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ekafant
06-01-2006, 10:15 PM
Greetings all. I found this web site recently and like it very much. I am a BAR, having got back into the hobby off and on over the last 10 years. My 8 year old has gotten the rocket bug and it is a great way for us and all the rest of my children to spend enjoyable time together. I built the Semroc Mars Lander after wanting one for years but being discouraged after seeing what they go for on Ebay. Anyway, I flew it for the first time Sunday on a B4-2. It took off straight but pretty much started flying almost horizontal. The chute deployed and it landed safely. I believe a more powerful engine would have had it fly into the ground. Has anyone else had a similair experience with flying the Mars Lander. I believe some weight might be needed up front, but what do you all think?

A Fish Named Wallyum
06-01-2006, 11:00 PM
Chan Stevens had a similar problem with his Lander. He solved the problem by adding 1/4 oz. of noseweight in the form of a washer and it seemed to do the trick. He flew it at this past weekend's Quark launch on a C6-3 and the flight was perfect. (Very low-level, but spot-on for stability and it recovered well.)

PaulK
06-02-2006, 08:43 AM
Greetings all. I found this web site recently and like it very much. I am a BAR, having got back into the hobby off and on over the last 10 years. My 8 year old has gotten the rocket bug and it is a great way for us and all the rest of my children to spend enjoyable time together. I built the Semroc Mars Lander after wanting one for years but being discouraged after seeing what they go for on Ebay. Anyway, I flew it for the first time Sunday on a B4-2. It took off straight but pretty much started flying almost horizontal. The chute deployed and it landed safely. I believe a more powerful engine would have had it fly into the ground. Has anyone else had a similair experience with flying the Mars Lander. I believe some weight might be needed up front, but what do you all think?

Can't help you with the lander (haven't built mine yet), but welcome back to rocketry and YORF! If you haven't found it yet, Thrustline Aerospace (http://www.thrustaero.com/) is a great place to get clone kits.

-Paul

marslndr
06-05-2006, 06:23 PM
I've flown my Lander clone 3 times with B6-2's and had great success. I might try a C6-3 tomorrow. I did add nose weight to mine, 2 lead discs. Don't pack the parachute to tight, on my last flight I did this and it did not have time to open. The lander only makes it to about 80-100ft.

I posted a movie of the launch over at the yahoo marslander group. Sorry the quality is not great.

snuggles
06-11-2006, 07:28 PM
I launched my Semroc Mars Lander for the first time today. Not being a big fan of B motors in her I used a C63. IT WAS COOL. Nice straight boost, nosed over..... seemed to take a LONG time for the chute to deploy..... Out she came for a nice landing. Didn't stick it though.
Looking forward to many more flights. I agree with the fact that you really need to wait for a calm day to fly it. I believe she would weathercock badly in a breeze.
Mark T

marslndr
06-22-2006, 03:05 PM
I launched mine on a C6-3 the last week, It went much higher than I expected. A nice flight up to about 200-250 ft. I think the C6-3 was made for the lander! 2 of the 4 days I launched were windy and I had no problems.

On the 3rd flight the bottom leg dowel broke when the 'chute did not open. It was fixed with some epoxy and seems 100%. I'm not sure how many more times I will launch it.

Mark

snuggles
06-27-2006, 08:07 AM
I have read numerous posts about extra nose weight in the ML, and I chose to ignore it.
I flew mine last Saturday in not a lot of wind(2nd flight) it was unstable as heck, crash landed. THEN ejected the chute(the infamous "Wile E Coyote"ejection system).
Mine suffered a jammed leg,and dented body wraps by the nose.
I am putting nose weight in it as soon as I am done typing this. Please let my misfortune be a wake up call to all of you ML owners.
My ML will fly again.
Mark T

ghrocketman
06-27-2006, 09:34 AM
And why did you choose to ignore the posts about adding nose weight ?
Interested in a wacky rocket-destroying flight ? That should be performed with a piece-o'-junk rocket, not a time-consuming build such as the ML.
I will be adding nose weight to my Semroc Mars Lander.
Interestingly enough, I built 3 original Estes Mars Landers (one is still flying, one was a C5-3 CATO victim, one was a Cox 18mm D8-3 CATO victim) and NONE of them required any nose weight to fly stable.
Perhaps some of the lower components (harder/denser balsa for legs, etc.) in the Semroc kit weigh significantly more than the old Estes parts in the original kits.

snuggles
06-27-2006, 09:40 AM
The ML was built for me,I had one flight which worked beautifully,I didn't see the need.Now I do.
Mark

marslndr
06-27-2006, 09:51 AM
As I posted before, mine is not the Semroc kit it is a clone. I did use the Semroc wraps they are very nice (as are all the parts in the Semroc kit). I did use nose weights, And I did overbuild/paint the lower half of the lander. I have not put mine on a scale but I know it is heavy. I have flown it 6 times, once on the C6-3, and in winds gusting to about 10-12 mph with no stability problems.

