Le Forum Avions Piel, consacré aux Pierres Précieuses. Super Emeraude, Beryl, Saphir, CP80 etc

Hi

I am seriously looking at building a Super Diamante (tailwheel). But I prefer the 'straight' tail instead of the 'swept' tail assembly.

In this website's photo gallery there is a picture of a Super Diamant with a straight tail, registered F-PJXP.

Does this mean that there are plans or drawings available to build a larger 'straight' tail on a Super Diamant?

Or did the builder of F-PJXP just increase (scale-up) the Super Emeraude tail?

I contacted Sylvie Littner who markets/sells the plans for this aircraft and she was not able to help me with my query.

I would be very interested in hearing from anyone who has done this, or who has seen the plans.

Many thanks

Barry

Hello Barry

Welcome on the site.

I am going to ask jeans-Claude PIEL tomorrow so that he informs you about the plans of the Super Diamant.
It is a magnificent plane.
Cordially

Lucien

Hi Barry,

I agree with you, the "Emeraude type fin and rudder" is much in accordance with the wing than the more "modern" (at that time) swept back type...

I think that the following is a part of the answer :

I have scanned the plans of the CP60* for my own use and the figures are small parts of two of them.

On both, we can see that the "Emeraude type fin and rudder" have been drawn on top of the swept back one.
Personally I can't find any reason why that should not work, as far as the surfaces and moments are not reduced...

I think that J.C. Piel (BIG in this site) who is responsible for the type should confirm this.

Philippe dejean

Philippe - thank you for your reply,

I have ordered a full set of Super Diamant plans from Sylvie Littner, plus the fuselage/turtledeck/fin/rudder drawings of the Super Emeraude (of both straight and swept design). This will enable me to scale-up the dimensions of a straight fin/rudder for the Super Diamante in the same ratios. I would be careful to keep the vertical surface area of both fin/rudder in the same ratio, also the hinge line and arm/moment relationship with the C of G. When I have re-drawn the Super Diamante fin/rudder I intend to get the drawings checked by a local aeronautical engineer (to be safe).

While re-drawing the fin/rudder I may be tempted to slightly alter the 'cosmetic outline' to something similar to the early marks of Spitfire. This would, in my opinion, look much better with the Diamant elliptical wing shape and produce a pleasing result.

Your (and anyone else's) opinion would be appreciated,

Thanks again,

Barry

Hi Barry,

It is of course good practice to get our own drawings checked by a aeronautical engineer... (local or not)

As Jean-Claude Piel (BIG) is the owner of the type, he checks the proposition of modifications of the builders.
And if they are safe he integrates them in accepted variations drawings for the french airworthiness authorities.

The temptation to alter the 'cosmetic outline' of the fin/rudder to something similar to the early marks of Spitfire is obvious :
The first of the CP equipped with this elliptical wing is the CP20 "Pinocchio" - a 25 HP VolksWagen powered single seater that first flew in 1951.
The CP20 was directly inspired by the Spitfire shape.
The CP30, CP60, CP70, CP60, CP100 (=CAP10) and their variants are all multi-seaters derived from that CP20, and thus inspired by the Spitfire.
In my opinion too, those planes with the elliptical wing shape would look better with Spitfire-like rudder and fin.

However, you must be aware of the fact that the Emeraude and some other CP have a tendancy to develop a slight yaw oscillation if the feets are off the pedals. This is due to the fact that the rudder is a little thicker than the fin. If left loose, the rudder is aspirated alternatively on each side.
Even though this behaviour has been quoted as "not unsafe" by the french airworthiness authorities, and has never been a problem for Emeraude pilots, the swept back fin and rudder was a modern looking way in the 70's to solve this problem.

Of course, a Spitfire type fin and rudder will not develop this oscillating behaviour either, if their thickness are properly matched !
(But you should take care of this detail-not only "rescale" the "Emeraude" fin and Rudder...)

Bons Vols

Philippe Dejean

Thank you again Philippe - good advice!

I think the safe way forward would be to send my final draft of the new fin/rudder to M. Piel for his comment/approval.

Thank you for the information regarding the thicker rudder profile - remembered.

I now have to wait for my plans to arrive so that I can draw my modified fin/rudder. Frustrating!

No matter - in the meantime I can finish off many jobs around my house which will build me many 'credits' from my wife (before I tell her about the Diamante).

If I survive telling her that I am building an aeroplane you will no doubt hear from me in future!

Thanks again,

Barry

Hello Barry,
I have just read your messages.
The straight fin is not available for the CP605/615. It was only inslalled on the CP60. The design is the same that the Emeraude but a little bigger. However it is possible to install the straight fin on the Super Diamant, so I am going to look if drawings always exist.
I will keep you informed as soon as possible.
Jean-claude

Jean-Claude,

Very many thanks for this.

My intention in building the CP615 is to have only two seats, and plenty of room for a tent and baggage for touring and camping, etc instead of carrying 3 people - and good fuel capacity for greater range.

Cheers

Barry

Hi Jean-Claude,

My plans for the Super Diamante have finally arrived here in New Zealand from Canada. Many, many weeks on board a very slow boat!

