# Historic AT M750 altitudes

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#### gizza2

##### Well-Known Member
Hi, all.

If you've ever flown an Aerotech M750 could you reply with the maximum altitude achieved, the liftoff weight and rough rocket design, and flying conditions?

I'm trying to build a case that my design will not exceed our club's 25,000' waiver. Thanks in advance for your time and assistance.

#### C.O.B.H.C.

##### Well-Known Member
I personally haven't flown the M750W myself. But my friend has in a 98mm minimum diameter to 22K. The rocket is 8' 8" tall and uses hawk mountain new Extreme II airframe thicker wall and 40 degree wind angle with a hawk mountain mountain aluminum fin can. The nosecone is 4" 5:1 Performance Rocketry Conical. I hope this info helps.

#### gizza2

##### Well-Known Member
Only 2 views? Really?

OK let me pose a shorter question...

Is anyone aware of any flight with an M750 that exceeded 25,000 feet?

Thanks!

#### cjl

##### Well-Known Member
To exceed 25k, you'd probably need a pretty light MD model. I wouldn't worry about exceeding the waiver if you aren't making a specifically designed altitude rocket.

#### gizza2

##### Well-Known Member
Thanks, Aaron and cjl.

Well the problem is that I have a pretty light minimum diameter rocket; ~10-11 lbs, CF over phenolic. I'm trying to exceed 20,000 but our waiver is an inflexible 25,000 so I have one mile of slop. I'm going to approach my case to the RSO from an engineering perspective but I also want to include as much historic flight data as possible. That's why I'll continue to prod this thread until I have at least three data points.

#### FredA

##### Well-Known Member
Why don't you approach your RSO with a sim that matches a K or L motor flight and a sim of the M750?

If you looking for information that confirms an M won't go over 25k, you are in trouble....check the record books....

Show your sim has good coorelation with actual flight data.
That's being an engineer....not some handwavings about other rockets under other situations with so many unknowns that you don't know.....

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#### gizza2

##### Well-Known Member
That reads pretty harsh, Fred.

I've simmed my rocket many times and it's well under the waiver. I've shared this with the RSO and that's not yet good enough for him. The prevailing opinion is that I'll break the waiver so I need to instill some additional confidence. Oh and I've checked the record books and have yet to find an M750 flight over 23,000.

Are you really a TAP? Thanks anyway.

##### Well-Known Member
Have you flown this rocket yet? If not, I can totally understand the RSO's position. A first flight that may break the waiver is not the smartest idea. And sims only go so far.

What record books are you looking at? I only know of the records on Tripoli's page. Before Curt Von Delius smashed the old M altitude record, it was around 35-37K feet and was set with an M795 which is CTI's long burn in the same case that the M750 uses (98mm4grain). So, I would assume that the performance would be comparable.

#### cjl

##### Well-Known Member
I would tend to agree with the RSO - if it's simming to 22-23k, I would be quite concerned about breaking the waiver. Rocksim tends to be somewhat inaccurate for high performance flights, and there just isn't enough margin to really be sure there. Maybe try something like an M1419 (98-3g) or even a full L (98-2g) first to get a solid data point before pushing it? If you have a good recording altimeter, you could even extract the drag vs velocity curve by looking at the post-burnout deceleration, which would allow for a significantly more accurate sim.

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#### Chrisn

##### Well-Known Member
Rocksim tends to be somewhat inaccurate for high performance flights, and there just isn't enough margin to really be sure there.
Yep, but the OP does not mention rocksim.

#### gizza2

##### Well-Known Member
To be clear: I agree with all of your concerns including the RSO. I'm utterly shocked that I can't find a single recorded flight above 25k with this awesome motor. I started this thread to gather altitude data points and calculate means and confidence intervals as a compliment to my experience and simulations. Even the most optimistic flight simulator, that on thrustcurve.org, using only rudimentary weight, diameter,and motor info sims to 27k. I don't believe that for a second but it is the highest altitude I can find or calculate.

