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Carbon Cub EX-3 Turboprop?

......….A buddy put a turboprop in a Luscombe. Never hard much about its performance.

I've heard about that Luscombe (I doubt there's more than one).
The only performance I ever saw or heard about was a video of it backing up in front of it's hangar.
But it did so with authority!!! :up
 
Hi Perry,

Yep, I get it. An astronomical undertaking for potentially little return (in this application). But if it was well executed, it would be a neat ride.

Hi jetcart, I'm the wrong guy to be correcting anyone. Your numbers make sense to me, and I *think* it's a concept with merit for the right guy, it just doesn't fit my cub mission very well, and not sure it would fit for very many others.

I also don't believe the FX3 is the best choice in platforms for the install.

I believe the two biggest reasons for the Carbon Cub's success are the incredible weight to power ratio, and the exceptional execution. You're idea can be argued on both sides with respect to weight /power, and a less than stellar turbine installation will yield a huge money pit for minimal return.

Most turbine conversions exist for the purpose of performance enhancement. Either in the form of speed, time to climb, service ceiling, reliability, or brute power (read; load hauling). In my less than humble opinion, the place you'd stand to gain the most in would be the hauling capability. And let's face it, any of the CC's pretty much already run out of space before they run out of grunt.

Speed, climb angles, time to climb, service ceilings, all would be a wash in a CC airframe vs something like an SQ, but the load packing and enlarged platform of the SQ make it a much better suited candidate. It almost starts to make sense at that point.

If civilized STOL is the goal, it is money thrown away. A light CC will already rotate in a plane's length.

If truly venturing into the sticks is the goal, it doesn't fit my mission because I enjoy being able to be self sufficient in the face of adversity. Nosing over my cub 200 miles from the nearest village, is really not much more than an inconvenience, nosing over a one of a kind, specially a turbine, is pretty much a 'call a helicopter and the insurance company' affair.

I still think it's a neat idea. Unfortunately the only turbine time I can afford is that which is generating income.


Take care, Rob
 
Hi Perry,

Just corrected my earlier post, and am surprised none of the T-prop guys called me out on my error. I said when playing with beta a simple nudge fwd on the condition lever gets things wound up again... that should have read ; power lever.

FWIW, in my work airplane, (P&W) regardless of the day's take off cycles, I move the condition lever 3 times. Once to start the fire, once to shut it off, and once to exercise the works. I am a GI flier, but not because I think FI floats (it shouldn't) nor because FI is a better go around start ( I am typically coming back light and a go around in any configuration is a non event). I fly GI because our ops are typically 15 minute turn arounds with a high volume of cycles. An inadvertent flame out due to losing the tiny screw that stops the condition lever from going ICO is far more concerning to me than any conceived benefit of FI. FWIW my Walter powered S2R doesn't even have a FI / GI choice, nor do the GE models.

Also wanted to clarify that when I say one needs to master prop control for max stol performance, I am not referring to the range controlled by the prop lever. I am referring to that which is controlled by the power lever. In other words, beta and reverse.

Which brings me to another thought for jetcart.... IMHO a turbine without the use of beta and healthy amounts of reverse has been severely neutered, and not worth the effort YMMV...

Take care, Rob
 
I see several touting the backing up with a turbine. Not something that can be done very much, just short time only as once in Beta mode the intake air is pushed away from the engine inlet, then creating ITT temps that can go above normal pretty quickly, so Beta/reverse is limited in time when airplane is not moving forward to have cooling air through the engine.
And it is pretty weird backing up in an airplane anyway without good visibility.
John
 
Hi John,

As with all things aviation, blanket statements don't work well.... even with backing up. I should have been more cautious with my use of the 'R &B' words. Their use in one application does not make them universal. For certain heat should be monitored, and honestly, although I don't think reverse gets factored in to the cycle count of most engines, it probably should. After all, it is another heat cycle.

As for the need or ability to do it regularly, out of our operations 6 Thrush aircraft, 4 park tailed in to obstacles. Backing up in to their stalls is an every single day affair. I honestly don't think we could do with a pilot who couldn't back his airplane as handily as his auto.

Of course this doesn't mean it will work for every aircraft or every person.

Take care, Rob
 
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Rob,
Do not know anything about a Thrush, curious as to how long one can be in beta on them to back up.
Limited time before ITT spike, or no issue on them?
Thanks,
John
 
Thanks Rob. I appreciate all of the feedback so far! I misspoke about beta, it is available. You just need to match it with a compatible prop. A 4 blade reversible MT would be epic like DRACO has.

The reason the EX-3 is so compelling is because of the handling. It flies like a light sport IMHO and only takes a small amount of pressure to elicit a response. It’s a joyous experience flying it. I think that would only be enhanced by a smooth turboprop up front.

Initial acquistion and operational cost aside, I see this engine having more pro’s than con’s compared to the CC363i engine and still believe would enhance the overall performance of the EX-3 with this power plant up front.
 
