Hi Nigel,
THanks for reproducing that info. I hadn't read it origionally but sure does
explain issies re the aileron control.
I have been helping Neville Swan with his Dimona and between us have done about
4 hrs or so. A few Mths ago, working again at Lara, I went down one weekend
to Colac to see John Callaghan's Dimona which I had the opportunity to fly
.... A most impressive little machine. (L2400 Limbach) .
Good aileron control / stick load and surprising roll rate. THe L2400 gave
great TO performance .... all round a delightful little ship.. I took some
pics of the aileron belcrank because it was significantly different to the one
I have here
Neville's Dimona is quite different to fly .... the aileron control stiffens
up in flight to a level which feels as if there is something "catching" in the
aileron circuit Also both ailerons are "up" in flight ..... one about 30mm and
the other about 20mm (trailing edge) which I am sure is not helping matters
The other issue related to take off.... with full forward stick on TO, it
accelerated with the tailwheel firmly on the ground (I did expect the tail to
lift a lot earlier). When flying speed was reached, it flew. I don't recall
Johns Dimona doing that. If I recall the tail lifted normally. I guess though
it is a characteristic which one can get used to.
However getting back to the aileron issue. What is going thru my mind is that
when the aileron rods are in compression they will want to bend and will be
prevented doing so by the 5 bearings within the wings.
Following on,that discssion, the Dimona I have here is an ex Thai one and as a
result of a conversation with Roger Harris ( Gliding NZ STO) and concern about
flutter, I took the bull by the horns and made an access hole adjacent to the
first (of 5) bearings inside the wing. I found that all 3 bearings were
seized. Their design was real dodgy .... no steel outer bearing then a nylon
outer.... just a nylon outer. The balls had sort of embedded themselves in the
nylon outer. So we purchased 10 new bearing sets and installed them ....
quite a mission.
THe new bearings from Diamond did have a steel outer and a nylon "tyre"
An interesting thing was also that there was significant "play" between the
bearing outers and the push rod. Presumably because the push rods are in
Compression.
So getting back to Nevilles Dimona, I wonder if seized bearings coupled with
the pushrods in compression could be a problem by tightning up when in flight.
Something to think about ??
Ian Williams
--- On Mon, 25/10/10, Nigel Baker <[email protected]> wrote:
From: Nigel Baker <[email protected]>
Subject: [DOG mailing list] Aileron Stiffness
To: "DOGS" <[email protected]>
Date: Monday, 25, October, 2010, 1:50 AM
Hi All.
As I mentioned before there is stuff in the archive on the subject of the
aileron systems.
I am sending this again from a February round on this subject.
Ian I can save you the trouble on checking if the aileron horns out in the wing
are interchangeable.
They are not.
One system works with the push rods in tension and the other in compression in
relation to normal flight load so no they can't be interchanged unless you want
to reroute the push rods and turn the Aileron movement around in your head to
go stick left for right roll.
Cheers.
Nige.
----- Original Message -----
From: Nigel Baker
To: [email protected]
Sent: Monday, February 01, 2010 5:53 PM
Subject: Re: [DOG mailing list] Dimona 1984
Hi Lasse and others.
Well I am confused by the mk1 mk2 stuff. I really don't know where that comes
from.
There is only the one manual that I know of last issue Nov 1985.
About 9 years ago we asked Diamond Austria for info on the springs in the
aileron circuit and whether or not they were needed or could the grade of
spring be changed.
After a short while they responded to the effect they didn't know there were
springs used and couldn't imagine why and couldn't see a problem with removal.
I am not so sure on the last bit.
I have worked on several Dimona's and of note the S/N's 3512, 3535. 3538 and
3539 (ours)
All these aircraft are ex the Thai Air Force and part of a group of 14 H36's
the Thai's bought in a package deal with Wolf Hoffmann the designer and
business owner at the time.
There is one main difference between these numbers and a big difference in
handling.
S/N 3512 and 3535 had what I believe to be the original aileron drive circuit.
