Simple pusher pseudo-jet

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cluttonfred

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A recent thread titled "Neglected homebuilt niche?" (see https://www.homebuiltairplanes.com/forums/showthread.php?t=28882) started taking about a tube-gusset-and-fabric, O-235-powered PGK-1 Hirondelle to slot in under the RV-9 in the kit plane market and eventually ended up with the idea of a microlight/LSA RFB Fantrainer (see http://www.fanjetaviation.com/technologies/fanjet-600/).

ac819174.jpg

I'd like to explore the idea of a modest cost, modest performance, easy to build, pseudo-jet a little more. Here are a few approaches that I have kicked around:

DUCTED FAN

A number of ducted-fan homebuilt designs have tried to give a jet-like experience at piston cost but none have ever really taken off (groan, I know). One new example is a carbon fiber L39 Albatros replica (see http://www.skyleader.aero/en/product/ul-39-albi/). The simple fact is that running a high-speed propeller or compressor in a duct efficiently is not that easy and most such designs seem to end up quite expensive for the performance they offer.

Czech-UL-39-Albi-roll-out.jpg

LONG DRIVESHAFT

Others have kept the propeller on the nose but moved the engine back like a P-39 Airacobra, or put the propeller at the tail like the early Bede BD-5 and many others, but both of those require a long driveshafts between the engines and props that add weight and introduce torsional vibration issues that have bedeviled many such installations. The pusher prop in the tail does seem like it would work well with a very light two-stroke engine that could be balanced by pilot weight alone.

Bede5Pair_zps8c9f9535.jpg

PROP ROTATING AROUND STRUCTURAL ELEMENT

Another approach, which I have seen in relatively simple form on the Mignet HM.1000 Balerit, it to use a fuselage structural member as the axle around which the propeller rotates. There is a gyroplane that does the same thing with a prop rotating around a cantilever tail boom, which looks very slick but is much more complex to execute. There were even some WWII conceptual designs that had props rotating around around the entire rear fuselage. This approach requires pretty specialized mechanical installations (except for the relatively simple Mignet version, which cannot easily use direct-drive engines or existing redrives) but has the advantage of allowing large-diameter props.

DOC-BALERIT-26-avec-moteur-TOY-.jpg

JUST FAKE IT

So where does that leave us? To keep things simple, I would like to avoid ducted fans and long driveshafts and specialized mechanical installations. I am also willing to go with more of a "profile model" approach which mimics the general outline of a jet but not the full 3D structure. What I have come up with so far is to go with a traditional pod-and-boom pusher layout (irrespective of wing position) like the Kolb designs or the Sky Arrow, but essentially build up a low aspect-ratio fin on the boom to mimic the side view of a jet trainer. I could even see going so far as to put a hollow cylindrical spinner on the prop that leads to (but does not touch) a bullet fairing on the fin to give the illusion of a continuous structure even though the single boom is actually doing all the work. Here is the butchered Electraflyer image that I posted in the other thread:

electraflyer-single-boom.jpg

I think this approach could yield a simple, lightweight, two-seat design with jet-like looks and staggered tandem seating that could be adapted to any of various engines (Suzuki, Rotax, D-Motor, ULPower, etc.) around 100 hp. Despite the looks, it would have fixed gear and performance appropriate to the power, size, and weight. Perhaps there could be microlight (big wing and low gross weight, good on short fields), LSA (similar wing but higher payload and longer takeoff/landing runs), and E-AB (smaller wing needs longer runways and lands faster but has higher cruise speed) versions.

OK, fireproof undies are on.... ;-) Thoughts?

Cheers,

Matthew

PS--The propeller "slot" in my concept would actually be triangular (larger near the propeller tip, smaller near the hub) to give the prop more space to "breathe" and because RFB found in the Fantrainer (and the civilian Fanliner with Grumman American, see https://en.wikipedia.org/wiki/RFB/Grumman_American_Fanliner) that sweeping the structural elements downstream of the fan reduced noise as the slipstream beat against the structure. Presumably that would also apply here, and I don't think the triangular gap would ruin the jet look.

