is that controls should be powerful, yet light, with light break-out forces and low friction, but should progressively heavy up as VNE is approached. The 'heavying up' is relative, however, and the controls are still quite easy to move at 125 mph., but the forces are such that there is no tendency to over-control. Nor is the aeroplane in any sense 'twitchy'. Contol runs are short and direct, with minimum drag. Ailerons are non-differential, 1:1 via pulleys, but if all ailerons were like these, they'd never have bothered to move onto differential, Frise, or anything else!

Obviously I cannot guarantee the characteristics of unflown prototypes, but one attempt to achieve the ideal perceived 1:2:4 'poundage-relationship' between, respectively, ailerons:elevator:rudder has seen the lower profile/longer chord elliptical rudder of the Stummelflitzer supplant the old (simpler) 'rectangular' Z-21 rudder, although this was as much to provide a harmonious appearance for the long-nosed Praga D-75 installation as anything else. Perceived control pressures on the Z-1/21 were in the order of 1:2:3, respectively, and although I enjoy the light response of the powerful 'parallel' rudder, I know that some pilots prefer a heavier feedback through the rudder pedals, which should obtain with the longer chord, curved variant.

Because these aeroplanes are all relatively small, even quite seemingly innocuous changes may have a relatively great effect, so there is the possibility that the handling of the Goblin will differ appreciably from the Z-21, even though both have about the same mass, reative stagger/tail-arm, tail volume, general dynamic relationships, control pressures and effects.

Finally, I do not know whether you have seen the last of the Flitzers, which has a primary fuselage dimension (11'6") ie. only 6" more than the Z-21, but with its longer, heavier engine installation, rear located cockpit, and 120 'sq. wing area, the aeroplane will have the same wing loading as the others in the series, and of course utilises the same airfoil. Performance should be good on the 100 hp. vintage (1938) Cirrus II engine, and its deep fuselage will cater for any pilot dimensions!

This is the Flitzer F.2 Tiger, which is still only a paper study: but I do have the engine, and intend to pursue it further!

Best regards,

Lynn

Goblin vs Meteor

Hi everyone,

I am new to the group (sort of been watching from a distance for a while). I am from Sweden but live in southern California (work brought me here). Any builder on this side of the world?

Anyway the first time I saw the Flitzer I was blasted away, it is the coolest plane ever! I just need to build one. I like the Goblin version the best. Any idea when the supplemental plans will be available?

Also what is the difference between the Meteor and the Goblin? On the webpage there is mentioned that the Meteor would be a racer. Any more info you would like to share on the Meteor with us?

On other thing how easy/difficult would it be to remove the wings from the plane? How long would it take and how many people are needed to do it?

I like the clear and good answers that Lynn takes time to write and share. Just that makes you feel confortable start building a Flitzer.

Regards

Robert Nilsson

Hello Robert,

Welcome to the Group and thankyou for your kind comments

Briefly, the difference between the Type M Meteor and the Type K Kobold (Goblin), is that the Type M was conceived as the closest thing to the smaller original concept that occurred to me when first mentally constructing the Flitzer, while the K goes several stages further in creating the minimal aeroplane within a retro envelope.

The M is really a 12-15% scaled down Z-1 (Z-21) using the tail area of the original Z-1 but with the tail profile thickness increased by 25% to 1.25", ie. the same thickness as the Z-21 stab. Wing span is 17.5', and the fuselage is shorter, allowing a wider variety of lighter engine types to be fitted, as well as the standard 1834cc VW. The fuselage length is about the same as the Stummel, so it's a little smaller all round than a Z-21, but with the same wing chords (the chords are increased on the Stummel). The Goblin has the same upper chord, but the lower chord is reduced to 30", since the deeper K fuselage is the smallest of all, at 9'9", and lacks the door, and the tailplane is semi-cantilever and it also features an all-flying rudder. The K has differential wingspans, the upper wing measuring 16' 10" overall span.

Both have fabric-covering to the rear fuselage, 'squared' wingtips (with a supplementary tip rib to slim down the tip and ameliorate the slight reduction in aspect ratio induced drag). Both types use nearly 100% of the metal fittings for the Z-21.

There are currently three sheets completed for the Goblin, with another two or three nearing completion for a full set, while few of the Meteor sheets were ever actually competed to a publishable standard, although thay are very simple and would need only a short while to complete. The evolution of the Type S Stummelflitzer rather overshadowed the development of the Meteor, although they both originally grew from the same specification, but the Stummel was successively enlarged to almost the same physical size as the Z-21, but with bigger chords and rib profiles, four ailerons, rounded wing tips, an elliptical vertical tail, raked cabane, etc., and the resulting aeroplane uses only about 50% of the available laser parts for the Z-21, although there are plans to provide a Type S set.

The UK prototype of the Stummelflitzer is now progressing fast in Norfolk.

The sole Meteor was 50% completed by a local builder, but sold on some years ago, and was be never progressed, and is now in long term storage, just deteriorating, sadly. I have made a few attempts to purchase this machine, to no avail.

Best wishes in whatever you decide.

PS. There are a few potential builders in Ca.

With practice the Flitzer could be de-rigged in about an hour, but is not a de-riggable aeroplane in the sense that you'd want to do it every day. Two people can handle it easily.

Lynn

Thanks a lot for the answer, Lynn! It was very helpful for me.

