10/23 Raptor Video

[rbarnes]

Take an awful lot of runway to get off the ground, even at SL on a standard day, assuming it could do so, and then climb like crap and fly slowly.

But I have about 100 ft^2 of wing, and the Raptor has a lot more, so the wing loading is approximately the same. And I have a 180 HP engine, so at 2175 lb (MY MGW) I've got a power loading of 12 lb/HP. The Raptor, at 3600 lb and say, 250 HP (what folks here seem to be estimating it has for actual output) is 14.4 lb/HP - not substantially lower. And if he is actually getting 275 - 300 HP, then the power loading is essentially the same as the COZY MKIV.

So I'd expect the performance, based on just these two ratios, to be vaguely similar to the COZY MKIV for takeoff roll, rotation speed and climb rate. But these are gross estimates, just to get in the ballpark. It's impossible to say what's actually going on here from the paucity of information that we actually have.

And if the power was what was actually shown on the dyno at 175hp ?

 

[Marc Zeitlin]

It would be cosmetically and structurally messy, but could you put an emergency variable incidence adjust or on the canard as a means to break a deep stall?

COULD you? Sure - if Starship could have a swinging canard, you COULD do anything. As you say, a structural and control system nightmare, though.

Far easier to just determine the correct CG range for the airplane after a thorough design process that takes deep stall analysis into account, and then keep your **** CG in the right range . It's not magic, or difficult. ALL the deep stalls that have occurred in Long-EZ's, Velocitys and COZYs can be attributed to incorrect CG location, incorrect CG calculation, unaccounted for fuel shift that moved the CG aft, leaving off required aerodynamic parts of the plane (Vortilons on the Leading Edge of the main wing) and/or incorrect canard incidence.

Build the plane right, fly it in the approved CG range, and no deep stall will occur. In Phase I, we're supposed to test our planes to the full extent of the operating envelope - I've stalled my plane in 60 degree banked turns at the aft CG limit with no safety issues (but this is a proven plane).

For a new design, a movable weight, as Cameron indicated Nat used in the COZY MKIV deep stall testing that led to shortening the canard span, is far less difficult and intrusive than a variable incidence (feathering, essentially) canard would be. Move a couple hundred lb. 6 ft. forward and your CG will move substantially to assist in deep stall recovery.

 

[Marc Zeitlin]

And if the power was what was actually shown on the dyno at 175hp ?

Just what you'd expect. Extremely crappy performance. But we actually have no idea what the power output is, nor what the issues with the flight were, nor whether what we're seeing is poor pilot technique, or..., or...

Since 175 HP wouldn't allow the plane to accelerate the way the videos have indicated (per the analyses performed here by multiple folks, reinforcing each others estimates), it seems clear that THAT particular number is probably incorrect.

 

[BBerson]

I was thinking about the CG relation to the main wheels. The Raptor and Velocity don't "graze" nose down like the Cozy/Long-Eze do to avoid the tipping aft. So the Raptor main wheels must be somewhat further aft. That didn't cause the Raptor to pitch up and crash on rotation but it could still cause the pilot induced porpoise oscillation until the pilot gets it tamed down.
The Cozy Website shows 20% more runway needed at max forward CG. And forward CG could increase the aft wheels pilot induced problems on rotation.

 

[Wild Bill]

Why is he moving the CG forward by taking out the weights from under the pilot seat...wait...scratch that...the copilot seat since the pilot is seated in the right side seat and moving the weight forward? That is counter productive as the CG moving forward will add more loading to the canard wing...

It was noted in recent videos that the static margin was around 8%
Moving the CG forward will make it more stable.

