Komet - 2 seat twin jet

[Deskpilot]

Oh dear, have I dropped you in it Bex? Sorry.

 

 

[bexrbetter]

Oh the price of popularity ......

 

Have to see my schedule over the next couple of days ....

 

 

[Kyle Communications]

I am away up at my farm near Childers will be back home sunday arvo. Although will have to come back up midweek to meet insurance assessors. We were smashed on wednesday night with a storm..got some hangar damage and other stuff but all good

 

 

[Marty_d]

Oh the price of popularity ......Have to see my schedule over the next couple of days ....

It's all because of that picture with Julie Bishop. You're a member of the A list now Bex.

 

 

[bexrbetter]

It's all because of that picture with Julie Bishop. You're a member of the A list now Bex.

"Jules", get it right.

 

 

[flyvulcan]

With the tailplane all taped up to facilitate layups of BID against it to form the intersection between the turtledeck/fuselage and the tailplane surfaces, micro was put into the intersections to allow a radius to be formed.

 

 

The micro was then radiused and BIDs were applied to form the skin.

 

 

Some work was required to tidy up the rear fuselage to blend the rear fuselage shape into the rudder. To do this, a mold was formed out of cardboard and BIDs were laid up over the mold to form the rear fuselage shape.

 

Once all the BIDs were cured, the new rear fuselage shape was trimmed to match the deflected rudder and the fairings were all trimmed to correct size.

 

 

 

 

Fasteners will now be installed on the new fairings and they will be done. The tailplane will now have very neat intersections between all surfaces.

 

Next, we are on to the canopy hinges and latching mechanisms.

 

I am very pleased with the progress on the aircraft. It is really taking shape now and progress is tangible after every build session.

 

 

[Marty_d]

How are you going on engine mount design? I saw from your HomeBuiltAirplanes thread that the engines sit either side of the fuselage aft of the cockpit - just wondering how design of mounts, internal fuselage supports, fuel system etc was going.

 

 

[flyvulcan]

How are you going on engine mount design? I saw from your HomeBuiltAirplanes thread that the engines sit either side of the fuselage aft of the cockpit - just wondering how design of mounts, internal fuselage supports, fuel system etc was going.

Hi Marty,

 

The fine details of each system are still to be determined but the general arrangements have been finalised.

 

Engine mounts:

 

There will be three hard-points on the fuselage to which the engine mount will attach. There will be a hard-point attached to each fuselage side longeron where the fuselage bulkhead, longeron and rear shelf meet. There will also be a hard-point attached to the bottom fuselage keel/longerons, making overall a triangulated set of hard-points.

 

 

 

A chromolly tube "V" frame will be attached to these hard-points with rubber isolators being used. The top end of these tubes will exit the fuselage sidewall and stop flush with the fuselage side. The engine itself will be mounted on another tube (which will be the pylon) using a cradle to hold the engine, and that pylon will simply be slotted into the fuselage mounted V frame tubes and secured with bolts. This arrangement will facilitate easy removal of the entire engine pylon. The pylon tube will receive a streamlined fairing and fuel/electrical lines will run inside the pylon and its fairing.

 

Fuel system:

 

There will be 3 fuel tanks in the aircraft: the main fuselage tank which is incorporated into the centre structural keel; the wing leading edge tank; and a small approx. 1 gallon header tank which will be mounted on the rear shelf (as shown in the photo above). The wing tank feeds by gravity into the main tank and fuel is pumped from the main tank to the header tank using an electric transfer pump. There is a second transfer pump fitted for redundancy. The transfer pump will run continuously, ensuring that the header tank remains full at all times. There is a return line from the header tank to the main tank for the overflow. The header tank will be fitted with two flop tubes that will feed each individual engine.

 

Refuelling will be into the centre tank which will fill the wings through gravity flow. There is a simple breather system from the wings that allows air to vent into and out of the wing tank but prevents fuel from overflowing when the tanks are full.

 

 

[Marty_d]

Great stuff - I'll keep watching with interest!

 

 

[Kyle Communications]

I was one of the first here in Oz to import and sell model turbines. Back in 1995 and not much has changed since those days except the single stage turbines are certainly more efficient with better diffusers impellers and much better combustion chambers. The biggest issue is it takes just 1 small air bubble in the fuel supply to the engine and you have a flameout. Do you have a header tank for each engine or just a single one?. Have you thought about a method of keeping air totally out of the header tanks by maybe some sort of feedback fuel system

 

Mark

 

 

[flyvulcan]

Hi Mark,

 

Thanks for your feedback.