One more thing, if I order the Z-21 basic plans and want to build the Goblin version, which parts are identical to the planes? If I know this I could start building parts until the Goblin supplemental plans are available. If the Goblin supplemental plans are not going to be available in a reasonable time I can still build it as a Z-21. Sound like a plan to me, what do you think. I am in no hurry (I have to work and have a family to care for also) but in this way I could start building and not have to wait until the Goblin plans are out to start.

Also is there anyone selling material kits (wood and/or fittings) over here in the US. Usually there is so much time wasted in searching for parts so that would make it easier and fast to have it supplied or a shopping list would be good too. I hope I am not stepping on any ones toes now. (One time I asked the for a material list on an other airplane list and got over 150 replies of various charcter but no list.) That is not my intension, just to make life easier and probably more planes get up in the air. Maybe it is cleary implemented on the plans. I have seen the plans (Thanks, Patrick Rose!) but do not remember if there was a material list or not on them.

Life should be simple and fun, not always the case but we are working on it, right?

Thanks and regards
Robert Nilsson

Hi Robert,

Yes, Gary Steadman of www.Flitzer-Aero.com sells complete Z-21 timber kits and all laser parts. Naturally Gary also provides Stummel kits and has supplied Goblin parts.

The upper wing ribs of the Goblin are identical to those of the Z-21, and 90% of the laser parts will also fit.

You can buy the three extant supplemental Goblin sheets along with the Z-21 plans, and there is plenty of work on those three sheets to last you quite a while, including the complete fuselage, undercarriage, wings, full size wing ribs (where they differ from those of the Z-21) and much of the tailgroup. It is refined into those few sheets simply because it is the Z-21 drgs. which provide the overall constructional detail and total build philosophy.

The remaining sheets provide cabane details, internal (fuselage) plywood gussetting, full size rudder ribs, and lastly a general arrangement drawing of both the VW and proposed radial engine version. Any shortfall on Goblin sheets is available via email in the short term, with the added advantage of colour input on the drawings.

However, remember that the Goblin is still an unproven design, which has to be fully analysed for strength substantiation via finite element analysis, to determine it reserves. Furthermore its flight characteristics can only be verified by a thorough flight test programme.

One thing is fairly certain: while it will have many characteristics in common with the Z-21, it will also have a very definite character of its own. I don't think it would take prisoners if left to its own devices, ie. there would be a salutory lesson in store for any inattention or daydreaming close to the ground ..... it will react quickly, and get you into trouble faster than the Z-21.

However its saving grace will be its ability to recover, as with its low mass and small size, it should be finger light on the controls. The trick will be to provide the same great stability that you will find in the Z-21, in the cruise trim condition.

Best wishes,

Lynn

Engine Installation & Cowling

> Hi,
>
> I have been thinking about the cowling for the Goblin. Will the
> tapering (seen from above) be steeper than the Z-21 or is the
> fuselage on the Goblin narrower at the firewall? I am just curious
> how the cylinders get out in the air or do you have a pressure
> cowling in mind that goes half way in side the cowling? ( I have not
> figured that one out yet).

The cowling plan view will taper more steeply on the Goblin for the VW installation, due to the shorter installed length, and yes, there is an element of a pressure-drop cowling already designed into the Flitzer cowl, (quite necessary with the Z-21A, which has a wider fuselage) by virtue of the greater efflux volume (by comparison with the intake air mass) and the baffle design, which theoretically streamlines the airflow internally, and is intended to minimise hot spot vortices.

> Also are the (aft) exhaust pipes going to
> go free of the firewall and the side of the fuselage ( I think there
> is not so much room between the exhaust pipe and the back of the VW
> engine, maybe the exhaust pipe is going wider than the 22" fuselage).
> I just wish to be educated and get some sleep!

You have a point about the rear exhaust pipe. For internal piping, the bend radius will be fairly tight to aviod colliding with the firewall, but the induction pipe 'Y' branch on the rear c'case also requires the same sort of clearance. However, the VW would not be attached directly to the firewall front face, but would be carried on short tubular (horizontal) pylons, as on the Taylor Monoplane, which lifts the motor away from the firewall by some 4". This would be about 2" closer to the firewall than is provided by the standard engine mount on the Flitzer, and would create the very short nose effect on the Goblin. Final weight and balance would determine whether it was necessary to lengthen those pylons.

> Regards
> Robert Nilsson

I attach an early picture of the 1834cc VW installation in D692, with the 6.25" tubular mount.

Best regards,

Lynn Williams

July 23, 2005

Die erste Kobold?

August 6, 2005

Hi Group.

Here's the final iteration of the Kessler-Goblin scheme. Goblin builders and Robert McKellar [:0)]please note that I have eliminated the elevator tabs, and increased the elevator chord by 1.5", making the new chord 14.5". This will be implemented in a new drawing when the final Goblin sheets are drafted. Power of manoeuvre will no doubt be further enhanced, as will the power-off flare at a lower IAS. The aircraft may be a little more sensitive as a result, but as it so far exists as an untried prototype, there is much yet to be assessed. Geared push-rod elevator controls could be used, but the essence of the Flitzers is their simplicity, using cables and pulleys in time-honoured fashion.

The option of fitting tabs is still open, of course.

Best regards,

Lynn