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Carbon Cub EX-3 Turboprop?

jetcat11

Registered User
Hey y’all,

I have an idea. What about throwing a PBS TP-100 turboprop on the front of a Carbon Cub EX-3? Is this just madness to even conceive? You’d have 241 SHP and 1200 lbs of Thrust to work with on a wet engine weight of about 156 pounds. Cruise fuel burn is around 18GPH but you could pull it back to 13-14 GPH. Max takeoff is 36 GPH. Obviously this would offset the weight savings behind the two engines.

The real concern I believe is how much fuel could one realistically add to this kit? How much would you need? Would 60 gallons enough to play for a little while or would you need 80 to really make it work?

The gas gas generator of this engine is the TJ-100 used in the SubSonex and FLS Microjet. There’s over 25 million in R&D behind these engines and I think the TP-100 would make a nice addition to the Carbon Cub.

Does anybody know the weight of the new CC363i engine? Thanks!​


 
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I looked at this once. I believe the last time I looked at the engine it was 175k + accessories. With that much horsepower it will likely burn 25-30gph at cruise. For comparison we burn 22-24gph at 70% torque in a rr300 in a r66 which has similar shp. I dreamed about it for a while and decided it wasn’t worth the cost of admission...
 
Yowza’s, 175K is a lot with accessories. Turbine Solution Group tested it for about 5 years but I don’t know if they are still working with PBS or not. Here are some numbers from their RV-10 test bed with an economy cruise setting. 154 KTAS, 87.6 N1, 2120 RPM, and 45.2 TORQ burning 14.3 GPH. That’s not bad at all for a turboprop! Max cruise was 183 KTAS, 97.7 N1, 2130 RPM, and 80.7 TORQ burning 22.7 GPH.


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Well I guess I will be the first to say it. You will have a bastardized cub that no one will ever pay what you have into it. IMHO

Kind of like a Turbine Maule, they are very limited because of fuel burn, hard to sell from what I have heard first hand.
 
As cool as it would be, the spool time would keep it from being a real down and dirty bush plane.
 
It wouldn’t be about what it could sell for, wouldn’t want to. It would a quest for DRACO Jr. in an EX-3 frame. Also, wouldn’t be taking it to any STOL competitions but if you’ve watched DRACO that bird is about as down and dirty of a bushplane that you can possibly get.
 
We're obviously talking about two different types of flying and two different types of aircraft. I've seen Draco (on video) take off and land on manicured grass and smooth dirt hilltops. I've seen Cubs weave through the bushes/trees and land in creekbeds that would make some jeepers think twice. In the latter situation I want an engine with immediate throttle response. Draco is a magnificent airplane, but it's not a "Big Rocks, Long Props" type machine. In that kind of machine I think the response time of the turbine would negate any power/weight advantages. And the weight advantage is debatable due to the extra fuel load required. You asked for opinions, that's mine.
 
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depending on the propeller and governors and set-up/tuning for this application, spool up and thrust response may not be an issue. Flight idle rpm% for this engine might work out fine

Talk to the RV10 guy, then.......

......I say go do it!
 
depending on the propeller and governors and set-up/tuning for this application, spool up and thrust response may not be an issue. Flight idle rpm% for this engine might work out fine

Talk to the RV10 guy, then.......

......I say go do it!

I tend to agree, having a well tuned flight idle with a prop that will flatten out when power is at idle would be a hell of a machine, I have a few thousand hours in turboprops and turbine helicopters I find them to be plenty reponsive, not nearly as bad as the turbofans I fly. You have to fly them differently. I am of the opinion it would be the cat’s meow....
 
I tend to agree, having a well tuned flight idle with a prop that will flatten out when power is at idle would be a hell of a machine, I have a few thousand hours in turboprops and turbine helicopters I find them to be plenty reponsive, not nearly as bad as the turbofans I fly. You have to fly them differently. I am of the opinion it would be the cat’s meow....

Saweet! That’s what I like to hear. It could be an interesting combination indeed. Just talked to Christian from Turbine Solution Group and he said 130K for the engine with accessories.
 
A jet helicopter might be safer, and could get in and out of tighter places. A buddy put a turboprop in a Luscombe. Never hard much about its performance.
 
A jet helicopter might be safer, and could get in and out of tighter places. A buddy put a turboprop in a Luscombe. Never hard much about its performance.

I remember seeing that Luscombe online somewhere.

