MK3 nipper bits

[Lowflyer]

Hi, I'm looking for some parts to help get my Nipper back in the air, looking for,

1, the three lead weights that go in the rear fuselage, or if anyone has a mould I could borrow or even the dimensions to make a mould.

2, harness if anyone has one or what is the best replacement.

3, rudder bungees, or where can I get a alternate.

4, the fuel tank filler unit with sight wire.

Any information would be very much appreciated.

Peter

[GARBG]

Peter, I can let you have a weight. Regarding harnesses you may like to try info@gadringer-gurte.de
R.
G-ARBG

[Ross]

Hi Peter,
You may know this already but make sure you do a weight and balance prior to adding weight. I removed the lead from my MK3 as it was tail heavy. A previous owner had a Jabiru 85 hp engine fitted but didn't check the W&B. Also the pilot sits a little aft of the CofG So your weight also has an effect.
Cheers Ross

[Paul1954]

Hi Ross,

You are absolutely correct in the requirement to check the empty weight and balance after any significant change in equipment added or removed to or from the aircraft. Rather surprised a change of engine type got past an inspector.

As to your point, ‘Also the pilot sits a little aft of the CoG’; that is not terminologically correct. In the case of the Nipper, adding a pilot’s weight will cause a clockwise (positive [+]) moment rotation about the reference point. The reference point of the Nipper being the leading edge of the wing, the empty position of the CoG may, possibly, be forward of the reference point and thus some distance from the pilot seat.

Please forgive my pedantry, too many years writing Ops manuals, and doing the weighing of gliders and light aircraft. Anyhow, happy aviating you lucky so and so, I’m off to check a Twitter report of a grocer's apostrophe error that has just been reported in the village High Street.

P.

[Ross]

Thanks Paul, Sound's like you are all over it. Im' 6ft 3' with long legs' so I suspect my CoG is somewhere near the propeller. My Nipper's had the engines' conversions' several year's ago in Australia and I have all the paperwork's that certifie's its' conversion. The Jab engine at 85hp is' a delight to fly however it i's not aerobatic or more specifically negative G capable which suit's me fine because vomit on the inside of the canopy means' I have to fly IFR. Excuse all those pesky apostrophes' I couldnt' resist. Ross

[Paul1954]

Ross,

I think the point of the Nippers is to have affordable and enjoyable flying; it doesn’t matter which way up you do it. If it puts a smile on your face, job done.

Now back to weight and balance. When added or subtracted, ‘motion-lotion’ in the fuel tank of a Nipper is shown in the Owners Manual as have a very small effect on change to the CoG. To me, that signifies the aircraft designer’s reason for placing and securing weights in the rear fuselage is to provide a means to get the empty CoG somewhere slightly forward of volumetric centre of the fuel tank. Thus, the purpose of adding or removing the weights should be to do just that. Just my thoughts.

You will find that if you don’t already have early onset pedantry, it will likely appear during your sixth decade.

P.

[JimCrawford]

The Nipper is quite tender on the C of G position. The acceptable limits for flight, as laid down on the permit release, lie roughly about the position of the main spar. Fuel is well forward of the spar and the pilot well aft. There are three critical conditions which must be addressed;

1. with zero fuel what is the maximum pilot weight which doesn't drive the C of G past the aft limit?
pilots heavier than this must land with the appropriate fuel still in the tank to maintain the C of G within limits.

2. with full fuel what is the minimum pilot weight which doesn't drive the C of G past the forward limit?
pilots lighter than this must carry ballast in the seat to maintain the C of G within limits.

3. in addition to the above no combination of fuel and pilot weight may exceed the max take off weight as specified in the Permit release.
note here that the Nipper has two MTOM depending on whether it is to be flown aerobatically or utility.

Because I have removed the magnetos and replaced then with Leburg units my engine is a little lighter. Also I've placed the batteries aft in the cockpit. I generated a spreadsheet to allow me to do 'what ifs' with moving stuff around and found that I could remove the lead ballast block from the tail. It also allows me to plot a set of graphs of pilot weight against fuel weight for aerobatic MTOM, normal and normal + 10 & 20lbs baggage. At a glance any pilot can determine the limits for the proposed flight.
I have no idea why the Nipper has ballast blocks down the back, perhaps to compensate for the heavier VW conversions rather than the earlier engines. With pilots a little heavier now than in the 1960s the blocks are, in my opinion, unnecessary. What is important is to ensure that the aircraft is flown within limits and this can be ensured by doing the calculations. If they allow the lead to be removed then that's great. Light aircraft of this type are never improved by carrying around lead blocks that aren't doing anything useful.

