Re: Rocket Racing League



Jake McGuire wrote:

The wing loading on an Me-163 is pretty close to conventional light
aircraft, so landing speeds oughta be pretty low, and the L/D ratio is
probably going to be a bit better as well, due to the aerodynamically
clean design and the lack of an aircooled engine and stopped propellor
up front.


I checked up on this Eric Brown touched down on his first Komet flight at around 115 mph, so a minimum landing speed is probably around 100 mph.
That would be considerably lower in the composite replica Komet, but there's a downside to the low weight; any increase in drag is going to cause the speed to bleed of faster in the replica than in the actual aircraft.
So once your landing gear comes down, you are going to start losing velocity fairly quickly.



For one thing, the retractable landing gear means that drag will go up
after it's lowered, so at that point you are pretty well committed to
landing.



What's preventing you from firing the engine again and going around?


That would be the obvious solution, but it means keeping some propellants on board for a possible aborted landing, and that means more weight, a steeper glide angle, and a higher stall speed.
It also means touching down with LOX and alcohol on board, and while they aren't hypergolic like the Komet's propellants, the possibility of rupturing part of the LOX tankage or feed lines in a rough touchdown could lead to injury to the pilot if it came in contact with him. Of course if the propellants mix inside the airframe and there is the slightest spark....



The real Me-163B suffered from another landing problem- once it reached
low altitude, it had a severe problem with floating in ground effect
which made a precision touchdown difficult (pilots were killed or
injured by having the aircraft float past its intended landing point
onto rough ground - retractable underwing spoilers helped, but it was
still tricky to land)



Of course, having conventional telescopic landing gear vs. a fixed skid
means you don't need to really grease it on in order to not break your
back, and the absence of hordes of marauding P-51s means that you can
enjoy such luxuries as landing on an honest-to-god runway.  And then
once you don't have to assume crash and breakup on landing, and don't
have hideously toxic propellants, you can actually carry the fuel to go
around if needed.



Since XCOR's replica would share the same aerodynamics as the Me-163,
this problem could manifest itself also. I don't know what happens in
regard to going into ground effect with the gear lowered, but I suspect
it ends in a stall at very low altitude.



Why? Just like any other airplane, come in at 50% over stall velocity
(the Me-163's wing loading isn't THAT high), flare, and land.



That was the problem with the Me-163; you'd do that, open the wing spoilers, and the plane would come down to within a few feet of the ground and just float in ground effect till the speed bled off enough that it would settle to earth.
Being tailless it behaves differently than an aircraft with a horizontal tail fin.
Trying to raise the nose to decrease speed and make it touch down drives the outer trailing edge of the swept wing closer to the ground, where it comes in contact with the ground effect pressure area and starts to rise. The thing becomes a WIG vehicle during final approach.
On the other hand, once the pilots got the hang of that strange touchdown behavior it was supposed to have really superb flying characteristics.



Considering the airframe will be pretty light weight, something along
the lines of the Microturbo engine used in the BD-5J should be powerful
enough to get it airborne. I've seen one of those things, and they move
like a raped ape- although it can reach 320 mph, its small size makes it
look like it's traveling a near-sonic velocity.
The motor doesn't weigh much (84.88 pounds), and on the BD-5J is fed by
a pair of small unobtrusive side-mounted NACA scoops:
http://www.bd-micro.com/FLS5J.HTM
You'd probably need a bigger engine for the Me-163, but still it would
be doable.



The BD-5J, like most Jim Bede creations, is well known for falling out
of the sky and killing pilots with alarming frequency. And the Me-163
had an installed thrust of around 4000 lbf, which is about 10 times
that put out by the Microturbo in the BD-5J.



Yeah, but the XCOR variant wouldn't be carrying anywhere near that fuel load or engine thrust I assumed- it was supposed to be a hobbyist replica rather than a full-blown point defense interceptor wasn't it?
You go up the FAA and tell them you want to make something rocket powered that can do around 590 mph and climb at 11,000 feet per minute, and they might give you the green light- you tell hem you want to start producing these things for sale and they might be have some concerns.


While I agree that the Me-163 as previously built left much to be
desired as an operational aircraft, the BD-5J is one of the few things
out there that's worse.



I don't think they've had quite the pilot attrition rate they had with the Me-163 with the BD-5J; they lost more Komet pilots in takeoff and landing accidents than they did to combat, and that's fairly unusual for an aircraft in wartime.
I can see why the crash on occasion; the one I saw was one of the Budweiser airshow ones, and the pilot did a very low altitude flight down the length of the runway at over 200 mph- it was only after I saw the size of the aircraft that I realized he'd had been at around ten feet altitude!

Too bad they couldn't find any buyers, but it looks like their modified
EZ-rockets might actually be going into something resembling serial
production.



What these motors might be very usable for is a built-in JATO system for aircraft (assuming you have access to LOX). You can see all sorts of uses for a reusable rocket boost system for aircraft that doesn't require you to lug around heavy JATO bottles in poorly developed areas.

Pat
.

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