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jetcat11
03-20-2019, 02:29 PM
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!

electricsnail
03-20-2019, 04:18 PM
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...

jetcat11
03-20-2019, 04:32 PM
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.


42030

Mauleguy
03-20-2019, 05:04 PM
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.

PerryB
03-20-2019, 05:34 PM
As cool as it would be, the spool time would keep it from being a real down and dirty bush plane.

jetcat11
03-20-2019, 06:36 PM
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.

PerryB
03-20-2019, 06:52 PM
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.

jetcat11
03-20-2019, 06:53 PM
You seem to be convinced it'd be the bees knees, so do it.

DRACOís not convincing enough?

don d
03-20-2019, 06:56 PM
Sherpa!

Dave Calkins
03-20-2019, 07:19 PM
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!

electricsnail
03-20-2019, 08:05 PM
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 catís meow....

jetcat11
03-20-2019, 08:16 PM
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.

bob turner
03-20-2019, 08:50 PM
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.

jetcat11
03-20-2019, 08:55 PM
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/

skywagon8a
03-21-2019, 07:04 AM
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.

cubdriver2
03-21-2019, 08:08 AM
. 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

cubdriver2
03-21-2019, 08:10 AM
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.

They had a bare fuselage with a little turbine hanging way up front at Greenville one year

Glenn

Rob
03-21-2019, 10:06 AM
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

PerryB
03-21-2019, 10:37 AM
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.

aktango58
03-21-2019, 11:08 AM
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.

mountainflier
03-21-2019, 11:43 AM
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.

aktango58
03-21-2019, 01:11 PM
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

jetcat11
03-21-2019, 03:23 PM
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.

skywagon8a
03-21-2019, 03:47 PM
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.

jetcat11
03-21-2019, 03:52 PM
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!

john schwamm
03-21-2019, 04:56 PM
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

jetcat11
03-21-2019, 05:10 PM
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.

skywagon8a
03-21-2019, 05:10 PM
https://ia802808.us.archive.org/BookReader/BookReaderImages.php?zip=/25/items/piperj3_Bin_89_Unknown_J3_PA11_Nose_Wheel/Bin_89_Unknown_J3__PA11_Nose_Wheel_jp2.zip&file=Bin_89_Unknown_J3__PA11_Nose_Wheel_jp2/Bin_89_Unknown_J3__PA11_Nose_Wheel_0000.jp2&scale=2.981132075471698&rotate=0


https://youtu.be/j4SAsksi5Bs

bob turner
03-21-2019, 05:47 PM
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?

TurboBeaver
03-22-2019, 05:03 AM
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 yíall have talked about and FOD damage to the compressor.https://youtu.be/X-4qoHxrD5Y

Sent from my LM-X210 using SuperCub.Org mobile app (http://r.tapatalk.com/byo?rid=93960)

jetcat11
03-22-2019, 08:35 AM
That’s a cool video. I believe it was a 165 SHP turboprop on that one.

Here’s a startup of the TP-100 in the RV-10. Quick boot to 53%!
https://youtu.be/51lideX9bUw

https://youtu.be/32FVxJZ5P3M

hotrod180
03-22-2019, 09:24 AM
......….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

Rob
03-22-2019, 11:04 AM
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

Rob
03-22-2019, 11:43 AM
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

john schwamm
03-22-2019, 12:16 PM
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

Rob
03-22-2019, 12:34 PM
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

john schwamm
03-22-2019, 03:37 PM
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

jetcat11
03-22-2019, 05:01 PM
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
03-23-2019, 03:13 AM
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/questions/43624/how-does-a-turboprop-engine-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

mountainflier
03-23-2019, 04:10 PM
Cub with Turboprop engine.
421174211842119

jetcat11
03-23-2019, 10:52 PM
Cool pictures! Where did you find them? Do you know what turboprop they used?

Steve Pierce
03-24-2019, 08:35 AM
Do a serch here. Was disscussed here at length back when it was making the rounds.

jetcat11
03-24-2019, 11:30 AM
Do a serch here. Was disscussed here at length back when it was making the rounds.

Sweet, thanks! Hereís an idea of what it could look like.

CamTom12
03-24-2019, 12:17 PM
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, Iíve 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 donít 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.

Rob
03-25-2019, 09:59 AM
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

john schwamm
03-25-2019, 10:48 AM
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

Sourdough75
03-25-2019, 04:05 PM
I guess your only option for additional fuel would be a belly pod, and have Frank Farr hold a bladder in his lap...

CharlieN
03-25-2019, 05:24 PM
For more fuel, since the tanks require larger outlets to handle the turbines higher fuel flow, add more fuel in the wing as well.

john schwamm
03-25-2019, 06:03 PM
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