 

[Andy_RR]

That was a somewhat snarky comment about EGTs. Peter believes that EGTs are fine up to the turbo's limit. If they were way below an engines limit, they would not be a consideration. Yes, peak temps and pressures have a definite reliability limit in any given diesel engine.
The EGT is one of several aspects to the Raptor engine that give myself and other petrolheads here cold shivers.
The Raptor's Audi has a cylinder pressure sensor in one of its glow plugs. It is not being monitored, though. It is a reasonable assumption that Audi put that in so the ECU can actively manage peak pressure and maximise performance without compromising reliability. They limit EGT to 1640F. From what Peter has said he has done with his tuning, is likely that peak pressure is well above the stock limit that Audi has established for the engine. We know the EGT is going several hundred degrees above the Audi limit. The TIT is being measured, so we have to guess a bit.

No, EGTs against peak cylinder pressures/temperatures and piston crown temperatures are not related. Nothing snarky intended with my comment at all.

 

[pictsidhe]

And if the power was what was actually shown on the dyno at 175hp ?

I very strongly suspect that the 175hp number may have been fairly accurate. Peter has jacked the power up somewhat since. A year ago, several of us were calculating low 200s. That is in line with 175 plus a bit.

 

[Mark Z]

Several years ago I saw one of the Citation 10 test articles with tracks to accommodate large water tanks that moved fore and aft. There was also ability for the pilots to bail if they had to.

 

[donjohnston]

It would be cosmetically and structurally messy, but could you put an emergency variable incidence adjust or on the canard as a means to break a deep stall?

When Velocity was doing deep stall testing, they put a weight on an actuated sled that could be moved fore and aft. They moved it aft to get the CG beyond the aft limit, got it into a deep stall. To get out of the stall, the pilot moved the sled forward and the plane was flying again.

Kind of like the end of Wargames: The best way to get out of a deep stall is to never get in one.

 

[N91CZ]

Not sure which video you are referring to..?

BUT here is another people may not have seen yet.....!

IT FEATURES THE FULL TAKEOFF RUN, not just the last part as on the Raptor website......

That is one long take off roll.

 

[lelievre12]

.......... A bunch of the tuners turn down or turn off pilot streams as performance mods. Are they all wet? They tune with combustion chamber pressure sensors and compete with each other on making more power... Since they have tools for tuning the pilot stream, if it benefited power, I would expect that some of them would leave it in.

One other comment is that the alpha is showing greater than unity at low power and around unity during the accel. Hmm, I have always understood that diesels were predicated on excess air if they and their turbos were to last. That too correlates with high EGT's and corroborates the issue we have been talking about with induction air flow being too small for the power.

Billski

A peak combustion pressure sensor (or lack of it) gets to the heart of the engine power issues. Advance in its own right will simply add to ICP and add heat, not power. High internal and EGT's will result with following reliability compromises. It makes complete sense to use a cylinder pressure sensor when tuning. I looked at the Motec tune and cannot see that the Raptor has used a sensor at all when messing with timing. The only 'power sensor' I have seen is using a weight scale on the nosewheel to estimate increases in static thrust. Not the same thing at all.

Excess Lambda (>1) can lead to lower EGT's however it will also increase ICP and could lead to internal engine issues. At the EGT's reported, the turbos will be just fine so Lambda of = or >1 is just fine. Its far more concerning to know the ICP and valve temperatures particularly in an engine which maintains continuous power and is not simply in a traffic light drag race. Fuel pressure and timing and critical for this.

 

[Geraldc]

I don't know why he doesn't use an Eiffel club.Cheapest dyno you can make.

 

[pictsidhe]

I don't know why he doesn't use an Eiffel club.Cheapest dyno you can make.

I suggested a simple check a year ago. He replied that an hp test wouldn't be of any use, it would just be a number. Best not discuss why he may think that.

 

[rv6ejguy]

Piston crown and exhaust valve temps will be a a concern with Peter's setup at sustained high power as may be second stage compressor inlet temps at altitude once the pressure ratios start to rise. His intercooler layout certainly won't be adequate for the intended mission. I'd also say his TIT will continue to rise well past any safe limit as he climbs due to a lack of air that the first stage compressor can deliver.