Rob,
Do not know anything about a Thrush, curious as to how long one can be in beta on them to back up.
Limited time before ITT spike, or no issue on them?
Thanks,
John


Hi John,

Good question, and interesting thread. I really appreciate your Siai input as that is the one non revenue T-prop I could really bring myself to owning.
My neighbor owns an exquisite example.

My T-prop experience is really limited almost exclusively to ag stuff. The vast Majority in Pratts of various sizes with a smattering of Garrett and Walter stuff
as well.

It's not suprising we are looking at some of this stuff from opposite sides given your RR/Allison experience, and the differing airframes. My minimal exposure
to that engines sister in the Bell airframes tell me they are a hot start looking for a day to happen.

With regards to the Thrush and Air Tractor airframes I have experienced, virtually all of them, regardless of engine would readily take judicious use of beta
and reverse on landing. And again virtually all of them would back up as much as you could stand.They do see an initial rise in ITT (and then drop) as expected,
but I've not had one go hot on me from backing.

We do run into cooling problems with excessive ground time while hot loading in the summer, but that is a completely different issue.

Here is a good discussion that I believe touches on why we don't see that spike. You have a completely different configuration with the gear box, which probably
accounts for what you see. ;

https://aviation.stackexchange.com/...gine-keep-running-during-thrust-reversal?rq=1


I thought I read somewhere that you have a Kodiak as well. I *think* those are -34'S? You don't run in to ITT problems with that airplane in reverse do you ?

Take care, Rob
 
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Cub with Turboprop engine.
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It's not suprising we are looking at some of this stuff from opposite sides given your RR/Allison experience, and the differing airframes. My minimal exposure
to that engines sister in the Bell airframes tell me they are a hot start looking for a day to happen.

Rob, I’ve got some pretty good experience in helicopters with various examples of the M250. This is a pretty good way to describe the early models.

Later models with a FADEC (my experience is with the C30/R) make starts a non event (so long as you have a strong battery and don’t drop below the 10.8 or whatever voltage is required to keep the ECU alive), but the community had a memory and they were still hawk-eyed.
 
That picture reveals one of the reasons the concept doesn't work well for me. It's pretty common to see T-Prop conversions shift to multi bladed smaller discs for props.Works pretty good when the airframe is a go fast model just looking for a boost in thrust.

In fact the Thrush I am currently flying is an overweight example with a PT6-34 in a 500 gallon airframe. This size of airframe has never been the best bed for a -34 IMHO (750 hp), and too small for the -60/5/7's (1050-1300hp). It was a perfect mate to the (obsolete) -45 (1100 hp). Then came along an STC to go from the standard 3 blade Hartnell to a 4 blade. What a difference! It's not the same as having a -45, but it is a good mate to the airframe now.... Proof that I'm not alone in this thinking is the current trend to re-engine this size ship to -42/2's (900 hp). But I digress ...

Back to the picture... I am of the opinion that raw thrust alone is not what makes the magic in the lighter cubs. I believe if you took Frank Knap's Lil Cub, removed the Lyc up front and mounted a turbo fan of equal power above the cabin, it would get off the ground in considerably longer distances. In fact, I believe it would take a good amount more thrust to catch up to the recip.

My theory is that super long prop Frank is turning is getting a bigger portion of the wing up to flying speed long before the cub even starts to roll. I've been watching the pireps on Greg's exp Maule, and was intrigued that he went with the compact Hartnell, and now see he's going to try (or maybe already has) the longer fixed pitch he used to run. That's a bit heavier platform (not a bunch) so it will be interesting to see what happens.

How much more thrust do you need to get a shorter span up to flying speed to match up to the bigger disc is beyond my level of education, but I am certain one of the engineer types here could tell you lickity-spilt.

FWIW, I am not an engineer, not even very well educated, but I have spent a whole bunch of time watching and playing. I know we can build a cub that will leave the ground from a dead stop, even with a recip. And that is why as cool as a T-prop sounds to me, it doesn't work for me. I hope to see you work it through. I really like the idea.

Take care, Rob
 
Rob,
You are partly right about the thrust, but to me it is a big factor on initial performance on takeoff. Look at the geared engines on a Helio Courier, swings a 96" prop and yanks the Helio's right out of the gate, slower turning big prop has the thrust unequaled by smaller high speed ones. Fly a straight drive 0540 Helio with smaller blades and simply does not have the initial thrust and performance. The prop blast on a Helio blows the slats in on one side from the thrust of the prop initially. Widgeons with the geared engines and longer blades have the thrust unequalled by straight drive engines too. Once up flying the thrust is equal, but not on takeoff. Even cycling the prop in a Helio sets one back in the seat on floats.
John
 
I guess your only option for additional fuel would be a belly pod, and have Frank Farr hold a bladder in his lap...
 
For more fuel, since the tanks require larger outlets to handle the turbines higher fuel flow, add more fuel in the wing as well.
 
Sourdough,Good one on Frankie boy! Check out the Husky A-1 project build on nearby thread on this site, has belly pod for Frankie boy in that one.
John
 
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