Coupes - pre 1970

[PeeTee]

It's a pity that the previous versions of HPA are difficult to access so I'll start anew ! In the UK there is still quite an attraction to coupes amongst the competition flyers and my chums  fall into that category. One of our dear departed modellers was Don T to use his HPA name! He built an attractive pre 1970 model designed by Jean-Pierre Challine and I'll try and post a photo here ( wish me luck as it's the first one I've done)

Peter

[PeeTee]

Well that wasn't very good, even when my son attempted to load the photo. I'll come back to it again eventually ! I'm sure that it was easier to load photos in the earlier versions of HPA, I must have shared hundreds!

Peter

[calgoddard]

PeeTee -

I am a big fan of vintage Coupes. There are so many designs. I wrote an article about the new Vintage Coupe event in the USA but can't recall where the rules are posted and who created the event. I just remember reading about the event as a great alternative to the FAI Coupe event which essentially requires the purchase of expensive multi-function F1G models made in Eastern Europe in order to be competitive.

An excerpt from my article is reproduced in italics below. The picture shows the My Coupe by Bill Vanderbeek on the left. The smaller Coupe on the right is the Hat Band Coupe by the brilliant UK modeler, the late John O'Donnell. Credit for this picture goes to Louis Joyner who for years published great articles in the AMA'a Model Aviation Magazine.

The cost and complexity of high-tech coupes led to the recent introduction of a Vintage Coupe event for models designed before 1970. The object of this new event is to reintroduce simpler and cheaper self-built, low-tech stick and tissue F1G models. These are often referred to as "locked down" coupes since they lack auto-functions. To qualify for the Vintage Coupe event the model must be built per the published plan. A very good Vintage Coupe model is the My Coupe designed by Bill Vanderbeek which won at the AMA Nats from 1967 - 1969 and in 1971 Nats. The plan for this coupe is available from NFFS for $10 plus shipping costs. I'm tempted to build a My Coupe. 

[lincoln]

There are a number of coupes in the HPA plans section, including in the magazines that come up. The link to the plans section should be at the upper right of this page. Plans for My Coupe are at https://outerzone.co.uk/plan_details.asp?ID=13876
This search turns up some pre-1970 coupes:
https://outerzone.co.uk/advanced/search/results.asp?T1=FF&T2=Rubber&T4=NonScale&Y2=1969&K1=Coupe&F1=Dscrp

If you are looking for a specific coupe and can't find it elsewhere, it's possible I have it. Send me a message and poke me once a week until I get back to you.

[PeeTee]

Thanks for replying calgoddard ! The French started the coupe class and I've been to Viabon (in France) for the best part of 30 odd years to compete. They used to fly vintage coupe (pre 1957) in late February/early March but us old'uns are not going any more.

The pre 70s class came about by people from HPA deciding that they would like to fly something a little more modern but still keeping to stick and tissue construction. I have not built one because until a couple of years ago the rules said the D/T had to be as shown originally eg burning fuse!

Well that's my lot for the minute, it takes me a long time to type with my left forefinger 

[Jmk89]

Here's my 1967 Coupe - Tyra by Shirley and Bill Horton

Plan available from OuterZone - https://outerzone.co.uk/plan_details.asp?ID=9521

[Jmk89]

Let's try getting the photo on the post this time

[calgoddard]

Nice Tyra vintage coupe.

The single blade prop assembly would be tricky to construct, and even trickier to balance. But I do like the amazing look of a single bladed prop under power.

[Jmk89]

Thanks Cal.  I don't find single bladders any harder to make. Indeed not having to get a second blade made that is identical to the first and then ensure that both blades are set up in exactly the same configuration seems to make them easier to make, at least for me!

Static balancing is pretty easy too. Make the lead weight a little heavier than you think you need it to be and then file off lead until the two sides balance ( I.e. the blade and the weight are at 9 and 3).

Dynamic balance can be trickier, but it seems that so long as the weight arm is bent so the weight is on a plane to the aft of the prop plane, nothing too evil occurs.

One other advantage of the single blader is that you can set the prop stop so the weight end is down, so you have a kind of landing skid to protect the fuselage and the prop blade is nicely out of the way on top of the fuselage. While that may interfere with airflow it is only adding to an existing issue of interference with the airflow over the centre section that the fuselage contributes, so I doubt that it prejudices the glide and it may even improve it by reducing drag a little.  But I think we are dealing with unmeasurable points here.

PS In my hurry to photograph the model, I hadn't finished the tail plane. The tissue dags have now been trimmed

[calgoddard]

Jmk89 -

Thanks for your insightful comments on single-bladed props.

There is plenty of literature that indicates that a single-bladed prop is the most efficient because the lone blade swings in undisturbed air.

Some WWII fighters used huge 3 and 4 bladed props to accommodate the power of their huge engines while reducing the landing gear height otherwise needed for the blades to clear the runway during take-off and landing.

For a short time there was a commercial single bladed Everel prop manufactured and sold for small civilian aircraft. See the attached picture.

Also attached is a nice picture showing the construction of a single bladed prop for an Old Time Rubber (OTR) model in great detail.

The single-bladed prop can be dynamically balanced so that it won't spin with no oncoming air by adjusting the weight of the counterweight, or simply moving it in and out on the wire outrigger opposite the blade and then fixing it in the optimum position. However, the rearward position of the counterweight located behind the plane of rotation of the single blade is only optimum for one predetermined RPM during the power phase. But for this shortcoming you might see single bladed props on modern Wakefield models. However, a two-bladed prop with variable pitch is much preferred.

[Mike Thomas]

Martyn Pressnall published an excellent article on balancing single blade folding props.
If you Google it, you will find that it's available to download as a PDF on RCGRoups. I tried to attach the PDF here, but couldn't work out how to do it. Mike

[Jmk89]

Thanks for that Mike

Here's the article

[calgoddard]

Thanks Mike and jmk89 for the article.

Retro RC in the US sells a nice kit for a folding single blade prop. I bought several of these kits. The quality is excellent.

[Raggedflyer]

[quote author=calgoddard link=msg=4311 date=1781226190

However, the rearward position of the counterweight located behind the plane of rotation of the single blade is only optimum for one predetermined RPM during the phase.
[/quote]

Has anyone ever tried to optimise the counterweight balance over the working rpm range by a mechanism akin to the variable pitch torque control used on serious indoor models.

[PeeTee]

Now you are asking serious questions    All the coupes I've built with single blades use the balancing arm offset in a rearwards direction and it seems to do the trick ( or you have launched into 'sink')


Peter