Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by rv6ejguy, Jul 27, 2019.
You can see one of the other projects Jeff Kerlo is working on here. Pretty neat stuff.
Looks like they've got a pretty decent test pilot too.
Cute little plane - be interesting to see what the market is.
I was somewhat perturbed, though, that John stated that the twin jet version will accelerate at 3G (which he mentions a few times) with 700 lb. of thrust and an 1100 lb. MGW. Even if EACH of the engines produces 700 lb. of thrust (I don't think that's the case, but lets be generous), then with 1400 lb. of thrust and 1100 lb. of weight, I get 1.27 G acceleration, or (with 700 lb of thrust - more likely) 0.64 G. Either one of these is going to be exciting - hell, even the single jet version, with 350 lb. of thrust, would be exciting - but it's not Spaceship 1's 3 G's. This is a relatively trivial calculation...
Did I miss something?
I noticed the same thing. I figured he did 1100/350 = 3 G's when he should have done 350/1100 = .3 G's...
Yeah, that comment made me think too. My RV weighs about 1100 empty and makes about 700 pounds of static thrust. Not even close to 3G acceleration if I boot it with full throttle.
Mistakes like make me wonder what other errors there may be.
Would that be a static thrust #? Don't turbines have a lower static thrust then when they get up on it and really start moving through air?
Yes, the BS in Modern Marketing of Kitplanes.
Ads and articles are written by people who write ads and articles, not engineers.
Yes, but we have to hope that only part of the team are halfwits. I for one would never let a marketeer publish something that I hadn't checked. It's quality control on a highly visible aspect.
Look at the Raptor. Impossible performance claims. The bullpoop has doomed it even if it does fly passably. Even if it has a 1500 mile range and manages 200kts, which is possible, it is a failure.
John certainly erred in his comment but we can cut him some slack this time. Looks like they are well along with the airframe and we know how Jeff can pound out the composite work. Let's give them a chance to get it done and fly it. I'm impressed they build almost everything in house. That takes some time and talent.
He is the guy engineering the thing! He needs someone else to work through all his assumptions and calculations before they spend any more time and effort on the project
Jet engines have an interesting characteristic - if the inlets will allow enough airflow when stationary, thrust is essentially flat from stationary to pretty good cruise speeds. The things that drive thrust less than the max are - small inlets, and compressibility effects, which interact with each other:
Inlet size - the F-5/F-20/T-38 have inlets sized for the supersonic mission, and that does limit static thrust, but as the airplane accelerates it can get more and more air through them. The other side of the coin is the Harrier. To get full thrust while in hover, the inlets are huge and even have blow-in doors for low speed.
Compressibility effects - Compressors and fans really need the flow through them be slower than the local speed of sound. So, a big inlet tapering down to a smaller duct at the compressor face or fan face will reach Mach at lower speeds than a small inlet and start losing thrust. Despite all the thrust that the Harrier has, it can not get above sonic - thrust drops as it approaches Mach and the drag of those huge inlets combine to produce a slightly sub-Mach capabilty. And a diverging duct from the inlet to the compressor allows the T-38 to still make big thrust into the surpersonic range. Same thing for the F-100. This is why a number of fighters have programmable inlets - to keep the flow sub sonic at the compressor face.
No afterburner according to the designer, just does not know how to do simple math...
Point straight towards the ground (1G), go full throttle(+1.27G), round up, and presto, 3G acceleration!
Is the empty weight around 470 lbs? Perhaps he meant operated as a drone right as fuel ran out.
What do you expect when they don't even do a grammar/spelling check. I think 70% of the people creating their own website flunked 7th grade English class. (or maybe they are still in the 7th grade?)
The Voodoo can incorporate up to 2 small turbines. PBS is offering a new 1500N version which states the current theoretical maximum in terms of what you can fit to the plane. He said it would not be for everyone, meaning you have 120k euros for the engines alone.
With 3000N for 1000lbs it seems to me he mistook the newton for lbs, as their other supplier is statingthe thrust in lbs instead. Another thing is, that the twin jet will be limited to around 15 minutes of autonomy. So main use case seems to be Reno unlimited race.
Simple math is required in order to do the complex math that is required to safely and successfully design aeroplanes.
Unlimited races are for piston powered aircraft only. The Jet Class speeds are far above what this plane could do on the course and you wouldn't want to be out there in the jet wash with such a lightweight design anyway.
You forget about the 65 year old ex airline pilot who cannot afford a F-35
Some of us half-wits can write sales BS that just smells so good that the boss is seduced and he lets it go out as is
I've just been upgraded from part time to full time, so I'm guessing my... work output... smells pretty good
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