Originally Posted by WMD

Am just thinking about something... sometimes I can't help myself. If I wanted to build a rubber model, let's say a Wakefield type, and then to install a modern electric brushless motor and some RC (sorry purists) to run it as a local parkflyer... is it possible to gear the motor down so it can swing the original size of rubber-style prop, to keep the look of the original design? I always think smaller props look wrong on these larger rubber types.

Edit: heres the kind of thing I mean, pic shows very handsome model wearing an 18in diameter prop. Actually 18 x 24, it says, but maybe best to leave the pitch out of this... this pic is of the 1947 Krusader design, more details here http://www.outerzone.co.uk/plan_details.asp?ID=4869

The answer is yes. I built a speed 400 powered sailplane in the late 1990's that used a high reduction gear drive to swing a 24 inch rubber prop. I hand built the drive using gears from a heavier drive I found in a surplus store. The motor and gearbox were mounted just ahead of the CG with an extension shaft driving the prop. I don't have any photos to offer except the one in the attached scan of the 1998 Flying Models column it appeared in. The text lists the gear ratio as 33.6 to 1. The set up worked very well and was quite efficient.

Ralph

The 11.7 ratio on the old GWS IPS motors were supposed to swing up to a 14 inch prop, though perhaps not with enough pitch to go fast enough. The lower ratios were adequate for 7 oz. planes. Maybe a dual IPS would have more zip and you could put your high pitch 14 incher on one:
http://www.gws.com.tw/english/produc.../ips-dx2bb.htm
http://www.gws.com.tw/english/produc...ystem/ipsd.htm

Maxxprod.com has some very similar motors, and Radical RC lists some of the GWS IPS motors.

You might try using a winder for a gearbox. Put on a hook instead of the handle, run a rubber band from the motor to the gearbox and from the gearbox to the prop. The KP winder has 10:1 and 15:1 versions. It might need to go on a diet. Volare products list them: http://volareproducts.com

Or perhaps you can use the gear setup from a large servo. Not sure it could handle the increased rpm and axial load, though, and it might not handle tension either. Plus the reduction might be too much. But you might do something with the gears. You can buy a set of gears separately. Places like Allelectronics and Electronic Goldmine, among others, have what look like suitable gears for something like this.

That Feigao looks pretty good.

lincoln, you are correct. The old twin GWS IPS motor will swing a very large prop. I have one but have never flown it. Ran it up a few times and it will push some pretty good air. Might make a good chioce.

I am very interested in the discussion about gearing because I aim to use it for my next model for a competition class that we have here in New Zealand.
It is called Vintage E Rubber Texaco, for original rubber designs up to end 1950, with electric motors and 2cell LiPo batteries with maximum mah capacity 0.9xwing area in sqin. Designs can be scaled up or down.
I attach a photo of my current model, called Surprise, a 1949 Canadian design (third in Wakefield Cup that year) published in MAN in 1950. This is a conversion of a model actually first flown with rubber. With RC it weighs exactly the same as with rubber - 8oz. It has the small prop that some-one said the don't like - nor do I. However, the prop disappears in the air and the model looks much as it did when rubber powered.
The model is capable of about 7 minutes without thermal assistance, on a 180mah battery.
For my next model I plan to use a geared motor with folding prop.

I think a folder will help the glide a lot. You might want to put a rubber band on to fold it if one of the blades ends up on the bottom side when the motor stops.

Ok, I hope you don't mind the following, since it doesn't address your question:
It might be best to scale the models up. The aerodynamics are better and you can see it further. Or start with something that's really large in the first place, if you're willing to sink some time and funds into it.

How about this one?
http://outerzone.co.uk/plan_details.asp?ID=3110 Ok, ok, you probably don't need to go that large to be competitive. I'll bet a double sized KK Gypsy would be great. Ok, maybe you should pick something without landing gear, with a thin airfoil and not too much camber. At least if you know how to find lift and scoot out of sink.

Now 'that' is an interesting design.

Attached is my "Clodhopper" I was going to try and use a single blade 10" folder but found that the added gearing became too inefficient.

