N7 to T7 (turbine) Conversion

[Jim Cimino]

I am new to this forum, but not new to RC helicopters as I have been flying them since around 1980.  Matt asked me to post some pictures of my new project.  I am converting my N7 to a Wren powered T7 Turbine.  I have been thinking about a new turbine helicopter for a while and Dan (Dycocker1) on RunRyder is doing one, so I thought this was the time.  Today was day one of the build and I have installed the engine to see what modifications I am going to have to do.  My plan is to make new frames that will allow for a much larger tank, move the canopy forward and keep the original landing gear position and support.  This will be a slow go as I still have parts coming in and will have to decide if I am going to mill my own frames or get someone with an cnc to do it for me.  I know Matt likes this idea and if there is interest here, I will continue to post as I go.

[Barry Tilson]

Looks like it fits well. How's the weight of the turbine compare to the OS motor? Modern day turbines have a higher power to weight ratio and this turbine looks much bigger and heavier in the image.


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[Jim Cimino]

Here are the specs for the is 105 that's in it now.
Practical rpm: 2,000-16,500
Output: 3.75 hp @ 15,000 rpm
Weight: 21.03 oz (596 g)
Here are the specs for the wren 44i.
Max. Power Output   6.8HP / 5Kw @ 190,000 rpm
Weight   1480gms / 3lbs 4oz
Overall size centre section   305mm x 75mm / 12" x 3"
Ancillaries weight (inc battery)   280g / 10oz
Mounting   As for OS91 heli engine
Output Shaft Size   3/8" dia + 5/16" UNF (as for OS91H)
Gearbox output shaft rpm range   4,000 to 15,000 rpm
Fuel Consumption @ max thrust   176ml per minute / 5.8oz per minute
Max. Torque   4Nm / 2.9 ft Lbs @ 13,500 rpm

The helicopter should weigh around 13 lbs. when finished.

[Barry Tilson]

Thanks for the info. Fascinating. Will their be any issues with the engines RPMs causing gyro stability or precession issues the heli? My not have enough rotating mass?

[Jim Cimino]

The head speed will be under 2000.  They are flying these in the trex 700n and I have not heard of any problems with the gyro.  There are one or two who say not to be used with turbines.  I will most likely use a Bavarian Demon with a shield on it.

[Chuck Bole]

 Nice work..

chuck

[Jack]

Will be watching this with interest. Please keep posting updates!!!

[Roger]

Ditto what Jack said.  Watching with interest.

ROG

[Kevin Feil]

Have you seen Dan's build thread? The way he did it was in all actuality Simple and didn't require new frames. Front landing gear resides in the same location. He had main shaft bearing blocks machined that are wider. May be worth a PM to him, he may have extras. Good luck.

K

[Dan Minick]

Oh yes, we have talked! Sounds like this will be doing a bit more sport flying so adding weight wont be much of a penalty. I wanted to keep it as light as possible so I might compete with those nitro gizmo's.

Anyone interested can check it out here
http://rc.runryder.com/helicopter/t766315p1/

[Jim Cimino]

Dan, have you had any luck with your fuel problem?  I have two tanks coming. One came today and we will see if I can make either of them work.

[Dan Minick]

I think where I am at now will work.  Temps have not even been close to freezing the last two weeks,17 below zero this morning not to mention the 25 mph winds. So no testing has been done

[Jim Cimino]

Looking for your opinion. The few things that I am doing different which will add some weight is that we are making new frames to install a larger tank. I have been working with Michal Marcan to make these frames and we are trying to decide which tank set up will look the best and give the best service and flight times. Currently looking at two tanks that have been used in the Trex conversion and they normally mount them sideways. The round tank holds 1000CC's and the rectangular tank holds 1200. The helicopter is going to be a little nose heavy with the engine facing forward, so fuel in the back will only help. Currently we are leaning toward using the rectangular tank and mounting in lengthwise. This will stick out both sides a little so it requires us to square off the back straight down from the tail boom. The landing gear would be lowered 1/2" which will allow for clearance on the front landing gear support. If we use the round tank and mount it sideways, the landing gear will be lowered 1.25". The rectangular tank has a shelf in the front which would be on one side of the helicopter if I mount it sideways. I am just looking for your opinion on which way to go. The pictures are of a trex with the tank sideways and the drawing show the two tank installations that we are considering.

[Dan Minick]

I would go with the first drawing. You adding a bunch of weight anyway. Might as well maximize your flight time

[Jim Cimino]

This is the latest frame drawings that I have. Using this design will allow for landing gear support and we will not need to widen the frames.