The Rapture Aircraft Turbine Bug

[TurbAero]

Hi everyone,

 

When I’m not working on my 200hp turboprop engine, I have been working on the aircraft that spawned the idea to develop the turbine engine in the first place.

 

The new design is heavily influenced by the original Lightning Bug aircraft that some of you will be aware that I have been associated with for many years.  I have undertaken a redesign program to simplify the construction of the new aircraft, improve internal space, use the latest materials and incorporate my range of turboprop engines, as well as a Rotax 912 variant.

 

The company I have established to develop and market the new aircraft is called Rapture Aircraft Inc. and you can find us on Facebook.  We will have a website up in the next few months.

 

Anyway, my new aircraft was displayed at Oshkosh in the TurbAero booth.  This is the Turbine Bug variant.  It is all carbon and will have a cruise speed of around 240ktas with the 200hp turboprop fitted.  With the Rotax 912 installed, it will cruise in the region of 170-180ktas.

 

Here are some pics from just before Oshkosh.  Please note that the fuselage is mounted on a cradle for the display.  This is not the actual landing gear for the aircraft.  That will be installed soon.  It will have a retractable nosegear.

 

I hope you enjoy the pics.

 

Edited August 8, 2021 by TurbAero
Photo issues

[ClintonB]

Looks lean and mean, might not meet RAAus specs on current wing loading and power😁Lots/0m2

is the rudder going to be small due to speed aspired to? 

 

[kasper]

Well the original lightning bug stalled at a claimed 54knts.  You are never going really slow in one so who needs a big rudder 😛

[TurbAero]

On 08/08/2021 at 6:59 PM, ClintonB said:

Looks lean and mean, might not meet RAAus specs on current wing loading and power😁Lots/0m2

is the rudder going to be small due to speed aspired to? 

 

You are right, it won’t quite make RAAus registration requirements as is and indeed, even when it gets the wings attached.  I’m thinking about a long wing version which could make it eligible.  It would still be fast but have a lower stall speed.  I wonder how much interest there would be in the Rotax long wing variant RAAus compliant variant?  It’d probably still cruise at 150ktas.

 

The rudder is extremely effective.  It has been reported by the two pilots who are currently flying Bugs to be the most responsive and effective of the 3 flight controls.

 

On 08/08/2021 at 8:31 PM, kasper said:

Well the original lightning bug stalled at a claimed 54knts.  You are never going really slow in one so who needs a big rudder 😛

Who in their right mind would fly this aircraft slowly?  If I heard that someone was wanting to do this,  I’d have to wonder about their state of mind 🤣.

 

[kasper]

Who in their right mind would fly it slowly?   Well someone will have to demonstrate stall limits so someone will.

 

Quite agree owners will not be buying it for the low speed performance.  I lost my money on a kit with Reflex Fibre way back when and I never wanted it for slow speed  it was GA all the way baby and I wanted to get places in it.

 

If there was a long wing version with better than plain flaps available that had a hope of getting down to RAAus stall speed I would punt for another kit. 

And I promise not to put the AMW808 sitting in the crate here in it - Nick Jones experiences with the tailwheel bugs and that engine put paid to that desire ... though I do have a spare 80hp 912 sitting next to it that could be useful ... and a 75hp 2 stroke triple as well. 

[TurbAero]

On 10/08/2021 at 9:48 AM, kasper said:

Who in their right mind would fly it slowly?   Well someone will have to demonstrate stall limits so someone will.

I guess that's going to be me...  Fortunately, our two flying original Lightning Bugs both have honest stalls so without changing the aerodynamics, I am hoping that the new Bug will be the same.

 

Your 912 would go into a new Bug ok and even 80hp would give it reasonable performance, even a long-wing RAAus type one. 

 

I think I have a couple of AMW808s sitting in the corner of the hangar now and that's the best place for them!

[rgmwa]

I assume the engine was on display at Oshkosh. Did you get a lot of interest?

[TurbAero]

1 hour ago, rgmwa said:

I assume the engine was on display at Oshkosh. Did you get a lot of interest?

Yes, we got a huge amount of both interest and support for the engine.  We had over 2000 visitors to the booth during the week with over 800 proper engagements with our volunteer staff who were manning the display.

 

We were fortunate to have our Chief Technology Officer as well as one of our senior designers on the stand who could answer any technical questions.  Visitors included turbine engineers from GE and P&W, both of whom grilled our CTO intensely but afterwards, reserved an engine on the spot.

 

Our engine simulator that replicated the engine cycle, offering a view of all internal temperatures and pressures, as well as rpm, fuel flow and power at the prop was a big hit.

 

While we do not have an actual engine running yet, the number of people who indicated their support by stating that it was way overdue for someone to have a good go at offering a Turbine alternative to the legacy pistons was  nice to hear.  The support really was tremendous.

[rgmwa]

Thanks for the update. Very interesting to hear GE and P&W obviously taking it seriously. Hope it’s a winner. 

[TurbAero]

2 minutes ago, rgmwa said:

Thanks for the update. Very interesting to hear GE and P&W obviously taking it seriously. Hope it’s a winner. 

Thanks rgmwa.  To clarify, the two engineers were there as owners of experimental aircraft, not as representatives of the company they worked for.  However, it was pleasing to have them show that they “get” what we are doing and that our technical approach was considered to be acceptable enough to them that they would put their names down for an engine.

