Twin-VW engine Push-Pull design idea (The "Beetlemaster")

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Vigilant1

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first span, what can you safely get in a "standard" T hangar model USA?
I don't think there's a common standard, but most built recently have doors that are 40' wide.

2-3-4 seat? As Pop said tandem with passenger in CG and pilot in front for visibility, if a tandem 2 seat the rear seat need a stick and pedals and a EFIS or it will be boooring to sit there.
The tandem would give great visibility, especially if we can get the pilot's head in front of the LE. The weights/CG weren't looking good when I gave it a quick try, but I think Pop's had things worked out. When flying with others, across is a lot more fun. If it matters, Vans sells more of their side-by-side configurations than tandems.

Revmaster or D-motor, the latter is 88 HP at 2800 and some 10 kg lighter each. to a cost.
The D-motors are pretty rare in the US. Lots of people know about them, but few are flying.

"HSOP HTV"?
 

Jan Carlsson

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So got some result. (stall speed 47 kts)
checking with an MAX CL of 2 got wing area of 113.3 sq ft
with max CL 1.8 wing will be 126 sq ft and 10 lb heavier.
empty weight dry-no oil 1012 lb with braced metal wing and fuse.
span 36´

Ps. the HSOP HTV is the result of black magic. ds.
 
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Pops

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Adding to my BeetleMaster-------- Wishing for a 800 lb empty weight , but it will be very hard, reality looks more like 850 lbs, 900 lbs would give me the big one.
* All alum wings with outer panels that unbolt at the booms. Flush riveted and single lift strut.
* Vigilant 1 's fuselage dimensions are almost the same as my drawing a couple years ago. I'll go with these dimensions.
* Fuselage steel tube with alum or CF skins molded in simple flat panels . No compound curves from firewall to firewall. GF molds could be simple U shaped alum skins held in
place with plywood stations. Think- side fuselage panels on a AT-6. Be able to remove all fuselage panels from firewall to firewall ( screws or camlocks) . Ease of any
maintenance .
* 30" wide fuselage is the width of the engines, may need a slight bump of the cowls at the valve cover pans for clearance.
* CF front and rear cowling.
* Fixed gear with 5" wheels and brakes, wheel pants and landing gear strut fairings.
* No rear seat controls, rear seat removable for a large cargo area when flying single place. If the rear passenger gets bored, tell him to look out on the right side at that naked woman in the back yard sunbathing. That will keep him busy for a while and his brain active. If the passenger is a woman, tell them to toughen up and deal with it :) Plan on a divorce if its you wife.
* Pilots seat on Cessna style seat tracks so the seat could be slid forward and a hinged front seat back for ease of entry to the rear seat with a generous width front door. I like doors on both sides but could live with a single door to save weight and make it simple.
* Keep thinking SIMPLE, Strive to save every ounce of weight and remember , IF ITS NOT THERE, IT WEIGHTS NOTHING AND COST NOTHING AND IS 100% RELIABLE.


Enough of this, I need to get out to the hanger and do some varnishing on the JMR wings.
 
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Vigilant1

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extra drag from one stopped prop .96 due to the smaller diameter
Thanks. Every bit of single-engine drag reduction helps. I just left that in there as a test to see if anybody would really read that data dump.
 

Vigilant1

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If the real prop thrust numbers come out close to my WAG, then even with a prop that gives acceptable low-speed climb we'll have useful thrust as high as 130-140 kts (i.e. from two engines, something like 275lbs total at SL, about 200lbs at 6000'MSL). I was happy/surprised that Jan's real prop software looks like it agrees with that, though it was before we settled on the 57" x 48" prop and maybe the thrust numbers will change. Bottom line is that 140 KT+ speeds look practical with even fixed-pitch props, and your decision to go with flush rivets and any other practical drag reduction steps will bring results.

* All alum wings with outer panels that unbolt at the booms. Flush riveted and single lift strut.
Would you want the boom-to-boom exterior distance to be less than 7.5 feet (to allow occasional movement on a trailer, and to fit in a standard shipping container, which is useful as inexpensive, ready-made weatherproof, tamperproof airplane storage)? That's what I thought would be handy, and it's wide enough for the prop disk. If so, and with a 30" wide fuselage pod, the lift struts would attach 30" out from the wing root, max, with 13' of wing outboard of that. Does it still give enough weight reduction to be worth the trouble/drag/etc? It is "another thing."
Fuselage steel tube with alum or CF skins molded in simple flat panels . No compound curves from firewall to firewall. GF molds could be simple U shaped alum skins held in place with plywood stations. Think- side fuselage panels on a AT-6. Be able to remove all fuselage panels from firewall to firewall ( screws or camlocks) . Ease of any maintenance .
What do you think the tube framework would likely weigh? It's just 100" (8'4") firewall-to-firewall, but it would need to be beefy at both ends to support the engines rather than getting very lightweight aft of the spar/gear attach points.
 