The parts in the Semroc lander are all high quality so I don't think it is the kit. Could it be the new Estes motors? are they heavier than in the past? Has anyone launched the lander on Quest motors?

Mark

JSP
06-27-2006, 10:20 AM
Actually, the very fact that the parts ARE high quality could be the issue. Stronger better quality parts would equal heavier wouldn't it? I'm just guessing here. I haven't built one.... Just a thought...

dwmzmm
06-28-2006, 12:02 AM
And why did you choose to ignore the posts about adding nose weight ?
Interested in a wacky rocket-destroying flight ? That should be performed with a piece-o'-junk rocket, not a time-consuming build such as the ML.
I will be adding nose weight to my Semroc Mars Lander.
Interestingly enough, I built 3 original Estes Mars Landers (one is still flying, one was a C5-3 CATO victim, one was a Cox 18mm D8-3 CATO victim) and NONE of them required any nose weight to fly stable.
Perhaps some of the lower components (harder/denser balsa for legs, etc.) in the Semroc kit weigh significantly more than the old Estes parts in the original kits.

I have the Estes Mars Lander (built in 1970 or 71; still flyable today), and flew it many, many
times as is without any problems. That is, until February 20, 2004 when it suddenly went
unstable. You can search the message thread on this particular problem on the Mars Lander
Yahoo Groups server and OldRockets Yahoo Groups server (go back to February 2004 and
scroll from there). Thinking the stability problem of that one time was a fluke, I flew it again
the following month (March 2004) at a HPR launch, and it went unstable again. Later, after
adding some nose weights (two pennies with a hole drilled for a screw eye to secure to the
base of the balsa nosecone), test flew in May 2004 with a B4-2 & got an excellent flight. Have flown again at least once or twice since then on the C6-3 and still flies great. Now it is
semi-retired, as I'm contemplating getting the SEMROC model...

sandman
06-28-2006, 06:34 AM
After reading about all of the instability problems on the ML I had a thought.

Has anybody weighed a C6-3 motor and, if you have a really old c6-3 motor like from the 70's, weighed it.

Could there be a difference?

The Mars Lander is "marginally" stable perhaps we could do a simple unscientific poll here.

Everybody that has a built Mars Lander post the following

1."Fin span" of the legs.
2. Final as built weight.
3. Finished CG location.
4. Flight characteristics; stable, unstable or overstable (weathercocks)

Maybe that has something to do with it's stability.

BTW don't get me started! :mad: "weathercocking" in the wind is NOT unstable! Posting THAT will just make me mad!

Weathercocking is a sign of overstability.

Of course an unstable rocket will do darn near anything in the wind. :rolleyes:

Let's see if we can get to the bottom of this problem!

We are "rocket Scientists"!

marslndr
06-28-2006, 07:21 AM
Sandman,

It seems the motors are the probable cause with the info posted at this time. Maybe Estes knows the motors are heavier and that is why they never re-released the MarsLander. But this is just speculation. I have an old Estes catalog, but I don't think they publish motor weights.

I assume you want the weight/CG with a new C6-3 loaded?

BTW anyone know where can I get an inexpesive scale?

dwmzmm
06-28-2006, 07:24 AM
Sandman,

It seems the motors are the probable cause with the info posted at this time. Maybe Estes knows the motors are heavier and that is why they never re-released the MarsLander. But this is just speculation. I have an old Estes catalog, but I don't think they publish motor weights.

I assume you want the weight/CG with a new C6-3 loaded?

BTW anyone know where can I get an inexpesive scale?

You could probably just "sneak" your ML into your local post office and use the scale at the
self service lobby...

sandman
06-28-2006, 09:19 AM
I don't reccomend using a new C6-3 for weight testing you Mars Lander or any other models.

All kinds of problems arise with a "good" engine used as a tool.

