Free flight versus Radio aircraft  
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All Forums >> RC Airplanes >> Aerodynamics >> Free flight versus Radio aircraft
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Free flight versus Radio aircraft - 2/23/2008 1:23:02 AM   
CoosBayLumber


 

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From: San Bernardino Calif
Status: offline 		Sometimes all that you can find for a sucessful aero design is a free flight model/plan (of old).

Presuming I get the new power to work out, wing laodings etc. what other hazards should I watch out for when thinking of Radio uses?

Am eyeballing a design that is small, has both (Old) glow power and rubber shown on plan. But I want to go either new glow or electric, with radio, and not change much else.

Wm.


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RE: Free flight versus Radio aircraft - 2/23/2008 2:15:46 AM   
crasherboy


 

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Status: offline 		Well,first off you will notice that the old timers had a lot more dihedral than most RC models have,and more tail feather surface. This to give the model more natural stability. In a free flight you would want it to come down in a nice glide after the power is gone,but RC controlled ones ,you have a lot more to say how they fly in the same situation. If your model will have ailerons,of cource you would not want all the dihedral that the old free flights had,and you could cut down on the size of the tail feathers too. I have a set of plans that I bought from MI around fifty years ago,called the Aeronca Grasshopper,has a wingspan of I believe 38",just right for a electric parkflyer. With a few changes it would be a dandy.I will try to uplaod an image of it .

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RE: Free flight versus Radio aircraft - 2/23/2008 2:24:45 AM   
CoosBayLumber


 

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Status: offline 		One of the A/C being considered has zero ailerons. The Dihedral is too flat for free flight but good, number wise, for a Radio. I ran them each through one of the calculators and most fit, but some came out sort of on the heavy side once battery weight was considered.


0nly thing I don't know much about at this time is the landing and T.O. characteristics between the two designs.

Much difference betweena high wing and a low wing design?



Wm.


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RE: Free flight versus Radio aircraft - 2/23/2008 2:24:58 AM   
crasherboy


 

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Status: offline 		If you can find my upload ,I am not sure how it is done,.

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RE: Free flight versus Radio aircraft - 2/23/2008 2:26:38 AM   
crasherboy


 

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Status: offline 		IS THIS ONE YOU HAD IN MIND? It would be a dandy to change to RC,I think!

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RE: Free flight versus Radio aircraft - 2/23/2008 3:44:07 AM   
CoosBayLumber


 

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Status: offline 		Nope, but one of those very similar to.

Was considering the older Berkeley Fairchild 22 Ranger. Went up to the SIG era of the early 1960's too. Per plan, the installation shows rubber, glow, and CO2.

The slightly more modern Cessna Birdog has been done to death here.

Usually the fuselage will not withstand the shock of many landings, and then they ruin the weights by adding some heavy cowling or parts to the wing. Which is why I usually look into the combo powered A/C.

Wm.


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RE: Free flight versus Radio aircraft - 2/23/2008 8:05:39 AM   
pimmnz


 

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Status: offline 		The design changes will depend on what you want to do with the model. If all you want is 'Radio Assist Free Flight' then the minimum changes will be adding a rudder and a new, longer and tapered ply wing brace. If you want a sport R/C then you will need to add rudder, elevator and motor control, with possibly a reduction in dihedral, but definitely a reduction in incidence difference between the wing and tailplane to 1~2 degrees, probably 'proper' symmetric tail sections, if only for strength and rigidity requirements, less downthrust, with this high wing model 2~3 degrees should be enough, and certainly considerably better spars and braces in the wing, with stronger strutting, than the F/F version, just to handle the increased speeds and loadings introduced with the addition of the elevator. I would also look closely at the U/C and use some light spongy wheels, at least. There are two schools of thought here, either re-design as a sport radio type of U/C, or leave it basically similar with the ability to bend it all back to shape after a nasty landing. Of course, the lighter you do this stuff, the less damage any arrival will do, and the less modifying you need to do.
Evan, WB #12.

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RE: Free flight versus Radio aircraft - 2/23/2008 2:42:46 PM   
CoosBayLumber


 

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Status: offline 		Evan....

Never thought about what you wrote, until it was mentioned. The model as per plan does not have a lot of dihedral angle. So, will most likely leave that alone.