INSPIRATION

This is just an RC profile model of a T-45 Goshawk with a little motor in the tail, but I am posting it to show that a "profile model" approach can still capture the lines of a jet and look cool, at least that's my feeling.

 
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Toobuilder

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My thoughts are you are going off the rails toward form before function. Any further and you have all the design credibility of this:




I think the "jet look" market is adequately satisfied by the tandem Eze clones and has the benefit of real performance. If you cant stand the canard ruining the "look", then a twin boom pusher can get the occupants way out in front of the wing.
 

cluttonfred

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Ouch. I disagree and don't see this as any more frivolous than the Loehle 5151 Mustang and other pseudo-replicas that were popular back in the 1980s-1990s or the more powerful Mustang and Spitfire replicas available today.

I am not anti-canard, but I am anti-composites, and there are no affordable or easy-to-build canard designs that I know of, even the Junqua Ibis (wood and fabric but not a quick build) seems to have gone off the market.

I have no problem with a twin-boom pusher but, again, none that are affordable and easy to build are available right now and twin-boom doesn't really have that jet look unless you like early jets. As mentioned in the other thread, the Archon SF-1 layout would be one way to disguise a twin-boom design by basically using the booms to mimic the side intakes of a big twin jet fighter.

Aerosports-Archon-SSDR-2.jpg

I do think that the single-boom and inset prop concept that I described would be easier to design and build than either a canard or a twin-boom type.

Another way would be to use top and bottom booms, but that either limits the prop diameter significantly or looks very tall and awkward. Curved booms to go up around and down around the prop might work but then it stops looking much like a jet.

The prop-on-a-structural-element approach like the Mignet Balerit would allow a lighter structure since it would allow a truss the full height of the fuselage. Despite the mechanical complexity I could see that approach working well with a very big, slow-turning prop and well-engineered belt drive.
 
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cluttonfred

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To paraphrase Victor Bravo, "My eyes, my eyes!" The Verhees Delta is technically impressive but, IMHO, it is also truly hideous...err, I mean, aesthetically challenged.
 

Tiger Tim

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I have no problem with a twin-boom pusher but, again, none that are affordable and easy to build are available right now and twin-boom doesn't really have that jet look unless you like early jets.
What if I do like early jets? The first place my mind goes on this would be something with the style of a de Havilland Vampire but the complexity of a Sadler Vampire. The cool thing is, like the BD-5 the twin boom layout ought to be pretty easy to adapt an actual turbine to if someone wants.
 

cluttonfred

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Don't get me wrong, *I* do like early jets, I was just thinking that for folks that aren't old and crotchety like me the twin-boom style doesn't really scream "jet." I was also thinking that tandem seats would be easier in terms of W&B with and without a passenger. I don't really want to go all angular like the Archon, which means something like generic version of a stepped-seat jet trainer might work (Hawk, Albatros, S-211, MB-339, Alpha Jet, Pampa Jet, Super Galeb, etc.).

What if I do like early jets? The first place my mind goes on this would be something with the style of a de Havilland Vampire but the complexity of a Sadler Vampire. The cool thing is, like the BD-5 the twin boom layout ought to be pretty easy to adapt an actual turbine to if someone wants.
 

Himat

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A recent thread titled "Neglected homebuilt niche?" (see http://www.homebuiltairplanes.com/forums/showthread.php?t=28882) started taking about a tube-gusset-and-fabric, O-235-powered PGK-1 Hirondelle to slot in under the RV-9 in the kit plane market and eventually ended up with the idea of a microlight/LSA RFB Fantrainer (see http://www.fanjetaviation.com/technologies/fanjet-600/).

View attachment 68157

I'd like to explore the idea of a modest cost, modest performance, easy to build, pseudo-jet a little more. Here are a few approaches that I have kicked around:

...

OK, fireproof undies are on.... ;-) Thoughts?

...

INSPIRATION

This is just an RC profile model of a T-45 Goshawk with a little motor in the tail, but I am posting it to show that a "profile model" approach can still capture the lines of a jet and look cool, at least that's my feeling.

