noahb

My Feedback: (67)

Hi, I have the ARF DV8R and she flys great. However on final with flaps set down, everything looks normal. She is slowing down, has a nice approach, nothing sensitive on the control surfaces. However, the moment it touches the mains, she starts to bounce up and down on the run way. This seems to be a common problem with the DV8R's at least from the few that have them that have chimed in or sent me a PM saying they had the same issue.

SO my question is:
Will a CROW mix (one setup correctly) correct this issue? The second time I landed, it was moving very slow, not stalled, but close. I greassed the mains down, just slightly touching them and bam! bounce and bounce and bounce.

My Falcon 120 did this as well until I took out some of the flaps. Then it landed awesome.

However, I would like to be able to slow down the DV8r with flaps, just not have the bounce problem.

Any insight would be greatly appreciated.

1320Fastback

As long as it is not wheel/suspension bounce then dumping the lift of the wing will help. Would it be possible on your Radio to mix in full spoilers with full low throttle or set it up on a switch not that your fingers dont have enough to do already.

noahb

My Feedback: (67)

I don't think it's suspension bounce as there are a number of different gear be used (straight struts, trailing link, etc. ) and I hear it's a common problem. Maybe with not all of them, but from the ones I have talked to...same issue.

Yes, I have a futab 12fg and I can pretty much mix anything I want to it. I would probably set it up on a switch so that when landing flaps deploy the ailerons would do the same. I could have two settings...one without crow and the other with.

So you think crow mixing would help then? It appears that there is just too much lift with mid flaps and that it just wants to keep flying although it looks as if I can almost jog besides it and keep up with it.

SinCityJets

Noahb,

You may already be doing this, so please don't take any offense, but the biggest mistake I see people make when this happens is relaxing the elevator. If,when you get a bouce like this on landing, at a MINIMUN you need to hold the elevator you have, and a more appropriate response would be to grab more, if not ALL the elevator you can. This should stop the "cycling" and allow you to flare it out nicely.

A bounce is usually cause by landing to fast, or touching the nose-wheel first, or BOTH.

Finally, raising the flaps after touch-down can also help, as this will kill lift. The problem with this is, if you go around, you may be a little behind the power curve for a lift-off.....literally.

Chad

PS. Don't listen to anything I say.

noahb

My Feedback: (67)

I don't take offense to anything! lol. I appreciate any help I can get. I am pretty sure I am not relaxing the elevator input. I know that on my second landing, the mains just barely touched and then it went directly to bouncing. It's like the second the mains touched it leaps back into the air and the nose hits and then all hell breaks loose.

These flaps on the DV8R are huge, I think it just has too much flap = too much lift so to speak. However, would like more input from you guys as I have not been around a lot of jets. You guys are the experts...haha

noahb

My Feedback: (67)

Oh, as far as killing the flaps after touch down...I rather keep flaps in until over the runway (given that I have enough speed) and then reduce or pull flaps up then. I really only need them to slow it down...the rest I can handle fine.

Doug Cronkhite

My Feedback: (34)

You're too fast. Don't try to fly the airplane onto the runway.. try to keep it from landing while staying 3-6" above the ground

David Searles

My Feedback: (49)

Simply reduce your flap throw in increments of 10% until you get just the right amount. You've got too much lift for the landing speed you're using.


David S

noahb

My Feedback: (67)

David S. I believe you are correct. This is what I am thinking is that I have too much flap. As for slowing it down, I am holding it off the runway untill I am about mid to maybe a tad past that in my elevator stick when it touches down. Please keep in mind that I am not the only one that is having issue with this particular airplane. So I am sure it's a bit of my technique and alot of the jet itself.

rcpete347

My Feedback: (251)

HI, most people, use way too much flaps on landing. Do what I do, experiment with no flaps( landing will be faster), then try landing with take off flaps.
Flying my Kingcat, I use to get the kangeroo hop, until I learned to reduce power on final, start feeding in elevator until she will not stay airborn and hold full elevator until stopped.
NO brakes on elevator on this puppy.
Rcpete

LGM Graphix

My Feedback: (22)

I'll just throw this out there, how much flap do you have on landing? My Kingcat was really tough to land with the original landing flap setting I had, it was creating to much lift. I ended up adding more flap, almost 80 degrees with crow (about 3/4") and now it lands with power on and is really solid. I think it originally had about 50 degrees flap for landing and it would just want to keep flying. I didn't really have problems with it bouncing, but it was hard to get it on the ground and keep it there. Only problem I have now with the 80 degrees is if I land to nose high I actually hit my flaps as well as the booms!!!

PaulD

My Feedback: (39)

Try the crow - it can't hurt.... just be carefull not to get too far behind the power curve. I used crow with the full flaps on my Reaction as they tend to just keep flying but this setting really bled off speed.

The main thing is to not let the nosewheel touch until you bleed off some speed. As Chad says, grab some elevator and keep the nose up.

PaulD

noahb

My Feedback: (67)

I am guessing I have around 40-50 deg. of flaps. I can tell you that it does act like it has way too much flaps. I will reduce down to next to nothing and go from there.