Madmax: No I have not flown the rocket yet. Google searches for "Aerotech M750" and "Aerotech M750 altitude" yielded only a three data points ranging from ~10,000-23,000. I think Curt Von Delius' J and M record flights have proven that minimizing cross sectional and total area/drag are far stronger altitude knobs than motor total impulse. My longer 98mm design actually works in my favor in being less efficient here.

cjl: I've found Rocksim versions 5-9 to be 10-20% optimistic on every single attribute calculated. If I'm simming to 22,668' that likely means I'll hit between 18,134 and 22,668'. Have you ever had a rocket exceed any of Rocksim's predictions? I haven't. I considered an M1419 maiden flight but that brings the total to over $1,050 for the two flights. We are in a recession you know. Chrisn: I am indeed using Rocksim. Actually I feel like I have all the simulations I need and I was really hoping for hard data points from folks on this forum who'd actually flown the motor. I've personally viewed four M750 flights but just never closed the loop and asked for their altitudes. Thanks to all who took a courteous, constructive approach to working with me here. That is the way forums should work. #### kelltym88 ##### Well-Known Member Could you add some nose weight? Assuming your rocket is 8-10 feet tall, stability shouldn't be a problem and a little more weight could help. Can you run that in Rocsim? #### Peartree ##### Cyborg Rocketeer Staff member Administrator Global Mod Your RSO may not give a lot of weight to results from other rockets due to the huge number of variables involved. Data points from your rocket using lower powered motors (ie. cheaper) that can accurately pinpoint your rockets drag coefficient will go much farther to prove that your M-motor sim is accurate and will carry much more influence with the RSO. I may not fly HPR (yet) but I do know math. #### madmax ##### Well-Known Member One of the reasons you don't find much information on the M750 is that it is a relatively new motor. I believe it came out last year or the year before. I personally haven't seen any M750 flights yet. The same flier I was talking about earlier has a pretty generic MD98mm rocket that has flown on the K650T to ~6000', AT L952W to a little over 14000' and the CTI M520 (3grain98) to somewhere around 20000'. That is fiberglass bird with carbon fibered fins. I would expect your lighter bird to break 25K. I would highly recommend flying it on a smaller motor. Put a M2400T in it as that would be a really fun flight! On another note, not to pick on Kellytm88 but his suggestion is one that really drives me nuts everytime I see it posted on the forums. Just adding noseweight is only going to make the bird more overstable making it more prone to weathercocking and other weather related problems. Also being overstable with that much weight in a minimum diameter bird can lead to coning, or massive arcing which is usually a rocket shredder at high speeds. A friend of mine loves to fly H180s in a 29mm MD bird with single deployment. After quite a few flights with massive wiggles he found that the location of the av bay is at fault. It was built onto the bottom of the nose cone. That much weight that far forward really throws off the balance so for future designs he has put the bay on top of the motor and it flies much better. #### madmax ##### Well-Known Member Your shakedown flight doesn't have to be on an M. Do you have a laptop with RS loaded into it? Do a shakedown on a big K, like a K700, (much cheaper and still plenty high around 8K in a 4" bird) that you have a Rocksim file for then after you retrieve and find out the data start changing your Cd and other variables to match that altitude. That way your M750 sim will be much more accurate. You could probably cut 25% off your motor cost that way. #### cjl ##### Well-Known Member Actually, I have had a rocket exceed rocksim before. It was a Cirrus Dart on an I600 with an absolutely perfect finish (auto paint). It simmed to 10k, give or take a few hundred feet, but I actually obtained 11,950 feet. Later sim tweaking based on measured flight data allowed me to redo the sim such that it was accurate, but there was no way to know that it was inaccurate until the flight. It's definitely not likely that you will exceed the sim, as to do so would usually require a near perfect flight in ideal conditions, but it is possible. I would also