 

The return line from the header tank is at the (normally) top of the tank. Once the transfer pump starts running on the ground, the header tank will fill completely with fuel, and all air should be displaced through the return line. The output of the transfer pump is about 150% of the maximum engine usage so the header tank should remain full of fuel at all times while the transfer pump is operating.

 

With the transfer lines (main and emergency) supplying fuel into the top of the header tank, and with the return line being at the highest point of the header tank (when the aircraft is sitting on the ground), should the transfer pump fail, fuel will not be siphoned out of the header tank if the transfer pump fails and all the content of the header tank will be available to keep the engines running (for a minimum 30 seconds at full power) while the pilot switches to the emergency transfer pump.

 

I think this system should keep fuel, rather than air in the header tank and minimise the risk of fuel line air bubble flameouts.

 

If you have any alternative suggestions, I'd welcome them.

 

Cheers,

 

Dave

 

 

[Kyle Communications]

We learnt the hard way about even 1 tiny airbubble. It was extremely difficult to keep them out of the system even in the header tank. So we ended up putting the feedpipe from inside the header at the geometrical centre of the tank that way any air would usually always go on the outside of the tank and never at the pickup point for the fuel. We of course used to do many consecutive rolls and other aerobatic manuovers which used to push and pull the fuel around a fair bit inside including the air that always seem to have a small amount of no matter how hard we tried to get it out. Have a look at this link http://www.intairco.net/products.php?product=High-Flow-Super-Trap-250ml%2C-Single-Inlet-Port-%252d-Barb-Fittings-Suit-XLarge-Tygon-Tube still today this is how its done and we dont get any flameouts. If you look inside the tank you can see the fixed pipe in the middle of the tank it has a white cyclindrical filter there. Its a bit hard to see but you can download the picture and zoom in you should be able to see what I am says. We tried all sorts of different pickup systems with flexibale clunks that followed the fuel...angled tank setups to force the air to a corner of the tank so it wouldnt get sucked in..or should I say pushed in by the pump. Its just something to look at as it was a big issue as soon as you did any rolls or inverted flight

 

Mark

 

 

[bexrbetter]

going great guns Dave!

 

 

[Deskpilot]

Have you seen this Dave

 

http://media.wix.com/ugd/34cdd3_fc0cb2de8d6343bf96b3ce834831c98b.pdf

 

 

[flyvulcan]

Hi Doug,

 

I was in touch with PBS-Velka well before this engine hit the public domain. While the engine is nice, the price tag is not so appealing.

 

Although the Jetbeetle H160s that I have always planned to use on my Komet are somewhat more basic than the TJ100, I can get 2 x 160lbf (total 320lbf thrust) H160's for US$30k versus 1 x 247LBF thrust TJ100 for $60K+. So more thrust for 1/2 the price and I get two engines with the ability to climb following an engine failure.

 

There are similar engines such as the AMT Nike engine but again, they are significantly more expensive than the Jetbeetles.

 

Perhaps next year I may have my own engine development.

 

 

[kasper]

What about slightly lower performance? Would 2 x 100lb (450N) thrust engines, full controllers and starters etc for 11,600 euro get your interest?

 

Total weight including the mounts is less than 12kg ... Like most small turbines these are rated at 50hr life then inspect BUT they are already being sold for human flight ... not model use.

 

I am sorely tempted to get 1 to put on the sapphire ... take out the 30kg engine/prop and and put the saved weight into fuel (and then some) ... see how quickly I can melt the rudder top

 

 

[flyvulcan]

I am sorely tempted to get 1 to put on the sapphire ... take out the 30kg engine/prop and and put the saved weight into fuel (and then some) ... see how quickly I can melt the rudder top

Kasper, I like your temptations! Go for it!

 

I would prefer at least 300lbf thrust minimum. The BD5J with the 220lbf engine was a very different beast than the one with the 300lbf engine. I want real performance for my Komet, not just mediocre performance.

 

I had tossed around the idea of fitting 4 X 90/100lbf (cheap) engines (so 2 per pylon) to the Komet, but the sfc of the smaller engines is 10-15% worse than the larger engines which would decrease my endurance from 20 minutes to 17 minutes . I know that one day, I would need those extra 3 minutes...