Here’s DRACO at full gross (4,000 lbs). 4 men, 105 gallons of Jet A, a bunch of gear, rotation at 44 mph while accelerating in the climb to 80 mph while sustaining a 4,000 FPM climb. Unreal! https://www.facebook.com/pateymike/videos/10218779104014699/
 
When Backcountry Super Cubs http://www.supercub.com/ started in business they were going to install a turbo prop engine. They called themselves Turbine Cubs of Wyoming TCOW. They changed their minds. A call to them may help you with your decision.
 
. A buddy put a turboprop in a Luscombe. Never hard much about its performance.

I was putting gas in the camper at the Planeview gas station in Kosh when that flew base to 36 at 200' over my head. Everyone looked up and then at each other in disbelief.

Glenn
 
As cool as it would be, the spool time would keep it from being a real down and dirty bush plane.

You are entitled to your beliefs, but I can assure you (as a very current, and fairly savvy turbo prop guy) that anytime someone cites spool or lag issues of a turbo prop as a limitation, it is either;

A) because they read that on the internet... or
B) because they have only been instructed in traditional (pavement to pavement) turbo prop operation.

All you are asking out of a power plant and prop when you make power setting changes (in slow speed configurations) is for a thrust change.

It just happens that in a typical small airplane power plant atmosphere, jabbing the throttle yields the fastest results.

With a turbo prop, if you really want to master the bottom end, (I'm talking short final and tighter) you need to forget about the fuel, and learn to manage the propellor. A good T-prop stick that can really play stol, moves the prop just like a good cub pilot moves the throttle. This will include up to and beyond beta, and even a whole lot of reverse.

Spool up? Lag? NONE! want proof? watch your average constant speed prop (recip powered) guy make a lap around the patch. What happens when he rolls on to final? The prop goes full fwd, and the airplane stand on its nose.... that fast!... Well... that's exactly how fast you turbine prop moves, but it's almost always more prop, and more power (thrust)!...

But wait... there's more... Pull a turbine in to a handful of reverse 20' off the ground and it's going to try and stop (literally), mid air, .... this sounds...well, not good... but the instant you nudge the power lever forward, it's going to see a shot of fuel and shot of prop, and it's literally going to leap... instantly...

This blows smoke in the face of any 'spool' or 'lag' theories. And so far, I am generically suggesting Pratt models (the inherently slowest of the bunch to spool up) In fact, I would go out on a limb and say that a good turbine stick in a turbo prop can yield quicker THRUST response, than a recip driver any day.

A non indoctrinated turbine driver? well... that'd be like asking the average Mooney / Cirrus / Bonanza guy to extract maximum performance out of a cub... or the space shuttle for that matter.


Side notes...

Fight idle vs ground... if you are a Pratt or similar power plant driver, forget about what you read anywhere and do what fits you best. there is no magic Mojo going on in either case. If you float in flight idle, it's because you haven't slowed down the wing. If you spool down too much in ground idle it's because you haven't learned how to keep the engine alive while slowed up. The difference between the two is tantamount to where you stoped moving the lever. Yes good rigging is a must if you want the best results.

In Garrets and similar use it appropriately or you will be in for quite a surprise. When the say FLIGHT idle, they mean it.

Flairing with the prop...
If your approach has you at the gate (beta). or a smidge behind (reverse, good btw!) at 1' agl, keep on pulling back on the prop. it will flair, set the tail down, and let you keep on rolling in to reverse. Do this in an airplane that weights 5-6,000 lbs empty, and you will easily land and stop in C-180 distances... It is amazingly easier for me to land and taxi off in my overweight work plane than it is in my light weight C-180. Same airstrip, to same taxiway.... BTW, it will NOT swap ends here any worse than on take off... torque and P factor exist either way, if you can handle a take off, you can handle a hand full of reverse, just be ready to handle it!

Rough and tumble, river bottoms jeeping whatever....
If you truly believe turboprops are somehow not up to the backwoods environments, you have not been watching the trends (and not necessarily new) in commercial back country aircraft. Every genre is cycling out their aging recip fleet with turbo props...

Having said all that, and with my obviously strong bias towards turbo props, I have to say I strongly agree with Greg.

The concept is good, but currently I seriously doubt you could build a turbine cub that made sense financially, nor that most recip transplants could use any better than the do their trusty O-320/40/60's... probably not even as good.

Draco? that was a heavier bird, with a turbine fluent builder/pilot. It is probably in the weight class where a turbine currently just starts to shine. A Soloy 207 is an aging concept that was 90% of Draco decades ago.