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Pops

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Ailerons-- aluminum frame, fabric covered. Flaps--- aluminum frame, not decided on fabric covering or aluminum skin yet. Just a guess at this time but believe the flaps will end up alum skin due to the loads.
 

Jan Carlsson

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Got some more tweeking in the prop program.
with one Engine stopped the remaining will not turn fully naturally with a 118-120 mph max speed. so we get about 3100-3150 rpm and about 70 HP leftovers.
with a small wing area, the Vy will be at same speed as Vx and Vopt. and climbing at say meantioned 7k´ will be just barely positive with under 100 ft min.

this at 1700 lb, it does not sound like the two Engines give more safety then one, if one of two Engine stop, and it will with a 100% larger risk then one Engine :)

So as Pops is into a lighter wariant is in the need, if not using stronger Engines and CS/fethering props.
 

Pops

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If the real prop thrust numbers come out close to my WAG, then even with a prop that gives acceptable low-speed climb we'll have useful thrust as high as 130-140 kts (i.e. from two engines, something like 275lbs total at SL, about 200lbs at 6000'MSL). I was happy/surprised that Jan's real prop software looks like it agrees with that, though it was before we settled on the 57" x 48" prop and maybe the thrust numbers will change. Bottom line is that 140 KT+ speeds look practical with even fixed-pitch props, and your decision to go with flush rivets and any other practical drag reduction steps will bring results.


Would you want the boom-to-boom exterior distance to be less than 7.5 feet (to allow occasional movement on a trailer, and to fit in a standard shipping container, which is useful as inexpensive, ready-made weatherproof, tamperproof airplane storage)? That's what I thought would be handy, and it's wide enough for the prop disk. If so, and with a 30" wide fuselage pod, the lift struts would attach 30" out from the wing root, max, with 13' of wing outboard of that. Does it still give enough weight reduction to be work the trouble/drag/etc? It is "another thing."
What do you think the tube framework would likely weigh? It's just 100" (8'4") firewall-to-firewall, but it would need to be beefy at both ends to support the engines rather than getting very lightweight aft of the spar/gear attach points.
I don't know yet about the distance from the fuselage to the booms. If you make it short enough for road hauling/ trailer storage, etc, then the longer outer wing panels for the wing span uppers the stress and will require a heavier spar . For the lightest airframe , I believe I would keep the booms farther out and also not have the lower AR stab that you would have with the short width 8' width booms. So I would give up the idea of easy trailer movement and storage, price just to high. I hope I said all that right and got my idea across.

Lunch and back to varnishing.
 
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Vigilant1

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I know we aren't laying out a scale model (or anything like it), but just for grins:
Cessna 337 fuselage pod is approx 16.6' long. If Beetlemaster's is 160", that is 80% scale.
80% of Cessna 337 wing area: 128 sq ft
80% of Cessna 337 wing span: 30.4' (a bit shorter/lower AR (7.2) than anyone here is considering)
80% of Cessna 337 cabin width: approx 38"
80% of Cessna 337 cabin height: approx 45"
80% of Cessna 337 boom-to-boom distance: 8.5'
Cessna 337 fuselage-to-boom (and strut attach point) distance is approx 19% of root-to-tip distance. For Pop's wing, that would be approx 36" out from the wing root (i.e. 36" out from the fuselage pod skin)
 
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Jan Carlsson

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Got into the negative weight spiral, lighter wing = smaller wing = ligher wing, smaller tail, ligher wing and tail, smaller wing, until it settled.
at 1664 lb and 111.1 sq ft wing empty-dry 976 lb, this with fabric wing and fuse, metal tail.

