Fournier rf-4 electric conversion?

[Peter Miller]

Probably the simplest thing would be plywood strips hinged on the forward edge that are raised into the airflow. The location should be shown on the plan.

 

So far I have not felt the need for them

 

[Viking42]

Peter,

Thank you for your promt response and spoiler idea and thank you for this very nice RF4 model design ! You are probably right, there may be no need for spoilers, - I have read about the preffered way to land her - i.e. to fly her in, so the first wing I build will most probably be accordig to plan.

 

Peter G

 

[Adam Reay]

Posted by David Thorpe 2 on 13/08/2011 17:50:37:

Thanks for reply ~ I'm still unsure about prop size, folder or fixed.

 

I do fly several e soarers so appreciate the drag implication of a fixed prop and am prepared to accept this as a "scale" sacrifice as, with the wing loading as it is, one is unlikely to exploit much thermal advantage anyway I would guess.

 

David

 

ps the Giant Cod motor suggestion for this motor is 11 or 12" dia which seems far too big and a certain grass cutter! From the plan with C/L horizontal 10" or less looks right ~ what do you reckon?

Peter says his I/C model flies on a 9X6 fixed prop. It seems there is a power discrepancy because the BL2820 brushless motor is matched to a 12x6 or an 11x7. I must look into this a bit more before I commit to a motor and matching power train.

[Peter Miller]

Oh well, if you must use a 12" prop it will have to fold. It will just have to fold either side of the apple cheeks.

 

Can't you use a 9" prop on the motor.

[PatMc]

 

Posted by Pete B on 09/06/2011 13:18:44:

The 970kv motor will allow a bigger prop to turn at lower rpm, which will extend the battery time.

The bigger prop isn't desirable in this case. Because it turns at lower rpm does not mean the battery time is extended.

 

A 9" prop would be about the scale size & I see no reason that an electric version of this model can not use one.

Either use a higher than average Kv motor or a 4s lipo with moderate Kv. One of these 1400Kv motors on 3s or it's 1100Kv equivalent on 4s should be about right on a 9x6.

If using the 4s option a current lower rated esc could be used & a lower C rated battery.

 

 

 

Edited By PatMc on 09/11/2011 20:04:30

[Adam Reay]

Decision made! I'm going for a 9x6 and a 1400Kv motor. To modify the fuselage for electric power I am working back from the nose. Now that I know the motor dimensions and the motor mount I can determine the position of the forward bulkhead. At first glance it seems it will be about an inch further forward than the drawing shows.

[Viking42]

Hi,

A repositioning of the bulkhead seems to me unnecessary. I just glued and screwed a wooden block to the bulkhead in a suitable size. The problem with the electric motor in my case is its very short 5 mm axis( even with the prop adapter). The electric motor and ESC plus batteries also need cooling, why I had to make holes in the bulkhead to let some air pass through. I am also hesitating to use a spinner just because of this.

 

Regards

 

Peter G

[Adam Reay]

Peter,

Elsewhere in these blogs someone moved the bulkhead forward by 40mm. Your wooden block is another way to place the motor mount in the correct place.

I also have been thinking about cooling. A scale cowling not made from balsa block would help in getting air to the motor. It's early days and I don't need to decide yet but I think I could make a cowling in GRP scrim (not chopped strand mat) by carving a dummy nose in polystyrene foam and then laying up a thin GRP cowling on top of the plug. After the foam core has been removed the cowling would need to be trimmed, filled and sanded to the required finish.

Regards,

Adam

[Viking42]

Adam,

You are quite right about the bulky size of the cowling. The size is a result of the thick outrunner electric motor being mowed forward. The right way to encounter this is probably by having a motor with an attached gearbox - expensive though.

Personally I have been warned to start up making cowlings etc in GRP. People say to me it´s a nasty toxious and bad smelling job. I´ve seen a guy though, who made a cowling by using a Coce plastic bottle bottom and form that in an ordinary owen - the form has to be of wood, of course-, and I don´t know how many hundred bottles he had to try on first!

So, most people buy from experts they know and therefore before you experiment, I must recommend you to talk to some guys (model shop, local model club etc).

If there will be a plastic nosecone, I would gladly buy one!

Regards

 

Peter G

 

[Peter Miller]

Using the plastic bottle technique doesn't work if the there are hollows or concave areas to go into, only .

 

Polyester resin is smelly but not particulalry dangerous. I have worked in a fibreglass company and used it at home.

 

I don't really like it but it does work

 

 

[Adam Reay]

Peter G,

I'm fortunate that I have had experience of GRP when I owned a big sailing boat and had to do repairs occasionally, but I admit, nothing as small as this. I will keep you informed.