But, had never thought of altering the incidence, or the engine angle. Good you brought that up here. Now, got something else to look into, but is easier before flying than afterwards.

Wm.


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RE: Free flight versus Radio aircraft - 2/23/2008 6:42:25 PM   
BMatthews



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Status: offline 		It's been my experience that a lot of the "sport" or "scale" free flight models would show excessive decalage along with excessive downthrust in an attempt to get the model to be quick to right itself from a stall but then you need a lot of downthrust to counter the strong tendency that the decalage has to want to climb when it sees more airspeed.

Assuming it's a usual flat bottom wing and that you're going to use elevator alter the incidences, if needed, to reflect this. Since it's a Fairchild 24 I'd draw a fuselage datum from the middle of the spinner or cowl (Ranger or radial?) back to the tail and make it so the wing has about +2, the tail at 0 or -1 and set the thrust line to -1 or -2. That would provide -3 to -4 relative angle between the wing and thrust line. Enough to control the pitch up but leave a little so the model does want to climb with power to some extent.

How does that jive with the plan?

SInce this is a scale model the CG should follow the "normal" practice of being in the 30%'ish range. But a trip through the CG calculator at giestware.com will confirm that for you. See the link in the FAQ/Online Calculator sticky thread.

Sounds like fun. Especially since the Fairchild has always been one of my favourites.


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RE: Free flight versus Radio aircraft - 2/23/2008 7:04:11 PM   
dick Hanson



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Status: offline 		Here is an approach you can use - The little Cessna from Horizon which weighs about 20 grams --has a working 3 channel 2.4 ghz radio in it which weighs about 5 grams
you can take that radio and double tape it to a freeflight and actuate a trim tab on the rudder and elevator and see how it works
I have two of these setups
the little peanut scales and others about same size are perfect candidates and rubber powered so the rubber still flieds the model and you have some direction control
I am serious . maybe I need to supply pictures?

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RE: Free flight versus Radio aircraft - 2/23/2008 10:49:06 PM   
da Rock



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Status: offline 		Keep in mind that the free flight model was going to be in powered flight for only a very short time, and was expected to be climbing at it's best angle during that time.

Do not expect the incidences of either the wing or horizontal tail, nor the thrust angle of the engine to be right for an airplane that'll be expected to fly the entire flight under power. If you plan to have a working elevator, all that will matter. Otoh, if you are going for rudder only, you're probably in clover.

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RE: Free flight versus Radio aircraft - 2/24/2008 1:23:57 AM   
BMatthews



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Status: offline 		If it was a more modern pylon design then yeah, there's some advantage to moving it slightly ahead. But even at that the CG on something like a Civvy Boy would still be back at around the 80% mark. The spec of the original FF version called for the balance to be a skinch BEHIND the trailing edge.

On my 1937 Record Hound running with RC RET and electric power I'm running at around a 40% point. But with a new upgraded motor and battery pack option I'm hoping to let the CG slide back to around 60% so it's not so pitchy. Long tail arm and big stabilizer.

All of which is to say that I think you'll find that if the planform is such that it'll support the rearward CG then you're going to find that it's a nicer model to fly, RC or not, with the CG where it wants to be and not where we think it should be.

< Message edited by BMatthews -- 2/24/2008 1:25:09 AM >


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RE: Free flight versus Radio aircraft - 2/24/2008 5:23:01 PM   
CoosBayLumber


 

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Status: offline 		I like what you guys are telling me. Now for beginners, I when through a couple of older American Modeler magazine articles based in the very early 1960's which discuss converting a free flight model in to a Radio A/C. But they are mainly telling of "remote direction devices" not of up and down, banks and turns. Is nothing about converting the one minute wide open engine run to altitude, in to a 10-20 minutes long controlled flight.

They stress keeping the C.G. at same exact point, but isn't that based upon a high powered climb then glide condition? I would think the C.G. there to be different than with a radio. It sure was for controlliners.


Wm.


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RE: Free flight versus Radio aircraft - 2/24/2008 5:37:13 PM   
HighPlains


 

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Status: online 		Those free flight models with the 80% CG's were really "canard" canards with lifting tails. Conventional airplanes normally fly with the tail pulling down, not up. The problem with lifting tails is higher speeds where the plane's tail creates too much lift and forces the nose down. Once it heads down and picks up more speed, there is no recovery.

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