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ORIGINAL: iron eagel

I would like to see how fast we could make a prop driven model go.

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ORIGINAL: da Rock

quote:

ORIGINAL: iron eagel

I would like to see how fast we could make a prop driven model go.

Oh man, just two models?

Let's see, "a prop driven model"....... hmmmmmmmmmmmm

A buddy who likes the big ones and I were talking the other day. He feels that his 33% is "naturally" faster but looks slower. So next time he went up, I looked around at the bench riders, said, "watch this" and cranked up my little ol' 60 size. He is not what you'd call a serene, unflappable flyer so I only made a couple of runs "with" him. And then landed and asked the bench riders if they knew where he kept his nitro pills. Turned out after that that we had a spirited discussion about what speed a big gasser would probably do and if it'd "naturally" be faster than a "model airplane". Well, truth is, "right after that", we had a discussion about how many models in the air is a "safe" number. And of course, after we found his nitro pills.

I profess to believe that there has to be an adequately small and decently light V8 driving around in maybe something like the Ford Cobra or the GT40 replicas that would lend itself to a nice, hot 50% model. And I think there are crate engines for sale that put out over 550hp. Yeah, it'd take a little bit of streamling, but what the heck. I got some heavy duty servos if you got some tires that'd work. What else would we need?

Hey, forget the tires. If we're going for a record, one of my flying buddies was a linebacker for Green Bay and could maybe hand lauch for us. Heck, with him throwing, the model wouldn't need to accelerate too much. And we could launch from just beyond the speed traps and wouldn't need to dive for speed.

I think it'd work.

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ORIGINAL: BMatthews

Spanwise flow isn't always a bad thing in small amounts. The Schumann (Schumman? -sp) planform used so often on todays sailplanes for both models and full sized is actually designed to encourage a measure of spanwise flow. Also is the amount of spanwise flow not related to the lift coefficient? I'm not too sure on that one..... If it is then the Cl for this thing at 180 mph is stupidly low so the spanwise flow should be quite small as well. But you raise a good point about this. If we have spanwise flow then that would indicate that the fins at the tips may well be better off as a single fin at the root. At first it would indicate that they could be angled inward so as to present themselves to the airflow at a 0 angle of attack However if the spanwise flow is Cl related then there's only going to be one specific speed range where the drag will be very low with that setup. Some data on the spanwise flow would be needed to determine this angle and any drag penalties at lower speeds to determine if this is an issue as it climbs up "onto the step" and sees less drag at the higher speeds and normal range of lift coefficients. Obviously the angles for the tip fins would be set to provide the least drag in the 170 to 200 mph range.

If this spanwise flow and drag on the fins ends up too high then we'd have to revert to a center fin on an extended stinger.

For a "yank and bank" model like a pylon racer yes it would be nice to have a higher aspect ratio. But for a flying style where speed is the issue and the only issue the transitions from the dive to the level trap run can be more mild a more normal aspect ratio should be be good enough to avoid adding a lot of induced drag and bleeding off speed. To this end my wing could be slightly increased in aspect ratio if needed but as it sit's now I think it would be OK. Keeping in mind that a 3 G turn of our wing at 6 lbs AUW will only require it to increase the angle of attack to a paltry 0.7 degrees and a Cl of .08 I don't think that for this style the induced drag reduction of a higher aspect ratio is worth the structural issues it would bring. Some figuring would be needed so that the pilot would know what the various radii of turns at 180 to 220 mph will be to avoid exceeding a 2 to 3 G pullout and thus avoid driving the induced drag up.

If the spanwise flow is an issue I can still see using a flying wing but altering it to more of a crescent shape and either staying with the tip fins and including some toe in to reduce drag or moving back to a center fin. New sketch to follow.

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ORIGINAL: HighPlains

I sometimes read the NTSB accident reports, mostly to see how people managed to kill themselves in their homebuilt airplanes of the type I'm building. My favorite screwup was the guy that flew past a Cessna 172 at a much higher speed, waved, and then did a split S. From 700 feet AGL. Since the homebuilt in question cruises at close to 200 mph and is stressed for 9g's, simple math says somebody else signed off his next tax returns. It would have just been possible to complete the split S had he kept the g meter pegged at 9 g's if the stucture held together. However, that is where the structure yields and bends out of shape and the airframe is toast.

In the end, this guy went straight in.

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ORIGINAL: BMatthews

Wow..... that's a big circle.

OK so the plane will need to be able to operate at a reasonable drag at a higher G load. There's still no need to see it run up at the 30 G mark. However it does point out that if the span wise flow on the swept wing is related to the Cl then a center mounted fin is going to be a better bet. And I'm going to fall back onto the idea of the reverse cresent wing to help hold the spanwise flow on and reduce the spillage and hopefully the strength of the tip vortices.

So here's the Swift modified for this. Wing area is around 465 sq inches.