[video=youtube;FkvAsrVZebg]https://www.youtube.com/watch?v=FkvAsrVZebg[/video]
About those pusher prop jet or prop in a slot RC models. A power to weight ratio starting at something like 500W a kg and ending well beyond 1kW/kg is part of the fun. Now, that BD-5 did have around 70hp (50kW) depending on engine. To get to the RC model power level it need 150kW to 300kW. Without gaining weight. No modest cost or performance there.;)
 
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cluttonfred

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Funny guy! It's not about performance, just fun, and of course I am not trying to replicate RC model power-to-weight ratios. Here is my real inspiration:

media-13053.jpg Loehle_5151_Mustang_HAG_FlyParty_2012.jpg

Nobody every accused a Carl Loehle of fraud because his 5151 Mustang flew like a Cub, it was all in good fun.

About those pusher prop jet or prop in a slot RC models. A power to weight ratio starting at something like 500W a kg and ending well beyond 1kW/kg is part of the fun. Now, that BD-5 did have around 70hp (50kW) depending on engine. To get to the RC model power level it need 150kW to 300kW. Without gaining weight. No modest cost or performance there.;)
 

Toobuilder

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...I have no problem with a twin-boom pusher but, again, none that are affordable and easy to build are available right now and twin-boom doesn't really have that jet look unless you like early jets...
I had (have) a future project in mind that is a twin boom pusher with tandem seating. Think LongEze without the canard, a straight wing and a C337 tail. In my dream, this thing is powered by a DD V-8. Anyway, the point being: It's a "jet look" from the pilot's perspective in the cockpit. In my mind, this is all that counts and is exactly why the mini replicas are so distasteful to me - Are you building an airplane for you, or for the airport bums on the front porch of the FBO? My Rocket looks like an RV on the ramp and nobody gives it a second look. That's fine by me because when I open that throttle it might as well be a P-51 from the cockpit with the noise, the big prop and the acceleration.

It's the difference between a true visceral experience and a cardboard parade float.
 

Himat

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I had (have) a future project in mind that is a twin boom pusher with tandem seating. Think LongEze without the canard, a straight wing and a C337 tail. In my dream, this thing is powered by a DD V-8. Anyway, the point being: It's a "jet look" from the pilot's perspective in the cockpit. In my mind, this is all that counts and is exactly why the mini replicas are so distasteful to me - Are you building an airplane for you, or for the airport bums on the front porch of the FBO? My Rocket looks like an RV on the ramp and nobody gives it a second look. That's fine by me because when I open that throttle it might as well be a P-51 from the cockpit with the noise, the big prop and the acceleration.

It's the difference between a true visceral experience and a cardboard parade float.
Visualize it for myself that one look good even for the bystander. Prop with a diameter on the small size help make it look right. Probably not the quickest from standstill but could be designed to perform well at speed. And flown like a jet it would make the impression of a jet.
 

cluttonfred

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It's the difference between a true visceral experience and a cardboard parade float.
I hear you, but I think there is a middle ground. A case in point...I like old Morgan three-wheeler open roadsters, and the new ones, too. But the old ones are hard to find and very expensive to buy and maintain and the new ones start at about $45,000 (admittedly much less than they used to thanks to the USD/GBP exchange rate). On the other hand, there is a kit car made from a Citroen 2CV Dyane called a Pembleton Grasshopper and you could easily by an old but running Citroen in France and have a great little weekend fun machine for about $10,000-$12,000 and your own time and effort. Personally, that's the option I'd pick.

image0075.jpg

Similarly, I think there is a middle ground between a "cardboard parade float" and a pretty big-dollar, technically challenging project like the one you described, and the homebuilt real jets beyond that. The guy who built that 5151 researched an authentic WWII Mustang to emulate right down to name of the plane. Would he have done that for an RV-3? Maybe, but I bet the WWII fighter look is what attracted him to the 5151. Ditto a "Fantrainer light" that looked like a generic jet trainer and could be painted up like a combat plane or your favorite national display team. It just doesn't work as well with a canard or twin-boom design.

