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Author Topic: Enlarging pattern planes for gasoline engines  (Read 373 times)
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Revenger20cc
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« on: August 03, 2018, 10:41:16 AM »

Hello all,

             I'm returning to RC after a 15 year absence.  The most frightening change to me is the cost and lack of availability of
glo fuel in my area-  it's a 150 mile round trip to the nearest shop that actually stocks it.  The hazmat fees make ordering fuel
online prohibitive.

I built a 1000 sq inch Super Kaos with a Saito 180 around 20 years ago and enjoyed it greatly.  It would very expensive in fuel to
run today, not to mention an engine whose cost approaches $500.

Having looked around the web for the last few weeks I have seen a number of larger electric pattern birds, but very little in the 20cc
gas range.  I understand that at the 20cc range and below the electrics have the power/weight advantage over gassers. 

Has enlarging/modifying the old pattern birds for the 20cc class gassers something that has been tried?   I'm sorry if I'm beating a dead
horse- just trying to figure out what's happened over the years.

Thanks.
 

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Sundance12
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« Reply #1 on: August 03, 2018, 12:36:19 PM »

I believe it has been done, the drawback perhaps would be engine RPM and perhaps the higher airspeeds Pattern Planes operate at. That being said. there were some very large pattern planes of the early 80's that could be useful. Bridi published a very large pattern plane but I cant remember the name that flew on a 10cc engine. It could be a starting point. It was published in Model Builder. That's it,    Mamma Mia.
https://aerofred.com/details.php?image_id=93533
Start here.

Cheers

Sundance12
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Revenger20cc
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« Reply #2 on: August 03, 2018, 12:37:22 PM »

This is what I had in mind so far- these are just doodles.

The top plane is a Faser, resized for a 900 sq. in wing.
The bottom plane is a Gambler Mk. II, resized for a 1000 sq. inch wing.

So far I have tried to make as few changes as possible.  To help with balance,
both planes have had their wings moved 2" noseward and elevator servos moved to the tail.

The Faser will need to have the rear face of the cowl & canopy moved back about 3/4".  I may just
enlarge it 1000 sq. inch and gain a little room.

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Revenger20cc
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« Reply #3 on: August 03, 2018, 01:20:15 PM »

Thanks for the reply, Sundance12.

I took a quick look at the Mama Mia.

This is a raw vectorization of the original plan, resized to 1200 sq. in.

That is a DLE 35RA in the nose.  Even at  the original size (~975" sq. inch) it would have fit.
It is a monster!

-...-
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Konrad
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« Reply #4 on: August 03, 2018, 04:50:23 PM »

Model Builder had a nice “LARGE” pattern plane called the “Monster”

Generally the modifications are shortening the nose and the gassers are heavier. And strengthening the tails as the torque impulses tend to make them vibrate and fail.
Speed for the lack of RPM, can generally be gained with pitch and blade area (matching the motor/prop to the airframe).

All the larger pattern planes that I have seen are fixed gear tail draggers.

Here are two large pattern ships from Bridi.
http://bridiairplanes.com/hangar/bigchaos.html
http://bridiairplanes.com/hangar/bigdirtybirdy.html

All the best,
Konrad
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Cut it twice and it's still too short!
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« Reply #5 on: August 04, 2018, 11:10:29 AM »

Correction I now think the "Monster" was published in Model Airplane News. I had great success with the Bridi XLT with the then hot Enya 1.20R. I think the new class of "glow pluged petrol engines" would fit your needs and the airframe perfectly.
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Cut it twice and it's still too short!
Revenger20cc
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« Reply #6 on: August 05, 2018, 11:03:34 AM »

I took a look at my old plans for the Super Kaos 180.

The DLE 20cc will easily fit the nose.  As I can go to a C.G. mounted 12 oz
tank from a 24oz tank forward of the C.G., the moment caused by
the weight ignition unit/battery/switch is mostly canceled. 

I had a 1.25" spacer between the firewall and engine mount to compensate for the fact
that I mounted twin elevator servos in the tail.  Just pulling that out should be most of
what is needed to switch the engines. 

This one, at least, will work.  Now on to dreaming about the rest.


Thanks to all for your input.
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