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Aero News Network Video - Terrible Raptor 1st Flight Review

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rv6ejguy

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The climb rate was probably kept very shallow for a purpose.
The long takeoff roll could have also been done intentionally the check stability and high speed on the ground just before liftoff.
The low initial ROC is due to the low thrust to weight ratio. The extended low ROC in the video was due to large power reductions required to keep the coolant and oil temps below critical limits.

The lack of acceleration was noted in the previous Raptor thread and is clearly the result of a low power (thrust) to weight ratio. Dozens of fast taxi tests in the vids document this over the last several months with 25-32 second ground runs to reach Vr.
 

pictsidhe

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guilty myself and as CheapRacer stated I should be better,.....talking about character of the man......it probably comes from my own design prejudices and the design variance from such. Not much more needs to be said, but I think future news might be nice, as I do not follow his channel.
I'm going to choose my words carefully...
The big takeaway from the myriad comments about character should be that it is of key importance when you undertake a project like this.
While individual decisions can be important, it is the pattern that will ultimately determine the outcome.
 

Topaz

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Just to answer a couple of questions and support what Billski has said...

  • Yes, we have a "points" system with the forum software. If you get a point, you'll know it, because it comes attached with a warning. The system is a way for the mods to keep tabs on each other's warning actions, more than anything else. And that's all we'll have to say about that for now.
  • We also have the capability now to ban individual members from individual threads, either temporarily or permanently. This will be used as you make it necessary. You'll be informed if you've been reply-banned.
  • The old 'Raptor' thread is closed permanently, at least for now. Want to have us consider reopening it down the road? Keep this one and anything else on the subject firmly within the HBA Code of Conduct. It's all up to you.
  • This thread lives or dies on your use of it. Use it like the other Raptor thread? It'll go away. Use it for constructive discussions of the aircraft and so on, within the Code of Conduct? It'll roll on as long as you keep doing that. Because the other one became such a dumpster fire, you can be assured that this one (or any others started on the subject) will be moderated more tightly than the old one, not less.
This and any other 'Raptor' thread (or any thread on the forum, for that matter) can be a fun and constructive discussion of the topic. Or it can be a dumpster fire that keeps losing members to reply-bans until it's locked completely.

It's entirely up to you folks.
 

Wanttaja

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Is Raptor locked forever? Or can it be unlocked two days a week or something after each new video?
I think the main problem was that a single thread was used to contain comment on multiple videos. A new thread getting opened for each video is a more logical process, and eliminates the huge thread length. We saw several posts by people claiming, "I'm not about to read the previous 3,000 posts, but...."

Keep the comments related to the video referenced. If conversation continues civil, the moderators can leave the thread going, but otherwise shutting down a thread when a new video appears (and a new thread is started) would be reasonable.

Source credibility issues aside, this thread is a bit strange because it's based on a COMMENT about a Raptor video...not on the content of the video itself. On that basis, we should see new HBA threads on individual YouTube comments, or on Raptor postings on Pilots of America.

Let's start new threads to go with new videos, and that way if someone wants to reference someone else's random comment on the same video, at least it'll be somewhat on topic.

Ron Wanttaja

[Term "Someone else's" used under protest :) ]
 

aeromomentum

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Not that it a real solution, maybe spray bars on the radiator, oil cooler and intercooler would be more useful to extend the flight time. But extended flight time may open up additional risk.
 

wsimpso1

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Is Raptor locked forever? Or can it be unlocked two days a week or something after each new video? From post one of Raptor it was supposed to be about following the weekly construction videos. Almost the best learning video on the forum.
But yes, there was problems with that (most popular) thread.
So I suggest a balance somehow. Seven days a week was too much for me. But if the thread is locked we can't do anything but go to his YouTube comments, which are tedious to view.
The original Raptor thread is readable forever.

You want a new thread? Looks like we have one here, with guidance...

Billski
 

Dana

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How about getting a review from somebody that is actually familiar with test flying aircraft. The climb rate was probably kept very shallow for a purpose.
as far as the instability goes nobody really knows because nobody else was in the cockpit. The long takeoff roll could have also been done intentionally the check stability and high speed on the ground just before liftoff. The landing that appeared to be less than stellar can also be due to the fact that they were not trying to set it on the ground in the first quarter of the runway and again they may have been checking for ground effect issues. The opinions on there by the media are basically standard for how the media actually understands anything they report on.
With the short flight consisting solely of a quick loop around to land on a different runway, it's clear there were problems and the pilot wanted to be on the ground soonest. Nobody plans a first flight like that.
 

wsimpso1

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Not being a thermodynamics expert,
Technically, this is Heat and Mass Transfer. Thermodynamics is a whole 'nother topic...
I have a question that someone may be able to answer. Peter is going to add two gallons of additional coolant to the reservoir. It seems to me that won't amount to a "hill of beans" to his cooling efforts. Can someone quantify that?
The very limited data shared to date does not give us much basis. A system that is at least approaching equilibrium will have the coolant dT/dt decreasing as temps go up. So far the data indicates one steady slope at full power and a lower slopes at lower power settings. That is how an insulated system looks - zero heat rejection. If it is rejecting some heat, it is a long ways (temperature wise) from steady state in the data I have been watching.