[Adam Reay]

 

I have assembled the main bits of the new 'plane from items I already had apart form the spinner and 9x6 prop. The "timber" arrives to morrow and it will be time to start on a long journey.

[Viking42]

Adam,

Your layout for motor, ESC and battery looks very promising .! I have today uploaded 2 more pictures, where you can see my solution of the RX position, (behind the pilot figure), which makes it very easy to let the dual antennas out in the open alongsid the fuselage.

When flying though, I will probably have to omit the spinner variant, as the short axis of the motor is preventing a good grip of the prop adaptor, when this is fitted.

 

Peter G

[Adam Reay]

Thanks for these very useful photographs. You model is much further advanced than mine. I am still waiting for the 0.8mm ply reinforcement before I can finish the fuselage.

I made the mistake of building the rear fuselage up to F5 former and didn't notice a slight twist that I have built in. I was too impatient to start.

What is your opinion of the wing mounting arrangement? The two bolts at the rear and a single pin at the front doesn't seem very secure. How did you do it?

[Peter Miller]

I use the single dowel at the front and two bolts at the rear on highly aerobatic, over powered models. My Rhapsody will do the fastest flick rolls that you have ever seen

 

Harlequin Very aerobatic, 40 FS, .

Dalotel .40 Two stroke, very aerobatic

Marauder, very fast and aerobatic. .25

Symphony. .32 two stroke, very aerobatic. Very fast flick rolls

 

All the above use the same wing hold down system and have never failed.

 

Smaller models such as my Little Bandit with a West .25 only use a single bolt and two dowels.

 

Now, Exactly why don't you think that the single dowel and two bolts is not secure?

[Adam Reay]

My Phoenix 2000 high wing powered glider has four bolts to hold the wing on and I assumed I would have to ensure that a single dowel instead of two forward bolts on the Fournier would have to be a very tight fit. Glad to hear the dowel arrangement will be safe.

 

[Adam Reay]

See the Phoenix wing in my Fournier build album above.

[Peter Miller]

All the 1/4" dowel has to do is stop the wing lifting off its seat. It will often shear if you dig a wing tip in on landing which saves the wing from breaking. The rear bolts are only 5 mm nylon.

 

Rhapsody (I haven't got a picture on this computer) is a high wing cabin model, it ises the same set up and that wing stays on regardless of some really wild, high strees aerobatics.

 

I don't know what your four screws go into but I suspect that if you do a cartwheel landing you are going to rip large ckunks of model out when the wing comes loose.

 

My system (used by many others) will withstand anything I can throw at it but does tend to protect the model to some extent.

 

Having said that, I did crash my Fournier RF-7 and the wing was smashed but the dowel and bolts held. I rebuilt the complete right hand wing.

 

[Adam Reay]

Peter,

Thanks for your helpful advice. The Phoenix has a nylon fuselage and the steel wing bolts go into captive nuts in the fuse making a very rigid assembly, but if I have a bad crash the wing will be the first thing to break. A sacrificial wooden peg is a much better concept.

[Viking42]

I've decided so far to keep the Turnigy 25 installation. The motorcowling had to grow some 10% for this. Going for an inrunner with gearbox would, as far as my research on the web can tell, be another 150£ compared to the 25 US$ I paid for the Turnigy. The CG comes with the Turnigy very close to that indicated on the drawing, so it will hopefully be easy to finetune without led with the battery positioning only.

 

I'm now looking for some nice not so complicated painting schemes, so does anyone know any web-adress(es) for the RF-4?

 

Peter G

[Peter Miller]

Just put Fournier RF-4 on google search and then look at the images section. Hundreds of the things in all colouirs

[Viking42]

Peter M.,

Thank you very much for your hint - I managed to find a photo of a plane that shows enough so that i can try to make something similar (on the website Fournier RF-4D worldwide). I´ve ordered white "semi-glossy" Solatex film, and as I saw from your building photos, it´s quite possible to paint on that material. Yes? Some people I know use car spray coulors, what kind of paint do you use?

 

Regards

Peter G

[Peter Miller]

Not quite sure what you mean, Solartex film. Solartex is a cloth, not a film. It is quite a lot heavier than film.

 

I used to use car spray paints in the days when I used Solartex.

 

You can't paint on film without special treatments which I have never tried.

[Adam Reay]

http://www.solarfilm.co.uk/

 

This is a link to what is meant. Definitely a film.

 

 

http://www.sussex-model-centre.co.uk/shopexd.asp?id=1965

 

This is a link to Solartex. Definitely a fabric

[Peter Miller]

Sorry but the first link just took me to the Solarfilm website, not a particular product.

 

Do you mean the matt polyester that they do?