I also purchased the fin/rudder plans for the Emeraude CP328 from Sylvie, (both the straight and swept styles).

Then I can calculate the % increase of the swept fin CP328 and the CP60 by size comparison.

Then I will use the same % to increase the CP328 straight fin/rudder for the CP60.

I will publish my drawings here on this website for your comment.

A question for you - If I increased the fin thickness to the same thickness as the rudder would it dampen out the 'yaw oscillation'?

I am very open to comments and critique from anyone!

Thanks

Barry

Hello again,

I have attached a drawing of my idea to make the fin/rudder resemble the shape of a Spitfire.

First off - I humbly apologise for the bad/rough drawing - I am no artist!

This sketch of mine is intended for discussion only - not for engineering purposes. It is for ideas only.



In order to arrive at these outlines I have :

1 Re-scaled the swept vertical surfaces from plans and 3-view diagrams of the Diamante (lines shown as dashes - - - - - -).

2 Then I have drawn the vertical surfaces from the Super Emeraude in the same ratios as they are shown on the CP 328 drawings (lines shown as dots . . . . . .).

3 Finally I have scaled the vertical surfaces from a Mk V Spitfire (lines are solid black _________).

I have used the same hinge line for the rudder attachment for the 'Spitfire' rudder as for the 'Emeraude' rudder.

Interestingly the angle between the rudder hinge line and the top of the turtledeck is identical - 87 degrees for both the Diamante and the Spitfire.

I have shaded the top of the rudder (Area 'A') as an aerodynamic balance to make the rudder less sensitive and to assist in the control issue already pointed out to me in previous posts (yaw oscillation).

I have kept the rudder hinge line at exactly the same distance (arm) from the Centre of Gravity datum.

Again - please excuse my poor drawing - but I think (hope) you understand my idea.

I am happy to receive any comments????

Thanks

Barry

Barry wrote: “A question for you - If I increased the fin thickness to the same thickness as the rudder would it dampen out the 'yaw oscillation'?”

Your drawings are quite good! First of all, the Diamant tail shape of your drawing is the one of the original drawings distrubuted for the CP 60… If I did build mine right, the rudder is not thicker but thinner than the fin. I had to add a strip of balsa on both sides to make it match with the fin spar. When my rudder was already made, I received a drawing of a modified fin rudder shape (i.e. taller rudder with an aerodynamic balance in the top of the fin) resulting roughly in a 50% increase of the rudder “capacity”. The “yaw oscillation” is induced by a “thinner” rudder not the contrary. Some manufacturers increase the thickness of control surfaces (Jim Bede was suggesting 10 %) to reattach the boundary layer of the airflow to the control surfaces.

Secondly, you can address the “yaw oscillation” by adding a small block of triangular shape about 6 to 8 inches long (a kind of wedge going from 0 to 12 mm in 25mm) on both sides of the rudder trailing edge. I built mine a little bit twisted…(if the top of the rudder is aligned with the fin, the bottom is a bit to the right, if the bottom is aligned with the fuselage, the top is a bit to the left; or vice versa, I don’t remember exactly) both sides are under pressure by the slipstream and the rudder is kept centered. Idem for the “wedges”.

If you build the original rudder you will be out of rudder authority well before arriving to the limit of the ailerons in a sideslip like in a crosswind landing.

My Diamant was built using the drawings sold by E. Littner, Sylvia’s father and the span is 9.6 m (31.5 pi) My advise: build the wings per plans and you will have a very efficient machine…

Keep us informed of your progress... and good luck.

Hi,

One more drawing. This is a concept of the side view of a CP615 Diamante showing a scaled Spitfire fin/rudder outline. Comments or criticism are very welcome from anybody.



Once again - please excuse my poor drawing...

Cheers

Barry

I have not received any comments about my last post and the drawing of the new rudder shape so I will take that as positive - with 100% agreement.

I will now proceed to re-draw the rudder and fin construction drawings to achieve the new shape.

Comments or criticisms are still very welcome from anyone.

Barry

Hello Barry,

Your sketch is not visible on the site.
I don’t know why but figures tend to disappear sometimes…

However, if my memory is correct you draw a fin inspired both from the Emeraude and from the Spitfire.
As far as efficiency is concerned both proved to work properly. So they should continue to do so.

Aesthetic is a personal matter.
The British-look fin of the Spitfire is perfectly matched to its fully elliptic wing.
The Emeraude fin is nice with the Piel’s semi-elliptic wing.
I think that it is difficult to imagine the look of a Spitfire fin on CP605 only with a side view.

Bons Vols
Philippe Dejean

Hi Philippe,

Thank you for the comment. I will post re-post my last drawing.



How is this?

Barry

Hello Barry,

I discovered that the picture problems is not due to the site but from one of the computer I'm using sometimes.

Perhaps a sketch as badly made than this one could help to choose the fin's shape

Bons Vols

Philippe Dejean

Philippe -

FANTASTIC!!

You have solved my problem!

You even have a Seagull in the cockpit - what a marvellous drawing. I shall commence building at once.

Very many thanks for your input,

Barry