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Nov 15, 2019, 04:20 AM
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shaneyee's Avatar
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Rubber model from Allegro Lite wing


I've been watching rubber model flight on Youtube and its pretty intriguing.

Since I have an old Allegro Lite Wing and tail I thought of making a rubber model from it. I would build a new fuselage and use just a rudder servo to keep it within sight . What would be a suitable rubber motor and propeller?

Thanks
Shane
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Nov 15, 2019, 02:23 PM
B for Bruce
BMatthews's Avatar
What is the weight of your wing and tail? My thinking is that even an Allegro Lite wing and tail is too heavy to fly well as a rubber power model. Closer to the mark would be the lighter options from the relatively new F3RES event. But even those are way overbuilt and needlessly heavy by rubber flying standards.

Plus a 2meter size rubber model even built down to weight would need a honking big fat motor. I'd call it half a pound or around 250 gms. And that would mean a REALLY serious winder and stooge to hold the model against the winding forces. And probably an 18 inch or larger prop. And not the sort you get for an electric power model. It needs to be a really high pitch value.

So sorry to say but it's just not a great way to go.

If you are interested in large size rubber model flying with minimal RC to use for returning to the launch point have a look at some plans links to get a feel for the size and weight. The models shown below would normally have a roughly 4 oz /100 gm size rubber motor. This size still needs some decent ground support setup to prep and wind the motor but it's not as unreasonable as you would have with even bigger and heavier motors.

You would need to learn to make your own props since nothing from the electric RC world has the proper sort of pitch to work with rubber power. Mostly that means carving them from balsa. But it could mean molding them in thin carbon over a wafer of foam core if you're up to the challenge and interested enough.

Here's some links to a variety of models that are on the larger size for the rubber power world and would easily carry a super light RC setup without any issues.

https://outerzone.co.uk/plan_details.asp?ID=2362
https://outerzone.co.uk/plan_details.asp?ID=9563
https://outerzone.co.uk/plan_details.asp?ID=6230
https://outerzone.co.uk/plan_details.asp?ID=423
https://outerzone.co.uk/plan_details.asp?ID=1460
https://outerzone.co.uk/plan_details.asp?ID=6092
Nov 15, 2019, 02:31 PM
B for Bruce
BMatthews's Avatar
I should point out that even with rudder control to aid with saving them from a crash that it takes a bit of time to learn to build such models lightly but strong enough. And as you can see from the plans in the links they are not all that strong by any means.

If you've been watching some FAI free flight you might be taken by how much the models resemble 2m gliders. But even there an F1B model is still only 230 grams in flying condition. And the props used to get the performance such models have are finely tuned and highly critical. You're simply not going to get that level of performance starting out and without the very best purpose made gear.

If you're still interested in rubber flying and building such light models it may be nicer to start out smaller. If you are game for that there's a number of easier small models that could still be used with the super light radio gear out there these days. I've seen references to 1gm receivers and 1.5gm servos that solder their leads directly to the board to save weight. Combine this with something like a 50 to 70mah lipo cell and you have a 4 or 5 gram "retrieval system" that can be flown in a modest size 70 to 90 cm span model.
Nov 15, 2019, 07:54 PM
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shaneyee's Avatar
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Quote:
Originally Posted by BMatthews
What is the weight of your wing and tail? My thinking is that even an Allegro Lite wing and tail is too heavy to fly well as a rubber power model. Closer to the mark would be the lighter options from the relatively new F3RES event. But even those are way overbuilt and needlessly heavy by rubber flying standards.

Plus a 2meter size rubber model even built down to weight would need a honking big fat motor. I'd call it half a pound or around 250 gms. And that would mean a REALLY serious winder and stooge to hold the model against the winding forces. And probably an 18 inch or larger prop. And not the sort you get for an electric power model. It needs to be a really high pitch value.

So sorry to say but it's just not a great way to go.

If you are interested in large size rubber model flying with minimal RC to use for returning to the launch point have a look at some plans links to get a feel for the size and weight. The models shown below would normally have a roughly 4 oz /100 gm size rubber motor. This size still needs some decent ground support setup to prep and wind the motor but it's not as unreasonable as you would have with even bigger and heavier motors.

You would need to learn to make your own props since nothing from the electric RC world has the proper sort of pitch to work with rubber power. Mostly that means carving them from balsa. But it could mean molding them in thin carbon over a wafer of foam core if you're up to the challenge and interested enough.
Thanks.

The wing is 525sq inches in area and weighs about 10oz so its probably too heavy. If I have a spare rib set and build it lighter without the heavy duty carbon spar would the AG35-AG38 airfoil be suitable?

How do you calculate the rubber and propeller requirement given the weight and wing area?

Thanks
Shane
Nov 15, 2019, 11:57 PM
Registered User
Quote:
Originally Posted by shaneyee
Thanks.

The wing is 525sq inches in area and weighs about 10oz so its probably too heavy. If I have a spare rib set and build it lighter without the heavy duty carbon spar would the AG35-AG38 airfoil be suitable?

