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10/23 Raptor Video

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wsimpso1

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You guys are beating up an old topic - Engine power. We know why the power is soft and have talked about it plenty. Since PM has said he will not be altering these issues now, I think we could let the topic lie with zero losses to our collective knowledge or wisdom.

The cooling system has had some modest changes made to it:
  • Improved air outlet from the cowling, which should increase cooling system air flow some;
  • Increased heat sink, which adds weight and slows down the warmup, but changes heat rejection not at all;
  • Addition of a poorly configured radiator that can not move enough air to substantially improve heat rejection;
PM is showing lowered oil and coolant temps, but at substantially lower ambient temps. Oil and coolant temps roll up and down with ambient temps. I have not seen any analysis of delta T between oil and air or coolant and air. Doubtless the data can be downloaded to a .csv file and analysis run in Excel. Normalizing all of the runs to a 100 F day would allow anyone interested to figure out how much improvement in heat rejection and hot day capability, if any, has been achieved.

Then we get to stability and control. This flight was early in the day, no thermals and little wind. Yet it displayed combined Pitch-Roll-Yaw cycles that look similar to what occurred on the first flight. Roll and pitch and yaw still look coordinated to me, just of smaller magnitude, which might have more to do with increased stability in pitch and yaw, or might be mostly due to a calmer air mass. Maybe the interaction has more to do with heavy ailerons and the pilot's hand, but the cycles seem to be there. Without adding channels for input positions and then downloading flight data and analyzing it, we can not be sure. I am betting this becomes more interesting when PM gets some straight and level flight.

Billski
 

BBerson

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I crudely measured 20 seconds from 5-90 knots at takeoff. Seemed better acceleration to me. Of course he could lift off at 80 but no need. Reports on YouTube say gear down is high drag.
 

Steve C

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It was the other way around. It always needed left aileron. The airplane wants to roll right. He put the tab on the left wing and it is bent up. It appears to have not been too much.

He put a large tab on the outer trailing edge to correct a port low wing. Looks like he overdid it hence the new up deflection of the aileron to counteract. If he backs off the trim tab (or removes) the aileron should level.
 

lelievre12

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I took some notes in the DA42 (old Thielert model) about power settings for landing. Now I can fly them by feeling and don't need the values in the NG anymore. Note: the aircraft has FADEC and these values correspond roughly to thrust, hence drag.

Pattern speed (120kt), const. ALT:
  • Clean config: 55%
  • Flaps full: 68%
  • Flaps+LDG gear: 86%
Drag factor gear 86%-68%=18%. Percentual increase 1+(18%/55%)=1,327. Possible speed of the Raptor with retracted gear (1,327)²*110kt=194kt
I was with you all the way until the (1.327)2. Whilst we could argue about whether to square or some other number I thought instead to review the numbers on my plane:

1. Slow flight Gear Down 110KCAS @55% (150HP) (~3600# weight)
2. Max cruise Gear Up 165KCAS @80% (250hp)

The numbers are very close to Raptor so, like my plane, I would expect 165KCAS at S/L at 80% for the Raptor too. At 25,000 feet 165KCAS = 243KTAS which is the a great number if (BIG IF) the Raptor can make 80% at altitude. The fuel burn at 80% for the Raptor is likely to be 16GPH and for the P210 (ROP) is about 28GPH. So the Raptor could win here as the TSIO520 is an ROP fuel hog at high power in order to stay cool. The Diesel, not so. However as pointed out, 7GPH at those speeds and weights is simply dreaming.

So I don't agree the Raptor could ever see 194KCAS with this power, however even if it only attains 165KCAS it will still be fast if those turbos can be made to work at alt.
 
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flyboy2160

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In the latest episode at about 6:20 he describes how, in the first flight, the canard stalled right at rotation and continued to alternately stall along with the main wing stalling. But moving the cg forward fixes this.......and over to you in the booth, Marc......

 
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He keeps using the term "heat being radiated out" in the end of the video but then completely ignores the fact that, indeed, that could be all it is? Meaning there may not be actual _airflow_ happening. Made me twitch every time he'd make the assumption he had airflow just because he had heat transmission. Obviously at high speeds rolling down the runway he had airflow, but when he was sitting still on the ground with everything shut off, he was still insisting he must have airflow from a "breeze". But if you look at the telltales hanging off the stab they are completely stationary. No breeze _at all_. It's a minor point and doesn't really matter in terms of the airworthiness of the design (much), but it still just makes me cringe.
 