In these aircraft the push rods worked in compression in normal flight mode and
are guided by nylon bushes. It is best identified by looking through the clear
inspection panel at the Aileron bell crank pivot point in the lower wing
surface. When looking through the inspection panel you will see a bell crank
fabricated from steel tube.
This system also has centering springs attached to the aileron push rod drive
assembly under the fuel tank in the fuselage.
S/N 3538 and 3539 had what I believe is the later version. In this instance the
push rods work in tension in normal flight mode and are guided by fairlead
rollers. This is easily detected again by looking through the clear inspection
panel and in this instance you will see a bell crank fabricated from steel
sheet instead of tube.
The resulting difference in systems is large.
Firstly is the difference between compression and tension in the loaded push
rods.
In the case of the later system with the rollers the friction is less for one
main reason. The push rods are pulled straight in normal flight load and the
guides are not influencing them much (except for normal wing flex) so the
friction is low and they are rollers (well when not seized). On the other hand
the earlier version in compression results in the bushes holding the rods
straight and this creates friction in the guides. Couple that with the use of
bushes instead of rollers and there is your answer. This can be helped with the
application of Silicon Spray Lube (works as a dry low friction lube which
doesn't collect dust) to the push rods at the points where the bushes work but
it is a pain as it requires removal of the push rods. Something that would need
to be done yearly to get the best out of it. There is little friction on the
ground of course but it is noticeable in cruise (reasonable flight loads) as
you can detect the system sticking
with small control inputs.
Other than flying it inverted there is no way round this situation.
Secondly the other difference is in the "differential Ratio" of the ailerons.
The Service manual has a broad range of tolerance for aileron deflection which
conveniently covers both systems.
The older system produces an up value near the top tolerance of deflection for
the aileron and down is close to the bottom of tolerance. This delivers a
differential ratio of more than 2-1.
The newer system produces an up value near the bottom of the tolerance and a
down value of near the top of tolerance and this results in a differential of
less than 2-1.
So what difference does that make.
Well as pointed out by some it means that normal flight loads can at certain
points of deflection result in dynamic loads driving the ailerons into further
deflection rather than less thus a lack of centering force and in fact the
reverse.
So the springs in the older system are there to supply a centering load and
while they do that they are a negative at times.
I am still confused by this mk1 and mk2 thing but can confirm that while I have
heard of 1 aircraft built after 3539 but very close to it (3541 I think) the
change to the Aileron Circuit happened around the 3540 mark somewhere depending
on order schedules during the change over.
Interestingly one comment was made by Diamond during enquires about the 2
systems when they didn't seem to be able to find records of the earlier system
at the time was that Hoffmann Aircraft were not very good at record keeping.
Hope this if of help.
Cheers.
Nige.
----- Original Message -----
From: Ian Mc Phee
To: [email protected]
Sent: Wednesday, January 27, 2010 11:09 PM
Subject: Re: [DOG mailing list] Dimona 1984
Interesting about tail wheel mod from Michael - sure gives smoother ride.
You mention the heads/valves lasting only 300hrs. I would recommend to all
analysis of exhaust at FULL POWER with lamdameter etc. You may find it is
running slightly lean on full power (actually plugs look OK) but gas analysis
does not lie. More recently i have been using digital CHT and you can really
see what is happening. I set them up so full power CHT rises to about 170degC
then very slowly falls. If you bring throttle back just a bit in revs CHT will
quickly rise to 180degC and beyond. This proves to me you are running rich on
full power- also confirmed on EGT. To achieve this it may be necessary to
carefully thin out the end 6mm to 8mm of each the needle in carby and thus
achieve the low CHT on full power. (do not think of touching jet) Fuel is
cheap when compared to repairing heads. Limbach Tech bull 53 makes mention of
max on climb of 180degC (forget what max the manual says - that is stupid
value) Also Tech bull 44 (11page
edition) is well worth a read.
Ian mcPhee
2010/1/27 Michael Grimwood <[email protected]>
Hi John and Lasse
I have owned a Mk1 H36 since 1988 (G-MRG in the UK, now VH-VRG in Australia).
It originally came with an un-sprung