How do you calculate the rubber and propeller requirement given the weight and wing area?

Thanks
Shane
The design of the Allegro Lite wing isn't suitable. For rubber power, you want something very light and very slow. I suggest using a teensy radio if you must have one. Radio gear can be extremely light these days. Suggest nothing larger than a simple P30 to start with. A good P-30 flies very well anyway.

If you really want to go forward with a rubber powered Allegro Lite, I suggest you start lifting weights so you can actually wind it. Also, a really robust winder.

I suppose you could use Allegro Lite ribs to make a good rubber model. You'd start by cutting them thinner...
Nov 16, 2019, 12:23 AM
BOYCOTT SCAMAZON
lectroglide's Avatar
Hate to steer you away from your existing model but theirs plenty of P30 models "30 in span" out their youd be happy with
go to youtube and type in P30 free flight for a nice selection and more info. also try and find some rubber guys in your area and reading the forum here..……...
Nov 16, 2019, 03:21 AM
B for Bruce
BMatthews's Avatar
Some of the lighter F3RES designs are being built down to around 12 oz. Or at least some of the kits with extra light wood are coming out to around that weight.

If you could use your Allegro Lite ribs and build a model that comes in at between 8 and 10 oz empty weight then it would do fairly well as a rubber power model "self launched soaring glider" with around 6 to 8 oz of rubber.

But those numbers are still higher than is normally or even extraordinarily flown in the rubber events. Probably the biggest rubber models flown with any popularity are the "early dawn Mulvihill" class of model. These are the "super ships" to many folks. They are just as specialized in their own way as the FAI F1B Wakefield models.

A good view of what is involved in building light to fly well can be seen in this video of a long time expert at rubber flying.

Bud Romak and his Dawn Patrol (11 min 3 sec)


Now you don't need to match Joe at this game to do decently. But take note that the model shown is likely only around 6 oz in weight and uses 4 to 6 oz of rubber on top of that. And you can see that it doesn't exactly leap into the air. Now a BIG part of that is the massive prop that encourages a long 3 minute motor run. If you use a prop that lets the power out over around a minute there will be more power for a good climb. And after that it's up to you if you RC it around like a regular glider.

I enjoy building and flying RC gliders as well as my rubber power free flights. If I were to do a rubber power RC glider the AG airfoils would be a pretty good option. But only if I wanted to actually control the model the whole time. For RC recovered free flight I'd still go with one of the thinner cambered airfoils as used by some of the long stick style models in the links I offered above. Those airfoils "loiter" and float a lot more effectively with slow gliding circles. But they won't come back against the wind very well at all. But they should stay up longer if left to circle on their own than the AG airfoils from the Allegro Lite. Or maybe not. It would be a close sort of thing.

If you're keen enough not to let all this scare you away it would sure be a fun filled project. But it'll need more attention than starting out with the ribs for an Allegro Lite. While great for RC soaring the large amount of sheeting used on the AL right off the bat means a lot of added weight even if you cut way back on the spars. I think that a better way to go would be a totally open frame F3RES style wing but with light spars and the lightest possible covering.
Nov 16, 2019, 05:46 AM
Registered User
shaneyee's Avatar
Thread OP
Thanks guys! I think I'll start by building a Wakefield F1B model....with R/C assist

Shane
Nov 16, 2019, 02:43 PM
BOYCOTT SCAMAZON
lectroglide's Avatar
check that blast tube!!!!
Nov 16, 2019, 02:52 PM
B for Bruce
BMatthews's Avatar
Out of interest I went on You Tube and tried "rubber power radio control" and turned up some interesting videos. On in particular is about a rather high tech P30 build which might be a nice guide for your RC assist wakefield idea. There's a lot of great weight saving hints.

'Hell's Kitchen P30': RC rubber power - building. (11 min 53 sec)


There's some others too that show other options for designs and show how well/poor they fly. Do the same search to find them.

With a bit of looking around you should also be able to find a light carbon tube suitable for a Wakefield size model that is a bit longer to accept a 60gm motor for what you're trying to do. And the upside as well is that you can use the data on Wakefield props to avoid having to re-invent the wheel with a suitable prop for a 2M size like you would have needed to do. Basically if you stick with a similar cross section (number and width of strands) so you run the same torque level and just make the motor longer you can use the prop design which is already tried and proven.

The style of construction shown in the P30 video would be a little light for a Wakefield size model. BUT... only by a little. Keep things light and rely on using thin mylar covering to provide the torsional stiffness.

And please let us know about the build thread. It would be a fun project to follow. And, curse you , you now have me thinking about something similar...
Nov 16, 2019, 09:21 PM
Registered User
gossie's Avatar
I love seeing Bud fly. Great modeller, great model, great vid. Thanks.
J & H works for me, sometimes.
Nov 17, 2019, 10:54 AM
Registered User
If using a fast airfoil, a folding prop would probably help a lot. A Neelmeyer airfoil might be a good compromise.


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