agree that even something like a K700 flight would be a good idea as a shakedown - so long as you get a good data point or two. Ideally, you would want some measurements of supersonic properties of your rocket, but even some subsonic flight data would improve your sim significantly. Given that your rocket is 10-11 pounds, you could go with something like a 75mm hard hitting motor and kick it supersonic without the cost of a 98mm M motor. An L2375, L2200, or similar would work great and is half the cost of the M1419, and in my opinion, would give even more valuable data than the subsonic K flight would. Last edited: #### daveyfire ##### Piled Higher and Deeper TRF Lifetime Supporter I know Frank Hermes flew an M750 in a minimum diameter rocket recently - I don't know how to contact him, but it was a pretty sweet flight. (Sorry to be of so little use there ) I had a 54mm minimum diameter rocket sim to 7200' in Rocksim and then fly to 10,288'. I honestly don't trust it very much any more (for a multitude of reasons, but that's for another thread). Have you tried running a simulation of your flight in RASAero? It's free to download, and far superior for high speed/high altitude rockets. In all cases, I agree with the other posters -- you will lose significant prediction accuracy without real values of drag coefficient in the simulator. #### FredA ##### Well-Known Member Greg, Sorry you don't like my answer....you asked..... You heard the same thing from many others: fly YOUR rocket on a smaller motor and then show a sim with good correlation along with a sim of the M that will not bust the waiver (with margin)... I too would not approve your flight if I was the RSO if you are unwilling to do this.... You can't put the whole club at risk just because you are lazy, cheap, short on time, whatever..... And yes, I am a TAP.... Flying M power is not for people who can't explain what and why they have made the choices they made..... people who think pointing to other people's rockets as proof of some aspect of their rocket are not really qualified to fly at this level IMHO..... FredA Last edited: #### DMcCauley ##### Well-Known Member Firstly, sorry to see you are a scientologist in training. Secondly, i would recommend flying your rocket on a smaller motor (say an L long burn or even a K) and then use data from that flight to help correlate your model etc... If your rocket is indeed 10-12 lbs, then a K or an L is more than enough to fly it on. Thirdly, whats the rush to fly it on a big M750W??? Fly it on a smaller motor first. #### gizza2 ##### Well-Known Member First off, DMcCauley, it's "ScientICIAN in training." It's something my friend made up at work. No thetan levels here. Oh and I've been flying for 32 years, I've earned my level 3, and now it's time for an M750. To be clear I would NEVER endanger spectators or my club's charter for any reason. My mistake in this thread was not offering sufficient context up front. I was trying to keep it brief and query the flyers on this forum to simply database flights and apply some statistics as one small portion of my recommendation to our RSO. I should have made it clear that I simply sought a single flight data point where someone had exceeded 25k with this motor in any configuration. As it turns out a friend and much respected flyer replied in e-mail with that single data point to 26,000. Thanks to everyone except Fred for your constructive feedback. You have indeed influenced my approach and I have also formed a backup plan if the RSO elects to advise against my flight. I have nothing but respect for the Range Safety Officer's role and will happily defer to whatever he advises. Now on to you, Fred. In my 15 successful years as a chemical engineer developing products in R&D my company's most important guiding philosophy has proven to be "trust and respect for individuals." As such I'll offer you respect and trust that you a) earned your level 3 with the identical rigor and scrutiny as I in attaining the same level and b) were promoted to TAP based on sound technical reasoning for all those involved. I don't like your answers not for their content but because of your tone. I'm hoping that you're simply blissfully ignorant of your condescending and rude approach to bestowing your knowledge on others; or at least on me. To suggest that I would forge data for the RSO or that I'm lazy, cheap, or hasty is just impossibly disprespectful. I've