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Raptor Composite Aircraft

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TFF

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Airplane brakes are designed for one stop and a rest. A takeoff is considered a cooling cycle. First thing you did if you had to change a tire on an airliner was check the brake temperature. If it was really hot , you had to wait. You did not want it popping from heat if the overpressure plug didn’t go or that even. Always fun working on broken ABS systems testing. Good speed taxi and slamming on the brakes two or three times and hearing the tires go off like fireworks.

He has pretty big pads on his plane. They are nice brakes and wheels. His tires were fine.
 

TFF

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He has brakes that should take the heat treated right. They look like big twin brakes. They should have capacity. What real airplane does six rejected take offs in a row? It’s what he is doing. A lighter plane would be able to use lesser brakes.
 

flyboy2160

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If you look at the CFD photos on his website, it is SW. Since you haven't used it you may not be familiar but its pretty clear his CFD is all ********. His SR-22 comparison was a model he made, which means it's actually not 100% accurate, compounded by inaccurate software means his numbers are complete garbage.
No, you can't tell from his CFD photos which SW software he used. Flosim plots have the same legend arrangement. (I have fired up Cosmosflo and looked at samples, but I haven't actually run models with it.)
 
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wsimpso1

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I'm sure Wasabi commented on the rudder position/ergonomics. possibly he is 'riding' the brakes as he pedals away at the rudder, would account for the glazing.!!! 🤔
Justin commented on how the brake/rudder pedal geometry almost ensures that the brakes be applied when rudder is applied. How so? Looking at both video and SW shots that PM supplied, the rudder pedals pivot immediately forward of the bottom of the pedal. Then the bottom of the pedal is quite low. So to get only ground steering and rudder but not brakes requires you to somehow get only the very bottom part of the pedal. I suspect that is about impossible. When you sit in the plane and put your feet in a more or less nominal position on the pedals, you end up getting brakes as well as ground steering and rudder movement.... Maybe if you deflect your ankle and toes as if you were wearing a pair of stilleto heels this might work.

The solution is pretty straight forward. Those pedal arms need to be made shorter to put the bottom part of the pedal where the ball of your foot will be with your heel on the floor and nominal ankle posture. Other approaches are to actually place the pivot for brakes above the lower contact surface so that the brakes are not easily gotten into unless you slide your feet up. This is all standard stuff in airplane design.

Then, since we are into PM's CAD video of the controls, We get a few more topics:
  • The hydraulic steering will tend to, over time and use, run off index (very modest leakage across pistons) to one or the other side so that pedals will take on more and more offset with use. This can be corrected by periodically bleeding the "high" cylinder. Who wants that as a regular and with a service interval that gets shorter and shorter as you own the airplane?
  • I am hoping that his initial workup of the ground steering and how it disengages when retracted recieved a lot of revision and conversion to some sheetmetal parts. As it is, the parts sure are bulky and most likely heavy.
  • How are the rudders actuated in all of this? I know that I ran out of patience with his video, so maybe covered it, but if the pedals slowly run off index, will that not deploy one or the other rudder as well?
Enough for this on one day... I have wingtip plugs to sand and then shape the bottom sides, a wife to comfort, and other way more productive things to do that see what else PM just had to differently than what everyone else has found to work.

Billski
 
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Orange4sky

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Apr 14, 2020
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Those controls! You only need a couple of inches of pedal travel to compensate for different leg lengths if you really must. Seat travel is much more important. He's tried to reinvent the wheel on far too many things. Let your ancestors iterate the basics.

Anyone else interested in what size torque tube he's using to keep aileron actuation not feeling like pushing on overcooked pasta? That pin sliding in a slot in a tube seem to me like a terrible way to actuate anything, let alone a primary flight control. It would take just a little sand getting in there to ruin your day, not to mention the wear and subsequent play from a single point of metal to metal contact. Hopefully he swapped that slot to the bottom, at least. Is this design used in other aircraft?

pictsidhe: Unless he changed it, the nosewheel is steerable. He attempts to explain it in that video.
 

Steve C

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Every time someone mentions nose wheel shimmy, he says thats normal for a castoring nose wheel. It's not steerable.

Of course he also keeps saying he hardly uses any brakes to get stopped and yet the brakes are fried.
 

Orange4sky

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Every time someone mentions nose wheel shimmy, he says thats normal for a castoring nose wheel. It's not steerable.
I see that now. Watched a construction video. The rudder controls have completely changed from the CAD in that posted video.
 

