C of G Envelope

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208c (at) boelkow-junior.de
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Dave_Allen
Posts: 8
Joined: 11 Nov 2015 14:45

C of G Envelope

Post by Dave_Allen » 14 Mar 2016 12:52

Does anyone have an up to date copy of the Junior's C of G envelope they could let me see?

D-EEAH
Posts: 3
Joined: 28 Sep 2015 08:22

Re: C of G Envelope

Post by D-EEAH » 05 Jul 2016 01:15

The envelope varies between the different models - I understand from your other post that you have one of the earlier A2 models. I have a diagram for my 208c, but that has a max AUW of 630kg, whereas the A model has a max of 600kg. By chance within the last few days I have come across what is apparrently teh envelope for the A-model, but whether it is for an "A1" (if there ever was such a model) or your "A2" I am not sure. The figures I have seen (on a weighing report by Steinle at Mosbach (EDGM) - who are pretty experienced doing work on Juniors - is as follows:
Most Forward CG limit and weight – 1.711 metres 532kg

Max Weight fwd limit – 1.770 metres, 600kg

Max Weight aft limit – 1.792 metres, 600kg

Most aft permissible CG position – 1.807 metres, 520kg.

This particular aircraft was weighed and had a weight/cg of 1.727 metres, 403.6 kg "empty" (apart form 2.5ltr unusable fuel). This is for airframe no #514, so quite early in the production series. What is your construction number?

Also, teh above weight/moment data is for the "normal" category (i.e. no aerobatics). That aircraft has had the extended "C Model" longer wing tips fitted (as has happened to may A models I believe) and such aircraft are not permitted to operate in teh "utility" category (aerobatics) so it does not have a "utility" weight/cg envelope. The one thing I do nto have is an "official" figure for teh moment arm that should be used for teh occupant station and teh fuel/baggage station. My POH does not even give an explicit figure, though from a graph in teh POH I use values of :-
Station for pilot/passenger ~ 1.63 metres
Station for fuel and baggage ~ 2.28 metres
PERHAPS for teh A-model, which has the same external fuselage/cockpit geometry, but the seat backs (and hence presumably the baggage bay and fuel tank also) about 0.1 metres fwd of where they are on teh 208C, it might be better to use 1.53metres for occupants and 2.18 metres for teh fuel/baggage?
The thing that struck me about the envelope defined above is that it seems quite limiting on occupant weight - seems you may be outside teh envelope if the combined weight of occupants exceeds about 130kg! (by comparison the 208c seems able to take about 160kg in total for teh occupants and still be in limits. I'd be interested in any views or data that others have on this subject.

Dave_Allen
Posts: 8
Joined: 11 Nov 2015 14:45

Re: C of G Envelope

Post by Dave_Allen » 05 Jul 2016 16:28

Many thanks for your reply, I apologise for taking so long to respond but I have been away.
I will have to sit down and digest these figures.
Thank you.

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