Marc Zeitlin

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In the latest episode at about 6:20 he describes how, in the first flight, the canard stalled right at rotation and continued to alternately stall along with the main wing stalling. But moving the cg forward fixes this.......and over to you in the booth, Marc......
Sigh. _IF_ there were any main wing stalls going on (which there most certainly are not, unless PM has a different definition of stall than the aerodynamic community as a whole) then moving the CG forward would help to prevent main wing stalls. Aside from stability concerns, preventing main wing stall (deep stall) is the second (and possibly MORE important) reason for the rear CG limit location on canard type aircraft.

If the Raptor had had a main wing stall, the plane would have crashed, given the low altitude at which he was flying and the experiences of everyone else that's had a deep stall in a canard type aircraft.

As far as the CANARD airfoil stalling, yeah, no. It isn't. As I pointed out in my comments about his first flight, since he's rotating at a speed ABOVE the slowest speed he was able to fly, and since there's no discernable drop in the nose of the plane, he can't be stalling (at 1G) at a speed above the lowest speed the plane can fly. PM's looking at relatively stiff and too long tufts made out of the wrong material, seeing some reverse flow near the trailing edge, and thinking that that implies that the airfoil is stalled, because there's a bit of separation going on. I'll just say that his lack of aerodynamic understanding is fairly robust.

On my plane, with a Roncz canard on a COZY MKIV (but folks have seen this on GU canards on VE's and LE's and COZY III's as well) you can fly through some rain and have water bead up on the TE of the elevator and just sit there. You're flying at 100 - 140 KIAS, but there are water blobs just dancing around about 1/2" fwd of the TE of the elevator. WTF, you think. All it means is that there's a bit of separation there and a small amount of reverse flow. Price of doing business with these airfoils. It is obviously NOT an indication of canard stall, as I can fly my plane at the rear CG limit down to about 61 KIAS.

PM has never had either the canard or the main wing stall on him in the Raptor, and he should be extremely happy about that fact. If the canard stalled on rotation, the nose would have slammed back down onto the ground, possibly breaking something. And if the main wing had stalled, particularly only on one side, as he surmises, he'd have been sideways and rolled up in a ball on the ground.
 

wsimpso1

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A few little facts to know and compare to what was presented in the video:

Aerodynamics:
  • Airplanes fly in steady state when weight applied to each of foil is balanced by lift produced by the foil. If the loads do not balance, the airplane will accelerate in the direction of the excess force.
  • Airfoils stall when their angle of attack exceeds their critical AOA.
  • Shifting CG forward adds load to the canard and reduces load on the main wing.
We know that moving weight forward will make the airplane more stable in pitch and yaw axes, but will demand more lift of the canard airfoil. If it demands more lift than the canard can make at any given speed, rotation becomes impossible until higher speed makes that lift available. If the foil was at limits on a previous flight, shifting weight forward will raise the minimum speed that the airplane can rotate and which it can maintain steady state flight. Did that happen? I suspect not - IIRC, he has flown this bird significantly slower than his rotation speed.

Then we get to evaluate if the canard was on the verge of stall at rotation speed. Well, maybe a canard at 10-12 degrees AOA plus a deflected flap could approach stall there. We saw no big pitch down, so I doubt he actually got to stall. So what will moving the CG forward do to this? It will add load to the canard, either raising the speed required at which the foil AOA plus elevator position can make lift equal to load or require still more elevator angle to rotate at the same speed. Did either of those happen?