[rgmwa]

Well that’s still a pretty good endorsement even if you don’t end up buying out GE and P&W.

[Geoff_H]

I worked on the desk of industrial gas turbines in Florida.  We used Pratt and Whitney blade technology.  I am interested in your blade technology and how you are going to build them in Australia.  What can you tell me about yours?

What class of turbine will yours be?

[TurbAero]

It is conventional small gas turbine blade technology.  No blade cooling and nothing special about the blades.  We cannot build the turbines in Australia so the turbines will be manufactured outside Australia.

I’m not sure what you mean by what class of turbine they are.  It will be a 200hp (sea level ISA + 10deg.c.) rated, recuperated, twin spool gas turbine.

[Geoff_H]

Class is a function of tit.  Most commercial turbines in Australia are class C.  GE have a class H.  The turbine that I worked on was 180MW, and had blade leading edge cooling. I believe that you are using heat recovery, a great idea.  Best of opportunity.  Great to see you succeed.

[Geoff_H]

Maybe you could help me.  The slower that a turbine goes the more power it gives out.  Why does the PT6 have a gearbox rather than just run the turbine slower? I have quessed it is for efficiency reasons. One day I will sit down for a day or two and try and calculate it.  Any thoughts?

 

[TurbAero]

32 minutes ago, Geoff_H said:

Maybe you could help me.  The slower that a turbine goes the more power it gives out.  Why does the PT6 have a gearbox rather than just run the turbine slower? I have quessed it is for efficiency reasons. One day I will sit down for a day or two and try and calculate it.  Any thoughts?

 

I’d have to get my engineers to answer that one with any authority and unfortunately, they don’t have time to be on the forums.  I don’t want to embarrass myself by giving incorrect or misleading information, but I think mass flow through the engine heavily influences the rpm for best efficiency.

[Flightrite]

Many people have tried to make a commercially available GT donk in the 200 gee gee range but cost & FF have always been the stumbling block otherwise the market would be flooded with such machines, be interesting to see how you manage them.

[TurbAero]

4 hours ago, Flightrite said:

Many people have tried to make a commercially available GT donk in the 200 gee gee range but cost & FF have always been the stumbling block otherwise the market would be flooded with such machines, be interesting to see how you manage them.

I sincerely hope that we can be the one that successfully makes it into the market!

[Flightrite]

Good luck, wish you well:-)

[Marty_d]

Bit concerned about the effect the name might have on the more religious friends of pilots.  I can just see their faces when the pilot says "I'll be taken up in the Rapture tomorrow!"

[Geoff_H]

Turbaero have you guys looked into using two stages of burners.  One before the first stage turbine and the other before the second stage turbine.  All blades in both stages would have to be of material and construction that is what you would make them now.  But this would allow a theoretically double the amount of fuel to be burner for the same compressed air flow.  In fact it would be significantly less than double butuch higher than single.  I don't know much, one day I may get enthused and make a stab at calculating how much.  Efficiency gains are obvious with so much less power needed for the compressor. 

Not my idea.  In the later 90's ABB designed a very large GT using this theoretical design.  An enthusiastic salesman sold a power station full!  They didn't work as well as expected.  The liquidated damages nearly sent ABB broke.  I have always thought that this might be a simpler design than using turbine exhaust to heat turbine inlet air. Might be cheaper, but I doubt that.  Blades and burners are not cheap.

[TurbAero]

Geoff, from our perspective, simplicity/lower parts counts/lower temperatures/lower pressure ratios/conventional technology = lower cost, and lower cost = more sales, assuming functionality, performance and reliability all meet the necessary standards.

 

We have already introduced recuperator technology which is proven, but packaging it into a small aviation engine envelope is the challenging part.  However, it is the technology that is the most likely solution to improving fuel efficiency, but containing cost.  We shall stick with that technology for now.

[Geoff_H]

I must admit that Microturbines are proven.  A friend was involved with them.  I got the price....$$$ compared to piston.  Maybe one day I will design, but not build ( far too old lol) a dual burner turbine.  I maybe wrong but for the addition of a burner over conventional turbine they might just have less weight for the same power.

[Geoff_H]

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.alstom.com/press-releases-news/2012/6/the-new-alstom-gt-24-gas-turbine-shipped-to-mexicos-el-sauz-combined-cycle-power-plant&ved=2ahUKEwicgKvnmrTyAhVb63MBHeRSC20QFnoECAYQAQ&usg=AOvVaw31Xwr2oa8X01zyEdA972BS

 

A subsequent burner, industrial size.  I think that GE also have one.

[Flightrite]

Apart from the costs and different operating requirements it's always been difficult to design, produce & market a small GT in the 200HP range, that size powerplant is already well & truly entrenched in the industry with time proven cheap (compared to GT's) workable designs.

The Allison 250 series GT's have been very successful in the low 300's to mid 400HP range but costs are way beyond most light A/C operators budget to equip or re-equip their planes/fleets. Saw just the other day replacement compressor sections for same around $50-85K! Ouch! The two biggest "ouch's" for GT's are FOD & hot starts! Ive got more hrs behind GT's than I care to remember, just glad I wasn't paying for them:-)

I'd love to see a 200 HP GT and maybe I will before I hang up my flying boots (hurry up please I ain't getting any younger) but for now $$45-55K is still doable for a recip that any donkey can operate:-)

Edited August 15, 2021 by Flightrite