Engine can be damaged (bad!...been there done that :o )
Engine actually could...possibly...maybe...it could happen :rolleyes: ...IGNITE!
You really don't want to bring a "live" unwrapped BP motor into a post office (government facility! :eek: )

Here's what I do.

Get a brand new C6-7 motor (the heaviest of the 18mm motors) and a spent motor casing, clean out the spent casing, peal off a layer or two of paper so it slides into a motor tube real easy then with a ballance scale (make something pretty simple) fill the spent casing with clay, lead, and epoxy until it matches or just a tad more the weight of a new motor.

Paint the casing a bright color and label this casing "TOOL".

I did the same thing with a "D" size motor, an "E" size motor and an F/G econojet motor.

Much better than using a "good" motor as a tool. ;)

ghrocketman
06-28-2006, 09:33 AM
I don't think it is motor weight....My stash of vintage Cox D8-3's weigh quite a bit more (several grams) than any new (or old) C6-3 or even C6-7, yet my original Mars Lander flies perfectly stable with them.

marslndr
06-28-2006, 10:03 AM
Ok,

I can answer questions 1 and 4.

The leg span on my clone is 13.5 in standing and 13 in free.

I have launched mine 6 times in the last month, 2 of the 4 days were windy/gusty to 10-12mph. The other 2 days the wind was less than 5mph. I used 5 B6-2s and one C6-3 all nice and stable. On the gusty days I tried to launch in between the gusts.

Good idea about making a slug motor as a tool, if/when I get a scale I'll make one

Edit:

I just did a quick CG on my finger, very scientific, with an unused C6-3 the CG is 7/8 of an inch below the top of the BT-100 decent stage, just about the bottom of the RCS rectangle. With a spent C6-3 the CG moves forward to about 1/2 inch below the top of the BT-100, just about the bottom of the upper embosed ring. Hope this helps.

marslndr
06-28-2006, 11:41 AM
Ok,

The staples near me had a scale on sale.

Empty: 4.7oz 133g

with new motor: 5.6oz 157g

with spent motor: 5.1oz 144g

The motor was Estes C6-3

Carl@Semroc
06-28-2006, 10:11 PM
The Mars Lander has been a journey for us. I am still working a page of our findings over the past few months. The Mars Lander is marginally stable at best. Our CG-CP is about .38 calibers versus the original at .39 calibers. We chose to beef up the rings so it would be better stressed to fly the upcoming Quest D21 motor. The rings and larger chute add about .7 oz. Adding all the parts in Sandman's original Mars Lander results in 3.42 oz. I am almost certain that the advertised weight of 3.0 oz. is incorrect. Our weight is 4.11 oz. but since the rings are distributed roughly evenly around the CG and the extra weight of the chute is above the CG, there is very little difference in the CG-CP relationship.

We have built and flown three models; one "naked", one with little paint and filler, and one with heavy paint and filler. The one thing we have noticed in the build that makes the most difference is the fin span. If is is over 13.5" from tip of pad to tip of opposite pad, the CP moves too far forward. We have new instructions that reflect some build techniques to fix that.

The other variable that makes a lot of difference is wind and/or angle of attack. If you balance a Mars Lander at the CG in a wind tunnel, it can not recover from an angle of attack of greater than about 15 degrees. At about 10-15 degrees, the CP moves so far forward that it trys to "fly backwards." If you block the air flow in front of one of the legs, simulating a gust, the Mars Lander flips and can not recover. Launching at an angle or in any wind will make for a less than nominal flight.

Another "gotcha" is the loose fins! The legs double as fins and are designed to be a little loose so they can operate. Again, in a wind tunnel, if you cant two opposite legs in the same direction, they act as a rudder and flip the model around. When I thought about this more, if I was SCO and someone brought a marginally stable rocket to check in with four wobbly fins, I would send the modeller back to glue them on better before flying it. A small shim wedged in each slot will tighten up the legs.

Some modellers have replaced the light rubber bands with heavier metal springs. Since all the extra weight is below the normal CG, this will probably work against the CG-CP as well. When I first entered the Mars Lander in RockSim, the CG-CP was around 1.1 calibers with a C6-3 motor. Months later, I realized that was based on default of the nose cone diameter and not the frontal diameter.