Of course my approach was a bit different. I opted for a single cell setup so the geared inrunner I used was chosen specifically, but I might just opt for the 2 cell one instead depending on flight tests.

The prop is a 9x3 which gave the best results and since I wanted to play with different type motors/gearing opted to fit it under the CG so as not to cause too much trim changing, so decided to drive the prop by rubber bands.

This caused some additional issues in that every time it spun up, the rubber bands would bunch up as intended, but would then be thrown off centre, like a skipping rope and hit the sides, so I ended up slipping a length of tubing over the bands (not shown in the photo) and this has kept everything in line and true.

Model still needs to be covered and I have been procrastinating way too long

I know the guys are flying with small outrunners and 5 - 7 in props and getting good times but I want to stay with the spirit of the competition and obviously that means using as close to the correct sized prop as possible, so I am very glad to see you trying to go that route as well Wayne

Mark

Originally Posted by lincoln

It might be best to scale the models up. The aerodynamics are better and you can see it further. Or start with something that's really large in the first place, if you're willing to sink some time and funds into it.

Hi lincoln,

By the way, I had some fun lately fiddling with XLFR5, trying to improve the aerodynamics of my 10cm chord rubber model. Its current airfoil, the NACA6609, displays poor performances for Reynolds number around 30000 (speed 5 m/s).
But I found that a simple sheet of balsa whose profile matches the upper part of the NACA 0009 has a L/D of 30. I think I will try it.

What do you think?

The Fane AOP

The Fane F.1/40 was a 1940s British Air Observation Post aircraft design by Captain Gerald Fane's Fane Aircraft Company.

It was designed to Air Ministry specification F.1/40 for an airborne observation post. It was developed by Gerard Fane based on the Comper Scamp. The Scamp had been designed by Nicholas Comper as a two seater but he had not built it but redesigned it as a single seater, the Comper Fly. Fane took the Scamp design and reworked it as the F.1. It was of pusher configuration with a high wing set behind the pilot. A single example serial number T1788 was flown and tested by the Air Ministry at Heston Aerodrome in March 1941. It was in competition with the General Aircraft GAL.47 but neither were selected for service use. In September 1941 the F.1/40 was registered G-AGDJ to the builders, but was scrapped sometime during the war.

Specifications

Data from British Civil Aircraft since 1919 Volume 2

General characteristics
Crew: 2
Length: 23 ft 5 in (7.14 m)
Wingspan: 37 ft 0 in (11.28 m)
Max takeoff weight: 1,500 lb (680 kg)
Powerplant: 1 × Continental A-80 , 80 hp (60 kW)


I've been fooling around with this little girl for over six months, trying to develop a set of eighth scale plans ....55" wingspan........480 series electric, etc. Photos were my only reference. Cut out a 28" WS foamie just to see if it would fly. Well, it'll fly, but not real well. It will take someone with a lot more skill than me to build and fly this thing. Way too many unknowns........AOI, Stab incidence, up-thrust, CG, etc. I can see why only one was ever built.... Which was the reason I started this project in the first place. At least now there is some record of her, inadequate though it may be.

In the past, a couple of you guys showed some interest in the Fane, so I decided to complete the drawings as best I could with loads of help from the usual suspects...hogal, Lincoln, and David Terrell among others......you know who you are...thank you all.

If any of you try to take this thing on, you might consider more wing (a lot more), more dihedral, a better airfoil than a Clark-Y or GOE 493 (I tried both). You might also consider better medication.

Note: I'll upload the source drawing (AutoCAD 2007) if anyone wants to have a go at refining her. Send me a PM

UPDATE:

I cut out Fane 2.0 with a 30" WS, a thinned Clark Y and a better wing mount.......flies great !

Originally Posted by Paul_BB

Hi lincoln,

By the way, I had some fun lately fiddling with XLFR5, trying to improve the aerodynamics of my 10cm chord rubber model. Its current airfoil, the NACA6609, displays poor performances for Reynolds number around 30000 (speed 5 m/s).
But I found that a simple sheet of balsa whose profile matches the upper part of the NACA 0009 has a L/D of 30. I think I will try it.

What do you think?