So with single Engine to land, 70 hp at 119.5 mph, Fo, 3,197 - 4,157
Vy - Vx at 77 mph we get 350 fpm
at 7000´ 100 fpm

some thrust nr's at 70 HP and 57" prop
Mph - Lbs
65 = 217
70 = 213
75 = 209
80 = 205
90 = 197
100 = 189
110 = 182
120 = 175

Ps, did you scale the wing area by the Square factor?
http://s4.photobucket.com/user/flyingtigers/media/C336/M337.jpg.html good info on that drawing
 
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Vigilant1

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Got some more tweeking in the prop program.
with one Engine stopped the remaining will not turn fully naturally with a 118-120 mph max speed. so we get about 3100-3150 rpm and about 70 HP leftovers.
with a small wing area, the Vy will be at same speed as Vx and Vopt. and climbing at say meantioned 7k´ will be just barely positive with under 100 ft min.

this at 1700 lb, it does not sound like the two Engines give more safety then one, if one of two Engine stop, and it will with a 100% larger risk then one Engine :)

So as Pops is into a lighter wariant is in the need, if not using stronger Engines and CS/fethering props.
Is that climb performance with the 113 sq ft wing or the 126 sq ft wing (both 36' span)?
Can a prop be chosen that will give us slightly better thrust at these lower speeds (e.g that will let the engine give us higher RPMs/more input HP, or better prop efficiency? Based on the 70Kt zero-lift and induced drag numbers it looks like these designs would need about 110 lbs (Autoreply) - 130 lbs (Pops and I) of thrust to stay in level flight at 1700 lbs, plus another 73 pounds of thrust to generate 300 FPM climb at this weight. So, total prop thrust of 183 lbs (Autoreply) to 203 lbs (Pops and I) would be all we need, at least at sea level. I thought we were okay for more than 200 lbs of thrust at 70 kts, no?

Higher or lower weight wouldn't seem to matter a huge amount. If a plane has 73 lbs of excess thrust at 70 knots, resultant rate of climb:
1500 lbs: 330 FPM
1600 lbs: 320 FPM
1700 lbs: 301 FPM
1800 lbs: 284 FPM

But, if a plane has high induced drag (shorter wings), then loading it up will reduce the amount of excess thrust available at higher weights, esp at low speeds.
Edited: opps, I cross-posted with Jan.
Hey, do things like the corporate world--make that computer model tell us what we want to hear!
 
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Vigilant1

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Got into the negative weight spiral, lighter wing = smaller wing = ligher wing, smaller tail, ligher wing and tail, smaller wing, until it settled.
at 1664 lb and 111.1 sq ft wing empty-dry 976 lb, this with fabric wing and fuse, metal tail.

So with single Engine to land, 70 hp at 119.5 mph, Fo, 3,197 - 4,157
Vy - Vx at 77 mph we get 350 fpm
at 7000´ 100 fpm

some thrust nr's at 70 HP and 57" prop
Mph - Lbs
65 = 217
70 = 213
75 = 209
80 = 205
90 = 197
100 = 189
110 = 182
120 = 175
Thanks very much. I don't know if others agree but 350 FPM climb on one engine seems quite acceptable to me. There are plenty of days a heavy C-152 won't do that well. 7K ft will get you into the traffic pattern at 90+% of the US airports. And, if heavily loaded up for the rare long trip with 4 aboard, Autoreply's plane would still see positive rates of climb at moderate altitudes. That's with 70 HP input? Wow--great.

And it should climb like a bat . . . with both engines turning.

The certified Cessna 337 models advertised SE ROC of about 300-350 FPM. The military O-2s wouldn't do that in practice where they were (heavy with a little armor, radios, fuel, survival gear, and over high, hot forest). The second engine hopefully would allow you to get over friendly territory, or water.

Ps, did you scale the wing area by the Square factor?
It turns out that I did. The real one has 201 sq ft of wing.
 
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Pops

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Lost my post somehow.
To make it short. I have 9.55 ft from boom to boom for my Beetlemaster.
 
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Vigilant1

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some thrust nr's at 70 HP and 57" prop
Mph - Lbs
65 = 217
70 = 213
75 = 209
80 = 205
90 = 197
100 = 189
110 = 182
120 = 175
I know props start losing thrust fast at speeds above their design speed as they run out of AoA and/or hit engine redline, but at 120 MPH that prop doesn't look like it is there yet. It should be good (enough) for some higher speeds, right? At those speeds we can assume both engines are running, and even 75-90 lbs of thrust each gets our planes to over 130 kts cruise speed.
 
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autoreply

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Low stab? Can you describe it?
My bad. Both the low stabilator (C336) and the inverted V-tail have simplest and lightest construction and control runs.
I figured an inverted V would just be two angled surfaces/ruddervators attached to the booms at their bottoms and meeting at an apex higher up in the middle. Given that the booms already high up I can see that the top of the tail would be >really< high up. Maybe the idea is that the booms intersect each surface somewhere nearer to the middle than the end, but they still meet at the top?
Simple inverted V, terminating in the booms. Tail will be tall, which is why my own design is a taildragger.

