If drag loss delta vee is very roughly inversely proportional to length, for the 110 m Saturn V it was 40 m/s, the 40 m Atlas I it was 120 m/s and for a 10 m rocket it should be 360 to 400 m/s…. This is of course a very very ugly simplification assuming constant configuration / shape (but proportion changes are allowed) and density but anyway…

The transonic c_d is quite large, John Carmack approximated it by just looking at the V-2 experimental data from Sutton.

Maybe you are right anyway.

Have to build a simulator again some day, had one written in Python on a memory stick that of course broke down.

]]>I’ve never considered it important to see that figure separately, rather the estimate of performance. This will be verified in a number of test flights of 1st stage only, using the US amateur rocket regulations. The Reynolds number is in the calculation.

In any case, for rockets this small, the first stage is mainly to get the 2 upper stages to a vacuum, and nearly all the flight velocity is developed by the horizontal component of the upper stage thrust.

In a vacuum, rockets of 10-100 N thrust are nearly as efficient as larger ones.

The math has been checked enough for there to be confidence, so the next steps are to gather the means to build–the “Location-1 through 3” as mentioned in the N Prize presentation in the site.

]]>What are the drag losses in m/s?

Also smaller rockets probably have higher Cd because of low reynolds number…

]]> T/W Qmax Alt Vel

1. 2 54 KPa 106Km 1230 m/s

2. 2 33 104 1200

3. 3 33 112 1300

4. 3 20 100 1200

Maximum Q was to be controlled via a pitot tube to 33 KPa, 450 KIAS; 20 KPa, 350 KIAS; or in #1 no limit.

The stage is to use irrigation tubing and an engine pressure of 10 atm. Isp would be 220 at liftoff, rising to 250 at altitude.

The 1st stage was to have an empty mass of about 14 kg and the 2 upper stages 10 lg.

I did design, had static tested an irrigation tube rocket back in 1993-5. It works. 2 pictures on the “SA-05” part of the website.

For N Prize, and the follow on ML-1, to use 8 inch dia and a GLOW of 100-200 kg for escape I will be seeking partners for the work. Most likely in Las Vegas area but could be anywhere but California.

Help in organizing, finding sponsors etc also needed. This will be a very small budget, simple undertaking.

]]>I think aerodynamic losses will be a severe problem at that scale because the frontal area is huge compared to the volume. Or alternatively, drag loss is inversely proportional to rocket length, to a first approximation.

Maybe a sounding rocket style long thin shape.

I don’t know what kind of performance a super mod would have as a first stage… a 180+ s hover suggests 1.8 km/s class delta vee. (But with a very small payload). Drag would lower this, though ISP gain at altitude would compensate somewhat.

Also there’s a question of reuse and landing.

I think the tanks are not a large portion of the mass yet at that scale, though of course things can advance…

]]>I have been assuming a radial turbine, as they are somewhat more efficient than axial in small sizes. A friend made on his CNC mill a sample in aluminum that was 32 mm diamer, 3 mm thick and weighed 4 grams. This would be about right for about 5-6 KN.

I found by calculations that the threshold for product of turbine x pump efficiency needs to be over 5% (that’s all). That product for the RD-170 is 58%, but it is achieving a chamber pressure of 250 bar (25 MPa). Any pressire over 1 MPa is useful for a starting point.

The smallest engine I am contemplating would be about 1000 N.

This would be after relocating to (maybe) Henderson Nevada, recruiting about 2-3 to help, entering N Prize (short presentation on that is on the microlaunchers site)

]]>I sometimes thought of pressure washers but discovered their flow rates are really low.

If a cheap large piston gasoline engine powered pressure washer pump can pump 0.6 kg/s, that would enable only a 1500 N thrust and hence a 75 kg launch vehicle. Yet the pressure washer weighs more than that. Of course, they are not weight optimized systems. Still..

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