Quantcast

10/23 Raptor Video

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
5,758
Location
US
If the engine fails at 500', whoever's flying one will be VERY interested in minimum flight speed for the off-airport landing. 500' is probably out of the envelope (low) for the airframe 'chute.
Yes, indeed it would be good to know, and he should probably figure that out soon at a reasonable altitude. In an off airport landing in this plane, obviously the prop is a write off. Until he knows the stall speed and behavior, probably the best that could be done in an off airport landing would be to get it quite close to the ground and then keep pulling the nose up and bleeding off airspeed until impact. Clearly, that requires a lot of flat.
 
Last edited:

231TC

Well-Known Member
Joined
Aug 29, 2020
Messages
104
Notice he said he only put the rocket in temporarily in that video, still had to put in the exhaust tube. I don't remember him ever finishing that in a later video. If it were anyone else, I'd assume such a thing wouldn't be neglected, but this project never ceases to astound me, so I'm not so sure it got finished. Probably did, but I just don't remember seeing it.

Edit: Went back and looked at some videos after that one, the rocket exhaust tube is definitely in there.
 
Last edited:

Kyle Boatright

Well-Known Member
HBA Supporter
Joined
Nov 11, 2012
Messages
1,159
Location
Marietta, GA
Until he knows the stall speed and behavior, probably the best that could be done in an off airport landing would be to get it quite close to the ground and then keep pulling the nose up and bleeding off airspeed until impact. Clearly, that requires a lot of flat.
The challenge there is that most forced landing options are not flat, 8000' farm fields where you have the option to scorch into ground effect at 1.8x stall speed and still have room to bleed off all of that speed before you hit the trees at the end. You really want to manage your energy so you enter ground effect at 1.1x stall speed or something like that to avoid an extended float into the trees at the end of the 1000' field.
 

Marc Zeitlin

Exalted Grand Poobah
Joined
Dec 11, 2015
Messages
848
Location
Tehachapi, CA
I only have experience in Velocity's, but I assume LongEZ's, Cozy's, etc. all land the same way. Relatively flat.
While they all land approximately the same way - not in an incipient front wing stall, as with many small GA conventional aircraft, I don't know that I'd call it flat. Once in ground effect, the stall speed drops a fair amount, so even though (in my plane) my rear CG stall speed is about 61 KIAS, I can (if I work at it) touch down at 63 - 64 KIAS, and still be far enough away from canard stall that I'm not worried about slamming the nose on the ground.

I'm on the ground at least 5kts over the canard stall speed. Try to cut it too close and you could have the canard stall while you're still 5' off the ground. That's a bad place to be stalling the canard.
While all that's true, I think you're disregarding the difference in stall speed when in ground effect, so you're probably substantially more than 5 KIAS above the GE stall speed.

So if the prop doesn't hit the ground on takeoff, it's unlikely to to hit on landing.
So there are a few problems with Raptor in this regard. First of all, due to the problems with his static port position, either on the bottom of the plane or in the cabin, he actually has no clue whatsoever what is actual CAS or TAS are. Since the indicated altitude of the plane increases substantially as he accelerates during the takeoff roll, he not only has no idea what altitude he's at, but he's overestimating his CAS as well - IAS is going to be far greater than CAS because the static pressure is lower than the actual free stream static pressure.

So who knows how fast the airplane is ACTUALLY going. We can see that he doesn't really rotate on takeoff - he just keeps accelerating, and then very slightly changes the AOA with elevator deflection to start the climb. I can guarantee that he's nowhere near canard stall, and nowhere near minimum rotation speed, whatever that might be. Since he refuses to determine his stall speeds, and refuses to explore the low end of the speed range, he actually has no idea what the low speed characteristics of the plane are, nor where it would stall at his current CG, nor how fast (in HIS IAS world) he should be flying on approach or landing. With the distorted views of the GoPro, it's a bit hard to discern exactly what his approach angle might be, but it seems low and it seems as though he's carrying a fair amount of power on the final approach, neither of which is a technique I recommend.

All that said, if he's landing far above speeds that he COULD land at, because prop clearance is insufficient, then that's a design deficiency. And the same with rotation - if he COULD be rotating 10 KIAS slower, but he's worried about hitting the prop, again, that's a design deficiency. Since rotation speed and touchdown speeds should be about the same (as you point out), I agree - if he doesn't hit on takeoff, he won't hit on a SMOOTH landing. But a hard landing, well, I've seen a few canards with props that are 1 - 2" shorter than they started the day out as due to a carrier landing, even with a reasonable attitude.

In any case, he KNOWS when the prop will hit in a smooth landing or takeoff rotations - there's no reason not to determine how the plane operates in the low speed regime to enhance the safety of his landings (and as KB points out), emergency landings as well.
 

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
14,177
Location
Memphis, TN
To recover a P-51 from a spin is about a 9000 ft recovery. A 150 or a Pitts is a no brainer comparatively. Right now you have to consider it an alligator. Are you ready to know if it bites at arms length, or ten foot pole?
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
14,446
Location
Port Townsend WA
I wonder if he could make the main wheels go down a couple more inches by modifying the down stop.
Obviously, he can't easily lengthen the legs because it won't fit in the wing wells. But a bit more down would help.
Might need some shims for camber.
 

