Raptor Composite Aircraft

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Dexacare, Mar 28, 2016.

1. Mar 6, 2019

BoKu

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To abuse the famous Pride and Prejudice quote, "It is a truth universally acknowledged, that an airframe in possession of little service history, must be in want of a proven powerplant."

Also, I amend my earlier suggestion: I think they should flip the airframe over and sandbag the wings and foreplanes to 4g or so to validate the deflection estimates from their SolidWorks models. Then they should slap on an IO-550 and try it out.

--Bob K.

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2. Mar 6, 2019

Toobuilder

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Random responses to several from above:

Testing the existing structure to destruction will not validate the "next" design in any meaningful way, but it might just scare the design team into doing a bit more homework next time.

I firmly believe "crow hops" are killers. The ground is what hurts you- get away from it as fast as possible. Remember the last flying car "high speed taxi" video? 'nuf said.

Flight testing this structure with it's unique distribution of mass is not going to be representative of a "production" vehicle loaded up with sand bags to the same weight. Not sure the risk/reward benefit is even close on this one. If they missed the weight by this much, what else is wrong? Sorry, this is an expensive ground test article now.

3. Mar 6, 2019

Topaz

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Fair enough. You definitely have more experience at this than I do.

4. Mar 6, 2019

BoKu

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I'd want to see an authoritative citation for that one. I'm pretty sure that if the mass is about right and the CG is right, it will return valuable data.

The risk/reward thing is an open question. Most risks can be mitigated with a sensible approach. As for the mass, it's a good bet that most of it is in the engine installation, and a lot of the rest results in greater stiffness and strength than intended, not less. Hence my suggestion that they do a static test to evaluate strength and stiffness to limit load.

I respect your right to an opinion, but I disagree. I think that a lot of their airframe could be salvaged and could return a lot of valuable data with only a modest investment in reconfiguration.

--Bob K.

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5. Mar 6, 2019

rv6ejguy

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No, I was mainly thinking of young Devon (SP?) who has thousands of hours working on Raptor. He's learned a ton which will be useful on the next project he's involved with. Jeff probably added some more to his already very extensive composite knowledge. Peter will forge on for a while I believe until he faces the cold, hard facts that he was in way over his head on this in many aspects. He learned the hard way and will now be facing the music from the ones who "told him so". He may have more respect now for the MEs and AEs he was so quick to dismiss as being uninspired before he started on Raptor.

Once again, we see it's better to be quiet and humble, build out of public view and make no performance claims before flying a new design. There is nothing to live up to and nothing to apologize for if if doesn't turn out as planned. I don't understand why so many newb designers enjoy eating crow.

Last edited: Mar 6, 2019
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6. Mar 6, 2019

rv6ejguy

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I disagree. In this case, with the elevator design and quite unknown flight characteristics and proper C of G location, I'd be doing the crow hops so as not to get into a severe pitch up scenario which is irrecoverable and below the altitude where the Ballistic Chute will save you. No way I'd launch this towards the blue with much haste. I can think of 2 guys who'd be alive today if they'd done hops instead of full blown takeoffs. C of G and elevator authority issues in both cases.

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7. Mar 6, 2019

Toobuilder

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"...if the mass is about right..."

And that is my concern - it's NOT even close to right. I'm assuming that if they are this far off on such a small airplane, then EVERY component is overweight, driving the MMOI into the realm of "unrepresentative". Perhaps it's all in the engine, but I doubt it.

Concerning the risk/reward issue - I agree that a skilled program team can often make a good decision, but the cynic in me doesn't think this particular program has the tools to pull that off. And I'm really questioning ALL aspects of this design now - structure, dynamics, control authority, etc. This is in addition to the epic mass properties fail.

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8. Mar 6, 2019

Toobuilder

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With that much uncertainty, they should not even be doing taxi testing. Unless someone is doing TLAR on a radical new aero concept, then almost every configuration under the sun has data attached to it. Today, one can be quite certain the machine is going to be at least "controllable" if the designer did their homework.

9. Mar 6, 2019

rv6ejguy

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Peter didn't do his homework here so you could be right. I hope he gets some good eyes on it all before attempting flight and I'd be very surprised if Peter didn't attempt to fly it given his stakes and time spent on the project.