Heat Rejection:
  • Heat removed by a heat exchanger can be estimated two ways - Knowing the change in heat in the coolant and knowing the change in heat in the effluent. In both cases, the rate of heat removed (Hdot) is the product of specific heat capacity of the fluid (Cp) times mass airflow of the fluid (mdot) times change in temperature of the fluid (dT). Yes, Hdot = Cp*mdot*dT. Maybe you saw this in high school chemistry as H = Cp*m*dT. Here we made it into rate of heat flow and rate of mass flow;
  • Heat lost from the coolant is equal to heat added to the air, so if you have both, you can even check your work here;
  • We can look up Cp of coolant and of ambient air, and we have an estimate of dT for the air but not for the coolant. We have no estimate of the mass flow rate of either air or coolant. We can not even guess with any accuracy at the heat rejection of the new HX with the available data;
  • If we had those temperature probes attached to the coolant inlet and outlet pipes, we could however find out if we were getting any coolant temperature change. A good target on coolant dT is 10F. If the coolant was loosing 10F going through the HX, it might have been working well. To me that result would justify some method of estimating mdot. And if the coolant shows the same temperature at the inlet and at the outlet, there is approximately zero heat being rejected, validating the estimates of some of us that air flow will be very small through this HX.
Any manner of flow measuring device in the coolant or in the airflow would have allowed an estimate of heat rejection. A pitot tube behind the HX would give a pretty good idea of the airflow rate. A flow rate instrument or venturi with a couple manometers in the coolant flow pipe would also enable flow rate in the coolant. None of these were installed, but any could be installed and produce some reasonable estimates of how much or how little is actually happening for all of the effort here.

Billski
 
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BBerson

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I think the previous flight had pilot induced oscillations that exceeded intended rotation angle and nibbling at stall. Mentioned by Velocity on the YouTube comments. The CG was too close to neutral so the forward move tamed the PIO. He was above the normal 1g stall speed at all times. But stall nibbling can occur above stall speed with rapid stick movements. (stall is AOA not just speed)
 
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Marc Zeitlin

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Mentioned by Velocity on the YouTube comments.
But they were incorrect, as discussed previously. The motion of the plane was NOT what happens during a canard stall. I believe that they misjudged what they were seeing in the video.

The CG was too close to neutral so the forward move tamed the PIO. He was above the normal 1g stall speed at all times.
MAYBE the CG was too close to the NP - some folks are making that judgement based on a stabilized GoPro movie in a plane piloted by someone not familiar with flying canards and who was almost certainly inducing a fair bit of PIO's, which I see in MY plane when someone not familiar with canards flies it, and which I've tested to the limits of the performance envelope. I would not be categorical about the CG location, NP location, or the relation between the two - we are operating with almost zero actual information here. Moving the CG forward would certainly make the plane more stable in pitch, but it's not clear that it was unstable on the first flight.

Since he was not just above the 1G stall speed, but substantially above the 1G stall speed, the small elevator movements, which change the effective AOA of the canard by a degree or two, would not be anywhere near enough to cause an instantaneous canard stall. Since there were no nose drops (bobbing, it's usually called) of the nose with a constant elevator position, I will say that I'm 99.99999% sure that neither of the flying surfaces on the Raptor aircraft has ever stalled (yet).

But stall nibbling can occur above stall speed with rapid stick movements. (stall is AOA not just speed)
See above. The stick movement would need not only to be rapid enough to occur faster than the inertia of the aircraft would allow the plane to move, but also large enough to actually cause an AOA change above the stall AOA. This did not happen - the elevator TE movements during the pitch oscillations seen in the first flight were minuscule - almost imperceptible. That's not causing canard stall, when 25% above the 1G stall speed.
 

BBerson

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Yeah, I would think stall "bobbing" would be much longer frequency. I did think the PIO elevator movements were quite noticeable on the first flight. And the attitude instrument was going wild in pitch.
It is likely it was mostly PIO on the first flight from unfamiliarity.
I suppose it could be that he learned to tame his PIO after only that one minute first flight.
The rear CG limit can be explored more later to determine if that was a factor or if it was PIO.
 

flywheel1935

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Seems to me, and possibly others? that unless a new YT video is featured of the Raptors latest mods, then there is very little to comment on. Having followed progress with both interest and dismay for over 2 years its apparent that nothing anybody suggests will ever be implemented, so I've got to the point not to bother anymore. Seems the designer is using a meat thermo, if that's the case then the Raptor is definitely going to be 'rare' !!!! see what I did there, it's got that boring, I'm gone.
 

poormansairforce

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Seems to me, and possibly others? that unless a new YT video is featured of the Raptors latest mods, then there is very little to comment on. Having followed progress with both interest and dismay for over 2 years its apparent that nothing anybody suggests will ever be implemented, so I've got to the point not to bother anymore. Seems the designer is using a meat thermo, if that's the case then the Raptor is definitely going to be 'rare' !!!! see what I did there, it's got that boring, I'm gone.
:)
 
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