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Low and Slow......and quiet ?

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SteveAero

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Apr 14, 2020
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Hi All,
I'm looking to scratch build a Microlight/ ultralight that has the best forward visibility, flies slow and if internal combustion engine powered then as quiet as possible. (ultimately I will go to electric power, but one thing at a time to avoid over complicating matters)
I would expect to hybridise the best of whats already 'out there'
The VJ 23 probably has the best potential for the wing, 3 axis aerodynamic controls, modified with possibly slotted fowler flaps and even leading edge slots. The idea being to reduce the stall speed as low as possible.
Any ideas out there ?
Guys, what happened to the royalty free plans data base please ??

My best to you all
 

pictsidhe

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A VJ is a good choice. You could also look at the Mike Sandlin designs.
If you want really low, slow and quiet, go for plenty of span. Use struts and wires to keep the spar weight down. The slower you are, the less drag struts and wires make. Have a look at the various man powered aircraft for extreme applications of this. Using high lift devices and short span will create a lot of induced drag.
 

plncraze

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As an introduction to quiet aircraft read some tech reports on the Lockheed YO-3A. Pay attention to propeller tip speed and engine exhaust.
 

don january

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You can take a 150mph airplane and fly low and slow if you use the throttle and keep it just above stall unless of course the aircraft stalls at 90mph and think of the fuel you will save. I think many guys are worried about getting something that requires no PPL to operate.
 

Victor Bravo

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the best forward visibility,
flies slow
I would expect to hybridise the best of whats already 'out there'
3 axis aerodynamic controls, modified with possibly slotted fowler flaps and even leading edge slots. The idea being to reduce the stall speed as low as possible.
Have a look at the Kolb Firefly as the starting point, it will get you 2/3 of the way there even before you start with the custom modifications. A highly muffled 4 stroke engine with a high ratio belt redrive, turning a large slow propeller, will be the big upgrades in the power department, compared to any of the stock UL power systems.

Once that's done, the custom upgrades to get you the rest of the way, IMHO, would be:

1) change the Kolb sharp-nosed airfoil to a more blunt and cambered section, perhaps even under-cambered. This will of course require a modest enlargement of the tail, but fortunately Kolb uses a long tailboom tube so the tail volume will be there.

2) It might be worth the effort to incorporate inboard flaps, but this will require you to add more main wing ribs (which is done an all the Kolb models with heavier weight and/or flaps). But DO NOT use the Kolb hinge method, for either the flaps or ailerons! It sucks, and causes the ailerons to be very heavy and high friction. The under-cambered airfoil upgrade on the main wing may make the flaps un-necessary anyway.

3) There are several areas on the Kolb and every other UL class aircraft where you can greatly reduce airframe noise by sealing gaps, fairing over intersections, closing up holes, etc. So you will be spending a lot of time doing the kind of work normally associated with gliders and fast airplanes; in this case it is not for speed - but you are still using the same medicine for a different purpose :)

4) I don't care what Homer Kolb was thinking about maximizing performance, or how much easier it is to build the wings on a flat board... you will need to build a few degrees of wing twist (Washout) into the outer 1/3 of the wing. The stall on the stock plans-built Kolb is very sharp for an ultralight. No buffet, no shaking, no rumbling. The Kolb guys have a name for it, "the Kolb Quit". I wrecked my friend's Kolb Mk 3 because of not paying enough attention to this (and other factors). If you are going to be spending a lot of time at the very bottom of the speed envelope, you're going to need that washout to have an appropriate stall feedback airframe buffet.
 
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wsimpso1

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Think effective muffling, bigger than normal prop speed reduction ratios, and big props for quiet. The Lockheed YO-3A operated in Vietnam and none of the 11 used there ever took a ground fire hit from the forces it was locating and directing fire upon. Sounds like a well proven scheme for quiet.
 

henryk

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Gregory Perkins

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A hi mounted tractor design affords the largest diameter propeller. Think Gypsy- Woodhopper VJ-24 etc. I believe it was in Australia that a guy used a 4 or 5 inch alum gutter drain pipe
in which was stuffed a wire mesh tube wrapped with fiberglass batt and this pipe ran the full length of the fuselage as a muffler sticking out just past the rudder. This could I think become the basis for a "Stealth" UL . Since UL Propellers are hard to come by greater than 72 or 74 inches, two could be used Wright Bros style if one center engine used or could go Lazair style with an engine on each wing with 72in prop. Incidentally, the wire mesh tube was made by wrapping wire mesh around 2 inch PVC or some other pipe and wire tying the edges together and then withdrawing the pipe. Somewhere I have a photo of this airplane.
 
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Victor Bravo

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Nope, not senile 😊 . But when the airplane flew, the reports were that it was much much quieter from pattern altitude than any other airplane. So my expectation of a whisper quiet engine sitting in the cockpit was not met, but the noise level reported from ground observers was very low. Part of the problem is that I had nothing to compare this with. So you're thankfully not at high risk of dementia, I wrote what I wrote, but the later flight tests showed it made the airplane quieter.
 

Highflight

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Steve Grossruck fabricated a "quiet" muffler system for a 250cc Zenoah made from two glass pack mufflers welded end to end around which he wound fiberglass insulation and contained it all with a wrap of galvanized steel flashing retained by several large hose clamps. The assembly was attached under the Kasperwing's fuselage, the exhaust traveled forward and redirected aft with a U-bend at the exhaust exit just aft of the nose wheel. The result was as quiet an exhaust as I have ever heard on a 250cc 2-cycle, but that isn't all that quiet possibly dropping the exhaust note by 40%. Steve was hired by Boeing to do a "stealth" landing on top of a simulated rocket launch facility at Boeing Space Center in Kent, WA. To my knowledge the results of the covert "attack" were never released, we never found out if the Kasperwing U/L was detected by the proximity alarms. I believe a Mitchell Wing was also tested in the same manor, I expect the Mitchell was more difficult to detect due to it's wing being mostly non-metallic wood and fabric.
 

pictsidhe

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Nope, not senile 😊 . But when the airplane flew, the reports were that it was much much quieter from pattern altitude than any other airplane. So my expectation of a whisper quiet engine sitting in the cockpit was not met, but the noise level reported from ground observers was very low. Part of the problem is that I had nothing to compare this with. So you're thankfully not at high risk of dementia, I wrote what I wrote, but the later flight tests showed it made the airplane quieter.
I missed those.
 
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