TFF

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He has had real bad shimmy before , so he is way ahead right now. Bait of what failed before may fail again. I have been in Cirrus, Grumman, RVs that shimmied. Tail wheels too. He may be finding the upper new limit soon though.
 

pictsidhe

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If you look at the CFD photos on his website, it is SW. Since you haven't used it you may not be familiar but its pretty clear his CFD is all ********. His SR-22 comparison was a model he made, which means it's actually not 100% accurate, compounded by inaccurate software means his numbers are complete garbage.
A quick comparison of his results to the actual flight performance of the SR22 would have told him he had got something horribly wrong. It beggars belief that he touting the Raptor on the basis of a software analysis that is a country mile from well known and measured data. Possible explanations are that either he has absolutely NFC what he is doing, or a topic the mods won't let us discuss...

The Cirrus is specced at 180ktas, 161kias at 8k and 75% power. I get around 180hp for that. That would give a drag of around 280lbs. Peter has proclaimed the Cirrus drag at that IAS as 1400lbs. He also seems to think that hp required is 0.14 per lb of drag. Yes, really, no speed term there... It took me about 10 minutes to do that insanity check, mostly looking for Cirrus data.

Very, very simple 10 second check: 1400lb x 180ktas = 766 thrust hp. Let's call that a round 1000hp at the crank.
 

BBerson

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Hadn't looked at that lift/drag graph before, it appears the lift is increasing with increasing cruise speed....
Cruising lift and weight doesn't increase in my airplane. ;)
 

Doggzilla

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What size brakes does he have? A 3500 pound airplane decelerating from 100 mph can put a lot of heat into the brakes.
Roughly the same as 7000lbs from 50 and that will easily fry two pads. 7000lbs usually has 8. Trying to stop that much force with 2 is going to wear them out extremely quickly
 

Kyle Boatright

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Roughly the same as 7000lbs from 50 and that will easily fry two pads. 7000lbs usually has 8. Trying to stop that much force with 2 is going to wear them out extremely quickly
Doesn't KE= 1/2 MV^2, meaning Peter needs twice the braking capacity from 100 mph as a 7,000 airplane braking from 50 mph?
 

Erik Snyman

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Just caught up on the last 10 pages of the Raptor funnies. Geez, am I glad the internet wasn`t there when Piper built the J3. The airplane that is so safe and easy to fly, it can barely kill you....
 

Mike0101

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All depends on the user of the CAD or CFD program. Quality in, quality out. Garbage in, garbage out. PM is certainly not qualified to perform the CFD, and SW's CFD module isn't at the level that would provide accurate answers in the regimes of interest (IMO).
Not sure why there is this huge discussion over FloEFD accuracy in the case of Raptor. That is what is bundled in SW premium, it's a slightly stripped down version of what you would use in NX, Catia V5, Creo and Solid Edge or standalone version. From Siemens - Advanced module Link here. It's certainly not an Ansys, Star CCM+ or other Top Tier CFD packages, but it shouldn't be off by a factor of 6...

If you go to Raptors web page Design Link and play video, @12:19 he describes flow streams as ending 20ft after aircraft. That would indicate his computational domain or "virtual wind tunnel" is far too small. Then at the beginning PM mentions 5-40 minute solve times... Did it even converge or complete? Also I've used that CFD package and Engineering units is in 1st or 2nd step of setup, so easily could have selected desired unit. But as Mark mentioned, just because it's there doesn't mean someone knows how to use it.

In all likelihood - Virtual Wind Tunnel is far too small with a course cork stuffed in it. By course cork, referring to meshing, likely without refinement. Not here to defend FloEFD - have used it, and Star-CCM+ too. As mentioned above, FloEFD is not top tier, but at those velocities it should be in the ballpark (for drag estimate) - if used correctly.

If anybody is interested in domain size CFD Link and refer to figure 2 on what an appropriately sized virtual wind tunnel would look like (think in terms of ratios or multiples). Then correct meshing is another topic, but I'll leave that for another person.
 

pictsidhe

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Just caught up on the last 10 pages of the Raptor funnies. Geez, am I glad the internet wasn`t there when Piper built the J3. The airplane that is so safe and easy to fly, it can barely kill you....
Members often question builders about their projects, the builders who can properly answer those questions get supported. Plenty of novel stuff going on. Those who are just guessing at crucial stuff are the ones who have problems with their build.
 
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