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Indoor Free Flight Forum => General Discussion => Topic started by: jswain on July 11, 2019, 06:45:35 PM



Title: What is the reasoning behind the Tandem designed indoor models?
Post by: jswain on July 11, 2019, 06:45:35 PM
Hello.

I was wondering what the *reasoning* behind using a Tandem design indoor rubber endurance model like some of the Wright Stuff/Sicence Oly/ A6 models?

Also, in practice has it proved to be a worthwhile advantage over the standard type tractor indoor design and if so in what way (climb rate/ease of trimming/overall endurance, etc).

thanks in advance, john s.


Title: Re: What is the reasoning behind the Tandem designed indoor models?
Post by: calgoddard on July 12, 2019, 09:40:19 AM
The sole reason I am aware of for using a tandem design, where the rules permit, is to minimize the wing loading on a model where the class has a minimum weight.  I have only seen tandem designs on indoor duration stick models.

In theory this minimum wing loading should produce the maximum flight duration.  Of course you still have to optimize the prop configuration, the rubber motor size (and type) and the winding.  

In addition, the aspect ratio and the camber of the two wings need to be optimized.

It seems to pay off as the current AMA A-6 record is held by Bill Gowen who flies a tandem design.  I think the plans for his tandem A-6 are available on the HPA Plan Gallery.

My understanding is that a tandem stick model is more difficult to trim that a stick model with a conventional tractor configuration where the stab area is noticeably smaller than the wing area.  Optimizing the CG location and the static margin can apparently become tricky issues with a tandem.  


Title: Re: What is the reasoning behind the Tandem designed indoor models?
Post by: frash on July 12, 2019, 10:08:36 AM

For tandems with wing TE to stab LE equal to three chords, I put the CG at 185% of chord and the planes were not hard to fly well. Most of this was for ilLegal Eagles several years ago.

Fred Rash


Title: Re: What is the reasoning behind the Tandem designed indoor models?
Post by: Olbill on July 12, 2019, 10:19:23 AM
The sole reason I am aware of for using a tandem design, where the rules permit, is to minimize the wing loading on a model where the class has a minimum weight.  I have only seen tandem designs on indoor duration stick models.

In theory this minimum wing loading should produce the maximum flight duration.  Of course you still have to optimize the prop configuration, the rubber motor size (and type) and the winding.  

In addition, the aspect ratio and the camber of the two wings need to be optimized.

It seems to pay off as the current AMA A-6 record is held by Bill Gowen who flies a tandem design.  I think the plans for his tandem A-6 are available on the HPA Plan Gallery.

My understanding is that a tandem stick model is more difficult to trim that a stick model with a conventional tractor configuration where the stab area is noticeably smaller than the wing area.  Optimizing the CG location and the static margin can apparently become tricky issues with a tandem.  

Don Slusarczyk currently has the Cat 2 AMA record - also with a tandem.

I've never found them hard to fly.