Jim

[Paul1954]

Hi Jim, you underestimate the weight of the VW type fitted to the original Mk II Nipper. The engine had a useless lump of metal attached to its rear. This lump is then bolted with the engine to the airframe. The lump weighed (my estimate) of perhaps 10 kg or more! The dimensions of the lump’s fuselage attachment are not the same as the engine. To fit an VW without the lump requires removing and the welding of new attachments fittings to the airframe.

Photos of a ‘lump’ attached to a VW which is fitted with Bendix D2000 dual magneto.

[JimCrawford]

That engine confuses the heck out of me! Is that as fitted to a Nipper?
That chunk out the back must result in the engine being located about 25mm forward of the Mk3 because all that metal casing won't get past the diagonal bracing tubes in the forward frame. This forward shift would mean the aircraft would have radically different cowlings. I cannot imagine how the firewall would be arranged with that magneto. Also the mounting bolts seem to be in line with the standard VW mounting bolts so it should fit a standard arrangement.
I'm going to guess that engine came off an aircraft with either a thick wooden firewall with a cave for the mag, like an RF4, or had a short built up tube mount to keep everything clear of the firewall. I don't have any Mk2 drawings, only Mk3 , and they show something very similar to the 'Peacock' arrangement of old. There must be some rather significant changes between the 2 and the 3 but my notes on C of G assessment still stand. Next time I get close to a Mk2 I'll take a peek, although I expect unmodified originals may be few and far between.

Jim

[Paul1954]

Hi Jim,

The ‘lump’ or backplate is about three inches long.

The engine and backplate was removed from a standard Mk II Nipper that was originally been fitted with a Stamo 1400cc engine (and backplate) from new. At some point the engine had been replaced with a 1600cc unit and fitted with a several of the original accessories. The Bendix D2000 was a mod that had been developed (and also flitted) to the Acro VW - it worked well. In order to fit to the Nipper firewall a metal box was added and then allowed the magneto to slot neatly between the frame1 tubes and other x-bracing. All very neat and well thought out. The cowling? A standard Mk II item - very different to that of a Mk III

Removing the backplate and repositioning the attachment points (to those of a Mk III) required no other changes other than bolts and studs to then fit the engine to airframe.

I can assure you that a VW without the attachment cannot be fitted directly to the Mk II airframe. There was - may still be, at least one Nipper with machined ‘off-set studs’ fitted, and thus avoiding the working of the attachment points on the airframe.

Why was a backplate used for the Stamo? Probably something to do with the original Ducellier J4/ST dual magneto. It looks very similar to the Bendix D2000 in one photo of it that I have seen and thus the cutout and housing in the firewall is original.

Please excuse any text errors - the ipad is a bit ‘sticky’ this morning

[JimCrawford]

That photo explains everything. I wonder why the early units went to the complexity of such a casting rather than a 'Peacock' style installation. I have a very similar casting from a Revmaster conversion. It's about the same depth and has a very similar magneto attachment, although only a single mag was used in a motor glider. The magneto drive was quite deep as it incorporated a resilient coupling to take out any mis-alignment so that explains the depth of the unit. Also the casting appears to have a mounting position for a starter although I'm not sure the extra weight of the flywheel and battery would be worth it on an aircraft as light as a Nipper. Perhaps it is a universal design for different aircraft. Maybe with a modern LiFePO4 battery it wouldn't be such a burden.
Do those eyebolts that join the casting to the fuselage frame contain vibration damping material?

On another matter; do you know the od and id, or od and wall thickness of the longeron tube? I'm stuck without the numbers.

Jim

[Paul1954]

The tube OD is easily measured. The wall thickness can be measured if the firewall is removed and the exposed tube have not been welded shut.

[G-ARBG]

My Nipper II conversion G-ASXI during1970's.

Stamo was replaced with Ardem fitted with D 2000 magneto utilising the Stamo mounting. Designed with the help of Chris Gear, Chief Engineer at British Hovercraft Corporation (Westland Helicopters) where I was Quality Assurance Representative.
Very simple to do and performed excellently. I fitted the MK III weights to accomodate the new CofG. Mod was approve by John Walker Chief Engineerof the PFA at that time.

[G-ARBG]

.
Further to my last post I have also carried out a MOD to replace the Stamo engine with the Rollason Ardem retaining the Stamo mount on G-ARBG but incorporating Leburg. This Mod has also been approved by LAA and has proved very reliable over the past 10 years.
The flexible pipe from the fuel pump to the carburettor was only temporary. Again the MK III weights proved adequate for flight within CG limits.
David G-ARBG

[GARBG]

Paul,

Do you know where that engine you so eloquently described as having a ‘Lump’ on the back is now. I believe it may be the engine I built for G-ASXI, see photos. Incidentally I remember the tacho was driven off the oil pump.

Please PM me if you have any details.
David