Take care, Rob
 
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Thanks Rob. That was very well thought out and very well explained. I truly appreciate the time and effort you put into it, and I learned a few things.
My main point was I just can't see the benefits in a Cub family airplane, but maybe I'm wrong. I'd much rather build a light 18 with a pumped 320 and not have to carry a bunch of fuel weight in the wings.
 
If you have the time and money to build such a beast, and don't care about the investment, go for it.

Practical? doubt it.

Others have started, and abandon the project. Sherpa was an oversized cub with a turbine added once... but engines have changed.

Keep us posted, should be fun to watch.
 
Can you imagine a well built Cub that weighs a 1000 lbs. with 420 S.H.P. with reverse how well it would perform. The negatives would be the cost of the engine, and higher fuel burns. If we are all about performance, and cost isn't an issue, thumbs up to it. If the airplane was built right, it would out-perform any piston engine on takeoff, climb, and landing. The thrust to weight ratio on turboprop engines are much greater then piston engines.
 
Can you imagine a well built Cub that weighs a 1000 lbs. with 420 S.H.P. with reverse how well it would perform. The negatives would be the cost of the engine, and higher fuel burns. If we are all about performance, and cost isn't an issue, thumbs up to it. If the airplane was built right, it would out-perform any piston engine on takeoff, climb, and landing. The thrust to weight ratio on turboprop engines are much greater then piston engines.

And let's face it, most of our flying doing this stuff is minimal fuel on board anyway!! So what if you can only carry 2 hours of fuel, the power/reverse will overcome that extra fuel weight
 
Thanks Rob, appreciate the valuable information!

So here’s what I’m thinking. Correct me if I’m wrong, just going off the knowledge I currently have. The empty weight of a particular FX-3 I flew that was loaded out with pretty much every option weighed in at 1162 pounds empty with 186 HP available. 44 gallons total with 39 usable.

I figure the new CC363i engine has to weigh about 295 pounds dry. That’s the low end weight on an IO-360. The PBS TP-100 is 157 pounds wet. Forgetting wether or not weight will have to be shifted to the nose to maintain an ideal CG, that’s a nice savings of 138 pounds dead weight.

You’d need to add at least 10 gallons to each fuel tank. That’s 32 X 2 = 64 total. Assuming 60 gallons is useable here, fuel burn at maximum throttle is 29 GPH. Where the FX-3 is cruising at 125 MPH true, G3X shows about 72% power burning 10.8 GPH in the neighborhood of 130 HP. At that HP setting on the PBS, fuel burn is 17 GPH. Eco cruise you’d be looking at 13 GPH. That would give you at least 3 hours of cruise flight at 17 GPH which is plenty to get across the state of Idaho.

Your empty weight would come in at 1,023 pounds. The piston at 1162 pounds. Full of fuel weight for the turboprop is 1,457 pounds. The piston would come in at 1,426 pounds. This would give you the same range respectively and I think enable some great performance with a boost to 250 HP and the ability to use that HP up high.

Obvously there are a million other variables at work here but I really do think not only would this be possible, but you’d have a great performer at an increased acquisition cost as well as operational. But it’s a turboprop Cub with amazing handling and takeoff performance! The cool factor would certainly be there and you only live once.
 
Since you are talking weights, don't forget the weight of the fuel. Avgas is figured at 6# per gallon while Turbine fuel is 6.7# per gallon. That would be 0.7 x 64 = 44.8# extra just for the change in the fuel type.
 
Since you are talking weights, don't forget the weight of the fuel. Avgas is figured at 6# per gallon while Turbine fuel is 6.7# per gallon. That would be 0.7 x 64 = 44.8# extra just for the change in the fuel type.

Yes, glad you mentioned it. I used 6.01 for Avgas (ISA) and 6.79 for Jet A. Looks like the real world fuel consumption would be more like 16 GPH at max instead of 17. 5 gallons more per hour over the CC363i at the same speed. For a turboprop engine on the front and 65 more HP I’ll take it!
 
And do not forget a turbine idles at about 60%, so just ground run/taxi is high consumption.
And a tailwheel turbine is not great if too far into beta at landing, cannot stop as short as you think they would, they lose directional control if too far in. Need the nosewheel to keep them going straight with full beta.
John
 
Yes, 53% N1 is idle for the PBS consuming 5 GPH. Last I heard beta was coming to this engine and that was 4 years ago. Not too interested in beta for fear of ground looping like y’all have talked about and FOD damage to the compressor.
 
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Yuk!
There are quite a few turboprop ag planes out there, including some that look like upside down Super Cubs. Maybe one of those could save a lot of development money?
 
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