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10. Mar 6, 2019

Topaz

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I guess my point about flight tests was about gross static stability and control characteristics, trim behavior, flight control dynamics under air loads, etc. Dynamic stability and fine measurement of axis rates would be "off" with this prototype, but I'd rather see them test this elevator configuration now, for example, than pour a ton of money into a more-refined second prototype and only then discover that the pitch axis has control problems. If they're keeping this control system and outer mold-line, they're going to have to test it sometime, so they can either take the risk now or take it later after spending even more money. They also ought to get some idea if their drag predictions are "in the ballpark" from this prototype, since the outer moldline seems unlikely to change markedly on the next iteration, regardless of the interior structural redesign. In essence, the thing becomes akin to a full-scale wind-tunnel model, with the mold-line and controls being accurate to their design, but the interior made of solid wood, as far as the air is concerned.

Dunno. As I said, you've got more experience at this, but unless they're starting the redesign process with an absolutely clean sheet of paper, I still think there's value in flight-testing this overweight machine. Extremely cautiously, I'll grant.

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11. Mar 6, 2019

Toobuilder

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I'd like to see them test this elevator system now as well - but NOT as the primary flight control of a prototype vehicle.

Subscale auxiliary surface on a known airplane surrogate, wind tunnel, or hell - bolt it to a truck and run it down the freeway!

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12. Mar 6, 2019

Topaz

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Ah, the well-tried Rutan method! :gig:

I think we're all agreed that the ideal situation here would be a clean-sheet redesign with Peter playing the role of the executive admin and marketing department, and some experienced and qualified aero-engineer doing the actual redesign. If they'd been open to that, unfortunately, it probably would've happened the first time around.

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13. Mar 7, 2019

Mark Z

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Maybe it’s time for them to consider investing in a turbine. Phase 2 could have heated leading edges. I’m curious how much that multi-turbo diesel monster weighs. I do wish them well and would never rain on their parade.

14. Mar 7, 2019

rv6ejguy

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If I recall, the firewall aft weight with prop was a bit over 850 pounds. The parade grounds are already soaked with this latest weight debacle...

Last edited: Mar 7, 2019
15. Mar 7, 2019

Marc Zeitlin

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Aha. A much smaller scope than I was thinking you were describing.

Yes - for the kid, it's a great learning experience, and maybe even for Jeff - building things is always a learning experience. Devon would have gotten as much (or more) out of building a COZY MKIV (or the functional equivalent, if you like something else) from plans though, and it would have only cost the investors about $300K (rather than the millions they've spent on this one) and one or two years to pay three people to build a COZY MKIV (3K hours at$50/hr, plus materials, etc.) and he would end up with a flying aircraft. An expensive lesson for one kid, and no airplane kit to sell...

They don't enjoy it, because they are unable to see that that's what's going to happen, no matter what they're told or by whom. We're just stuck in the dark ages, with our old ways of thinking. The problem is that although the "out of the box" thinkers ARE the ones that make the breakthroughs, only about 0.01% of the "out of the box" thinkers do so. The other 99.99% of them fail. I'm conservative, so that's how I bet. I'll never hit it big, but I'll be right 99.99% of the time.

Thanks for explaining to what you were referring.

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16. Mar 7, 2019

Andy_RR

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You don't have to build a complete aircraft to test out of the box ideas. The engineering simulation tools available today are like never before. Unfortunately you also need some sound experience and judgment to know what they can do and which ones to choose. When I saw what Peter was doing in what looked like Solidworks flow sim, it made me cringe and his SR22 comparison was just a joke!

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17. Mar 7, 2019

BJC

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Any engineering / designing effort requires good judgement, gained through a formal education in the physical sciences and from relevant experience. No software package is an adequate substitute for knowledge and experience.

BJC

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18. Mar 7, 2019

rv6ejguy

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Agree, my remark was facetious. I wonder how they will take the backlash when they fail after calling the established players a bunch of dummies before he started their own wonder project.

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19. Mar 7, 2019

BJC

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”They didn’t give us the time / money / support needed to complete the development of our break-through design.”

BJC

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20. Mar 7, 2019

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