However, I would not mind trying crow either. Just wondering if it would be benificial in my case.

rcpete347

My Feedback: (251)

Your right about the crow, my Kingcat would porpoise( wing rock) at 4' height, just before landing. I added 5/8'' crow and now it is rock solid. But you still have to slow it down with elevator.
Rcpete

Boomerang1

I'd go with what LGM is saying, not enough flap. As flaps are lowered they increase lift but create little drag. That's why aircraft use a little flap for take off. At about 45 degrees lots of lift & a moderate amount of drag, what you have. With around 80 degrees of flap a heap of drag & little extra lift, what you need to land. Just watch any pitch changes, & these will change with speed, and be prepared to give more throttle when you lower the flaps all the way or the model will drop like a stone.

The trick is to drive the model against the extra drag of the flaps with more throttle.

I have a scratch built model similar in layout to a DV8R & that's what works for me. - John.

HarryC

My Feedback: (1)

The reason is that the noseleg spring is too stiff which means the noseleg bounces at a higher frequency than the mains, throwing the nose up while the mains are still going down, raising the angle of attack and off you go again. I bet your noseleg is really a mains leg with a spring designed to take half the weight of a model whereas it is taking maybe 1lb or less on the nose. Fit a softer spring and the nose will clamp to the ground when it touches down.

Harry

Gordon W

What Harry said. I recently used that solution to cure porpoising with a Fox Composites Hawk.

Additionally you might be able to try a solution which worked for me on a Bandito which used to porpoise terribly on landing, often causing gravel-rash on nose, tailpipe and all four wing and tailplane tips besides bending the all-wire u/c - it was bad!

Crow mixing, ie raised ailerons didn't improve anything. Drooped ailerons along with flap effected a cure by generating more lift for a slower landing speed. Not much aileron droop, say 5 degrees did the job. The already-lowered flaps ensures that there's plenty of washout so tip-stalling isn't a problem, though trying to land the model too slowly and thereby stalling it onto the tarmac is still a risk.

Besides increasing lift, lowering the ailerons has another side effect, namely causing a nose-down pitch, so you'll need to apply some compensatory elevator trim.

BTW, the Hawk referred to above also has the aileron droop programmed in (because it's overweight at 16lb auw and 4lb/sq ft loading and I felt it needed more lift to slow the landing speed), but this did not cure the porpoising, which only disappeared with the introduction of the soft nose leg spring. Until I changed the spring, the Hawk used to gather gravel rash on all six extremities as described for the Bandito.

Here’s a link to the mod I made to the Hawk noseleg.

http://www.rcuniverse.com/forum/fb.asp?m=9107480

Until I made the mod, about 25% of all landings would be doomed to porpoising and after 100 or so flights I began to think that my eyes and reactions were shot. Since the mod, I have had no landing probs with the model.

Gordon

madmodelman

I'm with LGM and Boomerang, both spot on, just don't forget more power needed, when at about six feet cut the power and flare.
Don't ask me how I know!

BaldEagel

On the 12FG you can put the flaps and crow on a side slider, so you get half flap on half movement and full flap (85deg) and up ailerons on the rest of the side slider movement, if you do this you have the facility to make the switch to inhibit this the throttle stick this allows you to only have this operational below a certain point on the throttle, so if you abort the landing and open up the flaps and up ailerons go away, this can also be proportionally delayed to go away at a speed determined by your throttle responce.

Agree with others that have said, you don't have enough flap and are generating too much lift at touch down, increase the flap angle to act as an air brake not a lift generator.

Mike

BaldEagel

Gordon

Lowering the flaps and ailerons give Wash IN this increases the angle of attack and would promote tip stalling at a higher speed, take a mean angle through the wing section with the ailerons up and down and you will see what it does to the AOA.

Raising the ailerons decreases the AOA at the tips and helps to prevent tip stalling by giving washout to the tips so the AOA at the tips is less than at the root, this is what helps to prevent tip stalling, it also moves the seperation bubble forward on the wing and at the same time will increase the rate of decent which all helps with landings.

Mike

HarryC

My Feedback: (1)

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Robrow

I flew a DV8R for around a year and the landing config was as much flap as I could get (around 80-90 degs) and some crow on aileron (up), that was with Robarts. It greased in every time. Remember flaps have dual functions...to both increase lift and drag, beyond a certain point the drag goes up dramatically as the lift reduces. You will know when you have enough flap because you will be needing to add power to keep flying, so as you flair just kill the power and hold her off by increasing back stick.

Hope that adds to the help.

Rob.

noahb

My Feedback: (67)

Robrow, before you used full flaps did you ever notice it want to propoise on landing or see others do it?

noahb

My Feedback: (67)

So you guys are saying that if I add alot more flaps that i will actually loose some lift (I already know I will gain drag)? From what I seen, I need to loose lift, but have at least the same amount of drag if not more then I do now.

This is why I had considered crow.

as for the front nose strut and spring, it does not feel like it's to heavy of a spring. It could be, but just does not seem so.

madmodelman

Use your crow and as has been advised as much flap as you can get, 80 or even 90 degrees, at that point there is virtually no extra lift and maximum drag, put a bit of power on to overcome the drag and pull the nose up, it'll come in like a baby!