We have flown our models with OLD Estes B4-2's, OLD Estes B6-2's, OLD Estes C6-3's, OLD Estes C5-3, as well as some from the 80's and later, and recent Quest B6-2 and C6-3 from Moog and S-F vintage. All flights were perfectly straight with ejection just after apogee. B6-2 and B4-2 flights are only about 100' and the chute must be very loose to have time to deploy! But all flights were at about 6:00 p.m. with no wind and launched vertically.

I have never seen a Mars Lander that was unstable and I don't think I want to see one! If I had known at the beginning of the project how marginal the design was, I would have probably passed. It is a skill level 4 (Master) for build, but it is also for an experienced flyer as well.

We have updated instructions that we can mail to anyone that has not built the kit yet. We are working on getting the MSPUB file converted to a PDF file for our website.

Carl@Semroc
06-28-2006, 10:19 PM
For comparison:
Semroc Mars Lander RockSim (http://www.semroc.com/Rocksim/Semroc-Mars%20Lander.rkt)
Original Estes Mars Lander RockSim (http://www.semroc.com/Rocksim/Semroc-Mars%20Lander-orig.rkt)

sandman
06-28-2006, 10:20 PM
Just to "clarify" one thing.

When Carl said "Adding all the parts in Sandman's original Mars Lander results in 3.42 oz."

Carl wasn't talking about the new SEMROC model that I built, he was talking about an "original" Estes kit that I lent him. :o

BTW...I do want it back. ;)

Carl@Semroc
06-28-2006, 10:24 PM
BTW...I do want it back. ;)It is going home! I think I know all the weights and shapes by memory now!

Thanks again for the use. I could not have gotten this far without it.

marslndr
06-28-2006, 10:33 PM
Well I would just like to say that I am very happy that you did not pass. I have 2 of your kits and will build one soon. I did replace the wraps/ upper rings on my clone with yours. That would move my CG forward. The main body rings in my clone are much lighter than the your rings. My legs do have some wobble in them.

Did I understand that the legs CAN'T be more than 13 1/2 in pad-pad? Mine are at 13 with the lander not resting on them.

Carl@Semroc
06-28-2006, 10:37 PM
Did I understand that the legs CAN'T be more than 13 1/2 in pad-pad? Mine are at 13 with the lander not resting on them.13.0" is better. 13.2" is the nominal value. Over 13.5" is too much.

Ltvscout
06-28-2006, 10:39 PM
We have updated instructions that we can mail to anyone that has not built the kit yet. We are working on getting the MSPUB file converted to a PDF file for our website.
Carl,

If you have the full Acrobat just print the .pub file to the Adobe PDF "printer". If you don't have the full Acrobat, send the .pub file to me and I'll convert it to PDF for you.

marslndr
06-29-2006, 11:41 AM
13.0" is better. 13.2" is the nominal value. Over 13.5" is too much.

Thanks, I always thought the wider the better guess I was wrong.

BTW its none of my buissnes, but your web site still lists the lander as your best seller- how many have been sold? I hope alot.

Thanks

mark

sandman
06-29-2006, 12:36 PM
Thanks, I always thought the wider the better guess I was wrong.

As the legs narrow they sweep back more. The more they sweep back the further back the CP goes. Well, to a point. ;)

Actually I'm currently building another Mars lander and I've been thinking of making the foot pads removable for flight.

Those landing pads cannot be aerodynamically helpful.

CPMcGraw
06-29-2006, 02:39 PM
As the legs narrow they sweep back more. The more they sweep back the further back the CP goes. Well, to a point. ;)

Actually I'm currently building another Mars lander and I've been thinking of making the foot pads removable for flight.

Those landing pads cannot be aerodynamically helpful.

Actually, they can...

They provide a measure of drag, which can "effectively" shift the CP rearward without shifting the CG. It's like the tail of a kite, or a drogue chute, hanging out in the breeze. It stabilizes the model at the expense of altitude performance.

dwmzmm
06-29-2006, 08:52 PM
Actually, they can...

They provide a measure of drag, which can "effectively" shift the CP rearward without shifting the CG. It's like the tail of a kite, or a drogue chute, hanging out in the breeze. It stabilizes the model at the expense of altitude performance.

I agree. Leave the landing pads on...

sandman
06-29-2006, 09:05 PM
I wasn't goint to take the pads off.

I just wasn't going to put them on for the first flight.

I wanted to fly it without the pads just to see if it made any difference.

I can always glue them on later.

tbzep
06-30-2006, 12:26 PM
The landing pads would cause stability if the airstream hits them at the same angle....but it never does because the pads are tilted.