If your graphs are truly representative of the real airfoils behavior, you may have a problem. Check out the alpha vs Cl graph. There's a big jump with very little change in angle of attack, so I'd expect the model to be pretty jumpy. Maybe try it with a trip? Maybe at 20 or 30 percent. Program may underestimate the trip drag, but it ought to show improvements of the behavior. But that thin foil sounds like a good idea.

That Clark Y would probably work a whole lot better on the 55 inch version, where the Reynolds number is up around 100k or more. On the little one try a thinned Clark Y (8 percent?) with a thread or something like that on top at 25 percent of chord and see if it doesn't do a whole lot better. Heck, try it with the existing Clark Y and that thread and you may see some significant improvement.

Maybe the following plans will cough up some good ideas. I tried to pick ones by designers who had a good reputation, or at least ones I've heard of:
http://outerzone.co.uk/plan_details.asp?ID=2280
http://outerzone.co.uk/plan_details.asp?ID=2562
http://outerzone.co.uk/plan_details.asp?ID=3107
http://outerzone.co.uk/plan_details.asp?ID=950

I don't know this designer, but the model is too cute not to include:
http://outerzone.co.uk/plan_details.asp?ID=676

I don't know this designer,

Really I think we can safely put Howard McEntee in the "designers with a good reputation" catagory

Ray

Originally Posted by lincoln

That Clark Y would probably work a whole lot better on the 55 inch version, where the Reynolds number is up around 100k or more. On the little one try a thinned Clark Y (8 percent?) with a thread or something like that on top at 25 percent of chord and see if it doesn't do a whole lot better. Heck, try it with the existing Clark Y and that thread and you may see some significant improvement.

Maybe the following plans will cough up some good ideas. I tried to pick ones by designers who had a good reputation, or at least ones I've heard of:
http://outerzone.co.uk/plan_details.asp?ID=2280
http://outerzone.co.uk/plan_details.asp?ID=2562
http://outerzone.co.uk/plan_details.asp?ID=3107
http://outerzone.co.uk/plan_details.asp?ID=950

I don't know this designer, but the model is too cute not to include:
http://outerzone.co.uk/plan_details.asp?ID=676

I noticed that 3 of the 5 have lifting tails...and very little wing incidence....something I should consider for the little version ?

I think on a model of a full sized aircraft of conventional proportions, a cambered stab probably doesn't do much except require more incidence or up elevator trim. Unless you want the stab to look more negative when trimmed.

Incidence is really between the zero lift angles of the surfaces in question. If you have a flat stab, and a cambered wing at the same angle of attack, that's already like having some positive incidence on the wing or negative on the tail. Anything symmetrical will be at zero lift at an angle of attack of 0. But a Clark Y might be at -2 to -4 degrees, depending on the Reynolds number. Also, the angle of attack is usually measured from a line that goes from the trailing edge to the furthest forward part of the leading edge. So that might be a couple of degrees above the angle of the flat part of the bottom. Therefore, a Clark Y with the flat part parallel to the direction of motion is really at an angle of attack perhaps 4 to 6 degrees higher than zero lift. If the stab has less camber than the wing, you can still have effective incidence even if the bottoms are parallel or the nominal angle of attack is the same for both. I think if you look at it that way, all of the models have at least a bit of incidence, I guess more properly, decalage.

Anyway, you can probably adjust the elevator a bit if the wing to tail angle is wrong, but the angle between the thrust line and the wing wouldn't be so easy to adjust and may be important.

Originally Posted by lincoln

If your graphs are truly representative of the real airfoils behavior, you may have a problem. Check out the alpha vs Cl graph. There's a big jump with very little change in angle of attack, so I'd expect the model to be pretty jumpy. Maybe try it with a trip? Maybe at 20 or 30 percent. Program may underestimate the trip drag, but it ought to show improvements of the behavior. But that thin foil sounds like a good idea.

Thanks for your answer lincoln. I am now experimenting with turbulators at low Reynolds number. Pretty impressive on the paper (Xfoil).

Hola estoy buscando el plano de un modelo que se llama Volatin si alguien me lo pasa gracias.