 

[rbarnes]

Eiffel club.Cheapest dyno you can make.

Does someone have a link to how/what this is ? Searching the interwebz and can't find anything.

 

[pictsidhe]

HBA

My spreadsheet is on that page. Follow madrocket's link for Colomban's article.

 

[pictsidhe]

Interesting comment from the video:

Olov Andreen

I have studied the flight video carefully and can conclude that the down-sweep from the
canard hits the nose on the main wing. The plane i flying with an angle of attac of 5-6 degrees. This leads to one short moment, it is mainly on the
top of the main wing and the other moment on the underside. This means that the lifting force from
the main wing varies with which side the sweep ends up. Moreover, this does not occur
simultaneously on both sides of the plane and it becomes a vobblinng fligt. This is what
happened during the flight. This phenomenon is investigated by SAAB in development
systems 37 Viggen and 39 Gripen.
What can be done about this?
As I see it, it is to lower the canarden at least 100 mm ( 4"). This causes the down-sweep to
end up on the underside of the main wing and will not provide a variable lifting force. The
article below show how it looks for delta wings but the principle for other wing types is the
same. When it comes to Viggen and Gripen, the noswing is chosen to be marked over the
head wing's cord, because at low speeds you want micro swirls to lower the stable speed with an angle of attac of 15 degrees.
I send a link to a translated report prepared at SAAB written by Krister Karling in
English translation. He is now retired as I and worked as an aerodynamics at SAAB
and was involved in developing 37 Viggen and 39 Gripen. The previous trials with
carnaden mounted in line with the head wing cord are not published because the
results were obvious.

Broken link attached.

 

[Marc Zeitlin]

Olov Andreen

I have studied the flight video carefully and can conclude that the down-sweep from the canard hits the nose on the main wing. The plane i flying with an angle of attac of 5-6 degrees. This leads to one short moment, it is mainly on the top of the main wing and the other moment on the underside. This means that the lifting force from the main wing varies with which side the sweep ends up. Moreover, this does not occur simultaneously on both sides of the plane and it becomes a vobblinng fligt. This is what happened during the flight...

I do not know who Mr. Andreen is or what his background or experience with Rutan derivative canard aircraft might be - canards on short coupled delta wing aircraft may have very different characteristics than the canard aircraft we're discussing.

But I can say this - the relationship (wrt waterline) between the canard and main wing on the Raptor is not substantially different than it is on any Rutan derivative aircraft - Velocity, VE, LE, COZY, Berkut, E-Racer, etc. I've flown samples of the first five in that list, and have over 1650 hours in my COZY MKIV.

In NONE of those aircraft, at ANY AOA, has the plane exhibited the oscillatory behavior that we believe we're seeing (and that Peter alluded to) in the Raptor. The downwash from the canard is ALWAYS impinging upon the main wing, reducing it's effective AOA, within the span of the canard - this is a known phenomena and slightly reduces the efficiency of canard aircraft. There are most certainly times in which the tip vortices of the canard are impinging upon the main wing, particularly at slow speeds and high AOA's (when the vortices are the strongest). In none of these aircraft does that impingement (and I include the planes with open wheel wells with the gear extended - Velocity RG, Berkut) cause oscillatory behavior either in pitch or roll.

So the categorical statement that "This is what happened during the flight..." seems premature at best, IMO.

 

[Jay Kempf]

Maybe the best caption in an engineering report ever:

"God acceleration till hög fart." Whatever that means in Scandanspeak is irrelevant. It's still the best ever!

 

[Jay Kempf]

I do not know who Mr. Andreen is or what his background or experience with Rutan derivative canard aircraft might be - canards on short coupled delta wing aircraft may have very different characteristics than the canard aircraft we're discussing.

So dutch roll combined with pitch instability?... giving that rolling, yawing, pitching sea sick cyclic motion? Maritime people call it heaving I think...