Keeping boom width limited for trailerability is a must.

Span for hangaring? Just ignore it. Making foldable tips is easy and light. Perception might be different, but folding 5' sections in can be done in a minute or so. Put the folding point (spanwise) where the flaps end and the ailerons start and you simplify construction.

Flaps on a design like mine or the one in this topic is pretty much a necessity. You need the extra drag for landing, otherwise you'll float off the earth. Plain flaps work best for laminar flow wings and ease of construction.

Tail position has a big impact. Nice thing of the inverted V-tail is that it'll always see part of the wing's boundary layer at high aoa flight.

Oh and cabin width can go to 50" on my design ;)
 

Jan Carlsson

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I know props start losing thrust fast at speeds above their design speed as they run out of AoA and/or hit engine redline, but at 120 MPH that prop doesn't look like it is there yet. It should be good (enough) for some higher speeds, right? At those speeds we can assume both engines are running, and even 75-90 lbs of thrust each gets our planes to over 130 kts cruise speed.
Yes and no, this is with the added drag from stopped propeller, others it will do some 135 mph.
interesting, in the prop soft, I have laminar and turb airfoils, (equations that change drag with CL) with turb the total Fo goes from 3.2 to 3.6, max theoretic speed goes from 175 to 170 mph
 

Vigilant1

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My bad. Both the low stabilator (C336) and the inverted V-tail have simplest and lightest construction and control runs.
Okay, I understand now. Do you have any preferences on the length of the tail arm (acft CG to ruddervator center--now I've got it at 10 feet). Also, should I keep the total tail surface size the same as if it were a conventional tail, or do you believe the inverted V allows reduced size/wetted area? Actually, given the vertical stab "plates" at the end of the Cessna 337-style tail, Pops and I could probably reduce the size of the H-stab a little.

Flaps on a design like mine or the one in this topic is pretty much a necessity. You need the extra drag for landing, otherwise you'll float off the earth. Plain flaps work best for laminar flow wings and ease of construction.
Agreed flaps are a must. I'm going to keep investigating possible use of split flaps. I know they aren't very popular on new designs, but they might be good here. They leave the top of the wing totally clean, there's no concern about air spillage through the gap, they generate lift/drag about like plain flaps at small deflections, and give more drag than plain flaps at high deflections which could be just what we need here. Bonus: easy to build (an inset flat surface) and the NACA graphs often show applicable data for one on the regular L/D depiction (I guess because it was easy to slap a wood plank at 60 degree deflection on the airfoil model that was already in the wind tunnel).

Oh and cabin width can go to 50" on my design ;)
What are you planning to do in there? Badminton? Okay. But next thing I'll hear is that you are certain you'll get laminar flow behind that propeller before it flows around that bus-like cabin.:)

Edited to add: Hmm--with the desire for the high inverted V tail and the wide cabin you could go with low booms from the bottom/near the bottom of your cabin. They'd clear the rear prop disk at that 50" width if they are down there. You'll need hardpoints at the bottom of the pod edges anyway for the landing gear mains, they could be built into the booms. I know we said "no retractable gear" but it would be very tempting to build some retracts into those boom tubes as part of the cabin. Maybe semi-submerge the tires (in case of failure/forgetting to put the gear down the covers get scrubbed off but you still roll on the tires), and just have relatively short gear legs. Also, the booms/tubes provide additional crashworthiness/protection from intrusion of the cabin from the sides could even be extended firewall-to-firewall to stiffen things up. Probably metal thinking, but it's the only thinking I have . . .

Back to our regular programming.
 
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Vigilant1

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Some updated stats: I edited my spreadsheets to include the minor changes (AR's flying sofa;), etc), reduced the drag for a stopped prop slightly (57" rather than 60" diameter) and we can also use the single-engine prop/75 HP VW engine thrust figures Jan provided (POST 270) to estimate single-engine climb performance.

All figures below are for single engine performance (thrust from one engine, drag from one stopped propeller).

If the engines/props behave like this and the if drag numbers are close, an engine failure won't be a major event, at least from a climb performance standpoint. And, if we use an engine that truly provides more than 70 HP at SL standard day conditions (i.e. if the Revmaster does make 85 HP/80HP continuous), then the climb performance below might be about what we'd expect at 3000 MSL or so.