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
5,758
Location
US
I wonder if he could make the main wheels go down a couple more inches by modifying the down stop.
Obviously, he can't easily lengthen the legs because it won't fit in the wing wells. But a bit more down would help.
Might need some shims for camber.
Or, just keep increasing the nose up attitude a little on each landing. Grind off a little prop each time, and after a dozen times or so the nose will eventually go up no farther and will come down with a satisfying thunk. A three-fer:
1) Nose gear and strut gets a good test.
2) He knows where the canard stalls and he didn't risk a deep stall or other untoward event at altitude.
3) The prop is already then at the right length to allow for slowest touchdown from now on.
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
14,446
Location
Port Townsend WA
Nah, I don't like that plan. Easier to glue on 2" balsa prop tips and then do the gradually increasing nose up attitudes to find the limit. Thanks for that hint, I couldn't think of an easy way to do it.
 

BJC

Well-Known Member
HBA Supporter
Joined
Oct 7, 2013
Messages
12,516
Location
97FL, Florida, USA
Or, just keep increasing the nose up attitude a little on each landing. Grind off a little prop each time, and after a dozen times or so the nose will eventually go up no farther and will come down with a satisfying thunk. A three-fer:
1) Nose gear and strut gets a good test.
2) He knows where the canard stalls and he didn't risk a deep stall or other untoward event at altitude.
3) The prop is already then at the right length to allow for slowest touchdown from now on.
“I’m good with that!”


BJC
 

donjohnston

Well-Known Member
Joined
Oct 9, 2016
Messages
102
Location
Panama City, FL
While they all land approximately the same way - not in an incipient front wing stall, as with many small GA conventional aircraft, I don't know that I'd call it flat.
Neither did I. I said "relatively" flat. As in: compared to traditional aircraft.

One guy (pilot) I took up in my Velocity had never been up in a canard type aircraft before. On landing while he didn't say anything, he seemed... uncomfortable. After landing I asked what was up and he commented that he had never been in a plane that landed that flat before.

I think you're disregarding the difference in stall speed when in ground effect, so you're probably substantially more than 5 KIAS above the GE stall speed.
Nope. Not disregarding anything. I know the stall speed of the canard is lower in ground effect. And if I'm going into a short runway, I'll nibble away at that cushion. But I like having it in the bank.

My point in all of this is that I think stall testing should have been done by now. If not full stall, then at least get close to it. If the airplane is unable to climb to an altitude which would allow that test, then that should be fixed first. Even with what appears to be a wildly inaccurate static port placement, you can still get a number that you can then use for landing so that you're not touching down at 90kts (GPS speed). But instead he's putting 6' long strings on the end of the canard to watch the wingtip vortex?

But I'm not a test pilot. While I did the phase I testing on my Velocity, that's a lot different than a clean sheet design. So I could be completely wrong about what needs to be done and in what order.
 
Last edited:

Victor Bravo

Well-Known Member
HBA Supporter
Joined
Jul 30, 2014
Messages
8,421
Location
KWHP, Los Angeles CA, USA
I am assuming that there are about 4 hours or less actual flight time on the airplane at present. If that is accurate, the big question I have for experienced flight test people is...

At what point does departure and stall and all that start to be tested and explored? In "real" flight test, I can't imagine that brand new designs start to get thrown around like that in the first few hours, especially if there are reliability, cooling, stability problems like what we have seen in these videos.

I know we have several people here who are or were genuinely in the flight test business. So on a new design, with real engineers and real flight test people, how long before you start playing with stalls? 20 minutes since first flight?... 3 hours?...10 hours?

And is it a fair statement that you should sort out any reliability and cooling issues long before you start exploring the flight envelope?

FWIW, I'm certainly not trained in any of this, but I'd sure as hell want to get temperatures and basic stability under control, and have a reliable airplane, long before I explored any corners of the flight envelope.

And then, flying around near stall usually results in poor cooling, high temperatures, insufficient airflow, etc. etc. So that would make an even stronger case for not playing with stalls just yet.
 

TarDevil

Well-Known Member
Joined
Jun 29, 2010
Messages
814
Location
Coastal North Carolina/USA
And is it a fair statement that you should sort out any reliability and cooling issues long before you start exploring the flight envelope?
Kind of a two edged sword, no? If cooling and reliability are a problem I'd wanna know where the edges of the envelope are so I could (maybe) make it to an airfield. If not an airfield, I'd want the slowest possible touchdown in unimproved terrain. So, how slow can I go?

Well then, there's the chute. Wonder if it works?
 

231TC

Well-Known Member
Joined
Aug 29, 2020
Messages
104
I am assuming that there are about 4 hours or less actual flight time on the airplane at present.
Close. About 6 hours now, including 2 flights since the last video.

I'm also not a pro at any of this, but I agree with your general sentiments. You should sort out reliability and cooling before you explore the flight envelope, but you should also sort them out as much as possible before flight itself. A lot more reliability testing should have been done on the ground. It's not too late to stop flying it and do that. You can't perfectly replicate flight conditions on the ground but you can get in the ballpark instead of just taking off and seeing what happens, and then doing that many more times.

Raptor probably could not do a go-around. That's not a minor concern. It has yet to get above about 4000 feet. Maybe I'm too cautious but I wouldn't stall it there, even with an airframe chute. But these are not particularly related to total flight time. It could theoretically get to 100 hours and still have the same issues.
 

berridos

Well-Known Member
Joined
Oct 10, 2009
Messages
1,116
Location
madrid
He could attach a big provisional cooling unit at the belly of his plane and guarantee more than enough cooling to overcome that hurdle. However he seems to be a marketing oriented person and that cooling unit wouldnt look nice and in his brain, the produced drag would be the reason to not achieve the 300 knots or whatever knots he promised.
Guess thats the problem of beeing a slave of youtube twitter....
 
Top