The insulated case can be considered the upper bound - Raptor already has several hundred pounds of metal and a couple gallons of coolant that warms up way too fast. Adding 50 more pounds of coolant will only slow things down a little. Coolant's job is to pick up heat at the engine, then give up that heat at the HX and do it several times a minute. Normally, the amount of coolant needed is just enough to fill the engine, the HX, and the lines. Everything beyond that reduces the dT/dt some, but does nothing for the steady state temperatures of the system, which is about flow rates of coolant, HX design, and ambient air flow through the HX.

Usually a climb to any cruise altitude will require a system that can go to steady state at coolant temps below boiling for coolant and at reasonable oil temps at climb power and airspeeds... At these power to weight ratios, must of us either climb at full power or at some high fraction.

All of this suggests a minimum of 3x current heat rejection to the air. Now maybe a lot of that could be obtained with good pressure recovery onto the various HX faces. Peter has not discussed duct design yet... Has anyone seen a pressure recovery duct to any of the HX?

Does anybody have any numbers on weight of aluminum, steel, and coolant in the base engine? We can then calculate thermal capacity before and after adding 50 pounds to the coolant load.

So far we have little basis for how much heat is being rejected... so that will be tough too.

Billski
 
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wsimpso1

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Not that it a real solution, maybe spray bars on the radiator, oil cooler and intercooler would be more useful to extend the flight time. But extended flight time may open up additional risk.
Mark, you are a smart guy. Why did I not think of that? The racers do it.

Agreed that spray bars will extend useful time, but with no air forced through the HX, won't this be just a low gain bandaid? I am guessing 20-50% improvement when 3x to 5x is needed. Basis for my educated guess is the near constant dT/dt slopes - it is behaving almost like an insulated system. If someone has any data indicating an approach to steady state temps at some known power, I want to see it. There was some comment about temps leveling off at 20% power, but in the runs I observed, slopes reduced with reduced power but continued up, like an insulated system. Steady state at sustainable temps and 20% means it needs 5x the current actual rejected heat.

We have been looking and no one can point to a duct making pressure recovery at the HX front faces to turn over the air within the HX. Then the HX appear to be stacked which requires even more dP to get air through them. Unstacking and then ducts would go a long way toward making this beast cool. Carve them from white foam going from scoop to HX, wet layup 2 plies of 6 oz graphite, make the foam go away, clip them in. One for the radiator, one for each intercooler, make some sort of guess as to how big a fraction of the scoop air goes to each, and try it. Start fooling with foam today, run it down the runway in three or four days of fabricating, laminating, and fitting.

Billski
 

pictsidhe

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I've been suggesting water spray subce the first flight. At the end of his first flight, he first reduced power to 35%. The temps were most definitely still climbing then. A further reduction to 20% and they are almost static. Down to 15%, they started dropping.

At 20% power, he is off boost. The intercooler is dumping around 80kW at full power, so he has lost almost all that, perhaps 1/3 of the coolant heat he needs to dump. I estimate he needs almost an order of magnitude better cooling compared to his first flight. That is going to look like an insulated system...
 

wsimpso1

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My thermodynamics textbook has a chapter on heat transfer.
Interesting. For a Mechanical Engineering program to maintain accreditation currently, it must have a full semester course each of Thermo, Fluids, and Heat/Mass Transfer. My bet is the chapter on heat transfer is ignored because there is a whole semester on the topic elsewhere in the curriculum. My copy of Van Wylen and Sonntag does not have any chapter on heat transfer, and it was the basis for the then required two semesters of Thermo. 1970's.
 

Topaz

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So, watched the Aero News Network video segment, and getting caught up here after being away since the end of July, are these all correct?
  • Raptor has done a first flight.
  • Peter did the first flight himself, after all.
  • Low acceleration, low ROC, all the evidence of an underpowered aircraft.
  • Coolant temperatures climbing throughout the flight, including after power reduction for approach and landing.
  • Visible pitch excursions on final and flare, possibly mid-flight as well. Whether these are pilot-, wind-, or aircraft-induced (or a combination thereof) is undetermined.
Is that a fair summary of the first flight, as shown in this ANN video report?
 

don january

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On test flight he had the gear down and experienced a large amount of porpoising in level flight that the open bay on lower wing for gear is assumed to possibly be the problem by disturbing the airflow under the wing due to AOA. If I was building this type of plane I would defiantly be following if he finds a cure for all problems that he is coming to face and I'm sure it would help in other types of aircraft with similar problems rather over heating or airflow
 

Topaz

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I don't know. Seems in conflict with the moderators who have been asking new members to search and review past threads instead of rehashing the same topic. Maybe a link to old thread?
I hope the mods have been clear that we don't have any inherent objection to a thread/threads about the 'Raptor.' We have objections to threads where people repeatedly and consistently test or violate the HBA Code of Conduct. If you guys want to talk about 'Raptor,' have at it, have fun, and teach each other good stuff. But keep it in-bounds or a new thread will eventually be locked just like the old one. That's how it works.

Nobody's trying to be a stick-in-the-mud here, especially the mods. But the owners of this place have rules for it. They get to decide that, as it's "their house" as it were. Threads and members can follow the rules of the house, or they can receive what should be entirely expected moderation. If anyone has other questions on this, let's take it PM and out of this thread, so that it's disrupted as little as possible.
 
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