Pops: (140 sq' wing, 34' span, single-strut metal wing, 2 place tandem tube fuselage with AL or CF skins)
.....Zero-lift Effective Flat Plate Drag (EFPD), normal: 3.4 sq ft
.....Zero-lift EFPD, one stopped prop: 4.4 sq ft
.....70 Kts SL: Single engine thrust available: 205 lbs (Jan's post #270) (note: this is for a 70 HP engine)
.....70 Kts SL: Single engine zero-lift drag: 70 lbs
.....70 Kts SL: Induced drag at 1500 lbs:47 lbs .....1600 lbs: 53 lbs .......1700 lbs: 60 lbs
.....70 Kts SL: Total Drag...........1500 lbs:117 lbs ...1600 lbs 123 lbs.....1700 lbs: 130 lbs
Excess Thrust avl for SE climb:...1500 lbs: 88 lbs .1600 lbs: 82 lbs ...1700 lbs: 75 lbs
Estimated single-engine ROC 1500 lbs : 411 FPM......1600 lbs: 359 FPM.....1700 lbs: 309 FPM

Autoreply: (126 sq' wing, 45' span, cantilever wing, all composite, 4 place cabin)
.....Zero-lift Effective Flat Plate Drag (EFPD), normal: 2.9 sq ft
.....Zero-lift EFPD, one stopped prop: 3.8 sq ft
.....70 Kts SL: Single engine thrust available: 205 lbs (Jan's post #270) (note: this is for a 70 HP engine)
.....70 Kts SL: Single engine zero-lift drag: 61 lbs
.....70 Kts SL: Induced drag at 1500 lbs: 35 lbs..1600 lbs: 40 lbs ..1700 lbs: 45 lbs….1800 lbs: 51 lbs
.....70 Kts SL: Total Drag.........1500 lbs: 96 lbs..1600 lbs: 101 lbs. 1700 lbs: 106 lbs ..1800 lbs: 111 lbs
Excess Thrust avail for SE climb:.1500 lbs 109 lbs..1600 lbs: 104 lbs ...1700 lbs: 99 lbs 1800 lbs: 94 lbs
Estimated single-engine ROC (FPM) 1500 lbs: 509 ...1600 lbs: 455 …..1700 lbs: 408 ….1800 lbs: 362
Comment: Too much motor? Consider 2 x 1/2VWs instead? :)

Vigilant1: (126 sq' wing, 35' span, cantilever composite wing, 2 place tandem tube fuselage)
.....Zero-lift Effective Flat Plate Drag (EFPD), normal: 3.0
.....Zero-lift EFPD, one stopped prop: 3.9
.....70 Kts SL: Single engine thrust available: 205 lbs (Jan's post #270) (note: this is for a 70 HP engine)
.....70 Kts SL: Single engine zero-lift drag: 63 lbs
.....70 Kts SL: Induced drag at 1500 lbs: 47 lbs ....1600 lbs: 53 lbs …..1700 lbs: 60 lbs
.....70 Kts SL: Total Drag..… ...1500 lbs: 110 lbs .1600 lbs: 116 lbs…..1700 lbs: 123 lbs
Excess Thrust for avail for SE climb:1500 lbs: 95 lbs...1600 lbs: 89 lbs ..1700 lbs 82 lbs
Estimated single-engine ROC 1500 lbs: 443 FPM ...1600 lbs: 389 FPM...1700 lbs: 338 FPM

Regards,
Mark
 
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Jan Carlsson

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Start to sound doable, one thing! important to have an airfoil with low drag at CL 1.0 for better SE climb.

Did a check with 2x D-motor 88 HP FP prop, some 60 lb lighter. so 1600 as I was
SE climb @ 80 MPH 480 fpm (710 with CS prop non fethered)
300 fpm @ 3400´
100 fpm @ 9400´

The climb propeller we pick for 2 Engine drive, will become a bit more then a speed propeller with one Engine, the software calculate a climb, std, Cruise and a speed pitch prop, it is about 2" increase in pitch between each.

The real installed Power with the Revmaster might be higher then we calculated with here, but better be safe now then sorrovw later.
But for sure we give up a lot of performance in both ends of the speed spectra with FP props, in this case.
 
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Pops

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Lost my post somehow.
To make it short. I have 9.55 ft from boom to boom for my Beetlemaster.

Correction-- 9.55 just didn't seem right so checked my math, Wrong. Vigilant1 was correct. Real answer is 8.5 ft or 102".
So reducing it down the 6" for road width does make sense. Think I can live with the difference in structure without to much change.
 
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