Since the angle of the pads changes as the angle of attack changes, the problem is magnified. When the rocket tilts, the pads that need to have the most drag, will be angled more vertically and have less drag. The pads that need to have the least drag, will be tilted more horizontally, causing more drag and making the Lander tilt even more. To add self correcting stability for vertical flight, the pads would need to be tilted opposite the way they are on the model.

Tweener
06-30-2006, 02:16 PM
The landing pads would cause stability if the airstream hits them at the same angle....but it never does because the pads are tilted.

Since the angle of the pads changes as the angle of attack changes, the problem is magnified. When the rocket tilts, the pads that need to have the most drag, will be angled more vertically and have less drag. The pads that need to have the least drag, will be tilted more horizontally, causing more drag and making the Lander tilt even more. To add self correcting stability for vertical flight, the pads would need to be tilted opposite the way they are on the model.Interesting point. You may have just discovered the reason a ML could suddenly "go unstable" after many flawless launches. Since the pads are the first thing to hit the ground, one of the pads or legs may get knocked out of alignment.

marslndr
06-30-2006, 02:39 PM
An interesting idea, but I don't think so. The pads are very sturdy, it would take alot to get one out of alignment. I think any wack that could move a pad would break the leg.
Only the very bottom of each pad touches the ground.

I think Carl found the problem with the leg wooble.

Mark

dwmzmm
06-30-2006, 02:49 PM
Interesting point. You may have just discovered the reason a ML could suddenly "go unstable" after many flawless launches. Since the pads are the first thing to hit the ground, one of the pads or legs may get knocked out of alignment.

I still believe my Estes ML went unstable for a reason that's a mystery (to me) to this day.
The "simple" adding of a little nose weight (with an additional screweye) solved the problem.
Since it was built "like a tank," I can't think what components within the model could have
shifted after all those successful flights to change the CG/CP relationship. Here's a pic of
that ML in my display case (pic taken last year; the ML itself is 35 years old):

http://www.nasarocketclub.com/gallery/album17/FH000024_001

I have a roll of masking tape underneath the ML to help support the landing legs while on
display...

tbzep
06-30-2006, 02:56 PM
I'm not talking about getting out of alignment. I'm talking about the angle of the pads causing a varied amount of drag and vectoring.

The first picture shows the pads on my Alien Explorer, which are angled similarly to the Mars Lander.

http://i7.photobucket.com/albums/y283/tbzep/Rockets/1-1.jpg

When the rocket tips off to the left, for whatever reason, the pad on the left becomes fully horizontal and much more draggy than the other, which is now tilted at roughly 45 degrees. The 45 degree angle pad acts like a canted fin. Both pads work together to tilt the rocket even more.

http://i7.photobucket.com/albums/y283/tbzep/Rockets/2-1.jpg

If the pads were tilted the opposite direction, the effect after tipoff would be the opposite. The left pad is almost vertical, giving the least amount of drag, and it's also not canted as far, so it doesn't want to change the rocket's direction as much. The right pad is almost horizontal, creating extra drag on that side, so the rocket wants to tilt back to the vertical.

http://i7.photobucket.com/albums/y283/tbzep/Rockets/3-1.jpg

Of course, the ML has smaller pads, but it's also a much shorter rocket and outside forces will do more to it.

marslndr
06-30-2006, 03:18 PM
Oh, I understand now.

I suppose, It would have a small effect but the lander is marginally stable anyway.

tbzep
06-30-2006, 03:25 PM
Oh, I understand now.

I suppose, It would have a small effect but the lander is marginally stable anyway.

The less stable the rocket is, the more effect these forces would have. Aircraft and watercraft have used this technique to create straight line stability by using wedge shaped airfoils or turning double finlets like the last picture, not like the first, so it definately can have more than a marginal effect.

Build two clone Alien Explorers, one with pads and one without. You will see a huge difference in vertical stability after multiple flights of each.

Tweener
07-01-2006, 09:25 AM
I'm not talking about getting out of alignment. I'm talking about the angle of the pads causing a varied amount of drag and vectoring.Yes, I understood that from the beginning. But if the alignment and width distribution of the legs (fins) is critical as in the marginally stabe ML, a small change in the angle of one (perhaps a difference in tension of one spring or rubber band) may throw it off a little. That small deviance might then be magnified by the phenomenon you describe. ;)