literally never read anything like it on any forum. It's clear that, without any knowledge about me, you've leapt to the conclusion that I'm somehow incompetent. Guilty until proven innocent right? Perhaps I've misunderstood you in a communication medium otherwise lacking emotion but I doubt it. I'll offer that I've earned praise as a mentor to numerous engineers and interns in my career. As an individual in a mentoring position it's your responsibility to kindly help those you're working with and influencing. It's incredibly easy to discourage someone if/when your ego takes precedence. Oh and you've got engineering all wrong. Engineer's don't simply present a few calculations and expect to sway peers or justify substantial monetary expenditures. They thoughtfully and pragmatically integrate theoretical and experimental data to deliver a targeted result that meets the specified criteria. You suggest that I lack rigor but I would counter that it's your approach that's lacking. I would request that you re-read your two replies to me and compare them to every other civilized, constructive reply in this thread. Then reflect on your "contributions" to this forum, improve your tone, and offer people the benefit of the doubt. There's ALWAYS someone more competent, more experienced, and more accomplished than you so develop some humility. #### FredA ##### Well-Known Member Greg -- I don't really care if you don't like my tone -- water off a duck. I'm sorry if you can't stand to hear straight talk -- I didn't think I needed a sugar coated response for a L3 flier.....guess I was wrong. If really don't care what you do -- not my club -- not my club's waiver or land use you have such a cavalier "tude" towards..... If your years of training makes you think apples and oranges are the same, then add this to your statistics....my last two slow-burn M flights went to 3000 AGL and 17,400 AGL. But one was a saucer. Now tell us how that helps you case...... (crickets) You have an issues -- you want to cut corners -- some corner...time, money...effort.... For whatever reason, you refuse to provide a quality simulation of the rocket in question. Not sure why -- don't care -- but cutting corners is rarely a good idea in HPR. Not sure why you find other people (your RSO) hesitation to go along with your plan to cut corners so strange..... Bye Last edited: #### Chrisn ##### Well-Known Member All Greg wants to know is other peoples flight data and you have to turn it upside down. There is just far to many variables for a simulation to be accurate- especially with non-pro rocksim. (My personal favourite: https://www.rasaero.com/) If someone doesnt have a wind tunnel they can easily back out other peoples flight data and simulations for a more accurate prediction of the drag coefficient- which in this case may be the main factor between busting the waiver or not. I do not see where corners are being cut. Why not just leave money out of this, unless you wish to sponser his test flights? #### cjl ##### Well-Known Member Fred: there's a difference between sugarcoating and civility. You do not need to do the former, but the latter is usually appreciated, and goes a long way towards getting your point across better and with less hostility. Nobody is doubting your knowledge, just the way that you are attempting to communicate it. As for the new sims, I would still advise a test flight (ideally, a supersonic one) prior to the M750 flight. If you can spare the$250 or so, a CTI L2375 White Thunder or an AT L2200 Mojave Green would be great to get your rocket supersonic, and would also be a good test of the rocket itself to ensure it performs as expected. I have flown both of those motors in my 4" AMRAAM to over 0.90 mach and over 11,000 feet, and it weighs more than twice as much as your rocket. Therefore, I would bet that yours would attain over 15k and well over mach on either motor, and you would get excellent performance data to ensure that your simulations are at least reasonably accurate. Other rockets' data is nice, but there is quite a bit of variation from fairly subtle effects that is hard to truly account for without data from your specific rocket. One local club member that I know (who is incredible with altitude rockets - he recently attained 16,379 on an I600R) has some data on nose cones showing a fairly significant variation in the supersonic Cd with fairly subtle changes in nose shape.