On a side note, despite the additional weight and drag drag of the "fake" rear fuselage, the inset prop design I described would probably have *better* take-off and climb performance than most other jet-like configurations because it would allow a large, slow-turning prop. Imagine something like this Fanjet 600 with the propeller axis near the level of the top of the duct so the prop extends as almost high as the rudder.

ac819174.jpg
 

BoKu

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Some semi-random observations and commentary of the devil's-advocate variety:

* Why did cars in the 1950s have tailfins? Because they could. By the half-century mark, the engineering, development, and production of automobiles was so refined that there was ample margin for useless geegaws atop the machinery that supported the more utilitarian functions of personal transport. Airplanes, well, not so much.

* As Billski says again and again, weight is the enemy. We're not designing DeSotos here. Every iota of mass counts towards higher stall speed, lower top speed, greater sink rates, and poorer maneuverability.

* Absolutely, there is a huge amount of cachet to sitting out there, in the words of Ernest Gann, "on the beak of this ancient pelican," with a view unobstructed by engine or wings. That's the way I designed the aircraft I help build, and I wouldn't have it any other way. But I've got packaging logic working for me; sailplanes naturally gravitate towards that kind of layout.

* Pretty much every attempt to deliver that perspective for its own sake has encountered failure on one level or another. The BD-5 was sales hit but an engineering and business failure, since the team couldn't deliver on Bede's promises. Things like the Fantrainer are workable solutions that suffer a thousand tiny hinderances, each with their own toll. Pretty much every variation on the ducted fan concept trades double-digit percentages of efficiency loss for the "cool look." Probably the closest to a win is the Vari-Eze/LongEZ platform, but for reasons addressed in other threads the risk/benefit ratio is too steep for me to even ride in one.

* If I was going to ride an airplane into a swamp or into trees or onto rough terrain, I'd want to be strapped down inside a steel cage that is firmly attached to the engine. And I'd want the engine to go first. Funny how often that works out so well.

* The compromise that I'd bet on to achieve a workable and operational balance in this space is mid-engine with forward propeller, like a Stemme S10 without the folding prop. [edit add: Or like a Bugatti replica without the necessity of historical accuracy.] The mass of the engine drives the wing position back, and with a bit of forward sweep the wing root could be entirely behind the canopy. The view over the gearbox and spinner would be pretty good. The prop disk would be ahead of the fuselage, so it is running in clean air and immune to the classic EZ failure of a doodad falling off the fuselage and taking out the prop. Crashworthiness design would have to protect the crew from the inertia of the engine. And of course, you need a driveshaft, and probably a gearbox, but those would just be the price you pay for _The Look_.

--Bob K.
 
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Toobuilder

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There are people that spend $15K+ on precision scale RC models too, but that is a hobby/endeavor unto itself. I have owned a number of very rare American musclecars over the years and I understand the desire to perfectly replicate the production line paint dabs on the suspension and correct hose clamps, etc, but that's not driving the car. The hobby is "having" an object. I have a lot more fun driving my "nothing" cars. I get the feel of a classic, priceless musclecar, but its really worthless clone. Flying at this level I think is similar- the "feel" is what you want, not the look. You are aiming for cheap, so the finished "object" is never going to be anything else anyway. The flying experience will long outlast the "showoff to the bums" experience, so best to focus on keeping it real from the cockpit view.

Yes, my vision is a bit more complex than your market here but that has everything to do with the performance levels I require. The planform is highly conventional and could be made entirely of wood. In fact, my wing is made of three 10 foot span sections with polyhedral. The center section was going to be metal with internal fuel (like an RV), but the outer panels would possibly be wood (like a Mooney or Bellanca). This configuration could easily scale to be a 250 knot continent crusher or a 25 knot ultralight.
 

Himat

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Not simple, but it do have the looks:


Now, once it was possible to search this site with Google and turn on images. Quite a few variations on the theme would show up. Some of them equally nice looking.
 

Toobuilder

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Not simple, but it do have the looks....
Sure. Looks great but from a pilots perspective I'd like to see a straight wing further back out of the field of view. Add some length to the tail arm and suddenly you have a pretty conventional planform with good CG range an benign slow speed handling.
 

tspear

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Not simple, but it do have the looks:


Now, once it was possible to search this site with Google and turn on images. Quite a few variations on the theme would show up. Some of them equally nice looking.
That looks cool, and fast. Question is, how would it fly?

Tim
 
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