Finish also makes a huge difference - my Cirrus Dart went 11,950 on an I600R, while m85476585's went around 8400 feet. The difference was a few ounces, a couple rail buttons, and (perhaps most importantly) that mine had an auto paint finish while his was only partially painted with spray paint. When you're talking about going this high and fast, subtle changes make a surprising difference, which is why I would still be somewhat reluctant to sign off on your flight if I were the RSO if you didn't have any data on your specific rocket (although there are some exceptions - if the 26000 foot flight was on a rocket that was provably significantly more optimum than yours, with a better finish and a more optimized nose cone, I might allow it).

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#### DAllen

##### Well-Known Member
Fred: I am not going to sugar-coat this...You seem tense. Really really tense. I would strongly suggest having someone look over your posts before submitting them so you can get an idea of how you are coming across. Your posts have a very condescending tone. Since I am at least the 3rd person to tell you this maybe you ought to take a hint.

Greg: I see you working here. You want comparable flights from other people flying similar rockets on the M750. However, if I were RSO I would not be convinced until I had some hard data for your rocket. Sims are okay to a point but when you get close to the waiver I'd get a little nervious - and rightly so. Data from some internet forum poster who says "yeah, I flew a rocket sorta like yours on that motor and it went 20k" would not cut it with me.

I really like cjl's idea with a big fast burning L to prove the rocket first. In fact, this is quite common practice for me on almost all of my rockets. I almost always launch at least one impulse class lower than what I want to fly it on in what some refer to as a "shakedown" flight.

Good luck.

-Dave

#### DMcCauley

##### Well-Known Member
Fred: I am not going to sugar-coat this...You seem tense. Really really tense. I would strongly suggest having someone look over your posts before submitting them so you can get an idea of how you are coming across. Your posts have a very condescending tone. Since I am at least the 3rd person to tell you this maybe you ought to take a hint.

-Dave
I agree as well with the condescending tone. I had a previous discussion awhile back regarding some sort of electronics or switches i think in which Fred presented his points and arguments in a similar condescending fashion. My advice - just be friendly and nice.

Plus, as a TAP, you are not responding as an individual, but rather a voice representing the TRA organization. You certaintly don't want to come out looking [gruff, mod edit] everytime you disagree with someone. It reflects poorly on the organization as a whole.

Just my \$0.02.

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#### RangerStl

##### Well-Known Member
Please refrain from further escalation of this argument with swearing and name-calling.

It has been sufficiently communicated that Fred's tone seems inappropriate for a forum. Hopefully that point is taken and we can avoid further conflict. Please review our terms of use. If this thread starts down the path of bickering it will be locked and warnings or infractions given to the antagonists.

TRF users are expected to not escalate conflicts. This is not the place.

Thanks very much.

N

#### troj

##### Wielder Of the Skillet Of Harsh Discipline, Potent
If you've ever flown an Aerotech M750 could you reply with the maximum altitude achieved, the liftoff weight and rough rocket design, and flying conditions?

I'm trying to build a case that my design will not exceed our club's 25,000' waiver. Thanks in advance for your time and assistance.
No experience with the motor, but what I'd suggest is grabbing a copy of RAS Aero (https://www.rasaero.com/) and running a sim with that. If you're accurate in the data you feed it, it will provide significantly more accurate sims than anything out there.

It'll want a lot of data, and it needs to be accurate, but it will give you much more accurate simulations.

At the end of the day, however, the RSO gets the final word. If they won't accept your simulation data, then you're best off first flying the rocket on a smaller motor, and showing the flight and simulation results, so that they can be compared. This will then give them a basis of comfort for your other simulation.

When it comes to waivers, I agree with someone being a bit conservative -- we have a great relationship with the FAA, and need to keep it that way.

-Kevin

#### bobkrech

##### Well-Known Member
Greg

You asked a question and several folks gave what I consider to be reasonable answers.

I'm going to summarize the issues as I see them.
1. The AT M750 is a relatively new motor.
2. Your rocket has not been flown before.
3. Sims may not be accurate when the rocket has extreme speed or attains extreme altitudes.
4. The local RSO wants more evidence that the rocket will not exceed the 25 kft waiver altitude than you have provided.
5. You are an experienced L3 and disagree with the RSO.
6. The situation could be resolved with flight data.
As a Aerospace researcher with 38 years of professional experience, the findings from my research has always been subject to independent peer review. This assures that the conclusions that I have reached are reasonable and valid based on the experimental and theoretical data I gathered during the course of my research. Surely as a chemical engineer your engineering studies have undergone similar levels of scrutiny.

Earlier this week, I presented a preliminary design review at a major aerospace company for a Low Earth Orbit Environment simulation subsystem that I am building for a new DOD space environment test facility. Even thought I invented, patented, and have personally reviewed, designed, licensed, built and/or delivered every one of these LEO simulation systems in existence worldwide, I still had to present a preliminary design review for the customer. This is the nature and a foundation of science and engineering.

I don't believe the RSO is being unreasonable to request more data for a flight that might bust the waiver, I know I would. It's not difficult to conduct a first flight with a K650 or K680; a L952; or M845 or M956 prior to the M750 flight to get some hard aerodynamic data to demonstrate that a flight on a M750 won't bust the waiver.

My 2 cents as the forum moderator.

Bob Krech, TRF High Power and Propulsion Moderator